Regulatory Guide 1.124

Service Limits & Loading Combinations for Class 1 Linear-Type Component Supports

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Issue date:	01/31/1978
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RG-1.124 Rev 1
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U.S. NUCLEAR REGULATORY

COMMISSION

Revision I January 1978 REGULATORY

GUIDE OFFICE OF STANDARDS

DEVELOPMENT

REGULATORY

GUIDE 1.124 SERVICE LIMITS AND LOADING COMBINATIONS

FOR CLASS 1 LINEAR-TYPE

COMPONENT

SUPPORTS

A. INTRODUCTION

General Design Criterion 2, "Design Bases for Protection Against Natural Phenomena," of Appen dix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Licensing of Produc tion and Utilization Facilities," requires that the de sign bases for structures, systems, and components important to safety reflect appropriate combinations of the effects of normal and accident conditions with the effects of natural phenomena such as earthquakes.

The failure of members designed to support safety related components could jeopardize the ability of the supported component to perform its safety function.

SThis guide delineates acceptable levels of service limits and appropriate combinations'

of loadings as sociated with normal operation, postulated accidents, and specified seismic events for the design of Class 1 linear-type component supports as defined in Subsec tion NF of Section III of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. This guide applies to light-water-cooled reactors.

The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.

B. DISCUSSION

Load-bearing members classified as component supports are essential to the safety of nuclear power plants since they retain components in place during the loadings associated with normal and upset plant conditions under the stress of specified seismic events, thereby permitting system components to function properly.

They also prevent excessive com ponent movement during the loadings associated with emergency and faulted plant conditions combined

• Lines indicate substantive change from previous issue.with the specified seismic event, thus helping to mitigate the consequences of system damage. Com ponent supports are deformation sensitive because large deformations in them may significantly change the stress distribution in the support system and its supported components.

In order to provide uniform requirements for con struction, the component supports, should, as a minimum, have the same ASME Boiler and Pressure Vessel Code classification as that of the supported components.

This guide delineates levels of service limits and loading combinations, in addition to supplementary criteria, for ASME Class 1 linear-type component supports as defined by NF-1213 of Sec tion III. Snubbers are not addressed in this guide. Subsection NF and Appendix XVII of Section III permit the use of four methods for the design of Class I linear-type component supports:

linear elastic anal ysis, load rating, experimental stress analysis, and limit analysis.

For each method, the ASME Code de lineates allowable stress or loading limits for various Code levels of service limits as defined by NF-3113 of Section III so that these limits can be used in con junction with the resultant loadings or stresses from the appropriate plant conditions.

Since the Code does not specify loading combinations, guidance is re quired to provide a consistent basis for the design of component supports.

Component supports considered in this guide are located within Seismic Category I structures and are therefore protected against loadings from natural phenomena or man-made hazards other than the spec ified seismic events. Thus only the specified seismic events need to be considered in combination with the loadings associated with plant conditions to develop appropriate loading combinations.

Loadings caused USNRC REGULATORY

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I I by natural phenomena other than seismic events, when they exist, should be considered on a case-by case basis. 1. Design by Linear Elastic Analysis a. Su at Temperature.

When the linear elastic analysis method is used to design Class 1 linear-type component supports, material properties are given by Tables 1-2.1, 1-2.2, 1-13.1, and 1-13.3 in Appendix I of Section III and Tables 3 and 4 in the latest ac cepted version 1 of Code Case 1644. These tables list values for the minimum yield strength S, at various temperatures but only room temperature values for the ultimate tensile strength S.. At room temperature, S, varies from 50% to 87% of Su for component sup port materials.

Levels of service limits derived from either mate rial property alone may not be sufficient to provide a consistent safety margin. This is recognized by Sec tion III, since XVII-2211(a)

of Section III defines the allowable stress in tension on a net section as the smaller value of 0.6 S, and 0.5Su. To alleviate the lack of defined values of Su at temperatures above room temperature and to provide a safe design mar gin, an interim method is given in this guide to obtain values of S, at temperature.

While XVII-221 1(a) specifies allowable tensile stress in terms of both S, and Su, the rest of XVII 2000 specifies other allowable service limits in terms of S, only. This does not maintain a consistent design margin for those service limits related only to mate rial properties.

Modifications similar to XVII 2211(a) should be employed for all those service limits. b. Allowable Increase of Service Limits. While NF-3231.1(a), XVII-2110(a), and F-1370(a)

of Sec tion III all permit the increase of allowable stresses under various loading conditions, XVII-21 10(b) lim its the increase so that two-thirds of the critical buckl ing stress for compression and compression flange members is not exceeded, and the increase allowed by NF-323 1. 1(a) is for stress range. Critical buckling stresses with normal design. margins are derived in XVII-2200

ofSection HII. Since buckling prevents "shakedown" in the load-bearing member, XVII 2110(b) must be regarded as controlling.

Also, buckl ing is the result of the interaction of the configuration of the load-bearing member and its material prop erties (i.e., elastic modulus E and minimum yield strength S,). Because both of these material prop erties change with temperature, the critical buckling ' Regulatory Guide 1.85, "Code Case Acceptability-ASME

Sec tion III Materials," provides guidance for the acceptability of ASME Section III Code Cases and their revisions, including Code Case 1644. Supplementary provisions for the use of specific code cases and their revisions may also be provided and should be con sidered when applicable.

• I stresses should be calculated with the values of E and S, of the component support material at temperature.

Allowable service limits for bolted connections are derived from tensile and shear stress limits and their nonlinear interaction;

they also change with the size of the bolt. For this reason, the increases permitted by NF-323 1.1, XVII-21 10(a), and F-1370(a)

of Sec tion III are not directly applicable to allowable shear stresses and allowable stresses for bolts and bolted connections.

The increase permitted by NF-3231.1 and F-1370(a)

of Section III for shear stresses or shear stress range should not be more than 1.5 times the level A service limits because of the potential for non-ductile behavior.

The range of primary plus secondary stresses should be limited to 2S, but not more than Su to en sure shakedown.

For many allowable stresses above the value of 0.6S,. the increase permitted by NF 3231.1(a)

will be above the value of 2S, and will thus violate the normal shakedown range. A shakedown analysis is necessary to justify the increase of stress above 2S, or Su . For the linear elastic analysis method, F-1370(a)

of Section III permits increase of tension limits for the Code level D service limits by a variable factor. that is the smaller value of 1.2Sy/Ft or 0.7Su/Ft.

De pending on whether the section considered is a net section at pinholes in eyebars, pin-connected plates, or built-up structural members, Ft may assume the smaller value of 0.45S, or 0.375Su (as recommended by this guide for a net section of pinholes, etc.) or the smaller value of 0.6Sy or 0.5Su (for a net section without pinholes, etc.). Thus greater values of the factor may be obtained for sections at pinholes, which does not account for local stress and is not consistent with NF-323 1. 1 and XVII-21 10(a) of Sec tion III. A procedure to correct this factor is provided in this guide. 2. Design by Load Rating When load-rating methods are used, Subsection NF and Appendix F of Section III do not provide a faulted condition load rating. This guide provides an interim method for the determination of faulted con dition load rating. 3. Design by Experimental Stress Analysis While the collapse load for the experimental stress analysis method is defined by 11-1430 in Appendix II of Section III, the various levels of service limits for experimental stress analysis are not delineated.

This deficiency is remedied by the method described in this guide. 4. Large Deformation The design of component supports is an integral part of the design of the system and its components.

24-2 I!

A complete and consistent design is possible only when system/componeqt/component-support interac tion is properly consi'iered.

When all three are evaluated on an elastic basis, the interaction is usu ally valid because individual deformations are small. However, if plastic analysis methods are employed in the design process, large deformations that would re sult in substantially different stress distributions may occur. When component supports are designed for load ings associated with the faulted plant conditions, Ap pendix F of Section III permits the use of plastic analysis methods in certain acceptable combinations for all three elements.

These acceptable combinations are selected on the assumption that component sup ports are more deformation sensitive (i.e., their de formation in general will nave a large effect on the stress distribution iu the system and its components.)

Since large deformations always affect the stress dis tribution, care should be exercised even if the plastic analysis method is used in thl. Appendix F-approved methodology combination.

This is especially impor tant for identifying buckling or instability problems where the change of geometry should be taken into account to avoid erroneous results.

5. Function of Supported System In selecting the level of service limits for different loading combinations, the function of the supported system must be taken into account. To ensure that systems whose normal function is to prevent or miti gate consequences of events associated with an emer gency or faulted plant condition (e.g., the function of ECCS during faulted plant conditions)

will operate properly regardless of plant condition, the Code level A or B service limits of Subsection NF (which are identical)

or other justifiable limits provided by the Code should be used. Since Appendix XVII derived all equations from AISC rules and many AISC compression equations have built-in constants based on mechanical prop erties of steel at room temperature, to. use these equa tions indiscriminately for all NF and the latest ac cepted version of Code Case 1644 materials at all temperatures would not be prudent. For materials other than steel and working temperatures substan tially different from room temperature, these equa tions should be rederived with the. appropriate mate rial properties.

6. Deformation Limits Since component supports are deformation sensitive load-bearing elements, satisfying the serv ice limits of Section III will not automatically ensure their proper function.

Deformation limits, if specified by the Code Design Specification, may be the con trolling criterion.

On the other hand, if the function of a component support is not required for a particu-lar plant condition, the stresses or loads resulting from the loading combinations under that plant condi tion do not need to satisfy the design limits for the plant condition.

7. Definitions Design Condition.

The loading condition defined by NF-3112 of Section III of the ASME Boiler and Pressure Vessel Code. Emergency Plant Condition.

Those operating con ditions that have a low probability of occurrence.

Faulted Plant Condition.

Those operating condi tions associated with postulated events of extremely low probability.

Levels of Service Limits. Four levels, A, B, C, and D, of service limits defined by Section III for the de sign of loadings associated with different plant condi tions for components and component supports in nu clear power plants. Normal Plant Condition.

Those operating condi tions in the course of system startup, operation, hot standby, refueling, and shutdown other than upset, emergency, or faulted plant conditions.

Operating Basis Earthquake (OBE). As defined in Appendix A to 10 CFR Part 100. Plant Conditions.

Operating conditions of the plant categorized as normal, upset, emergency, and faulted plant conditions.

Safe Shutdown Earthquake (SSE). As defined in Appendix A to 10 CFR Part 100. Service Limits. Stress limits for the design of com ponent supports as defined by Subsection NF of Sec tion III. Specified Seismic Events. Operating Basis Earth quake and Safe Shutdown Earthquake.

System Mechanical Loadings.

The static and dynamic loadings that are developed by the system operating parameters, including deadweight, pres sure, and other external loadings, but excluding ef fects resulting from constraints of free-end move ments and thermal and peak stresses.

Ultimate Tensile Strength.

Material property based on engineering stress-strain relationship.

Upset Plant Conditions.

Those deviations from the normal plant condition, that have a high probability of occurrence.

C. REGULATORY

POSITION ASME Code' Class 1 linear-type component sup American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section III, Division 1, 1974 Edition, including the 1976 Winter Addenda thereto.1.124-3 I I I I

ports excluding snubbers, which are not addressed herein, should be constructed to the rules of Subsec tion NF of Section III as supplemented by the follow ing: s 1. The classification of component supports should, as .a minimum, be the same as that of the supported components.

2. Values of Su at a temperature t should be esti mated by one of the three following methods on an interim basis until Section III includes such values: a. Method 1. This method applies to component support materials whose values of ultimate strength Su at temperature have been tabulated by their man ufacturers in catalogs or other publications.

Su = Sur S , but not greater than Sur S~ur where Su = ultimate tensile strength at temperature t to be used to determine the service limits Sur = ultimate tensile strength at room temperature tabulated in Section III, Appendix I, or the latest accepted version 1 of Code Case 1644 S'u = ultimate tensile strength at temperature t tabulated by manufacturers in their catalogs or other publications Sur = ultimate tensile strength at room temperature tabulated by manufacturers in the same pub lications.

b. Method 2. This method applies to component support materials whose values of ultimate tensile strength at temperature have not been tabulated by their manufacturers in any catalog or publication.

Sy Su= Sur r ,where Su = ultimate tensile strength at temperature t to be used to determine the service limits Sur = ultimate tensile strength at room temperature tabulated in Section III, Appendix I, or the latest accepted version of Code Case 1644 S, = minimum yield strength at temperature t tabulated in Section III, Appendix I, or the latest accepted version 1 of Code Case 1644 Syr = minimum yield strength at room temper ature, tabulated in Section III, Appendix I, , If the function of a component support is not required during a plant condition, the design limits of the support for that plant con dition need not be satisfied, provided excessive deflection or fail ure of the support will not result in the loss of function of any other safety-related system.I 1.124-4 I or the latest accepted version I of Code Case 1644. c. Method 3. When the values of allowable stress or stress intensity at temperature for a material are listed in Section III, the ultimate tensile strength at temperature for that material may be approximated by the following expressions:

Su = 4S or Su = 3Sm where Su = ultimate tensile strength at temperature t to be used to determine the service limits Su = listed value of allowable stress at temperature t in Section III. S.= listed value of allowable stress intensity at temperature t in Section III 3. The Code levels A and B service limits for com ponent supports designed by linear elastic analysis which are related to S, should meet the appropriate stress limits of Appendix XVII of Section III but should not exceed the limit specified when the value of 5/6 Su is substituted for S,. Examples are shown below in a and b. a. The tensile stress limit Ft for a net section as specified in XVII-221 1(a) of Section III should be the smaller value of 0.6S, or 0.5Su at temperatbre.

For net sections at pinholes in eye-bars, pin connected plates, or built-up structural members, Ft as specified in XVII-221 1(b) should be the smaller value of 0.45S, or 0.375Su at temperature.

b. The shear stress limit Fv for a gross section as specified in XVII-2212 of Section III should be the smaller value of 0.4S, or 0.33Su at temperature.

Many limits and equations for compression strength specified in Sections XVII-2214, XVII 2224, XVII-2225, XVII-2240, and XVII-2260

have built-in constants based on Young's Modulus of 29,000 Ksi. For materials with Young's Modulus at working temperatures substantially different from 29,000 Ksi, these constants should be rederived with the appropriate Young's Modulus unless the conser vatism of using these constants as specified can be demonstrated.

4. Component supports designed by linear elastic analysis may increase their level A or B service limits according to the provisions of NF-323 1. 1(a), XVII 2110(a), and F-1370(a)

of Section III. The increase of level A or B service limits provided by NF 3231. 1(a) is for stress range. The increase 'of level A I [I

I or B service limits provided by F-1370(a)

for level D service limits, should be the smaller factor of 2 or 1.167SI/Sy, if S, : 1.2S, or 1.4 if Su -- 1.2Sf, where S, and Su are component-support material properties at temperature.

However, all increases

[i.e., those allowed by NF-3231.1(a), XVII-2110(a), and F-1370(a)]

should always be limited by XVII-21 10(b) of Section III. The critical buckling strengths defined by XVII-21 10(b) of Section III should be calculated using material properties at temperature.

This in crease of level A or B service limits does not apply to limits for bolted connections.

Any increase of limits for shear stresses above 1.5 times the Code level A service limits should be justified.

If the increased service limit for stress range by NF-3231.1(a)

is more than 2S, or S., it should be limited to the smaller value of 2S, or S,, unless it can be justified by a shakedown analysis.

5. Component supports subjected to the combined loadings of system mechanical loadings associated with (1) either (a) the Code design condition or (b) the normal or upset plant conditions and (2) the vib ratory motion of the OBE should be designed within the following limits: 4,5 a. The stress limits of XVII-2000

of Section III and Regulatory Position 3 of this guide should not be exceeded for component supports designed by the linear elastic analysis method. These stress limits may be. increased according to the provisions of NF-3231.1(a)

of Section III and Regulatory Position 4 of this guide when effects resulting from constraints of free-end displacements are added to the loading combination.

b. The normal condition load rating or the upset condition load rating of NF-3262.3 of Section III should not be exceeded for component supports de signed by the load-rating method. c. The lower bound collapse load determined by XVII-4200

adjusted according to the provision of XVII-4 110(a) of Section III should not be exceeded for component supports designed by the limit analysis method. d. The collapse load determined by 11-1400 of 4 S ince component supports are deformation sensitive in the performance of their service requirements, satisfying these criteria does not ensure that their functional requirements will be fulfilled.

Any deformation limits specified by the design specification may be controlling and should be satisfied.

' Since the design of component supports is an integral part of the design of the system and the design of the component, the de signer must make sure that methods used for the analysis of the system, component, and component support are compatible (see Table F-1322.2-1 in Appendix F of Section I1). Large deforma tions in the system or components should be considered in the design of component supports.1.124-5 Section III divided by 1.7 should not be exceeded for component supports designed by the experimental stress analysis method. 6. Component supports subjected to the system mechanical loadings associated with the emergency plant condition should be designed within the follow ing design limits except when the normal function of the supported system is to prevent or mitigate the consequences of events associated with the emer gency plant condition (at which time Regulatory Position 8 applies): 4"'5 a. The stress limits of XVII-2000

of Section M and Regulatory Positions

3 and 4, increased accord ing to the provisions of XVII-21 10(a) of Section m and Regulatory Position 4 of this guide, should not be exceeded for component supports designed by the linear elastic analysis method. b. The emergency condition load rating of NF 3262.3 of Section III should not be exceeded for component supports designed by the load-rating method. c. The lower bound collapse load determined by XVII-4200

adjusted according to the provision of XVII-4 110(a) of Section III should not be exceeded for component supports designed by the limit analysis method. d. The collapse load determined by 11-1400 of Section III divided by 1.3 should not be exceeded for component supports designed by the experimental stress analysis method. 7. Component supports subjected to the combined loadings of (1) the system mechanical loadings as sociated with the normal plant condition, (2) the vib ratory motion of the SSE, and (3) the dynamic system loadings associated with the faulted plant condition should be designed within the following limits except when the normal function of the supported system is to prevent or mitigate the consequences of events as sociated with the faulted plant condition (at which time Regulatory Position 8 applies):

a. The stress limits of XVII-2000

of Section m and Regulatory Position 3 of this guide, increased ac cording to the provisions of F-1370(a)

of Section III and Regulatory Position 4 of this guide, should not be exceeded for component supports designed by the linear elastic analysis method. b. The smaller value of T.L. x 2S/S, or T.L. x 0.7S/Su should not be exceeded, where T.L., S, and .Su are definedl according to NF.3262.1 of Section.

mI, and Su is the minimum ultimate tensile strength of the material at service temperature for component supports designed by the load-rating method. c. The lower bound collapse load determined by XVII-4200

adjusted according to the provision of F-1370(b)

of Section III should not be exceeded for I.I.

component supports designed by the limit analysis method. d. The collapse load determined by 11-1400 ad justed according to the provision of F-1370(b)

of Section III should not be exceeded for component supports designed by the experimental stress analysis method. 8. Component supports in systems whose normal function i' to prevent or mitigate the consequences of events associated with an emergency or faulted plant condition should be designed within the limits de scribed in Regulatory Position 5 or other justifiable

'limits provided by the Code. These limits should be defined by the Design Specificatioh and stated in the PSAR, such that the function of the supported system will be maintained when they are subjected to the loading combinations described in Regulatory Positions

6 and 7.

D. IMPLEMENTATION

The purpose of this section is to provide guidance to applicants and licensees regarding the NRC staff's plans for using this regulatory guide. Except in those cases in which the applicant pro poses an acceptable alternative method for complying with the specified portions of the Commission's regu lations, the methocf described herein will be used in the evaluation of submittals for construction permit applications docketed after January 10, 1978. If an applicant wishes to use this regulatory guide in uc veloping submittals for construction permit applica tions docketed on or before January 10, 1978, the pertinent portions of the application will be evaluated'

on the basis of this guide.1.124-6