ML100190066
| ML100190066 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 01/14/2010 |
| From: | Meyer L Point Beach |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LAR 241, NRC 201 0-0010 | |
| Download: ML100190066 (177) | |
Text
January 14,2010 NRC 2010-0010 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Point Beach Nuclear Plant, Units Iand 2 Dockets 50-266 and 50-301 Renewed License Nos. DPR-24 and DPR-27 Transmittal of lnformation to Support License Amendment Request 241, Alternative Source Term Seismic Evaluation Guidelines for HVAC Duct and Damper Systems
Reference:
( 1 FPL Energy Point Beach, LLC letter to NRC, dated December 8,2008, Submittal of License Amendment Request 241, Alternative Source Term (ML083450683)
(2) NextEra Energy Point Beach, LLC, Letter to NRC, dated November 20,2009, Transmittal of lnformation to Support License Amendment Request 241, PBNP VNPAB and CREFS Seismic Evaluation (ML093310308)
NextEra Energy Point Beach, LLC (NextEra) submitted License Amendment Request 241 (Reference I), Alternative Source Term (AST), to the NRC pursuant to 10 CFR 50.90.
The NRC requested additional information regarding the seismic adequacy of the control room emergency filtration system (CREFS) and primary auxiliary building ventilation system (VNPAB) credited in the AST analyses. Via Reference (2), NextEra submitted the results of the VNPAB and CREFS seismic evaluation to address this request.
The NRC has requested that NextEra provide a copy of the Electric Power Research Institute (EPRI) Technical Report I 0 14608 referenced in the seismic evaluation in order for the Staff to provide site-specific approval of the use of the report for the Point Beach Nuclear Plant. provides a copy of "EPRI Technical Report I 0 14608, Seismic Evaluation Guidelines for HVAC Duct and Damper Systems, Revision to 1007896," dated December 2006.
NextEra Energy Point Beach, LLC,6610 Nuclear Road, Two Rivers, WI 54241
Document Control Desk Page 2 This letter contains no new Regulatory Commitments and no revisions to existing Regulatory Commitments.
The information contained in this letter does not alter the no significant hazards consideration contained in Reference (1) and continues to satisfy the criteria of 10 CFR 51.22 for categorical exclusion from the requirements of an environmental assessment.
In accordance with 10 CFR 50.91, a copy of this letter is being provided to the designated Wisconsin Official.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on January 14,2010 Very truly yours, NextEra Energy Point Beach, LLC Larry Meyer Site Vice President Enclosure cc: Administrator, Region Ill, USNRC Project Manager, Point Beach Nuclear Plant, USNRC Resident Inspector, Point Beach Nuclear Plant, USNRC PSCW
ENCLOSURE I NEXTERA ENERGY POINT BEACH, LLC POINT BEACH NUCLEAR PLANT, UNITS I AND 2 LICENSE AMENDMENT REQUEST 241 ALTERNATIVE SOURCE TERM EPRI TECHNICAL REPORT 1014608, SEISMIC EVALUATION GUIDELINES FOR HVAC DUCT AND DAMPER SYSTEMS, REVISION TO 1007896 FINAL REPORT, DECEMBER 2006 174 pages follow
ELECTRIC POWER RESEARCH INSTITUTE Seismic Evaluation Guidelines for HVAC Duct and Damper Systems Revision to 1007896 WARNING:
Please read the Ex ort Control Agreement on the gack cover.
Technical Report Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.
Seismic Evaluation Guidelines for HVAC Duct and Damper Systems Revision to 1007896 1014608 Final Report, December 2006 EPRl Project Manager R. Kassawara ELECTRIC POWER RESEARCH INSTITUTE 3420 Hillview Avenue, Palo Alto, California 94304-1338 PO Box 10412, Palo Alto, California 94303-0813 USA 800.313.3774 650.855.2121 askepri@epri.com www.epri.com
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Copyright O 2006 Electric Power Research Institute, Inc. All rights reserved.
This report was prepared by ARES Corporation 142 Portsmouth Avenue, Suite 2 Stratham, NH 03885 Principal Investigators P. Baughman J. White This report describes research sponsored by the Electric Power Research Institute (EPRI).
The report is a corporate document that should be cited in the literature in the following manner:
Seisnzic Evaluation Guidelinesfor W A C Duct and Damper Systems: Revision to 1007896.
EPRI, Palo Alto, CA: 2006. 1014608.
REPORT
SUMMARY
This report provides guidelines that can be used to perform an experience based seismic capability verification of HVAC duct and damper systems in nuclear power plants. The report summarizes seismic experience data from strong-motion earthquakes for these systems and identifies the characteristics of systems that could lead to failure or unacceptable behavior in an earthquake. The seismic experience data show that HVAC duct and damper systems exhibit extremely good performance under strong-motion seismic loading, with the pressure boundary being retained in all but a handful of cases. This revision of the original report includes a successful trial application of the methodology to a non-seismically designed HVAC system.
Background
The Seismic Qualification Utility Group (SQUG) provides guidelines for seismic capability verification of nuclear plant electrical and mechanical equipment; relays, tanks and heat exchangers; and electrical raceway systems using seismic experience and test data. As part of this effort, the performance of HVAC duct and damper systems in 100 power and industrial facilities in more than 20 strong-motion earthquakes has been compiled into a seismic experience database. This database has been used to establish guidelines to seismically verify as-installed HVAC duct and damper systems and screen out potential failure modes and undesirable conditions that could lead to seismic damage or failure.
0 bjectives To provide guidelines that can be applied to as-installed HVAC duct and damper systems to demonstrate seismic ruggedness Approach The research team assembled data on the seismic performance of HVAC duct and damper systems from over 20 strong-motion earthquakes since 1971. The team studied these data to determine failure modes, capacities, and success parameters. They used the recorded experience data to develop guidelines for evaluation of ductwork and dampers. Following the original issue of this report, Southern Nuclear conducted a trial application of the methodology to verify the seismic adequacy of a non-seismically designed HVAC system at Hatch Unit 1. The trial application included a peer review by Dr. Robert P. Kennedy. The peer review comments are included in this report as Appendix G.
Results The guidelines in this report can be used to demonstrate the seismic capability of HVAC duct and damper systems. The recommended seismic adequacy review procedure includes documentation review, in-plant screening walkdowns, analytical review of selected duct runs and supports, and identification and resolution of outliers that do not meet the screening or analysis
criteria. Documentation is reviewed to determine input parameters such as system identification, function, system boundaries, operating conditions, materials, and seismic input. Field walkdowns, which should be performed by qualified personnel who meet SQUG experience and training requirements for Seismic Capability Engineers, are used to screen the HVAC duct and damper systems for known seismic vulnerabilities and undesirable conditions that could lead to damage or failure in a seismic event. The walkdown team reviews the as-installed HVAC duct and damper system against a checklist of conditions to assess acceptability. As part of the field walkdowns, the review team selects and details representative, worst-case samples of duct runs and duct supports for analytical review. The guidelines include criteria for this analytical review.
Appendix A of this report summarizes the seismic experience database for HVAC duct systems.
Appendix B summarizes the seismic experience database for dampers.
The revised report now incorporates lessons learned from the trial application of the methodology at Hatch Unit 1 and the recommendations of the peer reviewer. The trial application was successful and proved the methodology to be a practical, effective and cost-effective means to verify the seismic adequacy of HVAC duct and damper systems. There was a significant cost savings to the plant in not having to design and install seismic bracing on the ductwork.
EPRl 'Perspective The use of seismic experience data from actual strong-motion earthquakes has proven to be a reliable and cost effective method for seismic capability verification. Accordingly, SQUG has developed the Generic Implementation Procedure, which structures the method and applies it to some twenty different classes of nucIear plant equipment, relays, tanks and heat exchangers, and electrical raceways. As part of SQUG's ongoing effort to expand the method to new classes of equipment, this report extends the method to HVAC duct and damper systems and provides guidelines to demonstrate seismic adequacy of existing HVAC duct and damper systems. The appendices to this report provide a summary of seismic experience for HVAC duct and damper systems in a database that has been assembled from power and industrial facilities located in the strong-motion areas of over 20 earthquakes. This database provides valuable information on the performance of HVAC duct and damper systems in earthquakes, and will enhance the industry's overall database of seismic performance of equipment and systems.
Keywords Damper Duct Earthquakes HVAC Seismic Effects Seismic Experience Data Seismic Verification Guidelines
ACKNOWLEDGMENTS The authors wish to acknowledge the contributions of Mr. Donald P. Moore, Southern Company Services, who provided valuable insights from application of this methodology at Plant Hatch; Dr. Robert P. Kennedy, RPK Structural Mechanics Consulting, who performed peer reviews of Revision 0 of this report and the Plant Hatch implementation, and provided valuable comments; and Mr. Richard Starck, MPR Associates, who provided review comments during preparation of Revision 1 of this report.
The authors also wish to acknowledge the contributions of Mr. John Dizon, Facility Risk Consultants, and Mr. Farzin Beigi, ABS Consulting, for their contributions to the original issue of this report.
CONTENTS 1 INTRODUCTION ..................................................................................................................1-1 1.1 Background .................................................................................................................1-1 1.2 Overview of Guidelines ...................................................................................................1-2 2 APPLICABILITY AND QUALIFICATIONS ............................................................................2-1 2.1 Applicability .....................................................................................................................2-1 2.2 Qualifications .............................................................................................................. 2-2 2.3 Peer Review ....................................................................................................................2-3 3 WALKDOWN SCREENING GUIDELINES ............................................................................3-1 3.1 Overview of Walkdown Guidelines..................................................................................3-1 3.2 Structural Integrity Review ..............................................................................................3-2 3.2.1 Duct Span ................................................................................................................3-2 3.2.2 Duct Tie-downs ........................................................................................................ 3-2 3.2.3 Duct Joints ............................................................................................................... 3-3 3.2.4 Riveted Lap Joints ...................................................................................................3-3 3.2.5 Appurtenances .....................................................................................................3 - 3 3.2.6 Flexibly Mounted Heavy Equipment ........................................................................3-5 3.2.7 Branch Flexibility ................................................................................................3-5 3.2.8 Cantilevered Duct ...............................................................................................3-5 3.2.9 Duct Corrosion.........................................................................................................3-6 3.3 Support System Review ..................................................................................................3-6 3.3.1 Beam Clamps ......................................................................................................3-6 3.3.2 Channel Nuts ...........................................................................................................3-6 3.3.3 Cast Iron Anchor Embedment .................................................................................3-6 3.3.4 Broken Hardware..................................................................................................... 3-7 3.3.5 Support Corrosion .............................................................................................3-7 3.3.6 Concrete Quality ...................................................................................................... 3-7
3.3.7 Welded Attachments ..............................................................................................3-7 3.3.8 Rod Hanger Fatigue ................................................................................................3-7 3.4 Seismic Interaction Review ............................................................................................. 3-8 3.4.1 Proximity and Falling Hazards................................................................................3-8 3.4.2 Flexibility of Attached Lines .....................................................................................3-8 3.4.3 Differential Displacement Hazards ..........................................................................3-9 3.5 Pressure Boundary Integrity Review ............................................................................3-9 3.5.1 Duct Joints and Stiffener Spacing .........................................................................3-9 3.5.2 Round Duct Supports ..............................................................................................3-9 3.5.3 Flexible Bellows....................................................................................................3-10 3.6 Selection of Bounding Configurations ...........................................................................3-10 3.6.1 Selecting Bounding Duct Support Samples.........................................................3 1 3.6.2 Selection of Bounding Duct Configurations...........................................................3-11 4 ANALYTICAL REVIEW CRITERIA ........................................................................................4-1 4.1 Overview of Analysis Criteria ..........................................................................................4-1 4.2 Dead Load and Seismic Stress .......................................................................................4-2 4.2.1 Allowable Bending Stress for Rectangular Ducts ....................................................4-4 4.2.2 Allowable Bending Stress for Circular Ducts ...........................................................4-5 4.3 Pressure Stress in Ducts .................................................................................................4-6 4.3.1 Pressure Stresses in Rectangular Ducts .................................................................4-6 4.3.2 Pressure Stresses in Round Ducts........................................................................4-10 4.4 Pressure Stresses in Stiffeners .................. ................................................................4 2 .-
4.4.1 Stiffener Evaluation for Rectangular Ducts............................................................4-12 4.4.2 Stiffener Evaluation for Round Ducts ....................................................................4-14 4.5 Duct Support Evaluation................................................................................................4-15 4.5.1 Metal Frame and Anchorage ..............................................................................4 1 5 4.5.2 Rod Hanger Fatigue Evaluation ........................................................................4 6 4.5.3 Anchorage Capacity .........................................................................................4 6 4.5.4 Redundancy and Consequence Test ....................................................................4-16 5 DOCUMENTATION .............................................................................................................. 5-1
6 OUTLIERS ..........................................................................................................................6-1 6.1 Identification of Outliers...................................................................................................6-1 6.2 Outlier Resolution............................................................................................................ 6-1 7 REFERENCES .......................................................................................................................7-1 A HVAC DUCT SYSTEM EARTHQUAKE EXPERIENCE DATA ...........................................A-1 A.l Introduction ..................................................................................................................A-1 A.2 Earthquake Experience Database .................................................................................A-1 A.2.1 Facilities Surveyed in Compiling the Database .................................................... A-12 A.2.1 .1 1983 Coalinga, California Earthquake.........................................................A-36 A.2.1.2 1984 Morgan Hill, California Earthquake......................................................A-37 A.2.1.3 1985 Mexico Earthquake..............................................................................A-39 A.2.1.4 1987 New Zealand Earthquake .................................................................... A-40 A.2.1.5 1987 Whittier, California Earthquake............................................................A-42 A.2.1.6 1988 Alum Rock, California Earthquake..................................................... A-46 A.2.1.7 1989 Loma Prieta Earthquake................................................................A-47 A.2.1.8 1990 Philippines Earthquake....................................................................... A-51 A.3 Summary of Observed Damage ..................................................................................A-51 B HVAC DAMPER EARTHQUAKE EXPERIENCE DATA ......................................................B-1 B.l Definition of Equipment Class .......................................................................................B-1 B.l .1 Equipment Anchorage ............................................................................................B-1 6.1.2 Equipment Applications ........................................................................................6-2 B.1.3 Application in Nuclear Plants .................................................................................6-2 8.2 Database Representation for Dampers .....................................................................B-3 B.2.1 Basis for the Generic Bounding Spectrum ...........................................................B-13 B.3 Instances of Seismic Effects and Damage .................................................................B-15 6.4 Sources of Seismic Damage..................................................................................6-15 6.5 Caveats for Dampers ...................................................................................................B-16 B.6 References................................................................................................................... B-17
C DEVELOPMENT OF ALLOWABLE SPANS FOR SHEET METAL DUCTS .......................C-1 C.l Rectangular Ducts ......................................................................................................... C-1 C.2 Circular Ducts ...............................................................................................................C-2 C.3 Example Span Calculation.........................................................................................C-4 D SEISMIC AND PRESSURE TESTING OF HVAC DUCTS .................................................D-1 D.l Introduction....................................................................................................................D-1 D.2 HVAC Duct Test Programs............................................................................................D-1 0.2.1 Summary of Tests Performed for 1-VA Ducts.......................................................D-1 D.2.2 Summary of Tests Performed for Limerick Ducts ..................................................D-2 D.2.3 Tests Performed at Other Plants .........................................................................D-3 D.3 Conclusions From Test Programs .................................................................................0-3 D.4 References ....................................................................................................................D-4 E ROD FATIGUE EVALUATION GUIDELINES .....................................................................E-1 E.l Introduction .................................................................................................................E-1 FGUIDELINES FOR LIMITED ANALYTICAL REVIEW OF SUPPORTS ................................F-1 F.l Introduction .....................................................................................................................F-I F.2 Dead Load Check .........................................................................................................F-3 F.3 Vertical Capacity Check ...............................................................................................F-3 F.4 Ductility Check ................................................................................................................F-4 F.5 Lateral and Longitudinal Load Check..............................................................................F-7 G PEER REVIEW COMMENTS ...............................................................................................G-1
LIST OF FIGURES Figure 2-1 Seismic Motion Bounding Spectrum........................................................................2-2 Figure 3-1 SMACNA Duct Joints ...............................................................................................3-4 Figure 4-1 Rectangular Duct Configuration ...............................................................................4-7 Figure 4-2 Value of u for Rectangular Ducts [ I 51.......................................................................4-9 Figure 4-3 Load Going to Stiffener on a Rectangular Duct When US> 10.0 [6] .....................4-13 Figure A-1 Sylmar Converter Station. 1971 San Fernando Earthquake. Strap-Hung and Wall-Mounted Duct With Wall Penetrations ....................................................................A-29 Figure A-2 Glendale Power Plant. 1971 San Fernando Earthquake. Cantilever Bracket Supported Rectangular Duct .........................................................................................A-30 Figure A-3 Bay Milk Products. 1987 New Zealand Earthquake. Long Vertical Cantilever Supported by the Roof at One End and Guy Wires at the Other .................................... A-30 Figure A-4 El Centro Steam Plant. 1979 Imperial Valley Earthquake. Trapeze Rod-Hung Rectangular Duct With Close Up of the Trapeze Detail ..................................................A-31 Figure A-5 California Federal Bank Facility. 1987 Whittier Earthquake. Typical Strap-Hung Rectangular Duct With Vertical Cantilevers and Diffusers.................................... A-32 Figure A-6 Watkins-Johnson Instrument Plant, 1989 Loma Prieta Earthquake. Large.
Insulated Round Duct With Branch Ducts and Cable Supports ...................................... A-32 Figure A-7 Pacific Bell Watsonville, 1989 Loma Prieta Earthquake. Run of Trapeze Rod-Hung Rectangular Duct .................................................................................................A-33 Figure A-8 Valley Steam Plant Forced Draft System. 1971 San Fernando Earthquake ........ A-33 Figure A-9 Drop IV Hydro Plant. 1979 lmperial Valley Earthquake. Ceiling Mounted Ducting ........................................................................................................................A-34 Figure A-10 Watkins.Johnson. 1989 Loma Prieta Earthquake. HVAC Ducting Atop Roof Level................................................................................................................................A-34 Figure A-11 Magnolia Plant. Burbank. Ducting at Induced Draft Fan. 1971 San Fernando Earthquake ...................................................................................................A-35 Figure A-12 El Centro Steam Plant. 1979 Imperial Valley Earthquake................................. A-35 Figure A-13 Gates Substation. 1983 Coalinga Earthquake. A HVAC Diffuser Fell From the Suspended Ceiling ..................................................................................................A-37 Figure A-14 Wiltron Facility. 1984 Morgan Hill Earthquake. A 4-Foot Long Vertical Cantilever Broke From its Supporting Header and Fell..................................................A-38 Figure A-15 Wiltron Facility, 1984 Morgan Hill Earthquake. A Branch Line Tore at a Wall Penetration Due to Flexible Header Motion .................................................................A-39 Figure A-16 Fertimex Packaging Plant. 1985 Mexico Earthquake. A section of Duct Tore when the Duct Jumped off the Final Support in a Long Run...........................................A-40
Figure A-17 Caxton Paper Mill. 1987 New Zealand Earthquake. A long. Unrestrained Run of Duct Constructed of Riveted Lap Joints (Top) and a Taped Repair of a Sheared Joint (Bottom) ..................................................................................................A-41 Figure A-18 SCE Rosemead Headquarters. 1987 Whittier Earthquake. HVAC Dented From Sway of Adjacent Fixtures .................................................................................... A-43 Figure A-19 Ticor Facility. 1987 Whittier Earthquake. A Flexible Bellows has Torn Due to the Motion of an Attached Fan on Vibration Isolation Mounts.....................................A-44 Figure A-20 Sanwa Data Processing Center. 1987 Whittier Earthquake. A Duct above the Battery Racks Deformed at the Joints of an Angled Offset Section ..........................A-45 Figure A-21 East Ridge Mall. 1988 Alum Rock Earthquake. A Flexible Bellows Tore Due to the Motion of Attached Air Handlers on Vibration Isolation Mounts ........................... A-46 Figure A-22 Seagate Technology. 1989 Loma Prieta Earthquake. A Strap Support Broke and the Attached Duct Fell to the Floor ................................................................A-47 Figure A-23 Watkins-Johnson lnstrument Plant. 1989 Loma Prieta Earthquake. The Flexible Bellows Connecting HVAC Ducting to an In-Line Axial Fan Tore ......................A-48 Figure A-24 Watkins-Johnson lnstrument Plant. 1989 Loma Prieta Earthquake. The Support Anchorage for a Roof-Mounted Duct Was Distressed.......................................A-49 Figure A-25 Pacific Bell, Watsonville. 1989 Loma Prieta Earthquake. A Vertical Cantilevered Section of Duct Fell to the Floor With its Attached Diffuser ...................... A-50 Figure 9-1 Exploded View of a Typical Damper ......................................................................9-3 Figure 9-2 Typical Damper Blades or Louvers ........................................................................ 9-3 Figure B-3 Typical Damper Actuators .................................................................................B-4 Figure B-4 Pneumatic Damper at El Centro Steam Plant Subjected to the 1979 Imperial Valley Earthquake .............................................................................................................B-4 Figure B-5 Louver Style Damper on the Boiler Structure at the El Centro Steam Plant Which Experienced the 1979 Imperial Valley Earthquake ................................................B-5 Figure B-6 Pneumatic Actuator at the Puente Hills Landfill Gas and Energy Recovery Plant ..................................................................................................................................B-5 Figure B-7 Radial Type Damper at the El Centro Steam Plant Subjected to the 1979 Imperial Valley and 1987 Superstition Hills Earthquakes.................................................B-6 Figure B-8 Louver Type Damper at Humboldt Bay Power Plant .............................................B-7 Figure B-9 Radial and Louver Type Dampers at the Humboldt Bay Power Plant. Which Experienced the 1975 Ferndale Earthquake..................................................................B-7 Figure B-10 Motor-operated Damper at Adak Naval Station. Which Experienced the 1986 Adak Alaska Earthquake .......................................................................................B-8 Figure B-11 Damper at Adak Naval Station .............................................................................B-8 Figure B-12 Pneumatically Controlled Damper at UC Santa Cruz Applied Science Building Subjected to 1989 Loma Prieta Earthquake......................................................B-9 Figure B-13 Electric Motor for a Fire Damper at AES Placerita Cogeneration Plant.
Which Experienced the 1994 Northridge Earthquake ....................................................B-10 Figure 9-14 Pneumatic Damper With Long Actuator at Valley Steam Plant , Which Experienced the 1971 San Fernando and the 1994 Northridge Earthquakes.................B-10
Figure B-15 Pneumatic Louver Control Damper at Pasadena Power Plant, Which Experienced Several Database Earthquakes ................................................................B-11 Figure B-16 Heavy Pneumatic Controller With Independent Support for a Large Damper at Pasadena Power Plant Located Very High in the Boiler Structure..............................B-11 Figure B-17 Air Operated Damper With Floor-Mounted Actuator at Burbank Power Plant, Which Experienced the 1971 San Fernando and the 1994 Northridge Earthquakes .................................................................................................................. B-12 Figure B-18 Large Independently Supported Damper Controller at the Burbank Power Plant ................................................................................................................................B-12 Figure B-19 Inventory of Dampers Within Experience Database ........................................B-13 Figure E-1 Bounding Rod Fatigue Spectra ..............................................................................E-1 Figure E-2 Fatigue Elevation Screening Chart for ?4inch Diameter Manufactured All-thread Rods. Weight Corresponds to the Total Supported Load (i.e., on both Rods).
Length Corresponds to Clear Length ................................................................................E-2 Figure E-3 Fatigue Evaluation Screening Chart for 318 inch Diameter Manufactured All-thread Rods. Weight Corresponds to the Total Supported Load (i.e., on both Rods).
Weight Corresponds to Clear Length ...............................................................................E-3 Figure E-4 Fatigue Evaluation Screening Chart for 1/2 - inch Diameter Manufactured All-thread Rods. Weight Corresponds to the Total Supported Load (i.e., on both Rods). Length Corresponds to Clear Length ...................................................................E-4 Figure E-5 Fatigue Evaluation Screening Chart for 518-inch Diameter Manufactured All-thread Rods. Weight Corresponds to the Total Supported Load (i.e., on both Rods).
Length Corresponds to Clear Length ................................................................................ E-5 Figure E-6 Fatigue Evaluation Screening Chart for 314-inch Diameter Manufactured All-thread Rods. Weight Corresponds to the Total Supported Load (i.e., on both Rods).
Length Corresponds to Clear Length ................................................................................E-6 Figure F-1 Vulnerable Duct Elbow Adjacent to Rigid Lateral Restraint.....................................F-2 Figure F-2 Examples of Potentially Non-Ductile Support Connection Details and Configurations ....................................................................................................................F-6 Figure F-3 System Frequency Estimation using Beam-on-Elastic-Foundation Approximation ....................................................................................................................F-8 Figure F-4 Dunkerley's Equation Frequency Estimation Methodology .....................................F-8
LIST OF TABLES Table 2-1 Temperature Limitations for Duct Materials ...............................................................2-1 Table 4-1 Value of K for Rectangular Ducts [ I 51 ....................................................................4-10
& j Seismic Experience Database......... A-3 Table A-1 Summary of Sites Reviewed in ~ o r n ~ i l i the Table A-2 HVAC Duct Seismic Experience Database ........................................................A-13
1.IBackground This report provides guidelines for seismic adequacy review of HVAC duct and damper systems.
The screening guidelines are primarily based on seismic experience data that show that most types of HVAC duct and damper systems exhibit extremely good performance under strong-motion seismic loading, with the pressure boundary being retained in all but a handful of cases.
The guidelines provide a method to screen and identify features seismic vulnerabilities and weaknesses.
The guidelines rely on the evaluation of seismic failure mechanisms for duct and damper systems from seismic experience data presented in Appendices A and B of this report. The data show that the damage to duct systems are generally limited to direct seismic damage of the duct or supports, and local damage due to seismic interaction with adjacent commodities. Seismic damage to W A C duct systems documented in the seismic experience database can be attributed to the following categories:
0 Broken and Fallen Cantilevered Sections. Cantilevered sections of duct and duct diffusers have broken due to high inertia loading at weak joints, and due to inadequate flexibility of short duct segments to accommodate header movement.
- Opened and Sheared Seams. Light gage circular duct constructed with riveted lap joints have opened up and sheared in past strong-motion earthquakes. This damage has occurred at locations subject to high bending strain in very flexible duct systems.
Duct Fallen 08Support. The database includes one example where the end of a cantilevered duct section jumped off of its end hanger support and was damaged. The duct was not tied to the support, and was subject to high levels of seismic motion.
0 Equipment on Vibration Isolators. W A C duct has been damaged by excessive movement of in-line equipment components supported on vibration isolators.
The seismic experience database indicates that dampers possess characteristics that generally preclude damage in earthquakes. The experience database contains no instances of damage or significant seismic effects to dampers or their actuators.
Following the original issue of this report, Southern Nuclear conducted a trial application of the methodology to verify the seismic adequacy of a non-seismically designed W A C system at Hatch Unit 1. The trial application included a peer review by Dr. Robert P. Kennedy. The peer review comments are included herein as Appendix G. Revision 1 of this report incorporates lessons learned from the trial application and the recommendations of the peer reviewer.
Introduction The trial application was successful and proved the methodology to be a practical, effective and cost-effective means to verify the seismic adequacy of W A C duct and damper systems. There was a significant cost savings to the plant in not having to design and install seismic bracing on the ductwork.
1.2 Overview of Guidelines The guidelines for seismic adequacy review of W A C duct and damper systems include the following sections:
0 Applicability and Qualifications (Section 2) 0 Walkdown Screening Guidelines (Section 3)
- Analytical Review Criteria (Section 4)
Section 2 provides general requirements the W A C duct and damper system must meet to be able to use these guidelines for seismic verification. Section 2 also includes qualification requirements for individuals who perform the seismic adequacy review.
Section 3 presents guidelines for conducting in-plant seismic adequacy review of the W A C duct and damper systems including supports. These walkdown guidelines are used to screen out potential failure modes indicated by seismic experience data, and to ensure database representation of the duct and damper system. As part of the walkdown, representative worst-case examples of duct supports are identified by the walkdown team and detailed for analytical review. In addition, representative worst-case examples of duct runs are identified by the walkdown team and detailed for analytical review for duct systems that require pressure boundary integrity to be maintained.
Section 4 includes criteria for performing analytical review of representative samples of duct systems and supports selected by the walkdown team. When these representative samples do not pass the analytical review, further evaluations should be conducted and the sample expanded as appropriate.
The results of the walkdown are documented in wallcdown notes and forms included in Section 5.
Section 6 describes outliers and how they may be resolved.
References are included in Section 7.
A summary of the seismic experience database for W A C duct systems is included in Appendix A. The seismic experience database for dampers is included in Appendix B. These appendices provide details on the performance of W A C duct and damper systems at selected industrial and power plant facilities in actual strong-motion earthquakes. Appendix C contains an example calculation of allowable span tables from the trial application. Appendix G contains the peer review comments from the trial application.
2.1 Applicability These guidelines apply to existing heating, ventilation and air-conditioning (HVAC) ducts, dampers and supports. Appurtenances such as registers, access doors, turning vanes, filters, louvers, air diffusers and similar components normally attached to W A C ducts are also included. These guidelines apply to duct fabricated of hot-rolled and cold-rolled carbon steel, galvanized sheet steel, stainless steel and aluminum within the following maximum operating temperature limitations:
Table 2-1 Temperature Limitations for Duct Materials Material Maximum Temperature Hot-Rolled Carbon Steel 400°F Cold-Rolled Carbon Steel 400°F Galvanized Sheet Steel 400°F Stainless Steel 400°F Aluminum 300°F The guidelines are applicable to any W A C duct and damper system at any elevation in a plant where the nuclear plant free-field ground motion 5% damped seismic design spectrum does not exceed the Seismic Motion Bounding Spectrum of Reference [I] and the horizontal zero period acceleration (ZPAh)of the in-structure response spectra at the HVAC support anchorage does not exceed 2.0g. The Bounding Spectrum is shown in Figure 2-1. The 2.0g ZPAh restriction is from Reference [161.
Applicability and QzlaliJicalions
/SQUG Generic Bounding Spectrum I Ground Acceleration = 0.33 g Frequency (Hz)
Figure 2-1 Seismic Motion Bounding Spectrum 2.2 Qualifications These guidelines are intended to be applied by qualified engineers who meet the training and experience requirements defined in this section.
The Seismic Review Team (SRT) should consist of at least two engineers who meet the requirements for Seismic Capability Engineers (SCEs) as defined in Section 2 of Reference [I].
These individuals are required to be degreed engineers, or equivalent, who have completed a 1
SQUG developed training course on seismic adequacy verification of nuclear power plant equipment. They are required to have at least five years experience in earthquake engineering applicable to nuclear power plants and in structural or mechanical engineering. At least one engineer on each Seismic Review Team should be a licensed professional engineer.
In addition, qualified users of these guidelines must be familiar with the following topics:
e Content and intent of the guidelines HVAC duct and support design requirements of the Sheet Metal and Air Conditioning Contractor's National Association, Inc., (SMACNA), including References [4] through [7]
8 Seismic experience data for HVAC duct and damper systems
Applicability and QzialiJicaiions 2.3 Peer Review The earthquake experience based seismic evaluation approach presented herein relies heavily on the judgment and experience of the SRT. This judgment and experience is used in lieu of extensive analysis. The SQUG GIP, Reference [I], and EPRI SMA, Reference [14], also utilize an experience based approach. The USNRC required the implementation of these methodologies include an independent peer review of the judgments and conclusions made by the SRT as well as a sampling review of the limited analytical evaluations. As part of the application of the guidelines of this report, it is therefore recommended that use of the methodology include an independent peer review by a knowledgeable individual who is not a member of the SRT.
3.1 Overview of Walkdown Guidelines This section presents requirements for performing the in-plant screening review of HVAC duct and damper systems for structural integrity, support review, seismic interaction, and pressure boundary integrity. Requirements are also provided for the selection of boundinglsample configurations for subsequent analytical evaluation. Analytical evaluation criteria are covered in Section 4. Screening and evaluation work sheets (SEWS) for recording information from the in-plant screening review are provided in Section 5.
The HVAC duct system seismic evaluation consists of two phases, (1) an in-plant screening review of field conditions to evaluate as-installed configurations for seismic deficiencies and (2) the analytical evaluation of selected duct andor support configurations. The specific requirements for the evaluation are dependent upon the functional pressure boundary integrity requirements desired.
The in-plant screening review of HVAC duct systems encompasses the following:
Review duct system structural features that may lead to poor performance as illustrated by the seismic experience and test data (Section 3.2).
8 Review support system for undesirable conditions that may lead to poor performance (Section 3.3).
8 Review potential seismic interaction hazards (Section 3.4).
Review duct system features to provide a high confidence level that pressure boundary integrity is assured. These requirements are based on seismic experience and test data (Section 3.5).
8 Identify bounding configurationslsamples for analytical evaluations (Section 3.6).
Items not meeting the in-plant screening review should be identified as outliers. Outliers require a more detailed review (see Section 6).
An analytical evaluation should also be conducted for bounding configurations/samples of duct andor supports selected during the in-plant review. M e r e pressure integrity is required following an earthquake, duct and support configurations should be selected to provide representative, worst-case, bounding samples. This will typically involve a careful review of available drawings and collection of as-built information. Analysis of bounding configurations for duct and supports needing pressure boundary integrity can be used to assure performance of
Wallcdo~~nScreening Guidelines a larger duct population. Where structural integrity (prevention of collapse and falling) is the only concern, analysis of a random sampling of support configurations is sufficient, along with the satisfaction of the in-plant screening review requirements. If the selected configurations do not pass the analytical review, the sample population should be expanded to identify the population of HVAC system configurations that meet the required seismic criteria.
Regardless of the pressure boundary integrity requirements, the HVAC duct evaluation includes an assessment of structural integrity and potential interaction, and analysis of support configurations. If pressure boundary integrity is required, the HVAC in-plant screening review also includes requirements for duct pressure boundary assessment and a selection of bounding configurations for analysis. Items not satisfying the analytical evaluations are outliers that may require more detailed analysis or modification.
3.2 Structural Integrity Review This section describes HVAC duct and support attributes for review during the in-plant screening review walkdowns. These attributes have led to poor seismic performance based on past earthquakes and testing (see Reference [3], Appendix A, Appendix B and Appendix D).
3.2.1 Duct Span Duct span governs the seismic and dead load stress in the duct. Allowable duct spans and maximum cantilever lengths for applicable duct sizes must be developed prior to the in-plant screening review to enable screening of as-installed spans. The procedure for developing the allowable spans and cantilever lengths is given in Appendix C which is based on the analytical review requirements presented in Section 4.1. Lateral and vertical spans that exceed the allowable spans should be noted for further evaluation.
In addition, the following upper limits on vertical support spans apply based on review of earthquake experience data (from Reference [16]):
- 1. Duct support to support spans should not exceed 15 feet.
- 2. Supports should be provided within 5 feet from fittings such as tees and wyes in each branch of the fitting.
- 3. Duct cantilevered length (beyond end of last support) should not exceed 6 feet.
3.2.2 Duct Tie-downs Ducts should be secured to their supports to preclude the possibility of displacing, falling or sliding off during a seismic event. Systems do not have to be secured to every support unless the supports are at the maximum spacing described in Section 3.2.1. The HVAC duct should be securely attached to the last hanger support at the terminal end of the duct run. Similarly, supports configured to limit the lateral movement of the W A C duct system should also be attached to the duct. Seismic experience data indicate that a mode of failure for HVAC duct
Walkdown Screening Guidelines systems subject to earthquake loading is the duct falling off of end supports. An example of this occurred at the Fertimex plant during the 1985 Mexico City earthquake (Figure A-16 of Appendix A).
The SRT should use experience and judgment when evaluating where duct tie-downs are required. For example, attachment to the last support is not required if the distance from the end of the duct to the next to last support does not exceed the maximum allowable cantilever length.
In this case the duct would be seismically adequate without taking credit for the last support in the duct run.
3.2.3 Duct Joints W A C joints should be visually inspected to verify their structural integrity. Joints (including connected tees and elbows) that are observed to be loose, incomplete, corroded, or otherwise suspect (such as those repaired with duct tape or fiberglass, or missing rivets, screws, etc.) should be reviewed in detail. Seismic experience data have shown that such joints are often the point of excessive leakage or failure of W A C systems in an earthquake. A corroded riveted duct joint failed at the Caxton Paper Mill as a result of the 1987 New Zealand earthquake (see Appendix A, Section A.2.1). In addition, W A C without pressure boundary requirements and with runs consisting of slip joints without pocket locks, rivets or screws should be reviewed to assure that the differential displacement between the two adjoining ducts due to seismic loading will not cause joint separation. Figure 3-1 shows different SMACNA duct joints as described in Reference [4] to aid in identifying slip-type joints.
3.2.4 Riveted Lap Joints Round W A C duct with light gage riveted lap joint construction should be considered outliers and subjected to more detailed investigation. The seismic experience database contains isolated cases of damage occurring to this kind of duct construction, such as the failure at the Wiltron Electronics Plant during the Morgan Hill earthquake (Figure A-4 of Appendix A). More detailed investigation should be performed to assure the seismic adequacy of this type of duct.
3.2.5 Appurtenances Appurtenances attached to W A C ducts must be checked to assure they will not fall in the event of an earthquake. This equipment includes items such as dampers, turning vanes, registers, access doors, filters, louvers, and air diffusers. Earthquake experience data have shown that intake and discharge screens and vanes that are inadequately attached to the duct (i.e. only slipped into place and not fastened with screws or rivets) have fallen during seismic events.
Figure A-1 3 of Appendix A shows this type of failure. Appurtenances not positively attached to the duct that appear to be at risk of falling during an earthquake should be evaluated to determine if failure will affect the functioning of the W A C system and whether they will become an interaction hazard with other nearby safety related equipment. Appurtenances projecting from the duct (cantilevered) should be reviewed to assure connections are seismically adequate.
Walkdo~vnScreening Guidelines T MINE SLIP T REINFORCED P W N "S'SUP tT-h REINFORCED) instoe s u p JOINT SFANDING s STANDING s (ALT.)
STANDlNG S STANDING SEAM ANGLE REINFORCED
[BARREINFORCEO) (ANGLE REINFORCEO) T-15 STANDING SEAM CAPPED FLANGE Figure 3-1 SMACNA Duct Joints
Walkdown Screening Guidelines 3.2.6 Flexibly Mounted Heavy Equipment W A C systems often have heavy pieces of mechanical equipment mounted in-line with the duct.
Examples include fans, coolers, dryers, dampers with motor operators, and blowers. Earthquake experience data have shown that large pieces of equipment mounted in-line on flexible supports (e.g., without lateral and longitudinal bracing) can damage the duct froin excessive displacement during an earthquake. This occurred at the Watkins-Johnson Plant during the 1989 Loma Prieta earthquake (Figure A-23 of Appendix A). Mechanical equipment should be investigated to determine if the joints connecting the equipment to the duct are sufficiently flexible to accommodate any expected swinging of the equipment during a seismic event. Potential interactions between swinging mechanical equipment and the W A C duct or other safety related equipment should also be investigated (see Section 3.4).
Heavy equipment with connected HVAC duct may be floor-mounted on vibration isolation pads. Earthquake experience data have shown examples of excessive leakage and failures of such W A C systems due to insufficient restraint of this equipment. Excessive leakage and failures have been caused by floor-mounted equipment falling off their isolation pads and damaging attached ducts in the process. Figure A-19 in Appendix A shows one such failure where a flexible bellows was tom due to the motion of an attached fan on vibration isolation mounts.
The SQUG GIP [l] provides guidelines for seismic verification of HVAC equipment such as fans (axial and centrifugal), air handlers and chillers. Heavy equipment that is flexibly supported or on vibration isolation pads should be evaluated separately using the SQUG GIP or identified as outliers for further evaluation.
3.2.7 Branch Flexibility Earthquake experience data have indicated that "hard points" are prone to seismic damage.
Examples of hard points include locations such as wall penetrations and rigid supports on short stiff branches that are attached to flexibly supported duct. This type of seismic damage occurred at the Wiltron Electronics Plant during the Morgan Hill earthquake (Figure A-15 of Appendix A). Short, stiff branches on a flexibly supported header should be identified as outliers and checked for adequate flexibility to accommodate the expected header motion during a seismic event based on the guidelines in Section 4.1.
3.2.8 Cantilevered Duct Earthquake experience data include isolated cases of cantilevered duct sections separating and falling from the main duct header. An example of inadequate attachment occurred at the Pacific Bell Watsonville facility during the Loma Prieta earthquake where a vertical cantilevered duct section separated and fell to the floor (Figure A-25 of Appendix A). Another example occurred at the Wiltron facility during the Morgan Hill earthquake where a vertical cantilever broke from its supporting header and fell (Figure A-14 of Appendix A). Cantilever duct sections should be adequately restrained to prevent excessive loads at the cantilever attachment point. The cantilever should be supported so that the maximum allowable cantilever length is not exceeded.
Unrestrained short cantilever ducts that meet the maximum allowable cantilever length should be reviewed to insure positive attachment to the supporting headers.
WalkdownScreening Guidelines 3.2.9 Duct Corrosion Excessive corrosion of HVAC ducts should be evaluated for its effect on structural integrity.
Light surface corrosion is generally not a concern but heavy flaking or pitting might be. Seismic experience data have shown that significant corrosion may lead to poor seismic performance for many plant items. Corrosion reviews are especially important in damp areas of a plant such as pump houses. Evaluations should consider an estimated strength reduction due to corrosion.
Significant corrosion should generally be identified for repair.
3.3 Support System Review This section describes support attributes for review during the in-plant screening review walkdowns. These attributes have led to poor seismic performance in similar distributed type systems, such as piping, cable tray and conduit systems [1,3]. Existing duct systems judged to have similar, potentially poor seismic performance attributes, shall be documented as outliers.
3.3.1 Beam Clamps Beam clamps should not be oriented in such a way that gravity loads are resisted only by the frictional forces developed by the clamps. Beam clamps oriented this way might loosen and slip off in an earthquake and possibly cause a collapse of the system.
3.3.2 Channel Nuts Channel nuts used with light metal strut framing systems should have teeth or ridges stamped into the nut where it bears on the lip of the channel when slip resistance is relied upon to maintain structural integrity. Laboratory tests have shown that in a seismic environment, channel nuts without these teeth or ridges have significantly lower slip resistance capacity than those with the teeth or ridges. Excessive galvanization or loose and flaking galvanization on the strut channel may also lead to reduced bolt resistance to slippage. Channel nuts should be visually reviewed on a random basis to provide reasonable assurance that teeth or ridges are present when required for structural integrity, and that the nuts are properly engaged on the frame sections.
3.3.3 Cast Iron Anchor Embedment Threaded rod hanger anchor embedments constructed of cast iron should be evaluated because of potential brittle failure modes. Plant documentation should be consulted to determine whether anchor embedments are cast iron. Earthquake experience data includes examples where heavily loaded rod hangers threaded into cast-iron inserts have failed [8]. Failure modes include anchor pullout and anchor fracture where rods are only partially threaded into the anchor.
WalkdownScreening Guidelines 3.3.4 Broken Hardware Any observed missing or broken hardware for HVAC duct and supports should be noted so that repair or replacement may be provided. This includes examples such as missing nuts or bolts on connections, bent or damaged support members, dented duct seams, separated duct joints, torn expansion joints and similar defects. W A C related hardware that is missing or broken should be evaluated to determine the consequences that this would have on the HVAC system. In particular, it should be determined if the integrity of the HVAC pressure boundary could be affected.
3.3.5 Support Corrosion Excessive corrosion of W A C duct supports and support components (including anchorage) should be evaluated for its effect on structural integrity. Light surface corrosion is generally not a concern but heavy flaking or pitting might be. Seismic experience data have shown that significant corrosion may lead to poor seismic performance for many plant items. Evaluations should consider the effects of an estimated strength reduction or loss of support due to corrosion.
Significant corrosion should generally be identified for repair.
3.3.6 Concrete Quality Gross defects or large cracks in the concrete to which the duct supports are attached should be evaluated for their potential effects on seismic performance. Visibly large cracks, significant spalled concrete, and serious honeycombing in the vicinity of W A C duct support anchors should be considered as gross defects. The walkdown team should consider grossly defective concrete areas as outliers and include supports anchored to marginally defective concrete in the sample selected for the limited analytical review.
3.3.7 Welded Attachments Support connections containing obviously undersized welds, incomplete welds, or welds of poor quality (i.e., with significant burn-through) require analytical review incorporating reduced capacities. Seismic experience data and shale table tests have shown that welds not capable of developing the strength of connected members may be subject to a brittle-type failure mode during seismic loading.
3.3.8 Rod Hanger Fatigue Although no specific instance of fatigue failure has been identified for HVAC duct rod hangers, raceway shake table tests have shown that short, fixed ended, heavily loaded rod hangers may be subject to low cycle, high strain fatigue failures during seismic events [l and 81. Rod hangers that may be subject to high strain low cycle fatigue effects should be investigated in greater detail. The rod fatigue evaluation requirements outlined in Section 4.4.2 should be used to address rod fatigue concerns.
WalkdownScreening Guidelines Rods to be evaluated are characterized as follows:
a Rods double nutted to flanges of steel members e Rods threaded into shell-type concrete expansion anchors Rods connected by rod couplers to non-shell type concrete expansion anchors Rods threaded into rod couplers which are welded to overhead steel embedments.
3.4 Seismic Interaction Review The W A C duct system must be reviewed for seismic interactions. The walkdown team should be aware of issues associated with seismic interaction and be alert for potential seismic interaction hazards. Only credible and significant interaction sources'should be considered as outliers. Damage that may occur to the duct itself as well as to any safety related equipment that the duct may interact with should be considered. Detailed guidance on identifying and evaluating seismic interactions is given in Appendix D of Reference [I].
3.4.1 Proximity and Falling Hazards Seismic interactions may occur as a result of movement of the W A C duct andlor movement of adjacent plant commodities. The range of motion of the W A C duct system, and those components in the vicinity that may come into contact with the duct system, must be assessed.
Reference [16] recommends that displacement of unbraced W A C duct systems be estimated as the in-structure 7% damped spectral displacement corresponding to the support system's free-swinging pendulum frequency. For braced duct systems, Reference [16] recommends that a resonant frequency of 10 Hertz be assumed to achieve an upper bound estimate for the displacement.
Duct systems attached to or in the vicinity of unanchored components or unreinforced block walls could be damaged by the slidinglfalling of the component or failure and falling of the block wall. Such instances should be noted, and the stability of the component or block wall evaluated.
3.4.2 Flexibility of Attached Lines Distribution lines such as small bore piping, tubing, conduit or cable that are connected to dampers can potentially fail if there is insufficient flexibility to accommodate relative motion between the damper and the adjacent equipment or structures. Straight, in-line connections in particular are prone to seismic damage or failure. The walkdown team should review distribution lines connected to dampers to insure there is adequate flexibility between the damper and the first support on the building or nearby structure.
WalkdownScreening Guidelines 3.4.3 -DifferentialDisplacement Hazards Ducts spanning from one structure to another should be checked to assure that they can accommodate any relative movement of the structures. Experience data indicate there can be excessive leakage or failures for duct systems without sufficient flexibility at spans experiencing differential displacement [3]. If this condition is identified, stress criteria established in Section 4 of this report should be used.
3.5 Pressure Boundary Integrity Review This section applies to W A C duct systems where a high confidence level of pressure boundary integrity is required for functional considerations. Examples where pressure boundary integrity may be required include the following:
Systems with little or no margin for airflow 0 Systems where leakage could significantly change system balance 0 Systems that separate clean from potentially contaminated or hazardous material (such as battery room exhaust).
The following are in-plant screening requirements to achieve a high level of confidence of pressure boundary integrity.
3.5.1 Duct Joints and Stiffener Spacing Stiffeners prevent bulging of the duct panels due to internal pressure. Lateral joints such as companion angles, and lateral reinforcements, typically of steel angles, are considered as stiffeners. Earthquake experience and test data have demonstrated that duct systems that met the SMACNA guidelines performed well during earthquakes. Items to be checked for the given system operating pressure requirements include sheet metal gage, stiffener size and spacing, and panel dimensions. For bolted duct connections, it is also necessary to check minimum flange height, number of bolts, maximum hole spacing, and ring size where segments of round duct are bolted together. Applicable sections from the SMACNA standards include Section 7 of Reference [6], Chapters 4 and 12 of Reference [7], and Chapters 1 and 3 of Reference 151.
3.5.2 Round Duct Supports Round W A C duct runs supported such that the duct is point loaded should be considered outliers unless the duct is reinforced at the point of support. An example of this situation is a round duct supported by a rod hanger without a saddle.
Walkdown Screening Guidelines 3.5.3 Flexible Bellows Flexible bellows connecting W A C duct to in-line equipment may become damaged if they do not have enough slack to accommodate differential motion between the equipment and the duct. Bellows are typically not designed to resist any large differential motions imposed by the earthquake. If reasonable estimates of bellows flexibility cannot be determined by judging the available slack in the as-installed configuration, then manufacturer's data should be reviewed.
3.6 Selection of Bounding Configurations As part of the in-plant screening review, representative, worst-case W A C duct and duct supports should be selected as bounding configurations. The extent of the sample should be determined by the Seismic Capability Engineers based on the diversity, complexity and extent of the systems being reviewed. The samples should include representative samples of the major different types of duct and duct supports for the HVAC duct and damper systems being reviewed. As a general guideline, 10 to 20 different sample supports and 1 to 4 sample duct runs should be selected for facilities evaluating multiple HVAC systems. These selected configurations should be evaluated using the analytical review criteria in Section 4. Detailed evaluation of bounding, worst-case configurations assures the seismic adequacy of the entire population. When selected configurations do not pass the analytical review, the seIected population should be expanded to identify the population of HVAC system configurations that meet the required seismic criteria. For example, all supports and duct runs that are represented by the item that failed should be located and identified for modification or further (more detailed) review.
The procedure for the selection of boundary configurations for duct and support system analytical review is dependent upon the functional requirements of the system. For duct systems requiring structural integrity or reasonable assurance for pressure boundary integrity (where potential small tears or leaks are acceptable), the sample selection only needs to include worst-case bounding duct supports. For systems where full pressure boundary integrity is required, the worst-case bounding sample should include the duct run itself as well as the supports.
The walkdown team needs to understand the analytical review requirements presented in Section 4 prior to performing in-plant screening reviews and selection of bounding configurations. The goal is to establish a biased, worst-case sampling, representative of and bounding the major different W A C configurations in the plant. This bounding of worst-case samples will be subject to analytical review.
Notes should be taken describing the basis for selection of each configuration. The location of the selected configuration should be noted, and detailed sketches of the as-installed condition should be made. As-built sketches should include the duct and support configuration, dimensions, connection details, anchorage attributes, member sizes, and loading. Any additional information that may be considered relevant to the seismic adequacy of the selected configuration should be noted in detail.
- . + JTalkdown Screening Guidelines Building elevation should be taken into account when choosing W A C duct configurations as bounding samples. Identical systems at two different elevations in the plant experience different seismic environments. The higher the building eIevation, the greater the seismic demand. Therefore, it is possible that a system appearing to have few seismic vulnerabilities which is located at an upper elevation in a building may actually have a greater probability of failure than a system located at a lower elevation with a worse configuration. The walkdown team members should acquaint themselves with the differing seismic demand environments in the buildings being inspected by reviewing the floor response spectra before selecting the bounding sample.
3.6.1 Selecting Bounding Duct Support Samples The most heavily loaded support for each duct configuration should be selected as a bounding case. Long spans, insulated duct, supports carrying multiple ducts, top supports of vertical runs, heavy in-line components and isolated "stiff' supports on rod hung systems are indicators of heavy load. Duct support configurations to consider are long W A C runs with few supports providing lateral or longitudinal restraint, long vertical runs, runs with seemingly weak curved sections, and runs with large, flexibly mounted in-line equipment. Of particular importance are duct supports that appear to have more loading than originally designed for. Heavily loaded supports can be identified by the presence of other plant components attached to the supports, such as supports for pipe, cable trays, and conduit.
Selection of a bounding duct support should consider conditions where anchorage appears to be'the weak link in the load path. Duct supports with anchorage that appears marginal for the supported weight should be investigated. Anchorage with undersized welds, incomplete welds, or welds of poor quality should also be evaluated. Overhead support steel, such as steel angle, used specifically as an anchor point to support the duct system should have its anchorage to the building structure evaluated.
3.6.2 Selection of Bounding Duct Configurations When appropriate, the selection should include duct systems with evidence of extreme or over-pressure loads, andlor duct systems that appear to have unusual loading conditions. Examples include duct runs that support other equipment items (such as raceways or piping), ducts that are shielded, heavily insulated or covered with fireproofing, and ducts with suspect flexible joints.
4.1 Overview of Analysis Criteria Analytical evaluations shall be performed on the selected bounding or sample W A C duct and support configurations required to achieve duct system function following a seismic event.
The selection of duct and/or support configurations shall be consistent with the requirements of Section 3.6. The duct evaluation criteria are based primarily on the design approach utilized in SMACNA' s construction standards for round and rectangular industrial duct [6,7]. Equations for computing pressure stresses in duct and stiffeners are taken directly from SMACNA standards. Use of this procedure results in a conservative estimate of the true duct capacity and is compatible with test data from References [9] through [13].
The pressure boundary integrity review of W A C duct considers the combined effects of pressure, dead weight and seismic loads on the duct. The combined dead load and seismic stress is checked against a factored allowable working stress for acceptance. The general stress combination equations are given below:
Horizontal Rectangular Duct Vertical Rectangular Duct Horizontal Circular Duct Eq. 4-3 Eq. 4-4 Vertical Circular Duct EQ, < 1.7 Fb Eq. 4-5
Analytical Review Criteria Pressure Stress Where:
f,, = Dead load bending stress fp = Pressure stress EQ, = Bending stress resulting from DBE seismic loads in the vertical direction EQh = Bending stress resulting from DBE seismic loads in the horizontal transverse direction. The additional subscripts 1 and 2 refer to stress components from two orthogonal transverse seismic loading conditions Fb = Bending stress allowable (normal working stress allowable)
Fp = Pressure stress allowable (normal working stress allowable)
The 1.7 increase in allowable stress accounts for the short duration of seismic loading. This increase is consistent with realistic allowable capacities for cable tray support components in Section 8.3.8 of Reference [I].
The effect of longitudinal seismic loading on the ducts is typically not significant since these forces are usually distributed over many support points. The effects of longitudinal seismic loading should be combined with transverse and vertical seismic loading by the Square Root of the Sum of the Squares (SRSS) method in the stress calculations.
4.2 Dead Load and Seismic Stress Analysis for dead and seismic loads may be performed using either the equivalent static load method or the response spectrum method.
The equivalent static load method follows a tributary length approach using the spectral acceleration at the applicable frequency (use peak floor spectral acceleration if frequency is unknown). An equivalent static coefficient of 1.0 times the spectral acceleration is used which is similar to the static coefficient used for equipment items addressed in Reference [I]. For this method, the bending moment is approximated by [6,7]:
M=- w.! F o r ducts spanning over one or two spans) Eq. 4-7 8
w.t M=- (For ducts spanning over 3 or more supports) Eq. 4-8 10
Analytical Review Criteria where:
w = applied linear load (Iblin)
= tributary span (in)
M = duct bending moment (in-lb)
Other configuration anomalies, such as cantilevered duct sections, shall be considered on a case-by-case basis.
Bending stresses due to axial response of a duct system may result if the axial run of duct is not braced in the longitudinal direction along the run of duct. If the axial restraint is provided by the first lateral restraint around a bend in the system, then the bending stress in the duct at the lateral restraint should be checked also for longitudinal motion of a tributary span of the axial run.
Alternatively, longitudinal load resistance along an axial run may be provided by framing action between the duct itself and the supports if the duct is adequately attached to the supports. In this case, the additional bending moment in the duct (about the transverse horizontal axis) must be checked.
The response spectrum method requires modeling of sufficient ducting to analytically represent the expected dynamic response of the system. In general, this includes duct up to anchor points or equivalent restraint. Modal combinations are performed using the Square Root of the Sum of the squares (SRSS) method. The analyses should consider all modes up to 33 Hz and include a minimum 90% mass participation.
For both methods, a critical damping ratio of 7% is appropriate for determining the seismic loads. This damping ratio is a conservative estimate of derived damping ratios from actual shake table tests [9 through 131.
Bending stresses for dead weight and seismic loads are derived using the duct section modulus as follows:
Eq. 4-9 where:
f, = Bending stress (psi)
M = Applied bending moment (in-lb) 3 Z = Duct section modulus (in )
Analytical Review Criteria For rectangular ducts, Reference [6] limits the effective area of sheet metal for calculation of the duct section modulus to a 2-inch by 2-inch region at the four corners of the duct. A reduced section modulus is thus calculated by assuming only these comers are effective in resisting bending. For round ducts, the full section is available for resisting the bending moment on the duct [7].
In addition, frequency correction factors of 0.59 and 0.87 for pocket lock and companion angle constructions, respectively, must be applied to adjust the calculated rectangular duct frequency based on analytical correlation of test results (Appendix D). Duct joints that do not fit any of the Figure 3-1 duct joint types and cannot be shown to behave in a manner equivalent to one of them should be evaluated separately.
Allowable bending stresses differ for rectangular and round ducts, as detailed in the following sections.
4.2.1 Allowable Bending Stress for Rectangular Ducts The allowable bending stress for normal operating conditions as specified by SMACNA [6],
is 8 ksi for carbon steel, galvanized sheet and stainless steel materials. This corresponds to 0.27 times the minimum yield strength of 30 ksi for typical materials used for industrial duct construction, within the specified temperature range.
The SMACNA standard for rectangular industrial duct construction [6] does not include design of duct fabricated of aluminum. A reasonable allowable bending stress for normal operating conditions for aluminum may be taken as 4.9 ksi. This corresponds to 0.27 times the minimum yield strength of 21 ksi for aluminum materials, times a yield strength reduction factor of 0.86 for temperatures up to 300 degrees Fahrenheit.
The normal allowable bending stress for rectangular ducts may be increased by a factor of 1.7 for DBE loads as detailed at the beginning of Section 4. This increase may be taken for ducts having pocket lock and companion angle (or equivalent) joints. This applies to joint types T-1 through T-3 and T-15 through T-24 of Figure 3-1, since Appendix D tests were performed on joints that are structurally similar to these types of duct joints. The normal allowable stress should not be increased by 1.7 for DBE for ducts with potentially weaker joints that rely on friction or crimping. Joints such as types T-4 through T-14 of Figure 3-1 are examples of potentially weaker joint types.
Duct joint that do not fit any of the Figure 3-1 duct joint types and cannot be shown to behave in a manner equivalent to one of them should be evaluated separately.
Analytical Review Criteria
- . 4.2.2 Allowable Bending Stress for Circular Ducts The allowable bending stress for circular ducts as specified by SMACNA [7] depends on the duct materials, operating temperature and diameter to thickness ratio.
The normal allowable bending stress for hot rolled carbon steel (based on a minimum yield stress of 33 ksi and maximum temperature of 400 degrees Fahrenheit) is as follows:
F, = 10.7 ksi for D/t < 294 (hot rolled carbon steel) 3 140 F, = -ksi for D/t 2 294 (hot rolled carbon steel)
D t where:
D = Diameter of circular duct (in) t = Duct thickness (in)
F, = Bending stress allowable (normal working stress allowable)
The normal allowable bending stress for cold rolled carbon steel and galvanized sheet (based on a minimum yield stress of 32 ksi and maximum temperature of 400 degrees Fahrenheit is as follows:
Fb = 11.0 ksi for D/t < 285 (cold rolled carbon steel, galvanized sheet) 3 140 F, = -ksi for D/t 2 285 (cold rolled carbon steel, galvanized sheet)
D t The normal allowable bending stress for stainless steel is as follows. The following are minimum values that envelope parameters given in the SMACNA standard [7] for types of stainless steel typically used for duct. These values assume minimum yield strength of 30 ksi and maximum temperature of 400 degrees Fahrenheit. Higher allowable stress values may be obtained from Reference [7] for materials with a higher minimum yield strength and lower temperature, based on more detailed analysis.
Fb = 8.8 ksi for D/t < 113 (stainless steel) 993 Fb = - ksi for D/t 2 113 (stainless steel)
D/t
Analytical Review Criteria The normal allowable bending stress for aluminum is as follows. The following are minimum values that envelope parameters given in the SMACNA standard [7] for types of aluminum typically used for duct. These values assume a minimum yield strength of 21 ksi and maximum temperature of 300 degrees Fahrenheit. Higher allowable stress values may be obtained from Reference [7] for materials with a higher minimum yield strength and lower temperature, based on more detailed analysis.
F, = 6.0 ksi for D/t < 110 (aluminum) 662 F, = - ksi for D/t 2 110 (aluminum)
Dlt The normal allowable bending stress for round ducts may be increased by a factor of 1.7 for DBE loads as detailed at the beginning of Section 4. This increase may be taken for ducts having pocket lock and companion angle (or equivalent) joints. This applies to joint types T-1 through T-3 and T-15 through T-24 of Figure 3-1, since Appendix D tests were performed on joints that are structurally similar to these types of duct joints. The normal allowable stress should not be increased by 1.7 for DBE for ducts with potentially weaker joints such as types T-4 through T-14 of Figure 3-1. These joints are potentially weaker because they rely on friction or crimping to transfer force across the joint.
4.3 Pressure Stress in Ducts The effect of stress in W A C duct material from internal pressure shall be accounted for in the analytic evaluation of W A C duct requiring pressure boundary integrity. These pressure stresses are checked against pressure stress allowables established in the SMACNA guidelines.
4.3.1 Pressure Stresses in Rectangular Ducts The SMACNA design of rectangular ducts is based on simplifying assumptions which permit the reduction of the analysis from a three-dimensional to a two-dimensional problem. Each of the four sides of the duct is assumed to act as an independent two-dimensional panel. Duct panel stresses are computed based on thin plate bending equations found in Reference [15].
For a given rectangular duct, the largest cross-sectional dimension (i.e. width or height) is used for stress analysis (see Figure 4-1). The applicable plate bending equations are dependent on the ratio of this maximum duct dimension, S, to the duct stiffener spacing, L.
Analytical Review Criteria S = Max (H.W)
Figure 4-1 Rectangular Duct Configuration Two simplified models are used to calculate duct pressure stresses. The following notations are used:
Height of duct (in)
Width of duct (in)
Max (H, W) (in)
Stiffener spacing (in)
Duct thickness (in)
Young's Modulus of duct material (psi) adjusted for temperature. Use 9 . 5 ~ 1 psi 0 ~ for stainless steel, and 9 . 2 ~ 1 psi 0 ~ for aluminum. Slightly higher values may be obtained using more detailed analysis from Reference [7].
Poisson's ratio (dimensionless), taken as 0.30 for all duct materials Applied pressure (psi)
The duct panel is idealized as one-way plate bending over a fixed-ended span, L, with axial in-plane tensile reactions resisting the increase in panel length due to bending curvature.
Analylical Review Criteria Let:
T = Axial tensile reaction resisting the increase in length due to bending curvature Db = E t3/(12(l-v2))(plate bending stiffness coefficient) Eq. 4-10 To obtain u, use Figure 4-2 taken from Reference [15]. To use this chart, the variable U1 is first calculated as:
The quantity loglo(104u ~ ~then . ~ gives
) the ordinate of the curve in Figure 4-2, and the corresponding abscissa gives the required value of u. After determining U, the maximum stresses in the plate are caIcuIated as follows:
The maximum tensile stress is [15] :
The maximum bending stress is [15]:
Maximum total pressure stress is:
fp = fi + f2
Analylical Review Criteria Log lo4- for various values of U Value of p Figure 4-2 Value of u for Rectangular Ducts [15]
As the stiffener spacing exceeds the width of the critical duct section, the restraining effect of the panel side edges increasingly influences the stress distribution within the panel, requiring the use of a second set of stress equations.
The panel is modeled as a uniformly loaded rectangular two-way plate fixed on the two opposite edges at the stiffeners and hinged on the edges along the sides. The maximum bending moment occurs at the mid-points of the fixed edges and is given by [15]:
Ailalytical Review Criteria A list of K values for various L/S ratios, is given in Table 4-1.
Table 4-1 Value of K for Rectangular Ducts [I 51 Values of Parameter K US K US K 1.O -0.0697 1.7 -0.1090 1.1 -0.0787 1.8 -0.1122 1.3 -0.0868 1.9 -0.1 152
-0.0938 -0.1174
-0.0998 -0.1 191 1.6 -0.1 049 -0.1 250 The resulting stress is:
Through the use of equations Eq. 4-1 6 and Eq. 4-17, the panel pressure stresses can be calculated for any combination of system pressure and duct dimensions.
The allowable pressure stress for rectangular carbon steel, galvanized sheet and stainless steel ducts is taken from Reference [6] as:
= 24 ksi (carbon steel, galvanized sheet and stainless steel)
Fp The allowable pressure stress for aluminum ducts may be taken as:
F, = 15 ksi (aluminum) 4.3.2 Pressure Stresses in Round Ducts The pressure capacity of circular ducting is controlled by either buckling of the duct 'skin' or buckling (or yielding) of the duct stiffeners assuming negative duct pressure. Duct skin buckling is influenced by the duct end conditions. The following notations are used:
D = Duct diameter (in)
L = Stiffener spacing (in) t = Duct skin thickness (in)
P, = Critical duct pressure (psi)
= Critical stiffener spacing (in)
Analytical Review Criteria The critical duct pressure as determined in Reference [7] is dependent on the spacing of the stiffeners. The critical spacing of the stiffness is defined as the spacing beyond which the duct is regarded as unstiffened, because the stiffeners are no longer contributing to the capacity of the duct to resist negative pressure. The critical spacing is as follows:
When the circumferential stiffener spacing is less than critical spacing, the allowable duct pressure is as follows:
P, = 1 8 . 1 ~o6 1 (t/D)'" (D/L) psi (carbon steel, galvanized sheet) Eq. 4-19 P,= 1 6 . 1 ~ 1 0(t/D)'"
~ (D/L) psi (stainless steel) Eq. 4-20 P, = 5 . 6 ~o6 1 ( t / ~ ) ' .(D/L)
~ psi (aluminum) Eq. 4-21 When the duct is unstiffened or when the circumferential stiffener spacing is greater than the critical spacing, the maximum duct pressure is as follows:
P, = 16.2~1 o6 ( t / ~ ) 3psi (carbon steel, galvanized sheet) Eq. 4-22 P,= 1 4 . 5 ~ 1 0(t/D)3
~ psi (stainless steel) Eq. 4-23 P, = 5 . 1 ~o3 1 ( t / ~ ) 3psi (aluminum) Eq. 4-24 These formulas are valid for carbon steel, galvanized sheet steel and stainless steel up to 400 degrees Fahrenheit and for aluminum up to 300 degrees Fahrenheit. They are based on temperature adjusted Young's Moduli of 2 9 . 5 ~ 1 0psi ~ for carbon steel and galvanized sheet steel, 2 6 . 3 ~ 1 0psi
~ for stainless steel, and 9 . 2 ~ 1 0psi ~ for aluminum. Slightly higher values for pressure may be obtained for specific stainless steel and aluminum materials at lower temperatures by using more detailed analysis &om Reference [7].
The critical duct pressure should be used as the pressure stress allowable, Fp, and compared with the actual pressure.
Analytical Review Criteria 4.4 Pressure Stresses in Stiffeners 4.4.1 Stiffener Evaluafion for Recfangular Ducfs Let:
9 = Tributary load to stiffener (lblin)
P = Duct pressure (psi)
H = Height of duct (in)
W ' = Width of duct (in)
S = Max (H, W)
L = Stiffener spacing (in)
Fb(sTFF)= Allowable bending stress in the stiffener (ksi)
Following analysis of the panels, the duct stiffeners are checked for two conditions:
e Maximum deflection < SI360 Maximum bending stress in the stiffener I Fb(STIFF)
The load transmitted to the stiffener from the duct panel is dependent on the ratio of L/S.
The tributary load to the stiffener, q, is calculated as follows:
For L/S < 2.0, For 2.0 < L/S I 10.0, For L/S > 10.0, q = tributary load resulting from pressure p being applied on an area bounded by lines radiating at 45' from the ends of the stiffener (see Figure 4-3).
The stiffener stress evaluation for the above loading conditions is dependent upon whether the stiffener ends are fixed or pinned.
AnaIytical Review Criteria Stiffeners welded at their ends to stiffeners from the adjacent side of the duct provide bending moment transition and are considered fixed. Such stiffeners should be analyzed as follows:
where:
I = Moment of inertia of the stiffener (in4) c = Distance between neutral axis and extreme fiber of stiffener (in)
E = Young's Modulus of stiffener (psi) adjusted for temperature. Use 2 9 . 5 ~ 1 0psi
~ for stainless steel, and 9 . 2 ~ 1 0psi
~ for aluminum. Slightly higher values may be obtained using more detailed analysis from Reference [7].
d = maximum stiffener displacement (in)
LOAD GOlNG TO STIFFENER r-Figure 4-3 Load Going to Stiffener on a Rectangular Duct When US 2 10.0 [6]
Stiffeners are considered pinned regardless of whether they are bolted at their ends, tack welded, or not connected at their ends. Such stiffeners should be evaluated as follows:
Analytical Review Criteria The allowable bending stress in the stiffener is set as follows:
Fb(STIFF)= 24 ksi (Carbon steel, galvanized sheet steel)
Fb(sTIFFl = 19.2 ksi (Stainless steel)
Fb(STIFF)= 13.1 ksi (Aluminum)
Inadequate stiffeners will need to be supplemented. Stiffeners placed on only two opposite sides of a rectangular duct and meeting the above criteria are adequate as long as the panel width is less than 72 inches. For panels of longer size, stress concentration becomes excessive and additional stiffeners are required.
4.4.2 Stiffener Evaluation for Round Ducts The capacity of round duct stiffeners is controlled by buckling or yielding, where the theoretical buckling strength is proportional to the moment of inertia of the stiffener, and the yield strength is proportional to the area. Both of the following equations for moment of inertia and stiffener area for the respective material type must therefore be satisfied [7].
I >I = 1 . 6 ~ou8 1 L D) P, (Carbon steel, galvanized sheet steel) Eq. 4-32 I,> Im = 1 . 7 ~ 1 0L- ~D) P, (Stainless steel) Eq. 4-33 I >1 = 1 L D) P,, (Aluminum) 5 . 0 ~0-8 Eq. 4-34 As> AMIN = 6.3x10-~L D P, (Carbon steel, galvanized sheet steel) Eq. 4-35 A, > Am = 7.6x10-~L D P, (Stainless steel) Eq. 4-36 A, > AMIN = 103x1o ~L D P, (Aluminum) Eq. 4-37 where:
I, = Moment of inertia of stiffener (in4)
A, = Area of stiffener (in2)
P, = Applied pressure in duct (psi)
L = Stiffener spacing (in)
D = Duct diameter (in)
Higher values may be obtained for specific materials and for lower temperatures by using more detailed analysis from Reference [7].
Analytical Review Criteria 4.5 Duct Support Evaluation 4.5.1 Alleta1 Frame and Anchorage The selection of support configurations for evaluation shall be consistent with the requirements of Section 3.6. Simplified support evaluation requirements, consistent with those presented in Section 8 of Reference [l] for limited analytical review of raceway supports, are applicable for the seismic adequacy verification of duct supports. These include the following checks, applying to both the support structural framing and the anchorage to the building structure:
Dead load Vertical capacity (for greater of 5g or 6 ZPAhtimes Dead Load)
Ductility Lateral load check Longitudinal load check Rod hanger fatigue evaluation The 5 times dead load check is used in the vertical capacity check accounts for the dynamic characteristic differences in terms of system damping between the HVAC duct and raceway systems. That is, the 3 times dead load check established for raceways is factored up by the difference in spectral acceleration demand due to the lower damping in HVAC systems (on the order of 7%) as compared to raceway systems damping (on the order of 15%). The 6 times ZPAh check, where ZPAh is the zero period acceleration at the support anchor, is from Reference [16].
This controls when ZPAh exceeds 0.83g.
A discussion of the requirements for the dead load check, vertical capacity check, ductility review, lateral and longitudinal loads checks is included in Appendix F. The rod hanger fatigue evaluation guidelines are presented in Appendix E.
For systems in which detailed modal response spectrum analysis is performed, the duct support frame should be evaluated for the resulting seismic loads combined with dead loads.
Loads from other attached systems, such as conduit or piping, should also be considered. All steel components such as bracket members, support members, and internal support framing connections should be checked, using allowables as defined in Part 1 of the AISC [2].
The buckling analysis of vertical support members and lateral bracing should also follow the criteria of Part 1 of AISC [2]. It is recognized that many support configurations have structurally redundant members. If buckling is predicted to occur in a support member, the support may still be acceptable if the buckling does not affect the overall stability of the duct system. For example, if a lateral brace is found to buckle under imposed seismic loading, but vertical capacity is not jeopardized, the duct can be analyzed ignoring the presence of the brace. If the duct system stresses are acceptable without the lateral brace and spatial (proximity-related) interaction due to duct seismic displacement is not a problem, then the support is acceptable.
Analytical Review Criteria 4.5.2 Rod Hanger Fatigue Evaluation Short, fixed ended, heavily loaded rod hangers may be subject to low cycle, high strain fatigue failures during seismic events [8]. Rod hangers of concern are typically of fixed end connections.
These rods are characterized as follows:
e Rods double-nutted to flanges of steel members a Rods threaded into shell-type concrete expansion anchors Rods connected by rod couplers to non-shell type concrete expansion anchors Rods threaded into rod couplers welded to overhead steel embedments Rod hangers that may be subject to high strain low cycle fatigue effects should be investigated in greater detail. The rod fatigue evaluation guidelines outlined in Attachment E should be used to address any rod fatigue concerns.
4.5.3 Anchorage Capacity Capacity values for anchors should be taken from Reference [I]. The provisions of these anchorage guidelines should be followed, including edge distance, bolt spacing, and inspection procedures. Tightness checks are not required for expansion anchor bolts that are normally subjected to tensile forces due to dead weight, since the adequacy of the anchorage set is effectively proof tested by the dead weight loading. This applies to expansion anchors for overhead and wall mounted supports.
4.5.4 Redundancy and Consequence Test Isolated cases of a support not meeting the analytical review guidelines may be accepted if the W A C support system has redundancy so that postulated support failure would have no consequence to overall system performance. Adequate redundancy is demonstrated if the adjacent supports are capable of sustaining the additional weight resulting from the postulated support failure.
A summary package should be assembled to document and track the Seismic Capability Engineers' evaluation activities. Documentation should include records of the W A C duct and damper systems evaluated, the dates of the walkdowns, the names of the engineers conducting the evaluations, and a summary of results. Recommended data sheets for the summary package are given in Exhibits 5-1 to 5-5 and are described below.
Exhibit 5-1 provides a Screening and Evaluation Work Sheet (SEWS) that can be used to document the walkdowns. The SEWS includes reminders, as a checklist, for primary aspects of the evaluation guidelines; however, the walkdown engineers should be familiar with all aspects of the seismic evaluation guidelines during in-plant screening reviews and not rely solely on the checklist. The checklist items on the SEWS are worded so that all acceptable conditions are answered Y (for yes). Any condition that is answered N (for no) or U (for unknown) is an outlier.
The SEWS should be signed and dated by at least two Seismic Capability Engineers, one of whom is a licensed professional engineer.
Exhibit 5-2 provides a Duct Support Analytical Review Data Sheet for recording information on the supports selected as the worst case, representative samples.
Exhibit 5-3 provides a Tracking Summary for the Duct Support Analytical Review Data Sheets.
As items are completed and resolved, the responsible engineers should initial the line item on the tracking sheets to confirm final closure.
Exhibit 5-4 provides a W A C Duct System Analytical Review Data Sheet for recording information on the duct system selected as worst case, representative samples for systems required to maintain pressure boundary.
Exhibit 5-5 provides a W A C System Outlier Sheet (HSOS) for documenting outliers.
An outlier is a W A C duct system or support feature that does not meet the screening guidelines in Section 3, or a W A C duct or support that does not meet the analytical review criteria in Section 4. The HSOS identifies the screening guidelines that are not met, the reasons for the outlier, and the proposed method of resolving the outlier. Outliers are discussed in Section 6.
Photographs may be used to supplement documentation as required. When used as formal documentation for the summary packages, photographs should be clearly labeled for identification.
Exhibit 5-1 Sheet 1 of -
SCREENING AND EVALUATION WORK SHEET (SEWS)
HVAC System I.D.
Damper Equipment I.D.
System Description and Boundaries HVAC System Locations and Reference Drawings Duct Materials and Sizes Linear Weight:
Duct Insulation Total References Concurrent Pressure and Temperature Applicability
- 1. Operating temperature less than the temperature limitations in Table 2-1 Y N U NIA
- 2. Plant ground spectrum enveloped by the SQUG Bounding Spectrum (Figure 2-1) and ZPA, is less than 2.09 Y N U NIA Does duct meet applicability criteria? Y N U Pressure Boundary lntearity Review
- 1. Is pressure boundary integrity required?
IF the answer to the above question is NO, SKIP THIS SECTION and proceed to the Structural Integrity Review
- 2. Stiffener spacings are within the guidelines
- 3. Bolted flanged joints satisfy SMACNA requirements
- 4. No point-supported round duct
- 5. Flexible bellows can accommodate motions
- 6. No additional concerns Are the above caveats met? Y N U
Docunzentation Exhibit 5-1 Sheet 2 of -
SCREENING AND EVALUATION WORK SHEET (SEWS)
HVAC System I.D.
Damper Equipment I.D.
Structural lntearitv Review
- 1. Support spans satisfy the criteria Y N U NIA
- 2. Ducts are properly tied-down to the supports Y N U NIA
- 3. Industry standard duct joints are utilized Y N U NIA
- 4. Slip joints can accommodate displacements Y N U NIA
- 5. Round duct joints exclude riveted lap joints Y N U NIA
- 6. Appurtenances are positively attached to duct Y N U NIA
- 7. Heavy in-line equipment is adequately restrained Y N U NIA
- 9. Cantilevered duct section is attached to last support Y N U NIA
- 10. Ducts are free of corrosion detrimental to integrity Y N U NIA
- 11. System is free of obvious damage or defects Y N U NIA
- 12. No other concerns Y N U NIA Are the above caveats met? Y N U Support Review
- 1. Beam clamps are oriented to preclude slipping off the support
- 2. Channel nuts have teeth or ridges
- 3. No cast iron inserts
- 4. No broken or obviously defective hardware
- 5. Support is free of excessive corrosion
- 6. Welded joints appear to be of good quality
- 7. Anchorage appears adequate
- 8. No stiff supports or hard spots in long flexible duct runs
- 9. No short, fixed ended heavily loaded rod hangers subject to potential fatigue failure Y N U NIA
- 10. No additional concerns Y N U NIA Are the above caveats met? Y N U Damoer Review
- 1. Damper is similar to and bounded by the seismic experience data for dampers in Attachment B Y N U NIA
- 3. Attached lines have sufficient slack and flexibility Y N U N/A
- 6. Duct at the damper location free from signs of distortion that could interfere with damper operation Y N U NIA
- 7. No other adverse concerns Y N U NIA Are the above caveats met? Y N U
Documentation Exhibit 5-1 Sheet 3 of -
SCREENING AND EVALUATION WORK SHEET (SEWS)
HVAC System I.D.
Damper Equipment I.D.
Seismic Interaction Review
- 1. Free from impact by nearby equipment Y N U NIA
- 2. No collapse of overhead equipment, distribution systems or masonry walls Y N U NIA
- 3. Able to accommodate differential displacements Y N U NIA
- 4. No other adverse concerns Y N U NIA Are the above caveats met? Y N U IS THE HVAC DUCT AND DAMPER SYSTEM SEISMICALLY ADEQUATE? Y N U Supports Selected for Analytical Review Duct System Selected for Analytical Review Comments CERTIFICATION: (Signatures of at least two Seismic Capability Engineers are required; one of whom is a licensed professional engineer.)
Print or Type Nameflitle Signature Date Print or Type Nameflitle Signature Date
Exhibit 5-2 Sheet 1 of -
DUCT SUPPORT ANALYTICAL REVIEW DATA SHEET HVAC Duct System: Selection No.:
Plant Location:
Description and Sketch:
CERTIFICATION: (Signatures of at least two Seismic Capability Engineers are required; one of whom is a licensed professional engineer.)
Print or Type Name/Title Signature Date Print or Type Namenitle Signature Date
Docurnentation Exhibit 5-3 Sheet 1 of -
HVAC DUCT SUPPORT ANALYTICAL REVIEW TRACKING
SUMMARY
HVAC Duct Plant Selection Final System Location Number Resolution Desianation
Documentation Exhibit 5-4 Sheet 1 of -
HVAC DUCT SYSTEM ANALYTICAL REVIEW DATA SHEET HVAC Duct System: Selection No.:
Plant Location:
Description and Sketch:
CERTIFICATION: (Signatures of at least two Seismic Capability Engineers are required; one of whom is a licensed professional engineer.)
Print or Type NameKitle Signature Date Print or Type NameKitle Signature Date
Doctinlentation Exhibit 5-5 Sheet 1 of -
HVAC SYSTEM OUTLIER SHEET (HSOS)
OUTLIER NO.
- 1. OUTLIER IDENTIFICATION AND LOCATION HVAC System I.D.
Location
- 2. OUTLIER ISSUE DEFINITION
- a. Identify the screening guidelines that are not met, or indicate if the analytical review selection fails the analysis criteria.
Applicability Damper Review Pressure Boundary Integrity Interaction Effects Structural Integrity Review Support Analytical Review Support Review Duct Analytical Review
- b. Describe all the reasons for the outlier:
- 3. PROPOSED METHOD OF OUTLIER RESOLUTION (OPTIONAL)
- a. Define the proposed method(s) for resolving the outlier:
- b. Provide information needed to implement proposed method(s) for resolving the outlier:
CERTIFICATION: (Signatures of at least two Seismic Capability Engineers are required; one of whom is a licensed professional engineer.)
Print or Type Namerritle Signature Date Print or Type Name~Title Signature Date 5-8
6.1 Identification of Outliers An outlier is defined as a W A C duct, damper or support feature that does not meet the screening guidelines in Section 3, or a W A C duct or support selection that fails the analytical review criteria in Section 4. The guidelines and analysis criteria are intended to be used on a generic basis for seismic adequacy review of W A C systems (including supports). W A C duct, dampers or supports that do not pass the generic criteria may still be shown to be seismically adequate by obtaining additional information or by performing additional evaluations.
6.2 Outlier Resolution An outlier may be shown to be adequate for seismic loadings by performing additional evaluations to demonstrate there is adequate seismic margin. These additional evaluations and alternate methods should be thoroughly documented to permit independent review.
Methods to determine the available seismic margin are contained in EPRI NP-6041-SL [14].
In some cases it may be necessary to exercise engineering judgment when resolving outliers, since strict adherence to the screening guidelines is not absolutely required for HVAC systems to be seismically adequate. These judgments, however, should be based on a thorough understanding of the background and philosophy used to develop these screening guidelines as described in this report. The justification and reasoning for considering an outlier to be acceptable should be based on mechanistic principles and sound engineering judgment.
The screening guidelines contained in this report have been reviewed to ensure that they are appropriate for generic use; however, the alternative evaluation methods and engineering judgments used to resolve outliers are not subject to the same level of peer review. Therefore, the evaluations and judgments used to resolve outliers should be thoroughly documented so that independent reviews can be performed if necessary.
REFERENCES
- 1. Seismic Qualification Utilities Group (SQUG), "Generic Implementation Procedure (GIP) for Seismic Verification of Nuclear Plant Equipment," Revision 3A, December 2001.
- 2. AISC, "Manual of Steel Construction," gthEdition, American Institute of Steel Construction, Chicago, IL, 1978.
- 3. Porter, K., G. S. Johnson, M. M. Zadeh, C. S. Scawthorn, and S. J. Eder, August 1993, "Seismic Vulnerability of Equipment in Critical Facilities: Life-Safety and Operational Consequences," Prepared for National Center for Earthquake Engineering Research, November 1993.
- 4. Sheet Metal and Air Conditioning Contractors National Association, Inc., " W A C Duct Construction Standards, Metal and Flexible," Chantilly, Virginia, First Edition, 1985.
- 5. Sheet Metal and Air Conditioning Contractors National Association, Inc., " W A C Duct Construction Standards, Metal and Flexible," Chantilly, Virginia, Second Edition, 1995.
- 6. Sheet Metal and Air Conditioning Contractors National Association, Inc., "Rectangular Industrial Duct Construction Standards," Chantilly, Virginia, Copyright 1980.
- 7. Sheet Metal and Air Conditioning Contractors National Association, Inc.,
"Round I~ldustrialDuct Construction Standards," Chantilly, Virginia, Second Edition, September 1999.
- 8. The Performance of Raceway Systems in Strong-motion Earthquakes, EPRI, and EQE Engineering: March 1991. Report EPRI NP-7150-D.
- 9. Yow, J. Roland, "Status Report on the Recent History of W A C Ductwork Design for Nuclear Power Stations and Current Industry Activity for the Committee on Materials and Structural Design," Prepared for the American Society of Civil Engineers, September 1980.
- 10. McPherson, R. Keith, "Duct Test Report to Determine Load Carrying Capabilities and Cross Sectional Properties of Safety Related Duct for Washington Public Power Supply Steam Nuclear Project No. 2," April 1982.
- 11. Desai, S.C., et al., "Structural Testing of Seismic Category I W A C Duct Specimens,"
Second ASCE Conference on Civil Engineering and Nuclear Power. Volume I. Knoxville, Tennessee, September 1980.
- 12. Neely, B. B., and L. Warrix, "A Procedure for Seismically Qualifying W A C Ducts Used in Nuclear Power Plants," Second ASCE Conference on Civil Engineering and Nuclear Power, Volume I, Knoxville, Tennessee, September 1980.
References
- 13. Kato, T. and T. Nakatogawa et al. "Limit Strength of Rectangular Air Ventilation Ducts Under Seismic Design Condition," Transactions of the 10th International Conference on Structural Mechanics in Reactor Technology, Volume K2, 1989.
- 14. A Methodology for Assessment of Nuclear Power Plant Seismic Margin: Revision 1, EPRI, Palo Alto, CAYNTS Engineering, Long Beach, CAYand RPK Consulting, Yorba Linda, CA:
July 1991. Report NP-604 1.
- 15. Tirnoshenko, S. and S. Woinowsky-Kreiger, "Theory of Plates and Shells," McGraw Hill, Second Edition, 1959.
- 16. Advanced Reactor Corporation, "Advanced Light Water Reactor (ALWR) First-of-a-Kind-Engineering (FOAKE) Project on Design Concepts for W A C Ducting and Supports,"
April 1995.
HVAC DUCT SYSTEM EARTHQUAKE EXPERIENCE DATA A.1 Introduction This attachment documents the performance history of W A C duct and duct support systems under seismic loading. The bulk of data was obtained from extensive field investigations of systems that have experienced strong motion earthquakes. Further information on the performance of HVAC duct systems was gained from a literature search on earthquake damage in past earthquakes.
A summary of the known damage data for the performance of W A C duct systems when subject to seismic loading is presented. The seismic experience database includes many examples of ducts that have performed well in actual earthquakes. The presented data focuses on examples of ducts that have performed poorly in seismic excitations, with a discussion of the attributes of the installations that caused them to perform poorly.
HVAC ducting is found at nearly all industrial sites. The seismic experience database therefore includes a vast amount of data on the survivability of ducting installed in many different ways, and experiencing many different seismic excitation levels. The large number of duct systems that have survived earthquakes indicate the inherent ruggedness of these systems. The limited, smaller set of W A C duct systems that have been found to have performed poorly in a seismic event point out key characteristics of HVAC installations that may contribute to seismic damage.
8.2 Earthquake Experience Database The seismic experience database is founded on studies of over 100 facilities located in the strong-motion areas of more than twenty strong-motion earthquakes that have occurred in the United States, Latin America, New Zealand, and other parts of the world since 1971 (see Table A- 1).
The database was compiled through surveys of the following types of facilities:
Fossil-fueled power plants e Hydroelectric power plants a Electrical distribution substations 0 Oil processing and refining facilities
W A C Duct System Eartlquake Experience Data (I, Water treatment and pumping stations t~ Natural gas processing and pumping stations Manufacturing facilities Large commercial facilities In general, data collection efforts focused on facilities located in the areas of strongest ground motion for each earthquake investigated. Facilities were sought that contained substantial inventories of mechanical and electrical equipment or control and instrumentation systems.
Because of the number of earthquake-affected areas and types of facilities investigated, there is a wide diversity in the types of installations included in the database. For the W A C duct of focus in this study, there is a wide diversity in size, configuration, type of building, local soil conditions, and quality of construction.
The database currently includes in detail fourteen earthquakes from which duct data have been processed for this report. Each earthquake includes several different sites investigated within each epicentral area. The earthquakes investigated range in Richter magnitude (M) from 5.5 to 8.1. The strong motion duration is as high as forty seconds. Local soil conditions range from deep alluvium to rock.
The buildings housing the ductwork have a wide range in size and type of construction. As a result, the database covers a wide diversity of seismic input to duct installations, in terms of seismic motion, amplitude, duration, and frequency content.
HVAC Duct System Earthquake Experience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)"*
San Fernando, CA Sylmar Station Large electrical substation 0.65 Earthquake 1971 (M6.6)
Rinaldi Receiving Large electrical substation 0.50-0.75 Station Valley Steam Plant Four-unit gas-fired 0.40 power plant Burbank Power Plant Six-unit gas-fired power plant 0.25 Glendale Power Plant Five-unit gas-fired 0.30 power plant Pasadena Power Plant Five-unit gas-fired 0.30 power plant Point Mugu, CA Ormond Beach Power Large two-unit oil fired 0.10 Earthquake 1973 (M5.7) Plant power plant Ferndale CA Humboldt Bay Power Two gas-fired units, 0.30*
Earthquake 1975 (M5.5) Plant one nuclear unit Santa Barbara, CA Goleta Substation Electrical substation 0.26*
Earthquake 1978 (M5.7)
Imperial Valley, CA El Centro Steam Plant Four-unit gas-fired 0.42" Earthquake 1979 (M6.6) power plant Drop IV Hydro. Plant Two-unit hydroelectric 0.30 Humboldt, CA Humboldt Bay Power Two gas-fired units 0.25 Earthquake1980 (M7.0) Plant one nuclear unit
- Ground acceleration measured by an instrument at the site
- Average of two horizontal components
W A C Duct Systenz Earthquake Experience Data Table A-I Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)**
Coalinga, CA Main Oil Pumping Plant Pumping station feeding oil 050 Earthquake 1983 (M6.7) pipeline from Coalinga area Union Oil Butane Plant Petrochemical facility to 0.60 extract butane and propane from well waste gas Shell Water Treatment Petrochemical facility to 0.60 Plant demineralize water prior to steam injection into oil wells Coalinga Water Potable Water purification 0.52 Treatment Plant facility Coalinga Substation Electrical substation No. 2 Shell Tank Farm No. 29 Oil storage 0.38 Pleasant Valley Pumping station to supply 0.56*
Pumping Plant water from the San Luis Canal to the Coalinga Canal San Luis Canal Agricultural pumping stations 0.20-0.60 Pumping Stations (29) taking water from the San Luis Canal Gates Substation Large electrical substation 0.25 Kettleman Compressor Natural gas pipeline booster 0.20 Station station Morgan Hill, CA United Tech Chemical Large research facility for 0.50 Earthquake 1984 (M6.2) Plant missile systems development IBMISanta Teresa Large computer facility for 0.37*
Facility software development San Martin Winery Winery 0.30 Wiltron Electronics Plant Electronics manufacturing 0.35 facility Metcalf Substation Large electrical substation 0.40
- Ground acceleration measured by an instrument at the site
- ' Average of two horizontal components
HVAC Duct System Earthqualce Experience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)**
Morgan Hill, CA Evergreen Community Large college complex with 0.20 Earthquake 1984 (M6.2) College self-contained HVAC power (cont'd) plant Mirassou Winery Winery 0.20 Chile Earthquake 1985 Bata Shoe Factory Four-buildingfactory 0.64 (M7.8) and tannery San lsidro Substation Electrical substation 0.58*
Llolleo Water Pumping Water pumping station 0.78 Plant Terquim Tank Farm Oillacetatelacid storage 0.55 tank farm Vicuna Hospital Four-story hospital 0.55 Rapel Hydroelectric Five-unit hydroelectric plant 0.40*
Plant San Sebastion Electrical substation 0.35 Substation Concon Petroleum Petrochemical facility 0.30 Refinery producing fuel oil, asphalt, gasoline and other petroleum products Oxiquim Chemical Plant Chemical facility producing 0.30 various chemicals, including feed stock for paint ingredients Concon Water Pumping Water pumping station 0.30 Station Renca Power Plant Two-unit coal fired 0.30 power plant Laguna Verde Power Two-unit coal-fired 0.30 Plant power plant Las Ventanas Copper Copper refinerytfoundry 0.22 Refinery power plant
- Ground acceleration measured by an instrument at the site
- Average of two horizontal components
W A C Duct System Earthquake Experience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)**
Chile Earthquake 1985 Las Ventanas Power Two-unit coal-fired peaking 0.25 (M7.8) (cont'd) Plant plant San Cristobal Electrical substation 0.25 Substation Las Condes Hospital Four-story hospital 0.20 Mexico Earthquake La Villita Power Plant Four-unit hydroelectric plant 0.14 1985 (M8.1) -
SICARTSA Steel Mill Large modern steel mill 0.25-0.50 Fertimex Fertilizer Plant Fertilizer plant 0.25-0.50 Adak, Alaska Adak Naval Base Diesel-electric power plants, 0.25 Earthquake 1986 (M7.5) electrical substations, sewage lift stations, water treatment plant, steam plants North Palm Springs, CA Devers Substation Large electrical distribution 0.85*
Earthquake 1986 (M6.0)
Chalfant Valley, CA Control Gorge Two-unit hydroelectric plant 0.25 Earthquake 1986 (M6.0) Hydro Plant San Salvador Soyopango Substation Electrical substation 0.50 Earthquake 1986 (M5.4)
San Antonio Substation Electrical substation 0.40 Cerro Prieto, Mexico Power Plant 1 Geothermal power plant 0.20-0.30 Earthquake 1987 (M5.4)
Power Plant 2 Geothermal power plant 0.20-0.30 Bay of Plenty, New Edgecumbe Substation 2301115kV substation 0.5-1 .O Zealand Earthquake 1987 (M6.25)
- Ground acceleration measured by an instrument at the site
- Average of two horizontal components
HVAC Dzict Systein Earthquake Ekperience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)*
Bay of Plenty, New New Zealand Distillery Liquor distillery 0.50-1 .O Zealand Earthquake 1987 (cont'd) (M6.25)
Bay Milk Dairy Products 0.50 Caxton Paper Mill Paper and pulp mill 0.40-0.55 Kawerau Substation 2301115kV substation 0.40-0.55 Whakatane Board Mill Paper mill producing 0.25 cardboard Matahina Dam Two-unit hydro-electric plant 0.26*
Whittier, CA Earthquake Olinda Substation Electrical substation 0.65*
1987 (M5.9)
SCE Central Dispatch Data Processing Center 0.56" Headquarters SCE Headquarters Large office complex 0.42*
California Federal Bank Data processing facility 0.40 Facility Ticor Facility Data processing facility 0.40 Mesa Substation Electrical substation 0.35 Sanwa Bank Facility Data processing facility 0.40 Alhambra Telephone Three-story concrete frame 0.40 Station building Rosemead Telephone Two-story steel-frame 0.40 Station building Central Telephone Three steel-frame high-rise 0.15 Station buildings Wells Fargo Bank Data processing facility 0.30 Facility Center Substation Electrical substation 0.26*
Lighthype Substation Electrical Substation 0.30
- Ground acceleration measured by an instrument at the site
- Average of two horizontal components
HVAC Duct System Earthquake Experience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)**
Whittier, CA Earthquake Del Amo Substation Electrical Substation 0.20 1987 (M5.9) (cont'd)
Pasadena Power Plant Five-unit gas-fired 0.20 power plant Glendale Power Plant Five-unit gas-fired 0.25 power plant Commerce Refuse-to- One-unit gas-fired 0.40 Energy Plant power plant Puente Hills Landfill One-unit gas-fired 0.20 Gas and Energy power plant Recovery Plant Superstition Hills El Mesquite Lake 16 MW gas-fired power plant 0.20 Centro, CA 1987 (M6.3) Resource Recovery Plant El Centro Steam Plant Four-unit gas-fired 0.25*
power plant Loma Prieta Earthquake Moss Landing Power Seven-unit gas-fired 0.34 1989 (M7.1) Plant power plant Gilroy Energy Cogen One-unit combined gas 0.40 Plant turbine and steam turbine plant Cardinal Cogen Plant One-unit combined gas 0.25 turbine and steam turbine plant UCSC Cogen Plant One-unit diesel cogeneration 0.44 plant Hunter's Point Plant Three-unit gas-fired 0.15 power plant Protrero Plant One-unit gas fired plant 0.15 Metcalf Substation 500 kV substation 0.30 San Mateo Substation 230 kV substation 0.20
- Ground acceleration measured by an instrument at the site
" Average of two horizontal components
W A C Dztct System Earthqualce hiperience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)**
Loma Prieta Earthquake National Refractory Large brick & magnesia 0.30 1989 (M7.1) (cont'd) extraction plant Green Giant Foods Concrete tilt-up food 0.33 processing plant Watson Wastewater Sewage treatment plant 0.40 Treatment Santa Cruz Telephone Three-story concrete shear 0.50 Station wall switching station Watsonville Telephone Four-story concrete shear 0.33*
Station wall switching station Seagate Technology Concrete tilt-up 0.40 Watsonville manufacturing facility Santa Cruz Water Potable water purification 0.42 Treatment facility Soquel Water District One-story wood-frame office 0.50 Headquarters complex with small pumping station & storage tanks Lipton Foods Concrete tilt-up food 0.30 processing and packaging facility Lone Star Cement Large cement factory 0.25 Watkins-Johnson One-, two-, and three-story 045 Instruments concrete & steel-frame buildings for light manufacturing Riconada Water Potable water processing 0.30 Treatment Plant facility IBMlSanta Teresa Steel-frame high-rise 0.20 Facility complex for software development P
- Ground acceleration measured by an instrument at the site
- Average of two horizontal components
HVAC Dzict Systen~Earthquake Erperience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility Type of Facility Ground Acceleration (g)**
Loma Prieta Earthquake EPRl Headquarters Two-and three-story 0.25 1989 (M7.1) (cont'd) concrete-frame office San Martin Winery Winery 0.30 Central Luzon Baguio Telephone Telephone switching station --
Phillipines Earthquake 1990 (M7.7)
Cabanatuan Substation 230 kV substation --
La Trinidad Substation 230 kV substation --
San Manuel Substation 230 kV substation --
Moog Manufacturing Manufacturing plant --
Plant Valle de Estrella, Costa Bomba Water Water treatment plant --
Rita Earthquake 1991 Treatment Plant (M7.4)
Cachi Dam 1,000 MW hydroelectric plant 0.12*
Changuinola Power Diesel power plant --
Plant Limon Telephone Telephone switching station --
Moin Power Plant 140 MW thermoelectric --
power plant RECOPE Refinery Oil refinery Sierra Madre, California Pasadena Power Plant Five-unit gas-fired power 0.20 Earthquake 1991 (M5.8) plant Goodrich Substation 230 kV substation 0.30 Cape Mendocino, PALCO Co-generation Two-unit power plant 0.47 California Earthquake Plant 1992 (M7.0)
- Ground acceleration measured by an instrument at the site
" Average of two horizontal components
HVAC Duct System Earthgzlake Experience Data Table A-1 Summary of Sites Reviewed in Compiling the Seismic Experience Database (continued)
Estimated Peak Earthquake Magnitude Facility ~ ~ of pFacility e Ground Acceleration (g)*"
Cape Mendocino, Humboldt Bay Power Two gas-fired units, 0.24 California Earthquake Plant one nuclear unit 1992 (M7.0) (cont'd)
Centerville Beach Naval facility 0.40*
Station Landers and Big Bear, Cool Water Generation Four-unit power plant, 0.36*
California Earthquake Plant two gasfoil-fired and 1992 (M 7.6) two combined cycle units Mitsubishi Cement Plant Cement plant --
LUZ Projects Solar electric generating 0.35 station Northridge, California AES Placerita Two-unit electric gas turbine 0.60 Earthquake 1994 Cogeneration Plant generators (80MW), two heat (M 6.7) recovery steam generators and one 20 MW steam turbine generator ARC0 Placerita Two-unit electric gas turbine 0.60 Cogeneration Plant generators and two heat recovery steam generators Pitchess Cogeneration 21 MW electric gas turbine 0.50 Plant and heat recovery steam generator Olive View 6MW power generation 0.72 Cogeneration Plant and heat recovery system Valley Steam Plant Four-unit gas-fired power 0.40 plant Burbank Power Plant Six-unit gas-fired power plant 0.30 Glendale Power Plant Five-unit gas-fired power 0.25 plant (148MW)
- Ground acceleration measured by an instrument at the site
- Average of two horizontal components
HVAC Duct Systenz Earthquake Experience Data A.2. I Facilities Surveyed in Compiling the Database Information on each database facility, its performance during the earthquake, and any damage or adverse effects caused by the earthquake were collected through the following sources:
a Interviews with the facility management and operating personnel usually provide the most reliable and detailed information on the effects of the earthquake on each facility. At most facilities, several individuals were consulted to confirm or enhance details. In most cases, interviews are recorded on audio tape.
Observations by earthquake reconnaissance teams are documented and photographed.
Typical observations include descriptions and details of both damaged and undamaged installations or equipment and any indications of the cause of damage, such as substantial ground settlement or evidence of seismic interaction.
The facility operating logs provide a written record of the conditions of the operating systems before and after the earthquake. Operating logs list problems in system operation associated with the earthquake and usually tabulate earthquake damage to the facility. Operating logs are useful in determining how long the facility may have been out of operation following the earthquake and any problems encountered in restarting the facility.
The facility management often produces a report summarizing the effects of the earthquake following detailed inspections. These reports normally describe causes of any system malfunctions or damage.
a Earthquake damage can often be inspected prior to repairs if the facility can be surveyed immediately following the earthquake. This has been the case in most of the earthquakes included in the database.
Standard procedures used in surveying database facilities focus on collecting all information on damage or adverse effects of any kind caused by the earthquake. Seismic damage to well-engineered facilities is normally limited to only a few items except at sites that experience very high seismic motion, that is, in excess of 0.50g Peak Ground Acceleration (PGA), or greater than thirty seconds of strong motion.
Information on damaged and undamaged ductwork consists of photographs, measurements made at the site, visual observations, qualitative assessments of details and workmanship, and information supplied by personnel at the individual sites. This information includes typical assemblies, unusual details or systems, and supports that appear to be especially weak and prone to damage or failure.
An extensive search of the seismic experience database revealed thirty-nine sites infourteen different earthquakes where ducting experienced PGAs of at least 0.25g. Eighteen of the thirty-nine experienced 0.40g or greater. The database sites represented a wide variety of duct sizes, shapes, configurations and support types. Round and rectangular ducts were found at seventeen and thirty-five sites, respectively, with sizes ranging from six to seventy-two inches. The above data have been compiled and summarized according to database site, duct construction type and size, support type, building type, and noted damage. This information is shown in Table A-2.
W A C Duct Systenz Earthquake Experience Data Table A-2 HVAC Duct Seismic Experience Database Duct Type Support Type Damage Building Type Rod Concrete Block/ Framed Site PGA Round ~ u csize t Strap Frame Falling Dented Tilt-Up Frame angle Hung ever Shearwall Shearwall ADAK 0.25 X 10" 0 X ADAK 0.25 X X 10" 0 X X X ADAK 0.25 X 12x12 X X ADAK 0.25 X 12x12 X X ADAK 0.25 X X X ADAK 0.25 X 12x12 X X ADAK 0.25 X -24 0 X BATA SHOE X 0.64 X 1 2 X 12 FACTORY BATA SHOE X 0.64 X 36x24 FACTORY BAY MILK 0.50 X 24x24 X VERT' BAY MILK 0.50 CABLE RUN BURBANK 0.30 X 15"O X BURBANK 0.30 X LARGE NV BURBANK 0.30 X LARGE POWER BURBANK 0.30 X LARGE POWER BURBANK 0.30 X LARGE POWER CAL FED 0.40 X 60x48 X X CALFED 0.40 X 30x8 X X CAL FED 0.40 X 30x8 X X CAL FED 0.40 X 30x8 X X Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct Systenz Eai.tlzqziake Ejcyel.ience Data RC Reinforced Concrete NA Not Applicable
HVAC Duct Systenz Earthquake fiperience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Concrete Block/ Framed Site PGA Round ~ u csize t Strap Frame Falling Dented Tilt-Up Frame angle Hung ever Shearwall Shearwall COMMERCE 0.40 X 24"O X X COMMERCE 0.40 X X 24",12X12 X X 12"O X COMMERCE 0.40 X 24x24 COMMERCE 0.40 X 20-0 X BRACED COMMERCE 0.40 X 20"O X BRACED COMMERCE 0.40 X 1 6 0 24"O X BRACED COMMERCE 0.40 X 60x60 X X COMMERCE 0.40 X X 24"030X30 X X COMMERCE 0.40 X 24"O X X CONCON PROPPED X 0.30 X 18x12 PETROLEUM DEVERS 0.85 X NV X DEVERS 0.85 X NV DROP IV 0.30 X 18"X24" LIGHT CSW DROP IV 0.30 X 24"X4aU LIGHT CSW DROP lV 0.30 X VARIOUS LIGHT CSW EL CENTRO X 36x36 X X
$6 EL CENTRO
'Ti X X X EL CENTRO
'yi X 60"X24" X ANGLE X
EL CENTRO X 24x24"
- '422; --
LEGS ANGLE EL CENTRO
'Ti X 24x24" LEGS EL CENTRO
'Ti X 36"X72" X X EL CENTRO
'Ti X 36x72" X X Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct System Eartl?quaIie Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
HVAC Duct System Earthquake Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Concrete Block/ Framed Site PGA Round ~ v csire t Strap Frame Falling Dented Tilt-Up Frame angle ever Shearwall Shearwall EL CENTRO X X X
'Ti X EL CENTRO X 48"X 24" X EL CENTRO 48"X 24" X
'yi EL CENTRO X
'Ti X 54x54 VAR. NA EL CENTRO X
'Ti 48x48 EL CENTRO 42; X NV NA NA NA NA EL CENTRO
'zi X NV NA NA NA NA X
ELCENTRO
- yi X 48x24 EL CENTRO X NV X X EL CENTRO NV
'Ti X EL CENTRO
'Ti X X EL CENTRO
- - - 'Ti X LARGE X
EL CENTRO
'Ti X 36x120 PROPPED EL CENTRO X PROPPED EL CENTRO NV
'Ti X EL CENTRO
'Fi EL CENTRO .42, X 48x24 X X X 24x24 X STEAM .25 Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct System Eai.thqtialce Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Concrete BIocW Framed Site PGA Round
$: Duct Sire Strap ever Frame Falling Dented Shearwall Tilt-Up Frame Shearwall EL CENTRO .42, X 24x30 STEAM .25 EL CENTRO .42, X X STEAM .25 EL CENTRO .42, X 24x18 X STEAM .25 FERTIMEX OE- X 24x24 X X FERTIMEX X 24x30 X X X
- ; ;O FERTlMEX
- \ X 12x16 X X FERTIMEX
'62:- X 24x24 X X FERTIMEX X 24x24 X X
-'O; FERTIMEX
'62:- X 60x30 X FERTIMEX
'6255- X 12x18 X X FERTIMEX X 30x18 X X FERTIMEX OE-; X 24x12 X X FERTIMEX
'62:- X 16x16 X X FERTIMEX
'6255- X 72x72 X NA NA NA NA FERTIMEX X 24x12 X X
- ; ;O FERTIMEX
'62:- X NV NV NV NV NV X FERTIMEX X 24x24 NV NV NV NV X
- ; ;O Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
W A C Duct Systenz Earthqualce &pei.ience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
HyAC Duct System Eartliqzialce Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Concrete Block/ Framed Site PGA Round D U C ~size Strap Frame Falling Dented Tilt-Up Frame angle ever Shearwall Shearwall GLENDALE PROPPED 0.30 X 18x30 POWER GLENDALE NV 0.30 X POWER GLENDALE 0.30 NV X POWER GLENDALE 0.30 X 30x18 X POWER GLENDALE 0.30 X 24x18 X POWER GLENDALE 0.30 X 18x6 X POWER GLENDALE X 0.30 X 30x18 POWER GLENDALE X X 0.30 X NV POWER HUMBOLDT HUMBOLDT 2
25, X 36"O X X NV X BAY .30 HUMBOLDT 25, X X NV BAY .30 HUMBOLDT .25, NV BAY .30 HUMBOLDT 2.5, X X LARGE X BAY .30 HUMBOLDT 25, X X X 1 2 X 12 BAY .30 HUMBOLDT 25, X NV NV X X
BAY .30 HUMBOLDT 25, X X NV BAY .30 HUMBOLDT 25, X NV BAY .30 Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
W A C Duct Systern Earthquake Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Canti- Concrete Block/ Framed Site PGA Round ~ u sSize t Strap Frame Falling Dented Tilt-Up Frame angle Hung Lever Shearwall Shearwall HUMBOLDT .25, X 180 BAY .30 HUMBOLDT -25, X VARIES X BAY .30 HUMBOLDT .25, X CSW X NV BAY .30 HUMBOLDT .25, X 30"O BAY .30 HUMBOLDT .25, X NV BAY .30 -
HUMBOLDT .25, X 18"0 BAY .30 HUMBOLDT .25, X NV BAY .30 HUMBOLDT .25, X 18"0 BAY .30 HUMBOLDT .25, X 16"0 BAY .30 IBM SANTA X X 0.37 X 24x12 TERESA IBM SANTA X X 0.37 X 24x12 TERESA KETTLEMAN 0.20 X 16"0 LA VlLLlTA 0.14 X NV X LA VlLLlTA .14 X 18x18 X X HUMBOLDT .25, BAY .30 HUMBOLDT .25, X X X 24x18 BAY .30 HUMBOLDT .25, X 24x18 BAY .30 HUMBOLDT .25, X X X LARGE BAY .30 Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct System Eartl~qzralceExperience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rect- Concrete Block/ Framed Site PGA Round ~ u cSize t strap Frame Falling Dented Tilt-Up Frame angle Hung Rod Lever Shearwall Shearwall HUMBOLDT .25, X X BAY .30 IBM SANTA 0,37 X 24XVARIES X X TERESA IBM SANTA 0.37 X 24x12 X X TERESA IBM SANTA 0.37 X 24x12 X X TERESA LAS 0.22 X 36x36 X X VENTANAS LAS 0'22 X 18x18 X CSW VENTANAS LAS VENTANAS 0.22 X 120" 0 X X COP.
MEQUITE 020 24"0,36"0 X X LAKE MESQUITE 0.20 X 24x24 LAKE MESQUITE 0.20 24" 0 X X LAKE MESQUITE 0.20 24" 0 X NA NA NA NA LAKE MESQUITE 0.20 X 36x36 NA NA NA NA LAKE MESQUITE 0.20 LARGE X LAKE MESQUITE 0,20 NV X X LAKE MESQUITE 0.20 X 18x18 X X LAKE MESQUITE 0.20 600 X X LAKE Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
W A C Duct Systenz Earthquake Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
I I I I I I I I I I I I Site 1 1 / :il 1 P O I Round Duct Type Duct Size /
g: : " , 1 Support Type Strap / fz/ Frame I Damage Falling / Dented I Concrete Block/
Shearwall I Tilt-Up I Building Type Frame / Framed Shearwall I
MT. UMANUM 0.50 X VARIES X X CSW MT. UMANUM 0.50 X 2 4 X 16 X X CSW IMT.UMANUM 1 0.50 1 I X 1 24x16 / X / X I I I I I csW I I I I MT. UMANUM 0.50 X 16x12 X X CSW MI. UMANUM 0.50 X 16 X 18 X X CSW PAC BELL WATSON- 0.33 X 12x6 CSW IMT.UMANUM 10.50 1 I X ( 1 6 x 1 8 1 X I X I I I 1 1 csw 1 1 I I IMT.UMANUM 1 0.50 1 I X I 1 6 X 1 8 I X / X I I I I I CSW 1 I I I MT. UMANUM 0.50 X 16 X 16 X CSW MT. UMANUM 0.50 X 16 X 16 X CSW ORMOND 0,10 X 18 X 18 X BEACH PAC BELL 0'40 X 12x20 X X ALHAMBRA PAC BELL 0.33 X 24 X 8 X WATS.
PAC BELL 0'33 X 12x6 X CSW WATSONVILLE PAC BELL 0,33 X 24x8 CSW WATSONVILLE PAC BELL 0'33 X 16 X 8 CSW WATSONVILLE Legend: NV Not Visible FR Framed CSW Concrete Shear Wali BR Braced RC Reinforced Concrete NA Not Applicable
KyAC Duct System Ear.tl?qzialceExperience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Canti- Concrete BlocW Framed Site PGA Round ~ u cSire t Strap Frame Falling Dented Tilt-Up Frame angle Lever Shearwall Shearwall PAC BELL 0'33 X NV X CSW
.WATSONVlLLE PAC BELL 0'33 X X CSW WATSONVILLE PUENTE HILLS 0.20 X NV LEGS NA NA NA NA RENCA 0.30 X X X RlNALDl 0.50 X NV SAN MARTIN
'-2 X NV X SAN MARTIN X NV X X SANWA 0.40 X 30x18 NV NV NV NV X SANWA BANK 0.40 X X X X SCE 0'42 X 24x24 CSW ROSEMEAD SCE 0'42 X 30x15 X X CSW ROSEMEAD SEAGATE 0.40 X 180 X X SEAGATE 0.40 X 12"O 16"O X X X SEAGATE 0.40 X 12"O 16"O X X X SEAGATE 0.40 X 16"O X SEAGATE 0.40 X 2 40 X SEAGATE 0.40 X 24"O X X I I Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
W A C Duct System Earthquake Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Concrete Block/ Framed Site PGA Round D U C ~Size Strap Frame Falling Dented Tilt-Up Frame angle Hung ever Shearwall Shearwall SICARTSA 0.25 X NV X X X SICARTSA 0.25 X NV X X SICARTSA 0.25 X 42x42 X SICARTSA 0.25 X 1 2 X 12 NV NV NV NV X SICARTSA 0.25 X NV X X SYLMAR 0.65 X 12x8 BR SYLMAR 0.65 X 18x6 X STEEL BR SYLMAR 0.65 X 24x18 X STEEL BR SYLMAR 0.65 X X 28x18 NV STEEL BR SYLMAR 0.65 X X 18 0 NV STEEL BR SYLMAR 0.65 X 24x18 X STEEL BR SYLMAR 0.65 X VARIES NV STEEL BR SYLMAR 0.65 X VARIES X STEEL BR SYLMAR 0.65 X 24x24 X STEEL BR SYLMAR 0.65 X 12x6 X STEEL BR SYLMAR 0.65 X 36x18 NV STEEL BR.
SYLMAR 0.65 X 24x12 X STEEL BR SYLMAR 0.65 X 20x10 X STEEL Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct Systenz Eartl7qtraIce Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type SupportType Damage Building Type Rod Concrete Block/ Framed Site PGA Round ~ u cSize t Strap Frame Falling Dented Tilt-Up Frame angle Hung ever Shearwall Shearwall BR SYLMAR 0.65 X VARIES STEEL BR SYLMAR 0.65 X 60x18 X STEEL BR SYLMAR 065 X 18x12 X STEEL BR SYLMAR 065 X -30x12 X STEEL BR SYLMAR 065 X 20x8 STEEL BR SYLMAR 065 X 12x12 X STEEL ucsc 0.44 X 20"O CABLES FWCBW COGEN UNION OIL 0.60 X LARGE UNION OIL 0.60 X LARGE X X VALLEY 0.40 X 36x36 STEAM - -
VALLEY 0.40 X STEAM VALLEY 0.40 X 18x6 X STEAM VALLEY 0,40 X NV X STEAM VALLEY X 0.40 X NV SPRINGS STEAM VALLEY X 0,40 X NV SPRINGS STEAM VALLEY 0.40 X 14" 0 STEAM VALLEY 0,40 X LARGE X STEAM Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct System Earthquake Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type Support Type Damage Building Type Rod Canti- Concrete Block/ Framed Site PGA Round ~ u cSize t Strap Frame Falling Dented Tilt-Up Frame angle Lever Shearwall Shearwall WATKIN UNISTRUT X OS4' X 30x30 JOHNSON WATKINS- X OS4' 36"0,12"0CABLES JOHNSON WATKINS X 0,45 6"O X JOHNSON WATKINS X JOHNSON 0'45 X 30x30 UNISTRUT WATKINS 18x18 UNISTRUT X 0'45 X JOHNSON WATKINS UNIST. ANC 0'45 X NV JOHNSON WATKINS X 0.45 X 48x24 JOHNSON WATKINS Oq4' X NV NV JOHNSON WATKINS NV NV NV NV X Os4' X NV JOHNSON WATKINS- UNISTRUT 0'45 18 X 18 JOHNSON WATS PAC X 0.33 X NV BELL WATS PAC 18x8' X X 0.33 X BELL -
WATS. PAC CSW 0.33 X 12"X12 X BELL WATS. PAC X 0.33 X 18x6 X BELL WATS. PAC X 0.33 X 24x8' X BELL Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
W A C Duct System Eartl?quale Experience Data Table A-2 HVAC Duct Seismic Experience Database (continued)
Duct Type SupportType Damage Building Type Rod Concrete BlocW Site PGA Round fziL Duct Size Strap ever Frame Falling Dented Shearwall Tilt-Up Frame Framed Shearwall WATS.
WASTE 0.40 X 30x16 X X WATER WHAKATANE 0.25 X 18x10 X RC WHAKATANE 0.25 X X RC WHAKATANE 0.25 X 24x10 X RC WHAKATANE 0.25 X 24x12 X RC WHAKATANE 0.25 X 20x12 X RC WHAKATANE 0.25 X 16" 0 NV X WILTRON 0.35 X 12" 0 X X X X WILTRON 0.35 X 12" 0 X X X X WILTRON 0.35 X 12" 0 X X X X WILTRON 0.35 X X 1 20 X X X X WILTRON 0.35 X 12" 0 X X X X Legend: NV Not Visible FR Framed CSW Concrete Shear Wall BR Braced RC Reinforced Concrete NA Not Applicable
HVAC Duct System Earthquake Experience Data The large number of duct systems that have survived earthquakes indicates the inherent ruggedness of these systems. The light gauge sheet metal ducts were constructed with pocket locks, companion angles, and riveted connections. In many cases the ducting had no stiffener angles and still survived the strong motion. Generally, the database HVAC ducts were supported with either rod hangers or long sheet metal straps; however, there were also instances of frame-mounted ducts. Some HVAC ducts were hung with rope, cables, or wire. Rod hanger supports were typically trapezes which were attached to concrete ceilings with expansion anchors, or either clamped or threaded and tapped into overhead steel structures. Sheet metal strap supports were usually spot welded to the duct sides and attached to overhead ceilings with expansion anchors. Figures A-1 through A-12 illustrate some of the typical database duct configurations and supports that have survived past strong-motion earthquakes.
Figure A-1 Sylmar Converter Station, 1971 San Fernando Earthquake. Strap-Hung and Wall-Mounted Duct With Wall Penetrations
NVAC Duct Systein Earthquake Experience Data Figure A-2 Glendale Power Plant, 1971 San Fernando Earthquake. Cantilever Bracket Supported Rectangular Duct Figure A-3 Bay Milk Products, 1987 New Zealand Earthquake. Long Vertical Cantilever Supported by the Roof at One End and Guy Wires at the Other
HJTAC Dzrci Sysier~zEal-ihqz~alreExperience Data Figure A-4 El Centro Steam Plant, 1979 Imperial Valley Earthquake. Trapeze Rod-Hung Rectangular Duct With Close Up of the Trapeze Detail
NVAC Duct Systein Earthquake Experience Data Figure A-5 California Federal Bank Facility, 1987 Whittier Earthquake. Typical Strap-Hung Rectangular Duct With Vertical Cantilevers and Diffusers Figure A-6 Watkins-Johnson Instrument Plant, 1989 Loma Prieta Earthquake. Large, Insulated Round Duct With Branch Ducts and Cable Supports
HVAC Duct System Earthqziake Experience Data Figure A-7 Pacific Bell Watsonville, 1989 Loma Prieta Earthquake. Run of Trapeze Rod-Hung Rectangular Duct Figure A-8 Valley Steam Plant Forced Draft System, 1971 San Fernando Earthquake
4C Duct System Eartlzqzrake &pei*ience Data Figure A-9 Drop IV Hydro Plant, 1979 Imperial Valley Earthquake. Ceiling Mounted Ducting Figure A-10 Watkins-Johnson, 1989 Loma Prieta Earthquake. HVAC Ducting Atop Roof Level
HVAC Duct Syslen7 Eai-thquakeExperience Data Figure A-11 Magnolia Plant, Burbank, Ducting at Induced Draft Fan, 1971 San Fernando Earthquake Figure A-12 El Centro Steam Plant, 1979 Imperial Valley Earthquake
HVAC Duct System Earthquake Experience Data It is important to note that nearly all of the HVAC duct installations in the database facilities were designed and installed without specific consideration of seismic loads. Also, some facilities were up to forty years old at the time of their earthquakes. In addition to the effects of age, the initial installation and any subsequent modifications to database ducts and their supports included all of the normal oversights and deficiencies of industrial construction.
Ductwork ruggedness was demonstrated in most instances, but there were some cases in which one or more attributes led to seismic damage. A summary, organized by earthquake, of the configurations and structural characteristics which contributed to the damage is given below.
A.2.1 .I 1983 Coalinga, California Earthquake The Coalinga, California earthquake occurred at about 4:43 P.M., local time, on May 2, 1983, and had a Richter magnitude of 6.7. It was centered near the town of Coalinga which is midway between San Francisco and Los Angeles. Coalinga is situated in a large oil field that includes numerous petrochemical and other industrial and power installations.
Gates Substation is located on the 500 kilovolt (kV) intertie that runs north to south through the California Central Valley. The facility has two control buildings, several shops, and storage buildings. All of these structures are one-story structures of reinforced concrete block or precast concrete construction. All were designed to the seismic standards of the concurrent Uniform Building Code, seismic zone IV, or more stringent requirements imposed by the operating facility.
Gates Substation is located about fourteen miles southeast of the main shock's epicenter, and about an equivalent distance south of the nearest strong motion record at Pleasant Valley Pumping Plant. Standard ground motion attenuation formulae indicate a PGA of approximately 0.25g for the site's distance from the epicenter.
During the earthquake, a W A C diffuser fell from a suspended ceiling. The diffuser was slipped into place and supported from the ceiling, but was not attached to the HVAC ducting (see Figure A- 13).
HVAC Dzlct Systein Earthqzralce Experience Data Figure A-13 Gates Substation, 1983 Coalinga Earthquake. A HVAC Diffuser Fell From the Suspended Ceiling A.2.1.2 1984 Morgan Hill, California Earthquake The Morgan Hill, California, earthquake occurred on the Calaveras fault at 1:15 P.M., PST on April 24, 1984. The Richter magnitude 6.2 earthquake was centered approximately ten miles due east of San Jose. Despite localized pockets of damage to residences and co~nlnercialfacilities, the damage to structures was generally light.
Wiltron, located on Mast Street in Morgan Hill, manufactures microwave and com~nunication equipment for telephone and other companies. The facility is housed in a reinforced concrete tilt-up building which has a plywood diaphragm roof. Based upon the nearest recording instruments at Anderson Dam and the nineteen mile distance to the epicenter, the site experienced an estimated PGA of 0.35g.
At the Wiltron Facility, a four foot long vertical cantilevered section of W A C ductwork broke from its supporting header and fell to the floor (see Figure A-14). The round duct was constructed of riveted lap joints which failed under the cantilever's inertial loads.
HVAC Duct System Eartl?quakce fiperience Data Figure A-14 Wiltron Facility, 1984 Morgan Hill Earthquake. A 4-Foot Long Vertical Cantilever Broke From its Supporting Header and Fell Another section of HVAC duct at the same facility split a seam where a branch line entered a wall penetration (see Figure A-15). The damaged section was approximately ten inches in diameter, branching off of an estimated twenty inch diameter header. The seam pulled apart near the wall, approximately four feet from the branch point. The branch apparently was not flexible enough to accommodate the header motion, and the seam was too weak to resist the imposed differential displacement.
HVAC Duct Systeln Eartlzqzialce Experience Data Figure A-15 Wiltron Facility, 1984 Morgan Hill Earthquake. A Branch Line Tore at a Wall Penetration Due to Flexible Header Motion A.2.1.3 1985 Mexico Earthquake The Richter magnitude 8.1 earthquake of September 19, 1985 was centered near a large industrial area at Lazaro Cardenas on the west coast of Mexico. The industrial area includes a large steel mill and a fertilizer plant, as well as several other manufacturing and service facilities.
The industrial area is served by two large hydroelectric plants located on the Rio Balsas. Both the power plants and the industrial facilities are relatively new, having been constructed primarily in the 1970s and 1980s.
The Fertimex facility is a large fertilizer plant on an island at the mouth of the Rio Balsas.
Reconnaissance teams observed several sand boils and settlement as large as twelve inches on the island. The site's PGA is estimated at 0.25g based upon the nearest ground motion records at Zacatula; however, the section of the island which supports Fertimex's Packaging Plant is thought to have experienced at least 0.50g.
W A C ducting was damaged on the second floor of the packaging plant's switchgear building.
The second floor slab is approximately fifteen feet above grade. The two-story concrete-frame structure is about 120 feet long, fifty feet wide, and has eccentric rigidity due to the asymmetric location of brick in-fill and partial concrete walls. The eccentricity created high torsional accelerations in some regions of the structure. In one of these areas, the last section in a long duct run jumped off the fmal support. The resulting cantilever failed at an adjacent support (see Figure A-16). The W A C duct section was of pocket lock construction and was not positively attached to the rod hung trapeze support. Had it been attached, the damage would likely have been avoided. Also in the same area, one of the duct's rod supports pulled its expansion anchor from the concrete ceiling. The concrete quality was questionable and the ribs on the non-drilling shell anchor's cone expander were flat rather than slanted.
HVAC Duct System.Earthquake Experience Data Figure A-16 Fertimex Packaging Plant, 1985 Mexico Earthquake. A section of Duct Tore when the Duct Jumped off the Final Support in a Long Run A.2.1.4 1987 New Zealand Earthquake On March 2, 1987 at 1:43 P.M., a Richter magnitude 6.2 earthquake struck the eastern Bay of Plenty region of North Island, New Zealand. The earthquake was preceded at 1:36 P.M. by a M5.2 foreshock and followed at 1:52 P.M. by a M5.2 aftershock. The main event, centered about four miles northwest of the small town of Edgecumbe, propagated along a previously unmapped fault that opened a large surface rupture and caused widespread soil failures. Strong ground motion also affected the nearby towns of Kawerau, Te Teko, and Whaltatane. An average horizontal PGA of 0.26g was recorded approximately six miles from the rupture, and PGAs from 0.30g to 1.0g were estimated in the affected area.
The Caxton Paper Mill is located on the outskirts of Kawerau, about five miles from the fault and along a line extending in the direction of surface rupture. Based upon the ground motions recorded at the Matahina Dam and a comparison of the Modified Mercalli intensities for the dam and the paper mill, the mill's PGA is estimated to be 0.40g.
The facility's paper machine buildings (Nos. 2 and 3) are flexible high-bay steel frames and reportedly deflected excessively during the earthquake. Damaged HVAC duct was found in both buildings.
HVAC Dzrct Systein Eartl7qz~alceExperience Data At Paper Machine Building No. 2, there were several instances of sheared ductwork joints; however, no sections fell to the floor. The circular duct was inounted near the ceiling and constructed of riveted lap joints (see Figure A-17).
Figure A-17 Caxton Paper Mill, 1987 New Zealand Earthquake. A long, Unrestrained Run of Duct Constructed of Riveted Lap Joints (Top) and a Taped Repair of a Sheared Joint (Bottom)
A-4 1
HVAC Duct Systenz Earthqzialce Experience Data Paper Machine Building No. 3 is taller and experienced more damage. The round ductwork was fastened by riveted lap joints and supported from the roof truss with rod hangers and beam clamps. Large deflection of the ductwork pulled adjacent sections of ducting apart allowing a pdrtion to pry itself away from the supports and fall to the operating floor. Inspection of the fallen ductwork noted heavy corrosion at the riveted joint.
A.2.1.5 1987 Whittier, California Earthquake On Thursday, October 1, 1987, at 7:42 A.M., a Richter M5.9 earthquake occurred due east of Los Angeles near the city of Whittier, California. The shock caused damage over a large area of the Los Angeles Basin. The main shock was followed by numerous aftershocks, including a M5.5 aftershock at about 3:00 a.m. on Sunday, October 4, which further damaged structures already weakened by the initial shock.
The City of Commerce Refuse-to-Energy Plant is located approximately seven miles southwest of the epicentral area. The plant was constructed in 1985, and its buildings were designed according to the current Uniform Building Code for seismic zone IV. The 11.5 MW plant is housed in a large steel-frame structure, including an enclosed high-bay refuse storage pit, with adjoining office complex, open turbine deck, and open steel-frame boiler tower. The PGA is estimated as 0.40g, based upon the records at the Bulk Mail Center and a comparison of the Modified Mercalli Intensities at similar sites. The Bulk Mail Center is less than a mile south of the plant and has similar soil conditions.
Damage to the Commerce Energy Plant was minimal but included a W A C diffuser which fell in an office area. The diffuser was apparently not secured to the duct main run.
The main office of the Southern California Edison (SCE) Headquarters is located within a mile of the epicenter and has ground motion equipment located on site. The four-story concrete shear wall structure endured a PGA of 0.42g and sustained the most significant structural damage of the three buildings in the complex. A W A C fan in this building dislodged from its spring isolators and displaced enough to tear the flexible bellows coupling to the duct on its discharge side. A W A C duct was dented, but not torn, by impact from adjacent fixtures (see Figure A- 18).
W A C Dzicf System Earthqzialce Experience Data Figure A-18 SCE Rosemead Headquarters, 1987 Whittier Earthquake. HVAC Dented From Sway of Adjacent Fixtures The Ticor Data Processing Center is a two-story concrete tilt-up building constructed around 1980. It is a somewhat complicated structure combining steel and reinforced concrete internal framing with a spancrete second floor, a metal roof deck, and exterior concrete wall panels.
The building suffered substantial damage, including shear cracks in wall panels, spalling and fracture of the second floor slab, separation of joints between wall panels and framing, and a tom expansion joint in the roof.
Nonstructural damage was also extensive and included W A C duct. Roof-mounted HVAC equipment at Ticor was severely damaged and the system was shut down. Most of the equipment was mounted on vibration isolators without lateral (seismic) restraints. Two axial fans had shifted off their mounts, rupturing their duct attachments (see Figure A-1 9).
HVAC Duct System Earthquake Experience Data Figure A-19 Ticor Facility, 1987 Whittier Earthquake. A Flexible Bellows has Torn Due to the Motion of an Attached Fan on Vibration Isolation Mounts The free-field record taken adjacent to the SCE Headquarters is near enough to the Ticor facility to essentially be considered a site record. Both the Ticor and SCE sites are on soft alluvial deposits laid down from the nearby San Gabriel River.
The SCE free-field accelerogragh is likely representative of the effective free-field ground motion at Ticor. Although the peak acceleration exceeded 0.40g in both horizontal directions, and the response spectra show relatively broadband frequency content, the motion was very short in duration, with only three to five cycles of significant amplitude.
HVAC Duct System Earthquake Ekperience Data The Sanwa Data Processing Center is housed in adjoining steel-frame concrete panel sided buildings of about 100,000 square feet each, on four staggered floor levels. The center contains data processing equipment mounted on raised floors, as well as office facilities. The roof includes a penthouse for HVAC equipment.
The Sanwa facility is located in the Repito Hills, a shallow formation of sedimentary rock that penetrates the surrounding alluvial valleys. The nearest record at Garvey Reservoir, with a peak horizontal acceleration of about 0.40g7is a reasonable representation of the effective free-field motion experienced by the site. The strong motion instrument is founded on compacted alluvium, less than a mile and a half from the Sanwa facility.
HVAC ducts in the space above the raised ceiling experienced movement and permanent distortion without excessive leakage, failure or loss of function. In addition, a duct above the battery racks, approximately twelve inches by twelve inches, deformed but did not fall. The long run was supported at the ceiling by sheet metal straps and had no companion angles or stiffeners.
The duct deformed at the joints of an angled offset section which contained a W A C register (see Figure A-20).
Figure A-20 Sanwa Data Processing Center, 1987 Whittier Earthquake. A Duct above the Battery Racks Deformed at the Joints of an Angled Offset Section
HVAC Duct Systenz Eai-thqualce Ekpei-ience Data A.2.1.6 1988 Alum Rock, California Earthquake The Alum Rock earthquake had a low PGA (0.15g) and relatively minor damage; however, there was HVAC related damage in the third floor mechanical penthouse of the East Ridge Mall.
The damage occurred when air handling units, mouilted on vibration isolation springs without lateral support, deflected and tore the attached flexible bellows to the adjacent ducting (see Figure A-2 1).
Figure A-21 East Ridge Mall, 1988 Alum Rock Earthquake. A Flexible Bellows Tore Due to the Motion of Attached Air Handlers on Vibration Isolation Mounts
HVAC Dzict Systenz Earthqzlake Experience Data A.2.1.7 1989 Lorna Prieta Earthquake At 5:04 P.M., Tuesday, October 17, 1989, a Richter magnitude 7.1 earthquake struck approximately ten miles northeast of Santa Cruz, California. The twenty second earthquake occurred along a segment of the San Andreas Fault near Loma Prieta. Peak ground shaking as strong as 0.65g was recorded in both the horizontal and vertical directions in the epicentrai area.
The computer disk drive manufacturing plant operated by Seagate Technology is housed in a concrete tilt-up building made of adjoining one- and two-story sections. The site is located approximately two miles northwest of an instrument in downtown Watsonville. Soil conditions in the vicinity of Seagate are labeled "fluvial facies," a form of marine terrace deposits characteristic of the Watsonville area. The telephone building where the strong-motion instruments are located is embedded in flood plain deposits, unconsolidated sand and silt.
The Seagate site therefore appears to be on somewhat firmer soil. Based upon the observed effects within the building, a reasonable estimate of the peak horizontal ground acceleration is 0.40g.
The sections of Seagate's circular duct are lap jointed (without rivets or bolts) and hung from the ceiling with sheet metal straps. During the earthquake, a portion of the duct fell to the floor when a strap broke at the duct connection and the attached section pulled free of its joints (see Figure A-22).
Figure A-22 Seagate Technology, 1989 Lorna Prieta Earthquake. A Strap Support Broke and the Attached Duct Fell to the Floor
HVAC Dzrct Systenl Earthquake Experience Data The Watkins-Johnson Instrument Plant is an expansion of a small instrument assembly operation that was started in the 1950s. The site includes eight buildings of various construction and vintage built into the base of hillsides within a small valley.
The nearest instruments are at the Lick Observatory (CDMG) and in the Earth Sciences Building on the University of California, Santa Cruz. Both instrument sites are just over five miles away from Watkins-Johnson and each measured PGAs greater than 0.40g. The UCSC campus instrument sites are founded on sedimentary rock whereas the Watkins-Johnson plant is in a small valley with alluvial deposits overlying sedimentary rock. The site conditions at the plant are therefore somewhat softer compared to those of the nearest instruments. Using the records and a comparison of the Modified Mercalli Intensities, the Watkins-Johnson site PGA is estimated as 0.45g.
Building number six at the Watkins-Johnson Instrument Plant is a prefabricated steel structure.
Constructed in 1967, the structure has a W A C penthouse, roughly thirty feet above grade.
Inside the penthouse, the flexible bellows connecting circular HVAC ducting to an in-line axial fan tore (see Figure A-23). The duct was rod hung and the fan was supported with a rod hangerlspring arrangement. The bellows were not designed to resist the differential motion imposed by the earthquake.
Figure A-23 Watkins-Johnson Instrument Plant, 1989 Loma Prieta Earthquake. The Flexible Bellows Connecting HVAC Ducting to an In-Line Axial Fan Tore
HVAC Duct System Earthqz~akeExperience Data Also at Watltins-Johnson's building number six, the support frame anchorage for a large rectangular roof-mounted duct was distressed. The P-1000 unistrut frame and its clip angle anchorage were not designed to withstand the inertial loads. The duct was not damaged and, other than the minor anchorage distress, the support survived as well (see Figure A-24).
Figure A-24 Watkins-Johnson Instrument Plant, 1989 Lorna Prieta Earthquake. The Support Anchorage for a Roof-Mounted Duct Was Distressed
W A C Dzict System Earthquake Experier7ce Data Pacific Bell's Watsonville switching station is a four story concrete shear wall structure which endured a measured PGA of 0.33g. During the earthquake, a vertical cantilevered section of duct and its attached difhser fell to the floor (see Figure A-25). Closer inspection revealed insufficient positive attachment between the cantilever and the header.
Figure A-25 Pacific Bell, Watsonville, 1989 Lorna Prieta Earthquake. A Vertical Cantilevered Section of Duct Fell to the Floor With its Attached Diffuser
IN;4C Duct Systenz Earthqziake Ekperience Data A.2.1.8 1990 Philippines Earthquake On Monday, July 16, 1990, at 4:26 P.M. local time, the heavily populated island of Luzon, Republic of Philippines, was struck by an earthquake of magnitude 7.7. The earthquake was caused by major rupture along the Philippine and Digdig faults, extending approximately seventy miles along the northern edge of the Central Plains and into the Cordillera Central.
The Texas Instruments facility in Baguio City was about forty miles northwest of the epicenter in a region of extensive landslides. No accurate estimate of the ground motion exists. In one region of the facility, round, slip-jointed duct pulled apart at its seams and fell to the floor. The rod hung duct had no positive connection between sections and was attached to unanchored equipment and flexibly mounted fume hoods, creating the differential motion failure. The diffusers in the building's clean room also fell along with the room's suspended ceiling.
8.3 Summary of Observed Damage The cases of duct system damage listed above are generally limited to direct seismic damage of the ducting or supports. The database search also uncovered a number of instances in which HVAC ducting was dented or damaged by interaction with adjacent commodities. These cases include impact with flexibly supported piping, false ceilings, and equipment. HVAC diffusers have fallen from false ceilings on several occasions, typically when the ceiling is not properly restrained against lateral motion and the diffuser is not attached to the structural slab above.
In summary, seismic damage to HVAC duct systems from the seismic experience database can be characterized as follows:
Broken and Fallen Cantilevered Sections. Cantilevered sections of duct and duct diffusers constructed of riveted lap joints and simple friction connections have broken or fallen in past strong motion earthquakes. The cases of damage appear to be the result of:
- High inertial loading of the cantilever sections causing high reaction forces at relatively weak joints
- Flexible headers developing high seismic stresses in short duct segments not flexible enough to accommodate the motion 9 Opened and Sheared Seams. Light gage circular duct constructed with riveted lap joints have opened up and sheared in past strong motion earthquakes. This damage has occurred at locations subject to high bending strain in very flexible duct systems.
Duct Fallen off Support. The database includes one example where the end of a cantilevered duct section jumped off of its end hanger support and was damaged. The duct was not tied to the support, and was subject to high levels of seismic motion.
0 Equipment on VibrationIsolators. W A C duct has been damaged by excessive movement of in-line equipment components supported on vibration isolators.
HVAC DAMPER EARTHQUAKE EXPERIENCE DATA Dampers are sheet metal fabricated devices that consist of a 'system of parallel vanes or louvers to either permit or prevent air flow. The actuators controlling the position of these louvers can be operated manually, electrically or pneumatically.
18.1 Definition of Equipment Class Dampers are part of any heating, ventilating and air conditioning (HYAC) system, and are found at nearly all industrial sites. The principal functions of this equipment are control of air flow and isolation of HVAC systems. Some dampers at nuclear plants are used in safety related applications and must function under extreme conditions of violent weather, radiation, temperature, seismic shock, and high pressure transients (due to loss of coolant accident or tornado transient). Dampers are self-supporting structures that do not require additional integral supports or bracing. These devices are typically used in the following applications:
9 Inlet or outlet side of an air handler 0 In-line in W A C ducting 9 Mounted in walls to allow or prevent air flow between rooms Dampers may be operated passively, manually, or actively. The louvers of dampers are tied together by a common linkage which is externally controlled by an electric, pneumatic or manual actuator. Typical components mounted on an air operated actuator are air tubing, flexible conduit, solenoid operated valves and pressure gages. Air receiver tanks that supply air to the solenoid valves require separate evaluation.
B. 1.1 Equipment Anchorage Dampers are an integral part of the fans, air handlers and HVAC ducting and as such are characterized as in-line components. Dampers in fans or airhandlers are part of the equipment and are evaluated with the "Rule of The Box". Some dampers such as fire dampers are mounted in walls or ceilings and therefore are not considered as in-line components. These devices are normally attached to the supporting equipment, ducting, or penetrations in walls and ceilings by bolts, rivets, or welding along their perimeter. Heavy motor-operated or pneumatic dampers typically have their own supporting system.
HVAC Damper Earthquake Experience Data B. 1.2 Equipment Applications Dampers are typically operated pneumatically, electrically or manually. In the case of the pneumatically controlled and motor-operated dampers, such as flow/pressure control and isolatiodshutoff dampers, a pneumatic or electrical signal is sent to the actuator to either open, close or modulate the louver position. Some dampers, such as pressure relief and tornado protection dampers, are self actuated when quick differential pressure changes are detected and use counterweights or counterbalances to return to nonnal position. Some f ~ dampers e have fuseable link that would break in a fire and force the damper to close.
B. 1.3 Application in Nuclear Plants Dampers are used in all nuclear plants for control of air flow and isolation of HVAC systems.
Dampers are utilized in the W A C systems to perform one or more of the following functions:
Flow and Pressure Control - Used to control a given flow rate or pressure within a system.
Actuators may be electrical, pneumatic or manual.
Balancing - Used to establish a flow and pressure relationship within a system. Actuation is through a manual adjustment hand-quadrant that is left at a pre-set level.
0 Isolation/ShutoflControl - Used to isolate or seal off a portion of the system from,selected flows. This type of damper is used only in an opedclose application. Actuators could be electric, pneumatic or manual.
Backdraft Control - Utilized where reverse flow of air is undesirable or could cause system inefficiencies. Actuation is by counterweight or counterbalance.
Pressure Relief - Used to protect the system from excess pressure or damaging surges.
The dampers are closed under normal conditions and open very quickly when positive pressures are detected. Actuation is by counterweight or counterbalance.
Tornado Protection - Used at the intake or exhaust openings of the HVAC system.
During tornado conditions this damper closes automatically. Actuation is by counterweight or counterbalance.
Isolation Shutoff- Used to prohibit any leakage passing through the damper and downstream.
Actuators are typically either pneumatic or manual.
Fire Dampers - Mounted in walls or ceilings and is used for isolation of two separate but adjacent areas in case of fire.
HVAC Damper Earthquake Experience Data B.2 Database Representation for Dampers Figures B-1 through B-3 show typical co~nponentsof dampers.
m R NA l POSFION INDICATOR Figure B-1 Exploded View of a Typical Damper Hemmed Blades Bolted Blades Figure B-2 Typical Damper Blades or Louvers
W A C Damper Earthquake Experience Data MANUAL Morlul~ll~
vilh Two gcrtlbn positluwr rwenible Figure B-3 Typical Damper Actuators Figures B-4 through B-18 present examples of dampers within the database. The database inventory of dampers includes at least 175 examples, representing 20 sites and 14 earthquakes studied. Of this inventory, there are no instances of seismic damage.
Figure B-4 Pneumatic Damper at El Centro Steam Plant Subjected to the 1979 Imperial Valley Earthquake
HVAC Damper Earthqzralce Experience Data Figure 8-5 Louver Style Damper on the Boiler Structure at the El Centro Steam Plant Which Experienced the 1979 Imperial Valley Earthquake Figure B-6 Pneumatic Actuator at the Puente Hills Landfill Gas and Energy Recovery Plant
HVAC Damper.Eartl~qziakeExperience Data Figure B-7 Radial Tvpe Damper at the El Centro Steam Plant Subjected to the 1979 Imperial Valley and 1987 ~uberstitionHills Earthquakes
NVAC Danlper Earthquake Experience Data Figure B-8 Louver Type Damper at Humboldt Bay Power Plant Figure B-9 Radial and Louver Type Dampers at the Humboldt Bay Power Plant, Which Experienced the 1975 Ferndale Earthquake
HVAC Damper Earthquake Ekperience Data Figure B-10 Motor-operated Damper at Adak Naval Station, Which Experienced the 1986 Adak Alaska Earthquake Figure B-11 Damper at Adak Naval Station
HJ'AC Dan~perEarthquake Experience Data Figure B-12 Pneumatically Controlled Damper at UC Santa Cruz Applied Science Building Subjected to 1989 Loma Prieta Earthquake
HVAC Damper Earthqzialce Experience Data Figure 8-13 Electric Motor for a Fire Damper at AES Placerita Cogeneration Plant, Which Experienced the 1994 Northridge Earthquake Figure 8-14 Pneumatic Damper With Long Actuator at Valley Steam Plant, Which Experienced the 1971 San Fernando and the 1994 Northridge Earthquakes B-10
HVAC Danyer Earthquake Experience Data Figure B-15 Pneumatic Louver Control Damper at Pasadena Power Plant, Which Experienced Several Database Earthquakes Figure B-16 Heavy Pneumatic Controller With Independent Support for a Large Damper at Pasadena Power Plant Located Very High in the Boiler Structure
W A C Danzper Earthqzialce Experience Data Figure B-17 Air Operated Damper With Floor-MountedActuator at Burbank Power Plant, Which Experienced the 1971 San Fernando and the 1994 Northridge Earthquakes Figure B-18 Large Independently Supported Damper Controller at the Burbank Power Plant
-.- W A C Damper Earthquake Experience Data Figure B-19 presents a bar chart that illustrates the inventory of dampers at various database sites as a function of estimated PGA.
Peak Ground Acceleration (Average Horizontal)
Figure B-19 Inventory of Dampers Within Experience Database The database represents a wide variety of damper configurations. Pneumatic, motor driven and manual dampers are well represented. Some dampers in the database are housed in steel boxes which are anchored to the ground or to the building's structural steel. Heavy pneumatically operated dampers in the database have their own independent supporting system, and their usually long actuators attach to the side of the duct for louver control within the duct.
8.2.1 Basis for the Generic Bounding Spectrum The seismic experience database includes a vast amount of data on the performance of dampers of various configurations and installations which experienced many different seismic excitation levels. The Generic Bounding Spectrum developed by SSRAP [B-21 to represent the motion at typical data sites was based on the average horizontal free field motion from each of the four reference database sites: Sylmar Converter Station (1971 San Fernando), El Centro Steam Plant (1979 Imperial Valley), Pleasant Valley Pumping Plant (1983 Coalinga), and Llolleo Pumping Plant (1985 Chile). The average of the four ground motion spectra is referred to as the Reference Spectrum. This spectrum is a conservative representation of the ground motion level to which the earthquake experience data demonstrate seismic ruggedness. In other words, the Reference Spectrum is used as a measure of the equipment capacity which has been demonstrated by .
experience. The Generic Bounding Spectrum is obtained by dividing this Reference Spectrum by 1.5. This 1.5 factor is to account for the possibility that floor spectra within about 40 feet above garde in the nuclear power plant might be amplified over the ground spectra more than
W A C Damper Earthqualce Experience Data occurred in the database plants. Thus, the resultant Bounding Spectrum is directly applicable for comparison with Ground Spectra. The capacity as defined as either the Reference Spectrum or the Bounding Spectrum, coupled with caveats on equipment attributes and installation, is then compared to the demand as defined in the GIP Table 4-1.
El Centro Steam Plant experienced a peak ground acceleration of 0.42g during the 1979 Imperial Valley Earthquake. Strong motion at the site lasted about 15 seconds. The site ground motion is based on measurements from an instrument located within 112 mile of the plant.
This plant includes many pneumatic and manual controlled dampers. The positioners for these dampers are enclosed in steel boxes which are then anchored to the ground or the building structural steel. There were no instances of damage to the dampers or their operators in the earthquake.
The Sylnzar Converter Station located near the fault rupture of the 1971 San Fernando Earthquake, is estimated to have experienced at least 0.65g peak ground acceleration, with about 10 seconds of strong motion.
Eight instances of dampers are included in the database at this facility. None of the dampers experienced any seismic effects.
The Shell Water Treatment Plant is located about two miles north of the Main Oil Plant.
The peak ground acceleration experienced at this site during the 1983 Coalinga Earthquake is conservatively estimated at 0.60g.
At this site only one documented case of a butterfly damper exists in the database. This damper remained undamaged as a result of the earthquake.
The I B M a n t a Teresa Computer Facility experienced a PGA of 0.37g, with strong motion occurring for about eight seconds during the 1984 Morgan Hill Earthquake. This facility included several motion monitors, one located in the free field 100 yards from the main building.
The database includes one pneumatic operated damper at this facility. This damper was not damaged in the earthquake.
Valley Steam Plant experienced ground shaking during both the 1971 San Fernando earthquake and the 1994 Northridge earthquake. The peak ground acceleration at the site due to each of these earthquakes was approximately 0.40g. The plant, which includes four units with a total generating capacity of 5 13 MW, is located about 10 miles from the epicenter and three miles from the fault of the San Fernando Earthquake.
Twenty four of the pneumatically operated dampers at this plant are represented in the seismic experience database. None of these dampers sustained any damage due to the above earthquakes.
HVAC Danzper Earthquake Experience Data Burbank Power Plant, located in the BurbanMGlendale area of the San Fernando Valley, is estimated to have experienced a peak ground acceleration of 0.25g, with about 10 seconds of strong motion, during the 1971 San Fernando Earthquake. This plant also experienced the 1994 Northridge earthquake with an estimated peak free field acceleration of 0.30g. This plant consists of five steam generating units and two gas turbine units.
A total of 35 pneumatically operated dampers at this site are represented in the database.
No damage was reported to these dampers as a result of the above earthquakes.
Pasadena Power Plant has the unique distinction of being the only site included in the seismic experience database that has been shaken at comparable levels of intensity by four earthquakes, each producing a level of moderate ground motion comparable to a design basis event for a nuclear plant in the eastern United States. The Pasadena Plant experienced the magnitude 6.6 San Fernando earthquake in 1971, the magnitude 5.9 Whittier earthquake in 1987, the magnitude 5.8 Sierra Madre earthquake in 1991, and finally the magnitude 6.7 Northridge earthquake in 1994.
The peak ground acceleration experienced by this site during these shakings is estimated to be about 0.20g.
The database includes a total of 24 pneumatically operated dampers at this facility.
These dampers functioned properly during and after the above mentioned earthquakes with no damage.
AES Placerita Cogeneration Plant experienced a peak ground acceleration of at least 0.60g during the 1994 Northridge Earthquake [B-31. The estimated site ground motion is based on measurements from several instruments located a few kilometers &om the plant.
Twenty small motor operated fire dampers for Halon system isolation are included in the database for this plant. No damage, as a result of the Northridge earthquake, was reported for these dampers.
B.3 Instances of Seismic Effects and Damage The experience database contains no instances of seismic effects to dampers. The database contains no evidence of the malfunction of dampers during or immediately after an earthquake.
In addition, no instances of seisrnically induced damage to dampers were found in an extensive literature search. Therefore, dampers can be classified as inherently rugged equipment.
B.4 Sources of Seismic Damage The seismic experience database indicates that dampers possess characteristics that generally preclude damage in earthquakes. The experience database contains no instances of damage or significant seismic effects to dampers or their actuators.
HVAC Damper ~art17~zlake Experience Data 5.5 Caveats for Dampers The equipment class of Dampers described below has been determined to be seismically rugged based on earthquake experience data, provided the intent of each of the caveats listed below is met. This equipment class includes all components of dampers installed in W A C systems (or other types of duct systems). Fire dampers which are installed in walls or ceilings are also within this equipment class. Damper components are louver blades, actuators (pneumatic, electrical, and manual, as well as automatic counterweight and counterbalance actuators),
attached air tubing and rigid or flexible electrical conduit, solenoid valves and pressure gages.
Dampers are sheet metal fabricated devices that consist of parallel flaps to either permit or prevent air flow. Dampers are an integral part of fans, air handlers and W A C ducting and in case of fire dampers they are installed in walls or ceilings. The flaps or louvers of dampers are tied together by a common linkage which is externally controlled by an electric, pneumatic or manual actuator. Automatic dampers are operated by a pre-set counterweight or counterbalance.
Attachment of dampers to the W A C ducting or equipment is through bolting, riveting or welding provided around the perimeter of the damper housing. The pneumatic or electric motors that control the actuation are typically attached to the damper housing; however, they also could be mounted on a nearby wall or floor with rack and pinion connection provided for the actuator.
Dampers with heavy motor-operated actuators (typically greater than about 200 pounds) that are installed in-line in HVAC ducting are also represented in the database. This type of damper, however, should have its own independent support system.
The Bounding Spectrum represents the seismic capacity (defined as free-field motion at effective grade) of dampers when the damper meets the intent of the following inclusion and exclusion rules. Note, however, that when the specific wording of a caveat is not met, then a reason for concluding that the intent has been met should be provided on the SEWS.
DMPR/BS Caveat 1 - Earthquake Experience Equipment Class. The damper should be similar to and bounded by the DMPR class of equipment described above. The equipment class descriptions are general and the Seismic Capability Engineers should be aware that worst case combination of certain parameters may not be represented in the generic equipment class.
These worst case combinations may have reduced seismic capacity and should be carefully evaluated on a case-by-case basis.
DMPRLBS Caveat 2 - Damper Operator/ActuatorNot ofcast Iron. The intent of this caveat is to avoid the brittle failure mode of cast iron as evidenced by poor performance of some cast iron components in the past earthquakes. Note that the database does not contain actuators with cast iron components; therefore, it is not necessary to determine the material of the damper control components unless it appears to the seismic capability engineers to be made of cast iron.
DMPRS/BS Caveat 3 - Suflcient Slack and Flexibility of Attached Lines. Sufficient slack and flexibility should be present in attached lines (e.g., air tubing, electrical conduit) to preclude a line breach due to differential seismic displacement of the equipment and the line's nearest support. Also, for damper positioners with independent supports (i.e., not mounted integrally on the duct) the effect of differential displacement on the actuator (with actuator defined as the rod
W A C Danzper Earthqziake Experience Data connected at one end to the positioner and at the other end to the duct louver controls) needs to be considered. The issue here is to watch out for cases where the actuator is connected to a rigidly mounted positioner at one end and to a rod hung duct system at the other.
DMPRS/BS Caveat 4 -Adequate Anchorage. Damper controls when mounted on the ground or nearby structures should be properly anchored in accordance with the guidelines of GIP section 4.4. When the motor- or pneumatic operator is mounted on the duct at the damper location the adequacy of the attachment point to the duct skin or its stiffeners should be ensured.
DMPWBS Caveat 5 - Duct Distortion. The duct at the damper location should be carefblly investigated for any signs of distortion as this would interfere with the damper operation.
B.6 References B-1. Quality Air Design, "Design of Nuclear Dampers," Division of ACDC Inc.
B-2. Senior Seismic Review Advisory Panel (SSRAP), "Use of Seismic Experience and Test Date to Show Ruggedness of Equipment in Nuclear Power Plants,"
Sandia Report SAND92-0140, Part 1,1992.
B-3. The January 1 7, 1994, Northridge Earthquake: E8ects on Selected Industrial Facilities and Lifelines, Prepared by EQE International, Electric Power Research Institute, July, 1995.
B-4. The October 1, 1987, Whittier Earthquake: Egects on Selected Power, Industrial, and Commercial Facilities, Prepared by Electric Power Research Institute, and EQE Engineering Inc., December, 1990. EPRI NP-7126.
c DEVELOPMENT OF ALLOWABLE SPANS FOR SHEET METAL DUCTS Allowable span length charts for horizontal ducts with seismic loads are developed to check for conformance with SMACNA standards. These charts may be used during the in-plant screening review or to guide sample selection for analytical reviews. The screening charts consider seismic and dead weight loading; pressure loads are decoupled since they only influence duct thickness and spacing between duct stiffeners. Seismic loading consists of horizontal and vertical static approximations using peak spectral acceleration. Dead load stresses are summed absolutely with the Square Root Sum of the Squares (SRSS) of the vertical and horizontal seismic stresses.
Allowable span length calculation criteria are developed using analytical requirements presented in Section 4. HVAC duct systems not meeting these spans should be selected for analytical evaluation. The process for developing allowable span charts is described below.
C.1 Rectangular Ducts The evaluation guidelines (see Section 4) for rectangular ducts define the section property of a rectangular duct as being comprised of 2- by 2-inch angle sections at each corner. The maximum expected bending moment is approximated by:
M = - w12 (For ducts spanning over one or two spans) Eq. C-1 8
M = - w12 (For ducts spanning over 3 or more supports) Eq. C-2 10 where:
w = applied load (lbsrin)
& = span between vertical supports (in)
The rectangular duct allowable span length for the typical case (for ducts spanning over 3 or more supports) is determined by:
Eq. C-3
Developnzent of Allowable Spansfor Sheet Metal Ducts where:
p = duct wall material density (lb/in3). Note: an equivalent weight density should be used to account for additional material weight on the duct wall, such as joints and stiffeners.
F,, = allowable material stress (psi)
H = duct height (in)
W = duct width (in)
S, = horizontal peak spectral acceleration (g's)
S, = vertical peak spectral acceleration (g's)
R = (horizontal restraint span length)/(vertical support span length)
K, = a derived constant (in") based on a rectangular duct with a linear weight of 2pt(H+W), section moduli based on 2-inch by 2-inch angle sections at each corner, such that the section modulus about the horizontal is 8t[H-2+(2/H)] and the section modulus about the vertical is 8t[W-2+(2/W)], and an SRSS summation of seismic stresses, resulting in Note that the allowable span length equation is independent of duct thickness since duct section modulus and duct weight are both linear with respect to duct thickness.
For a given duct geometry, allowable span length screening charts can be developed using Eq. C-3 for various span ratios and spectral acceleration levels. Material allowable bending stress should be taken as defined in Section 4.2.1.
C.2 Circular Ducts The evaluation guidelines (see Section 4) for circular duct support spacing define the duct section modulus to be:
Z = 0.25n~~t ~ qC-4 where:
D = duct diameter (in) t = duct thickness (in)
Z = duct section ~nodulus(in3)
Development ofAl101vableSpans for Sheet Metal Ducts The maximum bending moment is approximated by:
wt ME- (For ducts spanning over one or two spans) Eq. C-5 8
wt M=:- (For ducts spanning over 3 or more supports) Eq. C-6 10 The design of duct support spacing for circular ducts is governed for small spans by duct bending. As the span length increases, buckling controls. Allowable stresses reflecting these modes of failure are given in Section 4.2.2.
The circular duct allowable span length for the typical case (for ducts spanning over 3 or more supports) is determined by:
Eq. C-7 where:
p = duct wall material density (lb/in3).Note: an equivalent weight density should be used to account for additional material weight on the duct wall, such as joints and stiffeners.
F,, = allowable material stress (psi)
S, = horizontal peak spectral acceleration (g's)
S, = vertical peak spectral acceleration (g's)
R = (horizontal restraint span length)/(vertical support span length)
D = duct diameter (in)
K2 = a derived constant (1b/in2)based on a circular duct with a linear weight of p n D t, a section modulus of n ~ ~ t land4 , an SRSS summation of seismic stresses, resulting in For a given duct geometry, allowable span length screening charts can be developed using Eq. C-7.
Developnzent of Allowable Spans for Sheet Metal Dzicts C.3 Example Span Calculation The following is an allowable span table for rectangular duct that was developed for the trial application by Southern Nuclear at Plant Hatch. The detailed calculation for the 20"x2OV duct is shown following the calculation.
TURBINE BUILDING EL. 164'-0" DWG. H-16050 Duct Duct Duct Wall Stiffener Height Width Nom. Duct Wall Trans. Angle Stiffener H W Bottom of Duct Wall Thickness Weight Stiffener Weight Spacing (in) (in) Duct El. Gauge (in) (lb1ft2) Angle (Iblff) (in) 10 22 178'-0 22 0.0336 1.41 1~1~118 0.8 48 12 10 178'4" 24 0.0276 1.16 none NIA NIA 178'-6 18 24 178'-6 22 0.0336 1.41 1~1~118 0.8 48 20 20 178'-6 22 0.0336 1.41 1~1~118 0.8 48 34 40 178'-6 20 0.0396 1.66 1~1~118 0.8 48 38 40 178'-6" 20 0.0396 1.66 1~1~118 0.8 48 40 40 178'-6 20 0.0396 1.66 1~1~118 0.8 48 40 44 178'-6 20 0.0396 1.66 1 318x118 1.1 24 Duct Duct Stiffener Est. Trans. Est. Wt. of Duct Height Width Weight Weight of Joint Joints Total Duct Density H W (Iblin of Joints Spacing (Iblin of Weight P (in) (in) duct) (Ib) (ft duct) (Iblin) (lb/in3) 10 22 0.092 4 8 0.042 0.760 0.353 12 10 0.000 4 8 0.042 0.396 0.326 18 24 0.119 4 8 0.042 0.984 0.349 20 20 0.114 6 8 0.063 0.960 0.35704 34 40 0.208 10 8 0.104 2.019 0.344 38 40 0.219 11 8 0.115 2.132 0.345 40 40 0.225 11 8 0.115 2.184 0.345 40 44 0.649 14 8 0.146 2.732 0.411
Developinent ofAllowabIe Spans for Sheet Metal Ducts sa = 0.85 s v = 0.33 Duct Duct Derived Derived Derived Derived Derived Derived Derived Width Constant Constant Constant Constant Constant Constant Constant H W K1(in-2) K1(inq) K1(in") K1(in-') K1(inq) K1(inq) K1(in-')
(in) (in) R=1.0 R=2.0 R=3.0 R=4.0 R=5.0 R=6.0 R=l0.0 10 22 0.3607 0.5918 1.0097 1.6093 2.3608 3.291 1 8.7058 12 10 0.4140 1.0285 2.0637 3.5142 5.3801 7.6604 20.9285 18 24 0.21 13 0.4348 0.8182 1.3570 2.0491 2.8958 7.8224 20 20 0.21 12 0.4880 0.9566 1.6137 2.4588 3.4919 9.5028 34 40 0.1 116 0.2423 0.4650 0.7776 1.I795 1.6709 4.5302 38 40 0.1 038 0.2351 0.4580 0.7706 1.I726 1.6640 4.5233 40 40 0.1005 0.2321 0.4550 0.7676 1.I696 1.6611 4.5204 40 44 0.0966 0.21 52 0.4169 0.6998 1.0635 1.5082 4.0958 ALLOWABLE SPAN BETWEEN VERTICAL SUPPORTS (FT)
Duct Duct Height Width Duct H W Weight (in) (in) (Iblft) R=l.O R=2.0 R=3.0 R=4.0 R=5.0 R=6.0 R=lO.O I0 22 9.1 43 34 26 20 17 14 9 12 I0 4.8 50 32 23 17 14 12 7 18 24 11.8 49 34 25 20 16 13 8 20 20 11.5 50 33 24 18 15 12 7 34 40 24.2 52 35 25 20 16 13 8 38 40 25.6 52 35 25 19 15 13 8 40 40 26.2 52 34 25 19 15 13 8 40 44 32.8 48 32 23 18 14 12 7
Developinent of Allowable Spansfor Slleet Metal Ducts The detailed calculation for the 20"x20" duct in the tables above is shown below.
EXAMPLE CALCULATION FOR ALLOWABLE SPAN LENGTH:
Sample Calculation for 2 0 x 2 0 Rectanaular Duct at Turbine Buildina Elevation 164:
Determine the duct wall equivalent weight density, including an allowance for joints and stiffeners. The duct material gauge, stiffener size, stiffener locations, and transverse joint locations are taken from the HVAC specification. [For purposes of clarity in this example, "112 SME (the applicable Plant Hatch eathquake loading) has been changed to "SSE.]
Ib wt22 := 1.41 .- From the spec., Section 9.8.1, duct material is 22 ft2 gauge for 2 0 duct height and width. Material weight per square foot is from SMACNA Table 3-3.
tnOm22:= 0.0336 .in Nominal thickness of 22 gauge material, SMACNA Table 3-3.
wt22 Pduct := -
tnom-22 Ib pduct = 0.29 - Weight density of duct wall material only.
3 in H := 20.h Duct height (vertical direction).
W := 20411 Duct width (horizontal direction) mductjer-in := 2.pduct.tnom-22.(H + W)
Ib Whuctjer-in = 0.783 - Weight of duct wall material only per inch of duct.
in Ib W t l x l x l-8 := 0.8.- Transverse joint stiffener for a 2 0 x 2 0 duct is one ft 1 x 1 x 118 angle bracing 4 ft. from joint (spec, Section 9.8.3b). Angle weight from AlSC Manual.
Development ofAIlowable Spans for Sheet Metal Ducts Wduct-stiffener := W~IXIXI-B.E[~.(H+ 2.in)l + (2.W)1 Wduct-stiffener = 5.6 Ib Total weight of stiffener.
Sstiffener := 4.ft Stiffener spacing (spec, Sect. 9.8.3b).
Wduct-stiffener Wstiffjer-in ::=
Sstiffener Ib Wstiffjer-in = 0.12 in Wjoint := 6.1b Transverse joints are 1 inch pocket slip or 1 inch bar slip on 8-ft centers (spec, Sect.
Sjoint := 8 4 9.8.3b). Assumed additional weight of joints, including long. seam.
Wjoint qointjer-in := -
Sjoint Ib qointjer-in = 0.06 7 Weight allowance for joints per inch.
In Wtductjer-in + Wstiffjer-in+ Wjoint-per-in p :=
2.tnorn-22( H + W Ib Duct wall material density for a 2 0 x 20" p = 0.358 -
3 duct, including allowance for joints and in stiffeners.
Determine the allowable span, L, between vertical supports.
Normal allowable bending stress for galvanized Fb := 8OOOpsi sheet from Section 4.2.1.
Fb-SSE := 1.7.Fb Increase allowable for the Hatch SSE earthquake per Section 4.2.1. This assumes the transverse joints are equivalent to SMACNA types T-I through T-3 and T-15 through T-24 joints.
Fb-SSE = 13600 psi
Developlnent ofAllowable Spansfor Sheet Metal Dtrcts Ib p = 0.358 - Duct wall material density calculated above.
3 in H := 20 W := 20 Duct height and width (dimensionless).
Sa := AH-TB~-~% Applicable accelerations are from Turbine Building Mass Point 5 at El. 209'-0.
Sa = 0.85 g g := 1.0 sv := Av-TB~-~%
Sv = 0.33 g Let R := 4.0 , Find Laow
-1 2
2 2 s,~.R~.W~ Sv .H H K1 := +
[(g-w+l.J 2 (:-H+.lJ] ( ~ H + l Y .
1 K.1 = 1.6137-2 in
-1 Lai~ow:=
[ (2H.in 160.Fb-SSE
+ 2.W.in).p.K1 1' Lallow= 18.1 ft Maximum span between vertical supports for SSE Lmax := 15 ft earthquake, R=4.0 Check this value by calculating duct stresses using Section 4 of Reference 8. Calculate duct section modulus using 2-inch by 2-inch region at the four corners of the duct. Calculate section modulus consistent with Reference 8 Secion C.l (treating the corner angles as a line and approximating the moment of inertia as equal to the sum of the Ad terms).
H := 20.in W := 20.in tnOm-22 = 0.0336 in Lallow= 18.1 ft
Development of Allowable Spansfor Slzeet Metal Dzrcts 2.in2) sX:= @in)(tnom-22).(H- 2.in + - Calculate section modulus.
3 Section modulus about the horizontal.
Sx = 4.865 in 2.in 2)
Sy := (841).(tnom-22 W - 2.in + -
).( w l 3 Section modulus about the vertical.
Sy = 4.865 in w := Wtductjer-in + Wstiffjer-in+ Wjointjer-in Ib w = 0.96 -
In 2
w.La110w Mx-DL :=
Mx -DL = 378 Ib ft Dead load moment.
2 (w)(SV) . ~ a ~ ~ o w Mx-SSE :=
10 Moment about the horizontal axis due Mx -SSE = 1251bft to SSE earthquake.
CW).(sa).(~a~~ow.~)~
MY-SSE :"
I0 My-ss~ = 5135 Ibft Moment about the vertical axis due to SSE earthquake.
Mx-DL DL := -
sx DL = 931 psi Dead load stress.
Developlnent of Allowable Spansfor Sheet &fetal Dzicts fx-SSE = 307 psi Stress due to vertical earthquake.
f y - s s ~= 12665 psi Stress due to horizontal earthquake.
Combining stresses per Section 4.1 :
ftotal = 13600 psi OK, this equals the allowable stress of 1.7 times 8000 psi (13,600 psi).
Allowable span based on stress is 18.1 feet, but 15 foot maximum span controls.
SEISMIC AND PRESSURE TESTING OF HVAC DUCTS D.l Introduction Several tests were conducted by testing facilities to demonstrate the inherent resistance of W A C systems to seismic damage in combination with pressure loadings. The test pressure loading (both positive and negative pressure) was generally several times the typical normal operating pressures in the ducts at nuclear power plants. Similarly, the seismic test loading, in the form of biaxial input motions or equivalent static loadings, was greater or equivalent to the maximum seismic demand at most nuclear power plants. The tests confirmed that the HVAC ducts constructed to SMACNA standards have adequate structural integrity and functional capability for the postulated DBE loads, as well as the normal operating pressure loads.
D.2 HVAC Duct Test Programs 0.2.1 Summary of Tests Performed for TVA Ducts Vibration testing of rectangular ducts, which included both pocket lock and companion angle duct constructions, was conducted. Three different duct sizes (60"x24", 48"x18", and 36"x24")
with width-thickness ratios ranging between 602 and 1671, and constructed to SMACNA standards, were tested. Four specimens of each duct size were available for testing for a total of twelve test specimens (six ducts with pocket locks and six ducts with companion angles). Each duct size was tested, non-concurrently, in the two directions perpendicular to the longitudinal axis of the duct specimen. The sheet metal thickness ranged from 20 ga. to 22 ga., and the duct span lengths varied from 14 to 28 feet. In order to tune the test setups to a first mode resonance of 8 to 11 Hz., which was the frequency range of the dominant response as defined by the required response spectra (RRS) with a peak acceleration value of 6.4g, a variable support was designed to alter the structural response of the ductlsupport system.
The tests demonstrated that both types of duct construction were capable of sustaining seismic loads of up to 6.4g with no or very little damage. The companion angle ducts experienced minor, highly localized failures in the duct skin that occurred as small separations in the duct skin corners or near a stiffener. These localized separations remained sufficiently closed that air delivery would not be significantly impaired. Ducts with pocket lock construction demonstrated an unexpected capability for sustaining high dynamic loads. The more flexible joints and higher damping in this type of construction are the primary reasons that no local failures, such as found with the companion angle ducts, were observed with the pocket lock construction.
Seismic and Pressure Testing of W A C Ducts The average damping values obtained from testing for companion angle and pocket lock ducts were about 7% and lo%, respectively. In addition, first mode natural frequency of each duct specimen was determined during testing. These tests revealed that the fundamental mode frequency of both pocltet lock and companion angle ducts was less than what would be predicted based on beam theory and using the SMACNA four corner method to calculate the effective moment of inertia of the duct section. The resulting reduction factors used to adjust calculated natural frequencies are 0.59 and 0.87 for pocket lock and companion angle constructions, respectively.
A11 duct specimens were subsequently tested to failure. The peak acceleration values of actual test response spectra (TRS) at failure ranged from 10.2g to 14.0g for the companion angle ducts, and from 11.0g to 16.2g for the pocket lock ducts. Analysis of the test results, using the acceleration levels sustained at failure, indicated a bending stress at failure ranging from 25.2 to 5 1.7 ksi calculated by the SMACNA four corner effective section method. The general failure mode for companion angle ducts was a gradual, very ductile failure, with no complete separation of sections and with no gross opening of the pressure boundary. The general failure mode for pocket lock ducts was usually a sudden opening of the crimped joint. A sudden, catastrophic type of failure resulted and actual separation of duct sections caused the span to fall to the test table.
It is noted that two of the pocket lock ducts could not be failed due to force limitations of the shake table.
0.2.2 Summary of Tests Performed for Limerick Ducts The test program for ducts at Limerick consisted of testing seventeen test groups. Each test group consisted of three identical specimens except for one test group which had one specimen. Fifteen test groups included rectangular ducts with sizes ranging from 24"x24" to 96"x48". All duct specimens were of welded construction with a minimum sheet thickness of 18 ga., and the actual width-thickness ratios varied from 502 to 1605. Stiffener angle sizes ranged from 1"xl"x1/8" to 3"x3"~1/4",with spacing ranging from 24" to 48".
All specimens were tested for negative pressure with the exception of one specimen that was tested for positive pressure. The average negative test pressure ranged from 17.8 to 104.2 inches of water gage and the positive test pressure was 48.0 inches of water gage. Duct spans were from 8 to 12 feet long, and all duct specimen were simply-supported on the ends along the bottom end stiffener widths with the exception of two specimens that were supported along their end vertical stiffeners mounted on the height of the ducts.
All ducts were subjected to live load or seismic load simulation tests, or both, followed by the pressure test to failure or to a maximum negative pressure of 14 psi (-407.0" w.g.). Application of live load and simulated seismic load was accomplished by predetermined steel weights and bagged sand. Test internal pressures (negative or positive pressures) were applied to the specimen by an electrical pump connected in series with an accumulator tank. Only ducts in two groups were subjected to simulated seismic loading. The test sequence began with the live load tests followed by the seismic load tests, if any. Thereafter, the pressure tests to failure began.
None of the ducts failed during the live load or seismic load tests. All ducts failed during the pressure load testing, with exception of the 8" diameter duct that did not fail.
Seisrnic and Pressure Testing of HVAC Ducts In general, the test results demonstrated that failure modes of ducts were not catastrophic and there was significant reserve strength after failure. The negative pressure loading was the most important loading, since the failure mode under positive pressure was stiffener buckling whereas under negative pressure loading the duct failure mode was either the stiffener buckling or the corner crippling of the sheet metal. Dead load, live load, and seismic stresses in duct acting as a beam between supports were relatively low. The test results also supported using duct width-thickness and height-thickness ratios of up to 1500, as opposed to 500 and 200, respectively, per American Iron and Steel Institute (AISI) requirements.
0.2.3 Tesfs Performed at Ofher Plants Similar duct tests were also conducted for CPSES and CP&L plants to verify the structural integrity of ductwork, particularly with longitudinal seam construction, under combined seismic and pressure (both positive and negative) loadings. The results of these tests are generally in agreement with the duct tests described in detail above.
D.3 Conclusions From Test Programs In general, the tested ducts were either constructed to the SMACNA standards or were of a less conservative construction. The tests, collectively, provided the following results:
0 The duct beam properties established based on the test results are comparable to the method prescribed by SMACNA guidelines but are less conservative.
0 The average damping values for companion angle and pocket lock construction were established to be about 7% and lo%, respectively.
Long spans of ducts (14' to 28') performed adequately under seismic input motions with a peak acceleration value of up to 6.4g.
When tested to failure, with seismic input motion peak acceleration values ranging from 10.2g to 16.2g, failure of the duct specimens was very gradual and of a ductile nature, except for the ducts with pocket lock construction in which the crimped joints would suddenly open and cause a catastrophic type failure.
The overall conclusion fiom these limited tests indicates that as long as brittle failure of duct section connections is precluded, duct deformation under increasing loads is very ductile.
Furthermore, for HVAC ducts with typical span lengths of about 15 feet and constructed to the SMACNA standards, duct capacity can be expected to significantly exceed typical demand under the combined normal operating and seismic loadings postulated for most nuclear power plants.
Seislnic and Pressta.e Testing of HVAC Dzrcts D.4 References D-1. Neely, B. B., Warrix, L, "A Qualification and Verification/Improvement Test Program for W A C Ducts Used in Nuclear Power Plants," presented at Century 2 Pressure Vessels and Piping Conference, August 1980.
D-2. Neely, B. B., Warrix, L., "A Procedure for Seismically-QualifyingHVAC Ducts Used in Nuclear Power Plants," presented at Second ASCE Conference on Civil Engineering and Nuclear Power, September 1980.
D-3. Desai, S. C., K. P. Buchert, and E. A. Marcinkevich, "Structural Testing of Seismic Category I W A C Duct Specimens," Second ASCE Conference on Civil Engineering and Nuclear Power, Volume I., Knoxville, TN, September 1980.
D-4. Dizon, J. O., E. J. Frevold, and P. D. Osborne, "Seismic Qualification of Safety Related W A C Duct Systems and Supports," 1993 ASME Pressure Vessel and Piping Division Conference, Denver, Colorado, July 1993.
ROD FATBGUE EVALUNlON GUIDELBMES E.1 Introduction Shake table tests have shown that the seismic capacity of fixed-end rod hanger trapeze supports is limited by the fatigue life of the hanger rods. Rod hanger trapeze supports should be evaluated for possible fatigue effects if they are constructed with fixed-end connection details.
Fixed-end connection details include double-nutted rod ends at connections to flanges of steel members, rods threaded into shell-type concrete expansion anchors and rods connected by rod coupler nuts to non-shell concrete expansion anchors. Fixed-end connection details also include rods with lock nuts at cast-in-place light metal strut channels and rod coupler nuts welded to overhead steel.
This attachment describes a screening method for evaluating rod hangers for fatigue based on the use of rod fatigue bounding spectra (shown in Figure E-1) and generic rod fatigue evaluation screening charts (shown in Figure E-2 through E-6).
lo0 Frequency (Hz)
Figure E-1 Bounding Rod Fatigue Spectra
Rod Fatigue Evaluation Gziidelines 1/4" THREADED RODS Figure E-2 Fatigue Elevation Screening Chart for % inch Diameter Manufactured All-thread Rods.
Weight Corresponds to the Total Supported Load (i.e., on both Rods). Length Corresponds to Clear Length The screening charts are directly applicable to hangers constructed of manufactured all-thread rods in overhead suspended system runs with uniform length hangers. The charts may also be used for evaluation of supports constructed of field threaded rods and for short, isolated fixed-end rod hangers in more flexible systems with relatively much longer rod hangers; guidance is given later in this appendix on how to adjust the parameters when evaluating these special cases.
A fatigue evaluation should be conducted for rod hanger supports that have rods with fixed end connection details. For rod hung W A C duct systems with rods of uniform length, the fatigue evaluation is conducted as follows:
- 1. Obtain the 5% damped floor response spectrum for the location of the support attachment point.
- 2. Compare the Bounding Rod Fatigue Spectra of Figure E-1 with the damped floor response spectra. For a given ZPA, if a Rod Fatigue Spectrum entirely envelops the floor response spectrum, proceed to step (c). If the Rod Fatigue Spectrum does not entirely envelop the floor response spectrum, then compare the Rod Fatigue Spectrum with the floor response spectrum (unbroadened) at the frequency of the support. Support frequency may be estimated as follows:
Rod Fatigue Evalzlation Guidelines where:
2 M, = Wequi,/g(lbs-sec /in) 3 KS = 24EIlL + Wequiv/L (trapeze support, Ibslin)
Wequiv= total dead weight on the pair of rod.,.supports (lbs) g = gravitational constant (386.4 i d s e c j E = Young's modulus of rod hanger material (psi) 4 I = moment of inertia of rod root section (in )
L = length of rod above top tier (in) 318" Threaded Rods (0.33gt0.50g and 0.759 ZPA'S)
EOE h.0 Minimum Acceptable Rod Length (L, in.)
Figure E-3 Fatigue Evaluation Screening Chart for 318 inch Diameter Manufactured All-thread Rods.
Weight Corresponds to the Total Supported Load (i.e., on both Rods). Weight Corresponds to Clear Length
Rod Fatigue Evaluation Guidelines 112" Threaded Rads (0.33g,0.50g and 0.75g ZPA's) 2.6 EOE wM Minimum Acceptable Rod Length (L, in.)
Figure E-4 Fatigue Evaluation Screening Chart for 112 inch Diameter ManufacturedAll-thread Rods.
Weight Corresponds to the Total Supported Load (i.e., on both Rods). Length Corresponds to Clear Length If the bounding Rod Fatigue Spectrum does not envelop the floor response spectrum at the frequency of interest, then a more detailed evaluation should be conducted (by requirements other than the screening evaluation requirements presented herein).
- 1. Enter one of the Fatigue Evaluation Screening Charts shown in Figures E-2 through E-6 corresponding to the diameter of the threaded rod. Use the curve associated with the acceleration (0.33g, 0.50g or 0.75g) of the Rod Fatigue Bounding Spectrum of the previous step. If hanger length is greater than minimum acceptable length, and support dead weight is less than maximum acceptable weight, then the support is acceptable. This chart is applicable for all continuously threaded rods. For field threaded rods see (d) below.
- 2. If field threaded rods are to be evaluated, then the screening chart may be used for modified rod lengths and weights. For field threaded rods, double the weight and decrease rod length by 1/3 before using the chart.
Rod Fatigue Evaluation Guidelines 518" Threaded Rods (0.33g, 0.50g and 0.75g ZPA's)
EOE I*", Minimum Acceptabie Rod Length (L, in.)
Figure E-5 Fatigue Evaluation Screening Chart for 518-inch Diameter Manufactured All-thread Rods.
Weight Corresponds to the Total Supported Load (i.e., on both Rods). Length Corresponds to Clear Length If isolated, short fixed-end rod hangers are used in a system with predominantly longer, more flexible hangers, a special evaluation should be conducted that decouples the response effects of the short isolated rod. The special evaluation proceeds as follows:
- 1. Estimate the frequency of the system, neglecting the isolated, short rod support.
The frequency estimation formula given above may be used, providing that the length of the longer rods is considered.
- 2. Assure that the rod fatigue bounding spectrum envelops the applicable floor. response spectrum at this frequency of interest.
- 3. Back-calculate an equivalent weight for the evaluation of an isolated short rod, using the frequency of the long rods as follows:
24Elg
= (2rifr)L3 - g12 (trapeze support)
- 4. Enter the appropriate Fatigue Evaluation Screening Chart (Figures E-2 to E-6) by using the above calculated equivalent weight and length of the isolated short rod hanger. If these parameters are in an acceptable region on the Fatigue Evaluation Screening Chart, then the isolated, short, fixed-end rod hanger is seismically adequate.
Rod Fatigue Evaluation Guidelines When using the charts, the simple equations given in this section for calculating response frequency should be used for consistency since these are the same equations used to generate the screening charts (that is, the screening charts are based on the simplified results obtained from detailed fatigue analysis, considering capacities determined by component test results).
314" Threaded Rods (0.33g, 0.50g and O.75g ZPA's)
EOE liW Minimum Acceptable Rod Length (L, in.)
Figure E-6 Fatigue valuation Screening Chart for 314-inch Diameter Manufactured All-thread Rods.
Weight Corresponds to the Total Supported Load (i.e., on both Rods). Length Corresponds to Clear Length
GUIDELINES FOR LIMITED ANALYTICAL REVIEW OF ShlPBPORTS F.1 Introduction A Limited Analytical Review (LAR) should be performed to assess the structural integrity of W A C duct supports chosen as representative, worst-case bounding samples of the evaluation scope of W A C duct systems. The purpose of the LAR is not to estimate actual seismic response and system performance during a DBE. Rather, the LAR is intended to demonstrate that the
.:. . W A C duct supports are at least as rugged as supports that performed well as evidenced by past experience, using empirical methods, plastic design principles, and engineering judgment.
There are several steps in the LAR process that must be understood in their entirety in order to ensure that the intent of the evaluation guidelines is met. These steps include the following checks, applying to both the support structural framing and the anchorage to the building structure:
- Dead load check
@ Vertical capacity check o Ductility review 0 Lateral and longitudinal load check Rod hanger fatigue evaluations The above checks are described in detail in the following sections except for the rod hanger fatigue evaluation. Guidelines for rod hanger fatigue evaluation are contained in Appendix E.
The first check to be performed is a standard, dead load design check. Supports not passing this check are outliers. This check serves the functions of an inclusion rule. Most of the earthquake experience database supports are conservatively assumed to have been adequately designed for dead weight. Adequate dead load design is thus the first important step for verification of seismic adequacy. This check is discussed in Section F.2.
The second check is the vertical capacity check. This check ensures high capacity of anchorage and primary anchor connections for the support, using simple calculational methods. Position retention is considered the most important aspect of ensuring structural integrity. This check is described in Section F.3.
Guidelinesfor Limited Analytical Review of Szpports The third check is a ductility review. This requires an assessment of how the support responds to lateral and longitudinal seismic motion, and what are the weak links in the support load path.
The next two checks are the lateral and longitudinal load checks. These checlts are static coefficient approaches for evaluating support capacity. If failure modes are ductile, then the lateral and longitudinal checks may not be required. See section F.4 for a discussion of the ductility review, and section F.5 for the lateral and longitudinal checks.
It is important for the evaluator to understand the functional goals (following the DBE) for the HVAC duct system being reviewed. If the seismic evaluation is being performed solely to ensure structural integrity, then support flexibility and ductility principles may be used to their fullest extent. Conversely, if duct system pressure boundary integrity is of high concern, then the evaluator must use caution when applying the ductility guidelines contained herein.
When ductile, plastic deformation of supports is allowed in either the lateral or longitudinal directions of motion, judgment must be passed on the potential consequences of this support behavior on the duct system. For example, consider an axial run of duct with an elbow at the end to a transverse run. If, in the longitudinal direction for the axial run, the supports are allowed to go into ductile plastic deformation, then the evaluator must ensure that the first lateral support around the elbow to the transverse run will respond in a similar manner. If not, the support may act as a hard spot, and cause potentially detrimental consequences to the duct elbow or that first lateral support on the transverse run (see Figure F-1).
RIGID CEILING SEISMIC LOAD v
FROM LONG Figure F-1 Vulnerable Duct Elbow Adjacent to Rigid Lateral Restraint
Guidelinesfor Liinited Analytical Review of Supports F.2 Dead Load Check A detailed dead load design review of the representative worst-case bounding sample W A C duct supports should be conducted using normal design working stress allowable loads.
The check should consider the as-installed configuration, connection detailing, and loading condition of the support. All components such as bracket and trapeze cross members, vertical support members, internal framing connections, and support anchorage should be checked.
All system eccentricities, including load to anchor point eccentricity, should be considered.
Evaluation of clip angle bending stresses may be excluded for trapeze supports suspended from the overhead. Loads from other attached systems, such as piping or conduit, should be considered.
Consideration should also be given to the seismic adequacy of the wall to which the W A C duct supports are attached. Reinforced concrete structural walls are not a concern but masonry walls should be checked to verify that they are seismically adequate. Anchorage into transite walls (asbestos fiber board) and gypsum board partitions should be considered outliers.
Reduced anchor bolt capacities should be used for expansion anchors in masonry block walls. The anchorage of partition walls and shielding walls should be checked.
F.3 Vertical Capacity Check The check concentrates on the support anchorage, focusing on the weak link in the support anchorage load path. High vertical capacity is one of the primary design attributes that is given credit for good seismic performance. The Vertical Capacity Check evaluates whether the vertical capacity to dead load demand ratio is as least as high as that of support systems in the earthquake experience database that performed well. The high vertical capacity provides considerable margin for horizontal earthquake loading.
The Vertical Capacity Check is an equivalent static load check, in which the support is subjected to a vertical load, Pv, defined as Pv = Fv (Dead Load),
where Fv is a vertical load increase factor defrned as Fv = Greater [5.0g, 6.0 (ZPAh)].
ZPAh is the zero period acceleration of the floor response spectrum at the support anchorage.
This check is limited to the HVAC duct support primary connections and anchorage. It is not necessary to evaluate clip angle bending stress or secondary support members. The lower support member of floor-to-ceiling configurations and base-mounted supports should be checked for buckling.
Guidelinesfor Limited Analytical Review of Supports Eccentricities resulting in anchor prying and eccentricities between vertical support members and anchor points should, in general, be ignored. This concept is the result of back-analyses of earthquake experience database supports and is consistent with limit state conditions observed in test laboratories.
For cantilever bracket support types, the eccentricity of the cantilevered dead load should be ignored.
For trapeze frame and rod-hung supports, load distribution between the two vertical framing members should be considered only if the center of the load is significantly distant from the centerline of the support frame. The bending strength and stiffness of frame members should be checked for transfer of the load between anchor bolts when overhead support is provided by light metal framing with anchor bolts spaced at relatively large intervals and when multiple anchor bolts are needed to resist the vertical load.
For most W A C duct support systems, the anchorage will be found to be the weak link in the load path. For these cases of W A C duct supports the Vertical Capacity Check is simply a comparison of anchor capacity to Fv times the supported load.
If the Vertical Capacity Check is not met, then the support should be classified as an outlier.
F.4 Ductility Check An evaluation should be conducted of the supports selected for review to characterize their response to lateral and longitudinal seismic motion as either ductile or potentially non-ductile.
The purpose of the ductility check is to identify support configurations that require a lateral and longitudinal load check (discussed in Section F.5).
Supports suspended only from overhead may be characterized as ductile if they can respond to lateral seismic motion by swinging freely without degradation of primary vertical support connections and anchorage. Ductile, inelastic performance such as clip angle yielding or vertical support member yielding is acceptable so long as deformation does not lead to brittle or premature failure of overhead vertical support.
Review of typical W A C duct support systems in the earthquake experience and shake table test databases indicates that many overhead mounted support types are inherently ductile for lateral seismic motion. Back-analysis of many database supports predicts yielding of members and connections. These database systems performed well, with no visible signs of distress.
Ductile yielding of suspended supports results in a stable, damped swaying response mode.
This is considered to be acceptable seismic response and use of the support plastic moment is permitted.
The ductility review of anchorage connection details is most important for rigid-type suspended supports. Supports with rigid, non-ductile anchorage that do not have the capacity to develop the plastic strength of the vertical support members can possibly behave in a non-ductile fashion.
Guidelinesfor Li~niledAnalytical Review of Supports Examples include large tube steel supports welded to overhead steel with relatively light welds, or rigid supports welded to large base plates and outfitted with relatively light anchorage. These types of support systems are not well represented in the database and are not preferable since they have a brittle failure mode.
The seismic design of certain W A C duct support members may have been controlled by high frequency requirements rather than design loads, yet anchors may have been sized by the design loads. These types of supports may have low seismic margin due to loads placed on the support which were not considered by the original design. Supports with rigid, non-ductile anchorage are subject to further strength review (see Section F.5).
Examples of ductile and non-ductile support connection details and configurations are described below and illustrated in Figure F-2.
Standard Catalog Light Metal, Strut Franzing Members, Clip Angles, and Bolts with Channel Nuts. Unbraced supports suspended from overhead, constructed of standard Catalog light metal, strut framing channels, clip angles, and bolts with channel nuts may be characterized as ductile.
This includes supports constructed of standard catalog light metal strut framing gusseted, clip angle connections.
Welded Steel Members. If an anchor point connection weld is stronger than the vertical member, then a plastic hinge will be able to form in the vertical member, allowing ductile response without weld failure. A support is seismically rugged so long as overhead support is maintained.
In this case, plastic hinge action in the vertical member prevents transmission of loads capable of failing the welded anchorage point. For open channel structural sections, an all-around fillet weld whose combined throat thicknesses exceed the thickness of the part fastened, may be considered capable of developing the plastic hinge capacity of an open channel section vertical member. If the plastic hinge capacity of the framing support member exceeds the capacity of the weld, then a brittle failure is possible, which is not acceptable seismic performance. For light metal, strut framing members, welded connections are likely to be non-ductile and thus not capable of developing plastic moment capacity of the framing member.
Ceiling Connection Plate Secured with Expansion Anchors. Supports with overhead anchorage provided by a plate attached to concrete with expansion anchors should be evaluated for ductility as follows. The anchorage may be characterized as ductile if it is stronger than the plastic flexural strength of the vertical support member. A simple anchor moment capacity estimate may be used, by multiplying the bolt pullout capacity times the distance between the bolts or center of bolt groups. In some cases, it may be possible to demonstrate ductility if the ceiling connection plate is the weak link in the anchorage load path. This is similar to the case of clip angle bending.
The key to characterizing a support as ductile or non-ductile is reviewing the anchorage load path, and determining if the weak link responds in the ductile or brittle manner.
Braced Cantilever Bracket and Trapeze Frame Supports. The presence of a diagonal brace in a support has the potential of significantly increasing the pullout loads on anchorage when the support is subjected to horizontal motion. This is a function of the support geometric configuration, the realistic capacity of the brace, and the realistic capacity of the anchorage. Non-ductile
Guidelinesfor LimitedAnalytical Review of Supports behavior is possible when the brace reaction of horizontal load, plus dead load, has the capability of exceeding the primary support anchor capacity. If a brace bucltles or has a connection failure before primary support anchor capacity is reached, then the suppol-t may be considered as ductile. Braced supports are subject to further horizontal load capability review with a focus on primary support anchorage.
Connections A and B are partially welded connection details. Partial welds cannot develop the plastic moment capacity of the vertical member, and are considered non-ductile.
Connection C is the non-ductile rigid boot connection.
Connection D is a rigid moment-resisting liame and should be checked for horizontal load.
Connections E and F are diagonally braced, and should be checked for horizontal load Figure F-2 Examples of Potentially Non-Ductile Support Connection Details and Configurations
Guidelinesfor Liinited Analytical Review of Supports Unbraced Rigid Trapeze Frames. Trapeze frames constructed as moment-resisting frames, such as those with a number of stiff cross-beam members welded to the two vertical supports have the potential of significantly increasing the pullout loads on anchor bolts when the frame is subject to horizontal motion. Non-ductile behavior is possible when the rigid frame anchor point reactions to horizontal load exceed the anchor capacity. Unbraced rigid trapeze frames are subject to further horizontal load strength review with focus on anchorage.
Floor-mounted Supports. Plastic behavior of floor-mounted supports may lead to structural instability. Ductility, as defined by these guidelines, only applies to suspended systems.
Floor-mounted supports are characterized as non-ductile, and are subject to further horizontal strength review with focus on stability.
Rod Hanger Trapeze Supports. Supports constructed of threaded steel rods with fixed-end connection details at the ends of the rods behave in a ductile manner under horizontal motion; however, relatively short rods may undergo very large strains due to bending imp0sed.b~
horizontal seismic motion, at the fixed ends of the rods. Low cycle fatigue may govern response.
Rod hanger trapeze supports with short, fixed-end rods should be evaluated for low cycle fatigue effects.
If a support is characterized as non-ductile or has questionable ductility, then its lateral load capacity should be verified, as discussed in Section F.5. If a support is characterized as ductile, and the duct system as a whole, depending on the functional goals, is judged capable of handling anticipated plastic deformation of supports, then it may be judged that no further lateral or longitudinal load check is necessary.
F.5 Lateral and Longitudinal Load Check A Lateral and Longitudinal Load Check should be performed for the bounding case W A C duct supports that are characterized as potentially non-ductile. The Lateral and Longitudinal Load Check is in the form of an equivalent static lateral load coefficient.
If a support is non-ductile or has questionable ductility, then it should be analyzed for dead load plus a transverse acceleration of 1.0 times the Peak Spectral Acceleration (PSA) of the in-structure response spectrum, at 5% damping, for the anchor point in the plant where the W A C duct system is attached.
To evaluate a given support, transverse loads for the two horizontal axes should be applied, and capacities checked, non-concurrently. That is, two separate load cases should be checked.
For example, one load case would be dead load plus loads due to north-south seismic motion, and the second would be dead load plus loads due to east-west seismic motion.
For these loading conditions,judgment must be used to ascertain the tributary mass, or length of duct run, to consider for each direction of load. As a general guideline, tributary length of duct for consideration for each direction of load should include one-half the length of duct to the next supports, on either side of the support being evaluated, that resist load in that direction.
This general rule may not always apply, and tributary spans should be adjusted as judged necessary based on stiffness considerations for the duct systems.
Guidelinesfor Liinited AnaIytical Review of Supports It is not required that the PSA always be used; this is intended to be a "first screen" method.
If a reasonably accurate estimate of dominant mode response can be made, then the spectral acceleration associated with the frequency estimate may be made. As appropriate, beam-on-elastic-foundation approximations or Dunkerley's equation approximations may be used (separately or together). These frequency estimation approaches are shown in Figures F-3 and F-4. When these methods are used, the basis for their applicability should be documented with the LAR calculations.
For IDuse SMACNA 2-inch comer section method. Ks and P are typical.
Wequiv = WP fs = (1/2x)(Ks gl~equiv)"~
fD = ( O . ~ ~ ) ( ~ / ~ ) @ I ~ ~ ! W L D ~ ) " ~
0.87 is for companion angle duct. Use 0.59 for pocket lock.
&stem = VC2 + f ~ ' ) ~ ' ~
Figure F-3 System Frequency Estimation Using Beam-on-Elastic-Foundation Approximation For ID use SMACNA 2-inch comer section method. Ks and P are typical Wequiv= WP fs = (112~)(Ks iiWequiv)'"
fD = ( o . ~ ~ ) ( K I ~ ) ( E I ~ ~ / w P ~ ) ' "
0.87 is for companion angle duct. Use 0.59 for pocket lock.
fsYstem= [(llfs)' + ( l l f ~ ) ~ l - ' ' ~
Figure F-4 Dunkerley's Equation Frequency Estimation Methodology
Guidelinesfor Linzited Analytical Review of Supports The simple equivalent static load coefficient method may be too conservative for very low frequency supports with long drops from the ceiling anchorage to the HVAC duct. The static coefficient method predicts very high connection bending moments in these cases. In this case, the bending moment imposed on the ceiling connection may be limited by peak seismic deflection and not seismic acceleration. An alternative loading condition of dead load plus reaction forces due to a realistic estimate for imposed seismic deflection may be used. Seismic deflection may be calculated by using floor spectral displacement at a lower bound frequency estimate, considering only single degree-of-freedom pendulum response of the support.
For diagonally-braced supports with ductile overhead anchorages, the load reaction imposed on the support anchorage during the Lateral Load Check does not need to exceed the buckling capacity of the brace or its connections. For diagonally-braced supports where the anchorage is not ductile, the portion of the lateral load that is not resisted by the brace should be redistributed as bending stress to the overhead connection. The loads in the diagonal brace will cause additional vertical and horizontal loads on the anchorage, and should be accounted for.
An upper and lower bound estimate should be used for buckling capacity of the brace, whichever is worse, for the overhead anchorage. There is considerable variation in test data capacity for light metal strut framing connections. An upper bound estimate of 2.0 times the manufacturer's suggested capacities can be used for these connection types.
PEER REVIEW COMMENTS Peer Review Colnrncnrs on EPRX Seismic Evnlustion Gnide1:linesfor HVAC Duct and Dataper Systems RP. Kc~nedy February 7,2004 The EPHl Tcdmical Report 1007896mtitled Seismic E'~~aItla!jot?
Guidelinesj%r.HYAG Dtrci rtnd Danger r n t c n ~ \Ref.
s 1) pro~idcsart emhyuakc cxpericnw based approach for veriflring the scisinic adequacy of HVAC duct and dwtpcr systems. It i s my undcrshnding that Ref. 1bas not bwn suhJectcd to a dclailed rwleiv by an indcpcndcnr peer review pmd in ii manner similar to that porfarmed for odler classes ~Fequiprnentevaluated using an ca~%hqunke esperience bascd sisn~ic evaluation approach. Although not lion1 im independent peer review panel, this report presents my individnal independent p e a tevim*of the seismic cvaluaiion guidelines presented in Ref. I.
'f'hc seismic evaluntion approach recorninended in Ref. f consists of a t\iro-step process. Tl~efirst sttr, consists nf a detailed in-plant seismic ~'illkdoxv~~lt screening rm;tav of the HVAC duct sysfenls to be evaluated. 'This review is to be conductcd by a Seismic Itcvicvv Team [SRT) t h u ~consists of at Icast RVOqualified engineers thtrt lmlst mutqally agrec that rhe walkdo\vn revictved 1WAC duct systcm has passed the seismic scrrening so that it is eligible to have its seismic dcquacy verified by the earthquake wprimcc. b a s 4 :dppwach- Guidance for this bcismic waIkdowfi review is presented in Section 3 of Ref. I.
For fl~esecond step, the SRT seIecis a bnunding senlple ofEWAil3 duct systems nnd supports to be subjected to a simplified anaIytjcaI review. Ueltfs Tot this malyticsl review are presented in Section 4 ofRef. I. The sirnplificd flnal}~icalapproach presented in Secticm 4 o f Ref. 1 is very similar to iho &sign-by-Rule :tpproach presmred in Rcf, 2 for HVAC duct systems and rhcir sbrpports.
Ref. 2 iva very thoroughly re\ic.wcd and accepted by an independent,peer review panet.
The above summarjzed two-step process is also very sh~ifarto the earthquakc c y ~ r i e n c boscd e approach de\reloped by SQUCi n n d p ~ s t n t e din Section 8 of'ReE 3 fw Cablc and Col~duitRaceway Systcrns and thcir supports.
Ref. 3 ivas also very thoroughly reviewed and accepted by an independent peer review pane!,
REX Structursl Mechanics CsnsuIting 28625 Mountnin Meactocy Rond, Escuodido, CA 91(YZ(i IT60)7814510
- t76R)751-3537 (RI) emsil: rpkslruct@t?esrlhllnti.nd
Peer Review Comlnents I sctrlcd as chaimmn of'thc fr\c mcmhr indepcndcnt Scnior Scismic Rt-vjcw and Advisory Pi~neI(SSMP) whic1.i provided considerable teelmical review rind advice during rbe deveiopmmt of the SQUG {Ref. 3) approach for evaIuating rkc scismic adequacy uf2(f cizlsscs ofcqaiprncnt plus Cablc and Conduit Racmvay Systems and their supports. S S W (Ref. 4j uaanimovsly c~~drrrsed the SQUG (Ref. 3) approach for use m existing components in existing nuclear power plants.
Fvrthemrrre, I served as tr member of w $burmemlw independent pand esublishcd ljy the U.S. Nuclear Regirlatory Collmmission to provide advice on the irse of tisis earthquake experience based appraacll for the seismic qualificstion of
~iewequipment2cable trays, onrf HVAC duct systems in new pfat~ts.In Chapter 5 ofRcrf, 5, this panel explicitly cndunlr-xl the earthquake cxpcrience based Drrsip
&f:-Rtcieapproach proposed in i17d 2 for HVAC ducts and their suppnrls. 'Ihe i~tdependenlpnner stated:
'The Penel h11y supports tile idea of 'design-by-rule' for IWAC ducts. This requires siniplified design pmoedures with minor computntior~alneeds. TIie Panel observed &at, in the past, si@ilie&nrttcflisrki ware exp~qdedfor nuclmr power pimts to rundlyzt:
a:rrddesign HV,4C ducts. The lessons learned froin pnst prncrice and e.xpcriiwce, iEirtcarpotnled in the new design rules, will sigific~ntiy reduce cosr svithout sacdficiag cnnfidcnce irl!perfomatlee.
'Ihcehre, the Panutel not mly endones ct new design appra~lchbut SO c?ncnuragesit.
~ J detailed material prcs~'ntcdin Ref+ I has not Thercfijre, even I ~ c > u ~the hci-9 rc'oiewcbby an independent peer review- panel, thc ovcfdll approach has hem revie~vcdmd endorsed by independent peer review paneis.
My review of Kef. I has heaviIy concel~irntedupon whether in~portnnt aspects of die SQUG approach [ReL 33 for Cable Rrrcmvays ntrd the Design-by-Rule ayl3rrracfi (Ref. 2) for HVAC systems snd dteir supports Iiwe not bee^
incarparated into Kcf, 1.
Ztl general, 1 iind the ssismic euaithatiufi guidelines for HVAC Duct add Dampcf Systun~sand their supports prcscntcd in Ref. 1 to bc cxccllcnt, I3owcvcr; 1 bdicvr? that R.cL 1 is deficient in certain details that arc inctudrd in either ReC 2 or 3. Rwse minor deficiencies ere discussed in the remainder of his rqort. I
.reeo~me~sd that these iniric~sdeficlcncies be corsected. Each mirror deficiency a t ?
be casily cn~eciedand wilI have very little overall impact on lhe use of Ref.I.
Peer Review Conzinents
- 3. hlipnr.Defip,ictgiein Ref. I 3.1 Limits on Anp~icabilitv In Section 2.1 of Ref. 1, it is stated that &e guidelir~esrn applicable to any I M C duct and damping system at any cicvatjon in a pliik~twl~rrethe nuclear:
plant f~e-fieldF>und motion 5% damped seismic design spectrum does not,
~ ~ ~ CBounding Spcctrutn of Ref. I .
exceed tlac S C ~ S Ih.10fi0n 1 do not emsider rhls Iiinit 10 be sufiicienl. HVAC duct systems ran be sirpported at very high elevatiot~in a ~arietyof btiiidins whcrt: the in-sh~chirc-responsespectra [TSRS) be mudl higller than the f ce-field pound motion, I don't believe thd ihe expirrience daia adqu;liteIy cwers this situation.
Sectian 3.1 of Ref. 2 resbicts its proposed Lk3sign-by-fiwkmethod to situations tvhcrt: &c horizontal zero period wcclcrition {.2PA41,) 84 $theHVAG srIpporr ancharage does not exceed 2,Og. 1 doubt that very nlaily situations cxivt where 2FAkcxcecds 2.Og when the free-field speclrurn is less than f11e Bowding Spectrum. Even so, X sttr)ngly believe that the ZPAh1 ~ than ~ s2.0~limit is an fr~lpolrtantadditional Elmitation thar sllould be inchadd Ref. 1. I doubt that it ciln be demonstmted Lhst any of the IhTVAC duct earthiqwake experience &tit base illcIuded sittiations 'rvhcrc%PAbexceeded 2 . 0 ~ Without
. a significant tmount of sztclz data, the 2 . 0 limitatinn
~ is nwded.
3.2 Duct Spon Lenpths Bcfwccn Vmlicgil Supports Section 3.2.1 ofRef: 1 suggcsts that tables ot'nflowisbfc duct spms and maximum ca!.rtilever lengths fur various duct sizes be deuelagcd prior to die seismic walkdorrirr screening of duct systems, l)evc;'edoptnentniftiiese allo-wable spPn t n b h should be ei prewalkdnwn requinemcnt and not Just n suggestinn.
Sectjot13.2. I rcfcr~to Appendix C as an example of how a tnbulatio1-1o f allowable spans can bc. dcvefoped. Here again, Appendix C should be a requirement and not just aa example. Furthern~ore,it worxld he heIp.ful to #~ave an example application of Apjzendirt C with m ulxampfe set of scrccnir~gtables for same reaktic sirustion.
In addi~jan,somc irppcr 'timi1cirl uertical support spms should be established. 'J'tris limit sl1o111dbe based ilporl spans obsemed in khe carbhqule fspcrlcncc dsta bast. Ref. 2 which was based on h e espcrience data in lteE 6 established the folfrr~virtglimits 08% support spans far tf~e Design-by-Rtri method:
1 Ducr support ro support spans should na exceed I5 feel.
Peer Review Cornn~ents
- 2. Suppnrls shnuId be provided within 5 feet from iiltings such iI.S +rsand Ys in each branch of &e fitting
- 3. Dxrct canlilc~crcdlength (bcyoncl end uf last svppart} should not a c e d G f.!~t.
These limits ore intended to pIme the duct spaas within the limits of extensive wrthquake espotifinm data. Unless significant amormts of new ewtbquako experience data can be used to justie higher span limits. 1Ieliicve Lhaa t%csclimits fiom Rcf. T should be incorporated into Ref. I.
3.3 Seismic Interilosion Re&
s tfic SET conduct a seismic intemctlufi Sec1ioi.l~3.4 of Ref, X ~ y u i r c that review. Hou~cv~r~ very little guidance b giv'm.in Ref. I for the Proxinip
]interaction revie\v. A key demenl of this mmciew is to estimate the seismic ifidweed diglac.cment oi'botk the dtlclt syrslems and of stry adjacent item that might damage the duct U])QII ili~pact,Some guidance on flourto make these displiacenmt estimalcs fbr the duct system st~a~tlcf be included in Ref. 1. At least some limited guldancc i s presented in Section 3.3 &Ref. 2. This guidance could at least senre us a star! fur guidance in TCef, 1.
3.4, V&rml Capacity Check Section 4.5.2 of Ref 1 rtqriirrs u Vertical Capacity check of the vertical supports, Furtlrer guidmct: is gived in Appmdis F, 'Ilbis check is to verifq-that the duct siipporis lie within ihc rmgc of duet support cq~aeitieswithin the earthquake expcricnce data base.
Secriap 4.5,1 deals only with the metai fime. Sectioa 4.5.3 deals with anclaowgc. Na Vertical CapaciQr check is req1.tiredi in Secrian 4.5.3.It 13eedsto madc ?'cry clear in Section 4.5 that the Vertical Capacity cksck applies both to the metal frame and the anchorage, Appendix F does pmperly include anchorage iin this check. Even so, it should be made clear in Sation 4.5, The fourth paragraph on P ~ g 4-14 e of Section 4.5.1 slates that it j s permitted to exceed: AISC nllo~'i~able stresses in ceriain s4tuatims. However, it k my underst~dingthat c$:,ssentiullyall OF the succes$ful duct supporn in the Ref. 6 eartilquake experience data 'nase pass4 thc Vc?rtitaTCapacity. chcek ar irSIlSC sllo$iiabtes t ~ ~ ~sCsV C ~ S For
. this reason, Scction 6.1.2 of Ref. 2 requires that ihe Vcrlical Csprtciiy check to be passed at ATSC aillo\vzble stress levels. Unless it can be dernonsfrated &st a significant number af thr succ~)ssfui duct supports In
-4.
Peer Review Comments the earthquake exgeriencr. dala do not. Fass thc Vertical Capacity check at lrZISC allowable strtss leve[s, I strongly recon~inendthat tile Vertical Capacity check he limited la the AfSC nllowable stresses.
Rei: 1 does not ctcarly delina~tethe Tinnits of the Vertical check, For ductile fiiiure modes, only primary strases from vertical loads need to be irtcluded, Stresses rdieved by small dispiacetnen~sdo tacit have to be inctuded in
%heVertical Capacity check. Some useful guidance on this topic is given in Section 6J.2 o f RcE 2, 171e Verticnl Capacity clit.ck is made fur a vcrlicoi lasd Py defined by:
Py = FY * {Dead LoBJ) cjl wrhereFir js a v d c d Inad inmcase factor defjned in Ref I by:
Fv = 5.08 (2) 711cindependent peer review pat~elwhich =viewed KeL2 did nor consider F,r 1iom Eqn. (2) to be adequale for Mgh seismic lareral f-brccs.As a result Ref: 2 Uses:
Fv = ~reater[5.0~, F.U(DA~ I] 131 where *LjpAl,i s the zero pctriiod accelemtioln znt the support awhor. Tlre net efd:ecf of this change is to increase FV ~irhce? ZPA;, cxeeeds 0.833.
- Inm y opiaion, Ref. I sl~outduse Eqn. (3) $0dafino Pv unless it can be demonstrated that a signifiwnt number nf the suc~cssfsllduGt supgorts in the data bmc will nat pass the Vcrtical Capacity cficck when Fv f i ~ mEqn. (2) is apfaccd by Fv from Eqb. (3).
3,5 Peer,Review Requirement BIG ea~hquakeexperience based seismic evaluation appmaclzes presented in Refs. 1 tiwcvugh 3 rely heavily on tho judgment and experience ol'the SKT. '&is jradgll~altand ~xpcrirnccis usod in lieu of t r ~ ~ e ~ sal~iliyses, ive AS a resullf5both the SS'T(RIareport (Ref,4) and the SQtTQ npproacf~(Ref. 3) require independetlt pen: acvietv of the judgments arrd conclusions made by the SR'F ss well as a sampling review of the limited analytical ev;ifr~atiuns.
Peer Review Conli7lents Ho~vwer,Ref. I dacs not rcquire this independent peer review. E cof~dder this to be s fatal ilcljcjency in Ref. I dial ]nust be corrected. Independent pcm revicv 3s an integral part of an expwieme tiascd approach, I fillly concur with and ~iulppon.the use of the Rcf. 1 seismic evalt~ation gttidelines for HVAC duct end damper sysfen~sand their s~~pports so long as tile mitior dcfidencics identified in Section 3 are corrected, In the meantink?, I suggest that us% afReK.f shwld itnplemetlt Ithe changes recornmeatted in Section 3 for their plant specific use. I doaft bclicv:~~ that any of t h ~ ~~chsnges f: will signiiicantly afye~tthe usef~~lntxess oERGF,I.
References 1 EPRl, Sei+strzf~ Hkilc D~ictu33d &>?per $5,vt~fns, f i ~ n b a r i ~CuicIefitzes-fir n
Technical Report 1007596,April 2003 2, ARC, Adt-'nnc:edLighfiJrtxferReactor (dLFVR) Fir~1-c$a-Kind-Eng8r1eering (FOAm) Projeei off Design darrcsptrfa~'HYAC Ductilg arod S?~ppot'ts, ApriI 1995
- 3. Seismic Qualification Utilities Group (SQUrJ}7 @e?tericiwpientefltnriorz Practedtt~e(GIPJforSeisntic ?Ge~cl'$f2~a?iorr qfhrwtearPIartz Eqtiiprnerrr, Revidon 3A, bccembef 2001
- 4. Senior Seismic Review Rdvisov Palel ( S S W ) SUse of Srskrnic.
E~pcriencearrd Tfrsf&tcr M Sho~vR f ~ g g ~ A ~qPPEq~i$xar~nt
~esx in dWvcl~m=
Power Slarrrs, Sandin Repm SAm92-0140, Pwt 1, f 992 5 , Bandyopadh~yay,K.K.,Kana, D.D.,Kennedy, R,P,, and SdiiW, A.J., An E $ l d t ~ ~~ f~S!,i? e t h d i i b i ~?;CJf$~iic
~ f ~ ~Qwl@c~tion 0f~X9urjurneftt.Caidt?
, DUC&iu i ' J t IF??Plt~rzfs T ~ q t x .s,tr~d by Use oJExperfenc~ Bat&
NlJREG#CR-Grl-Mprepsmd for U.S Nuclwr Regulnlory Co~nrnission~ J~rlf 1997 6, ARCl Advu~rcedLighrJ*YatcrRenc~orf/fL@9?,lFirsf-gfa-Kictd-Ettgr'fteeri~g (KIA@) ;)~'~jecr on the Performar~ceqlpNVACDr~cttscr,2dS1dppurIsirr EaF.thgrrakes nrzd Tesrs, April 1995
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