ML20099B877
| ML20099B877 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 07/27/1992 |
| From: | Mccarthy D CAROLINA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NLS-92-203, NUDOCS 9208030132 | |
| Download: ML20099B877 (14) | |
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Carolina Power & taght Company JUL 271992 SERIAL: NLS-92-203 g:p United States Nuclear Regulatury Commission
., ATTENTION: Document Control Desk Washington, DC 20555 BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOE i AND 2 DOCKET NOS. 50 725 & 50-324/ LICENSE NOS. Ot'R-71 & DPR-62 MICCELLANEOat E r2EL VERIFICATION PROGR.\M ;, Ah
- 1 Gentlemen:
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- On July 7-8, 1982, representatives of the Nuclear Regulatory Commission str'f visited .he h' h'y['.
Drunswick Steam Electric Plant to discuss the mkcellaneous steel design basis documentation
,. program. D.aring the meeting, Carolina Power & Light Company agreed to provide the information
, ;7'
- requested b) de staff in twc submittals. The Con +ani .ndicated the first submittal would be
?!"3 provided by July 24,1992 and the second submitta! would be provided by August 7,1992. Per s.$ telephone conversacion with Mr. R. H. Lo on July 24,1992, CP&L is provid:nD this submittal on July 27_1992.
Enclosure 1 provides a listing summarizing tha information being provided in this submittal and g,. ' ' , ._ y CP&L's planned August 7,1992 submittal. Enclosuro 2 provides the information requested by the CJ staff. h.g ,, bb 7. Please refer any questions regarding this submittal to Mr. W. R. Murray at (919) 546-4661 w: , Yours very truiy,
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D. C. McCarthy Manat,er Nelear Licensinp Section WRM/wrm (steel-1.003) Enchsure cc: Mr. S. D. Ebneter Mr. R. H. Lo Mr. R. L. Prevatte r L n U U 0 0 ;1 : , l%%*it@"a5EmummmM1mmamuxnaram / 00 t DR l 9208030132920$324 ADOCK 0500 PDR
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ENCLOSURE 1 . BRUNSWICK STEAM ELECTRIC PLANT, UNITS 1 AND 2 NRC DOCKET NOS. 50-325 & 50-324 OPERATING LICENSE NOS. DPR-71 & DPR-62 i MISCELLANEOUS STEEL VERIFICATION PROGRAM The miscellaneous steel programmatic and technical issues listed below have been identified for inclusion in CP&L's July 24,1992 response: PROGRAMMATIC ISSUES
- 1. Provide a copy of the Phase i procedure.
- 2. Clarify specific actions to be :ompleted prior to start-up
- Describe Phase I and Phase Il
- Rationale for representative platform samples
- Rationale f_ - 'is that are not included in samples
- Rationale fc. .mgn confidence level for restart
- 3. Incorporate a mechanism for making procedural prograr' edjustments for potential
' changing conditions.
- 4. State ex91icitly the extent of compliance with 10 CFR Part 50, Appendix B.
TECHNICAL
- 1. Provide a copy of DG 11.20 (Revision 3).
- 2. Provide the basis for addressing thermal loads.
- 3. Provide the rationale for addressing ncccessibb inspection areas.
- 4. State explicitly how appropriate dynamic load factors (response spectra) will be used in analysis.
- 5. Discuss the methodology for addressir g interface loaoc. (cable trays, conduit, HVAC, piping).
- 6. Address the accuracy used in data collection.
- 7. Address joint fixity.
- 8. - Address bolt torque in miscellaneous steel connection.
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_ . . .. .. . . - _. -. - - . . . - ~ . - _ . . . _ _ _ _ . . . e i a f i The miscellaneous steel programmatic and technical issues listed below have been identified for inclusion in CP&L's August 7,1992 response: i PROGRAMMATIC ! 1. Discuss the root causes.
- 2. Provide the Phase il procedure.
- 3. Address miscellaneous steel in other Category 1.
i TECHNICAL f 1. Compare long term acceptance criteria with Updated FSAR and provid6 justification j for any deviations (include use of AISC 8* edition).
- 2. Provide justification for not considering tornado !oads, t
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ENCLOSURE 2 BhUNSWICK STCAM ELECTRIC PLANT, UNITS 1 AND 2 NRC DOCKET NOS. 50-325 & 50-324 OPERATING LICENSE NOS. DPR 71 & DPR-02 MISCELLANEOUS STEEL VERIFICATIDN PROGRAM OVERVIEW: The Miscellaneous Steet Verification Program was started to develop necessary documentation to bring Licensee Event Report 1-88-35 and Unresolved item 89-18-02 to closure. This program will ; also address the Notice of Daviation cited in NRC Inspectio'i Report 9214. Assessments [ performed during this program will be in compliance with the design criteria (also called long-term ( criteria) delineated in the Brunswick Plant Updated Final Safety Analysis Report (FSAR). The Updated FSAR commitments are that the miscellaneous steel be designed according to the requirements of the American Institute of Steel Construction (AISC) Specification for the Design, Fabrication and Frection of Structural Steel for Buildings. The Uodated FSAR states that the initial design w's to the 6* Edition of the AISC Specification and that current work is to the 8* Edition. Th ; Updated FSAR does not allow an increase in the allowable stresses during severe environmental conditions (e.g., Operating Basis Earthquake) but does allow a factor of 1.S times the basic allowable stresses for the abnormal and extreme environmental conditions (e.g., Design Basis Earthquake). As stated above, the long-term design criteria for the Brunswick Plant is in compliance with these provisions and the current evalu. cas will be made using the 8* Edition of the AISC Specification, which meets the Updated FSAR. When an element does not meet the long term design criteria, an operability review will be performed on a case-by-case basis. In those situations the specific criteria will be available for NRC review. Such cases will be brought into FSAR compliance prior to restart after the next refueling outage. The extent of the Miscellaneous Steet Verification Program to be completed prior to start-up will consist of a combination of walkdowns and evaluations sufficient to conclude that miscellaneous steel operability issues do not exist in the plant. As outlined in our July 7,1992 meeting, our current assessment for start-up scope includes the following:
- Phase I walkdown in Reactor Building -
- Phase ll walkdown in drywell Perform bounding analysis of selected platform sections in both the drywell and Reactor Building i
If initial walkdowns and preliminary analysis demonstrate sufficient margin , CP&L may revise the start-up scope, in any case, the overall Design Basis Reconstitution of miscellaneous steel will be completed in conjunction with the established outage schedules. Ani changes to this scope will be communicated to the NRC. PRDGRAMMATIC ISSUES ITEM 1: Provide Phase I procedure. E2-1
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RESPONSE
i A copy of the Phase i procedure was submitted to the NRC at the July 7,1992 meeting. ] Comments received during the Ju;y 20,1992 conference call between CP&L and the NRC will be included in a revision to the procedure.
- ITEM 2
- Clarify specific actions to be completed prior to start-up: i
- Describe Phase I and Phase 11
- Rationale for representative platform section samples l
- Rationale for items that are not included in samples
- Rationale for high confidence level for restart
RESPONSE
- a. Des:ription of Phase I and Phase 11 i information from walkdowns obtained by CP&L in 1990 and 1991 indicates that the construction of miscellaneous steelin the Reactor Building outside the drywellis generally of good quality. However, minor variances such as an occasional missing weld, loose or missing bolts, minor dimensional variations, and minor gaps hatween connecting angles and the attaching member have been found. None of these issues were found by CP&L to adversely affect safe plant operation.
These 1990 and 1991 walkdowns, which include a total of nine areas outside the Reactor Building in both units, were initiated due to LER 1-88-35. This LER identified an overstress condition on one beam in each Reactor Building. The issue was also identified by the NRC as Unresolved hem 89-18-02. I Although there are no major known construction-re!ated irregularities in the drywell platform steel, it is being included in the program because of similarities with the miscellaneous steel design and construction. L The large amount of miscellanecus steel requires a considerable effort to forma!!y document and evaluate. For this reason, a two-phased p.ogram is planned. The objective of Phase I and the early part of Phsse 11is to establish early in the program a high level of confidence in the design and construction of miscellaneous structural steel. Both phases
- will occur simultaneously. However, Phase 11 will continue toward formal documentation of I the design basis of part of CP&L's Design Basis Reconstitution Program.
Phase i Procram The Phase i Program consists of an engineering walkdown of the miscellaneous steel i- outside the drywell. This engineering walkdown is directed toward providing an immediate
- sppraisal of miscellaneous steel members end connections outside the drywell by teams of experienced civill structural engineers. Phase Iis based on the concept employed by SOUG for resolution of USl A-40, in that it user trained, experienced engineers to provide an E2-2
k i . j immediate assessment and identify outliers, it is designed to identify significant
; deficiencies. It is not intended that the specific SOUG General Implemeatation Procedure (GlP) be implemented in this program. ,
The engineering teams visually compare the actual conditions against the drawings. Each f team consists of two members, with each engineer independ -w evaluating each steel I member. The walkdown team will categorize each steel member and connection into one i of five categories: i
- a. No evident design and/or construction-related irregularities
! b. Minor design and/or construction-related irregularities but no significant effect in load carrying capability , c. Requires modification (outlier) { d. Regt ires further evaluation (these items will M further ovaluated by conventional '
+
tect niques to ensure that the member has acerate capacity)
- e. Not accessible i
"eports prepared by the engineering team provide a technical justification if the mem-ber/ connection is placed in categories b, c, or d. The approar.h used and typical results are reviewed by a Technical Advisc,ry Committee, which includes three natior; ally recognized
. consultants. Modification packages will be prepared for those identified in the evaluation to iequ;re modification.
i The drywell platform steel will be evaluated to an equivalent level early in the Program, but in a slightly different way, in the interest of maintaining personnel exposures as low as reasonably achievable, the activities discussed above will be incorporated into the Phase il program for the drywell, reducing the man-hours required to be spent in the drywell. The Phase 11 program for the drywell will be expedited to the extent necessary to allow an engineering evaluation before plant start-up. Details are provided below. Phase I! Proaram i The Phase 'l program applies to both the drywell platform steel and the miscellaneous steel l in the Reactor Building outside the drywell. Phase il consists of two major parts. One part ! consists of a preliminary analysis of representative platform sections in the drywell and in
- the Reactor Building outside of the drywell. The current scope is defined as three platform i section evaluations in each building to be used as enveloping cases. These platform i sections will be selected to be representative worst cases in their respective areas as .
l follows:
- 1. The platform section that has attachments with the largest loads
- 2. The pladorm section tnat has the most attachments 1
i
- 3. The platform section that is considered the most critical based upon its function and l expected capacity l
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1 4 The preliminary analysis willinclude the most critical load case that incluNs the design - (DBE) earthquake. It will be consistent with the FSAR commitments in that the absolute j sum of the worst case horizontal plus vertical seismic motion will be evaluated. Loads will ^ include results from the IE Bulletin 7914 program and other major attachment loads derived
, from data obtained from a walkdown. The platforms will be evaluated against allowable 4
stresses for abnormalloads of 1.5 times the 1978 Edition of the American institute of Steel Construction Specification, which is consistent with the Updated FSAR for current work. A second part of the Phase li program provides more detailed verification and
- documentation of miscellaneous structural steel. ThN activity will occur concurrently with the Phase i program and part 1 of the Phase Il program 11 consists of method'cally verifying that miscellaneous structural steel is consisunt with the best available design documents and recording any identified differences. This portion of the program concentrates on taking photographs of members, connections, embeds, and surface-mounted plates; reviewing these photographs to identify any differences from the design drawing and other construction-related irregularities, and measurement of those '
l components identified as irregular (i.e., not in accordance with design drawings and/or with standard practices), i
! Prior to plant operation, the drywell platform photographs will be reviewed and walkdown 4 results will be evaluated by an engineering team to identify any modifications required , before plant start-up.
The Phase i program and tne portion of the Phase il program that will be completed before plant operation will provide a high confidence level that the miscellaneous structura! steel at
- the Brunswick Steam Electric Plant is t.dequate to it action in a safe manner for defined enveloping plant loading conditions.
l The Phase 11 program will continue after plant operation to complete data collection outside l the drywell. In addition, the data collected will be used to update the drawings and as input for calculations. Final calculations will be neepared to represent all the structural steet j affected by this program. These calculations win satisfy all Updated FSAR commitments, including lead cases and acceptance erneria. Consistent with the Updated FSAR, the criteria will be based upon the 1976 tidition of the AISC Specification. l t b. Rationale for Selection of Representative Enveloping Platform Sections 4 The selection of representative platform sections for preliminary analysis is one of several tasks frected toward developing a high confidence level early in the program that the structural steel will function properly under all defined loading conditions. The selection of specific platform sections is based upon the use of enveloping cases. The concept of design by envelop is an acceptable, common practice among design engineers for structures that have a commonality of configuraan, material, applied loads, and
- acceptance criteria. Likewise, verification of design can be based upon a similar approach.
u%
- Miscellaneous Steel Outside Drvwell:
The miscellaneous steelitems outside the drywell are generdily elevated platforms that
- consist of standard steel shapes and are connected to each other with clip angles and/or seat angles that are either welded or bolted. Each of the r,latforms was designed, fabricated, and erected using the same criteria and procedures.
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i 4 in selecting the representative cases, loading is one of the more important factors, s'nce the I other factors are essentially the me. These platforms are loaded in a similar fashion, i primarily by a combination of harigers from below that support piping, raceway and HVAC, and occasional equipment resting on the steel. To provide assurance that a representative ! enveloping loading case is identified, the platform sections with the estimatw Qhest load and the platform with the most loads will be selected, l i
- Drvwell
! The drywell haa five (5) total platforms, each at a different elevation. The upper three ! drywell platform sections are similar in construction and loading, the two lower platforms i are different. However, the lower drywell platform sections consist of very heavy radial members connected by generally smaller tangential members. The radial members of the l lowest (elevation 17 foot) platform consist primarily of wide flange members, whereas the
- elevation 38 foot platform radial members are built-up box members. Because of these dif ferences, each of the two lower platform sections will be evaluated individually.
{ l The upper three platform sections cre conWerably smaller, primarily serve as personnel access, and have few attachments. All the platforms have similar size and type members < which are connected with similar type clip angles. They were designed, fabricated, and erected using the same criteria and procedures. l
- c. Rationale for items not included in Phase I Analysss i
i As indicated in the previous responses, the available data suggests that the construction-related irregularities which are identified are relatively minor in terms of their effect on the load carrying capability of miscellaneous structural steel. The program that has been developed for completion prior to plant start-up !s adequate to identify and resolve such I construction-related irregularities that could affect the ability of the steel to function in a safe and adequate manner for all the defined load cases imposed on the structura during
- plant operation. The part of the program that will be completed prior to plant operation will
- both resolve any irregularities that may have resulted from construction and maintenance l activities, and ensure, on an enveloping basis, that the steel is capable of supporting the critical design loads.
l d. Rationale for High Confidence Level for Restart , The program is intended to confirm that the structure is constructed according to the l- original design drawings and that any significant deviations are assessed for adequacy prior to start-up. The program addresses these considerations directly, relying mainly on walkdowns. The l Phase I program for the miscellaneous steel outside the drywell usss experienced i civil / structural engineers to walk down the affected areas and visually' compare each l accessible member with the design documents to identify potential differences or other irregularities. This is a relatively simple and sure method to identify issues that may have a significant effect on structural performance. Significant design and/or construction-related irregularities (those that could affect load carrying capacity) identified as a result of this process will be further evaluated and/or modified, as required, to restore the load carrying capability of the structure. A similar program will occur in the drywell, except that the E2-5
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- evaluation will be performed by use of photographs of members, connections, embeds, and d
surface mounted plates included in the program and walkdowns of selected members to capture and resolve significant design / construction-related irregularities. l In addiuon, the validity of the original design is being reinforced by an analytical evaluation of the structures using conventional techniques, based on enveloping concepts, as i discussed above. Modifications will be made as determined necessary to ensure that the structures have adequate design margin. With these considerations addressed, a high confidence level exists that the structures will safely perform their function for all design loading considerations; . ITEM 3: l Incorporate a mechanism for making procedural program adjustments for potential changing j conditions. '
RESPONSE
e The Phase 11 Walkdown Procedure has beer revised to permit adjustments in t.se walkdown program as the work progresses, in additim, a " Miscellaneous Stee! Verification Procedure" document is being prepared as a top-tier document to control the walkdown review and resolution process. This document will be applicable to both phases. This document has provisions to - continually review the results of walkdowns and evaluations and assess the adequacy and usefulness of the data collec'ed, consistency of the results, and adequacy of resolution of design and construction-related irregularities. As the walkdowns proceed, the results will be reviewed to verify that the proc' dure is workable, appropriate data is obtained, and that the personnel collecting the data understand the requirements and are comfortable with the procedure and the work process that it imposes. Program changes may also be made to address the broadness issue as well as to provide flexibility in adjusting the scope of the program. The approach and results of the work performed under both phases will be reviewed by an ! independent Technical Advisory Committee which consists of senior engineer personnel, including three national ly recognized consultants not associated with the implementation of the verification program. This team will meet periodically and provide guidance to the work process, as necessary. The input from the Technical Advisory Committee will be used in making decisions on program , adjustments. ITEM 4: State explicitly compliance with Appendix B.
RESPONSE
The Buchtel QA program for the Brunswick Steam Electric Plant is delineated in the QA Program
?lan (OAPP), Rev. O, dated June 17,1992. The QAPP references and identifies portions of the i
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current revision of Bechtel Nuclear Quality Assurance Manual (NOAk) which are applicable to this ! project, consistent with Bechtel's activities on this project. l The NOAM contains quality policies which correspond to each of the 18 Criteria oi 10 CFR 50, Appendix B. The quality policies contained in the NOAM are based on, and consistent with, the Bechtel QA Topical Report, BO TOP-1, Rev. 4A, dated February 1988, which has been reviewed 4 and accepted by the NRC, on a generic basis. The policies comply with the OA program requirements described in ANSl/ASME NOA 1, ANSI N45.2, end various OA-related N45.2 daughter standards. As for the extent of ccmpliance with 10 CFR 50, Appendix B, the OAPP delineates compliance with the Appendix B criteria, consistent with the plant walkdown and engineering activities within Bechtel's scope of work. TECHNICAL ISSUES ITEM 1: Provide a copy of DG 11.20 (Revision 3).
RESPONSE
A copy of Design Guide 11.20 has been provided to the NRC in a previous meetin u . As stated earlier, the representative, enveloping platform section analysis will be checked against the BNP UFSAR licensed criteria (1.5 x AISC,8* Edition, Allowable Stresses) against DBE loading only. Anchor bolt acceptability will be per IEB 79-02, Supplement 1 criteria using a factor of safety of 2. Licensed damping ratios will be used. In the event of localized exceedance of 1.5 x AISC allowables, those will be noted and individus;;y justified, in addition, exceedance of a upper bound shear stress of .55 Fy will be nt :ed. Thic :.riteria will support the overall acceptability of the structural steel for startup as applied to the representative cases. ITEM 2: Provide the basis for addressing the thermal loads.
RESPONSE
The thermal loads addressed in this item are those that result from restraint of thermal growth of structural members subject to uniform temperature changes. Reactions from pipe thermal loads are included in evaluations as part of the attachment loads. Thermal loads are in general self-limiting and induce secondary stresses in the affected members. The self-limiting aspect is due to the fact that an) local deformation that will relieve the constraint will also reduce thermal stresses. Such deformations include minor movement or distortion of connected components (e.g., clip angles, beam webs, slip of bolted connections, and embeds) and smalliateial displacement of the beams to accommodate thermal growth. In such cases, the in-plane load carrying capability of the member will not be significantly affected since these deformations are small and will be out-of-plane. E2-7
J 4 Consisu it with the above pnilosophy, power plant design practice is to allow for effects of thermal loads, considering tree layout and connection types u ,ed in each structure, as depicted in the structural design drawings. The ccmmon design philosophy for structural steel was to provide clip angle or beam seat angle (with a restraining angle at or near the top flange) connections which I minimize thermal stresses. i
- in genersi, the structural layout is such that the restrained thermal expansions are limited to less f than 1/8 inches at each end. Such an expansion is considered negligible considering the play avsilable between the bolt and the bolt hole, and flexibility of the clip angle or seat angle juints.
l These considerations have led to a structural layout which permits thermal growth in general. . It is recognized that there are box beams with we!ded connections at the lower elevatiors cf the
- drywell that may restrain free thermal growth. However, the drywell platform layout pctmits both 3 radial and vertical thermal growth. Previous uxperience indicates that the radial bearns and columns will have small thermal stresses dua to the restrained thermal growth. The tangential beams closer to the center have been observed to develop larger thermal stresses; however, these
- mcmbers are relatively short with small thermat growth and, as discussed above, minor end i
deformations will relieve tne thermal strr.se'- $ Where thermal effects are considered significant, such as a beam with both ends welded between two rigid supports, evaluations will be made to ensure adequacy of design. In such cases, it is j reasonable to permit inelastic deformation so long as the induced strains are limited to about three times the yield. However, slotted holes are generally provided in such situations to facilitate construction as well as to allow therrr.al expansion and, therefore, the strain limitation is not expected to be invoked except in isolated cases, j ITEM 3: Provide the rationale for addressing inaccessible areas.
RESPONSE
Inaccessible areas are anticipated to be mainty connections to embeds and surface-mounted plates. In inese cases, phutographs will be taken for visible segments of the component. Using those i- photographs, an assessment will be made as to the consistency of actual conditions, if it is judged that the actual installation is consistent with the design drawings, no further action will be taken, if such a judgement cannot be reached, further evaluations may be made using " similarity" or .
- margin" concepts if the comp 3nent or assembly is similar to another component or assembly which is accessible, the similarity concept may be used as the acceptance criteria, i.e., if the accessible item is acceptable as is, so is the inaccessible item. For unique cases, a reduction in capacity may be assumed (e.g., a factor of 0.75, similar to the SOUG General Implementation 3 Procedures and the component is checked using the actual loading conditions. If the component i still cannot be judged to be acceptable using the above logic, further action consistent with the
- nature, type, and condition of the component will be taken.
4 i . ;M 4: State explicitly how appropriate dynamic load factors (response spectra) will be used in analysis. E2-8 I I
i l i
RESPONSE
2 ! Dynamic effects will be determined either by dynamic analysis or by equivalent static analysis l methods. Where dynamic analysis is used natural frequencies of the platic.rms will be obtained j' using conventional dynamic analysis techniques as part of the analytical evaluation. The natural frequencies will account for both global and inuividual beam behavior in both the vertical and appropriate horizontal direction. These natural frequencies wm cv used in conjunction with the appropriate floor response spectra to determine an appropriate amplification factor in each of the
; horizonal and vertical directions to account for seismic effects. Damping for the miscellaneous structural steel will be consistent with that specified in the Updated FSAR. An appropriate multi.
mode factor will be applied to a,: count for the effects of higher modes, rigid body effects, anc
- modal variations. For the equivalent static analysis method, where natural frequencies are not
, obtained, the seismic amplification will be taken from the peak of the response spectra times a multi-mode factor for the appropriate damping value. l ITEM 5: I ! Discuss the methodology for addressing ir'terf ace loads (cable trays, conduit, HVAC, piping). 4
RESPONSE
i All large bcm (i.e., greates than 4 inche diameter) piping supports included in the IE Bulletin 79 4 4 program will be imposed or, the structures included in *.his program. i Small bore piping, non-O piping under 10 inches in diameter, cable tray of four tiers or tuss, , conduit, and HVAC loads are generally substantially lower than the IE Bulletin 79-14 piping loads. To account for these non-lE Bulletin 79-14 commodity loads, field data will be collected from typical areas in the plant, converted into uniform loads, cnd assigned to individual meinbers. The l conversion into uniform loads willincludo seismic effects and will encompass vertical, horizontal, l . nd torsional effects on individual beams. These non lE Bulletin 79-14 loads will be developed by considering typical spans and typical support configurations used at the Brunswick Plant. Sein mic loads will be obtained by using the peak of the appropriate respcoso spectra, and an appropriate multi-mode factor. Because of the independent nature of each support, the tiniform load factcr for each direction will be based on an SRSS response from the individualloads on each member. , As inoicated above, torsional effects will also be addressed. Because of the support contiguration i for these supports, a significant tor:,ional component is not expected. llowever, torsion loads which may be imposed on the miscellaneous steel or drywell steel will also be determined as part of this effort and converted inte an equivalent torsional effect on the steel beam. ITEM 6: Address accuracy used in data collection. 1 l E2-9
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RESPONSE
Measurements will be taken which support related engineering calculations within reasonable analytical accuracy. With this objective in mind, accsptable measuring tolerances may be rather , large in some cases. I The criteria for accuracy of measurements included in the walkdown procedure is consistent with
- the guidance given in Welding Research Counsel Bulletin 316 and 353. The specific attribute being measured and its potential effect on the end results hs alluded to in the preceding paragraph) were also considered in the development of the criteria.
ITEM 7; i Address joint fixity, i
- RESPnNSE
- In general, the analysis of the steel members that are connected in an interrelated fashion will be 9erformed usino staridard finite element methods. The only exception is those cases where the configuration is so simple that the structural behavior can ccrrectly and completely be captured by classical manual methods. Joint fixity will be treated in the classical manner. Connections by clip l s ngles or seat angles will be treated as pins (i.e., transfer of shear in all directions across the connection). Where the member is continuous or connected in a fashion that there is sufficient
- stiffness in the connection relative to the attached members to transfer moments, both moment j and shear transfer will be imposed. End connections will be treated in the same manner. In
' general, only shear transfer will be allowed at support points for the platform, unless there is a
~
- demonstrated capability for momeat transfer.
l ITEM 8: Address bolt torque in miscellaneous steel cornactions. t
- RESPONSE:
It should be reengnized that most of the miscellaneous stcel connections are simcle clip angle or seat angle connections end can adequattly function as bearing-type connections. Bolt torquing is nnt a significant factor in their performance under the applied loads, in fact, the 8* Edition of the AISC SpecUication states * . . because the performance of bolts i.1 bearing is not dependent upon an assumed minimum level of high pretension, thorough inspection requirement to assure full and compM:e compliance with pre-tightving criteria is not warranted."
, The 6* Edition of the AISC Specification specifies that "...boltu shall be tightened to a bolt tension not less than the proof load given in the applicable ASTM specification for the type of bolt used."
The proof load is approximately equal to 70 percent of the strength of the bolt material. + Consequently, the pretension corresponding to the proof load is greater than the bolt load based on the basic allowable bolt stresses. For A325 bolts, the ratio of pretension to allowable load ranges , between 1.4 ano 1.6. Thus, even considering the 1.5 increase in allowable stresses for the faalted i
- . conditions, these bolts will be seldom. If ever, stressed to a greater stress level than their initlal installation. Furthermore, relantion in these bolts is negligible if the installation is in accordance 1
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j . . with the AISC specifications, i.e., all joint scrfaced are free of scale, dirt, burrs, or any other defects. Therefore, bolts that are properly installed initially will maintain their functionality l' throughout the design life of the structure. Loose bolts or bolts wi;h gaps between the fraying surfaces have seldorn been found during the preliminary walkdowns at the Brunswick Plant. Hence, their numbers are expected to be very small. ! The walkdcwn procedure requires identification and recording of 6ny loose bolts or bolts with gaps between the fraying surfaces. These cases will be dispositioned on a case-by-case basis. . Generic l resolution of this issue calls for re-tightening of these bolts or re-evaluation of the connection without relying on such bolts, j in view of these discussions, it is concluded that the evaluation program adequately addresses this issue and no other specific action, such as re-torquing of the bolts in general, is needed. a o 1 { i l i i i A I l i i i I i i 4 4 4 (' ' E2-11 i-i w
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