Regulatory Guide 1.122

Development of Floor Design Response Spectra for Seismic Design of Floor-Supported Equipment or Components

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Issue date:	09/30/1976
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RG-1.122
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U.S. NUCLEAR REGULATORY COMMISSION September 1976 REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 1.122 DEVELOPMENT OF FLOOR DESIGN RESPONSE SPECTRA

FOR SEISMIC DESIGN OF FLOOR-SUPPORTED EQUIPMENT OR

COMPONENTS

B. DISCUSSION

Criterion 2, "Design Bases for Protection Against Nuclear facility structures can be approximated by Natural Phenomena," of Appendix A, "General Design mathematical models to permit analysis of responses to Criteria for Nuclear Power Plants," to 10 CFR Part 50, earthquake motions. Because of the large number of

"Licensing of Production and Utilization Facilities," re- degrees of freedom that would be necessaiy. and the quires, in part, that nuclear power plant structures, possible ill-conditioning of the resulting stfqiiess matrix systems, and components important to safety be de- if the complete plant were treated in a singl*ieiathemati- signed to withstand the effects of earthquakes without cal model, the plant is usually dvided intQ. several separate systems for analysis P.-Urs's-Thus itis usual loss of capability to perform their safety functions. Para- graph (a)(1) of Section VI, "Application to Engineering that there arc one or more . ,t" matheail .= models of sup- I, M;

Design," of Appendix A, "Seismic and Geologic Siting porting structures. Each supporting structure normally Criteria for Nuclear Power Plants," to 10 CFR Part 100, supports one or rte systems or p*ieces of equipment.

"Reactor Site Criteria," requires, in part, that safety- Also, different m"-.l ofl"*,h`arme structure may be related structures, systems, and components remain required for.* For these reasons, the Fffemnt',*urposes, functional in the event of a Safe Shutdown Earthquake mathen .Mo Aused to generate the seismic excita- tion *l ..for s ectsent separate analyses of supported (SSE). It specifies the use of a suitable dynamic analysis as one method of ensuring that the structures, systems, .syterZ,_..,-. eq~upment may not be suitable for the and components can withstand the seismic loads. *t.Wed-Aoidized analyses of the supporting structure.

Similarly, paragraph (a)(2) of Section VI of the sarkl appendix requires, in part, that the structures, sy.i.ms, I'1ost equipment having a sr'all mass relative to that and components necessary for continued opezation""th- :of the supporting structure will 'lave negligible interac- out undue risk to the health and safety4*f ie puf1*. tion effects on the support structu, -and will need to be remain functional in the event of an t~qratinrnBasis included only in the mass distributicin of the mathemati- Earthquake (OBE). Again, the use of suit .d>.amic cal model for that structure. For such equipment, a analysis is specified as one method of ensurt'iAiat the separate analysis will be performed using the floor design structures, systems, and nents can withstand the response spectra or time-history excitations at the equip- seismic loads. ment-support locations derived from the analysis of the supporting structure. This guide addresses the acceptabil-

• This guide cri e ds acceptable to the NRC ity and development of floor design response spectra

• staff for 4 l g tw ori ontal and one vertical floor only. Time-history motions that will give results design . o t various floors or other equip- comparable to the floor design response spectra are also ment-su locafs of interest from the time-history acceptable.

motions Iting from the dynamic analysis of the supporting cture. These floor design response spectra There are, however, other major equipment systems are needed for the dynamic analysis of the systems or such as the reactor coolant system whose stiffness, mass, equipment supported at various locations of the sup- and resulting frequency range should be considered for porting structure. inclusion in the model of the supporting structure to USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission. U.S Nuclear Regulatory Commission. Washington. D.C. 2V566. Attention Docketing and Regulatory Guides ate issued to deoctibS and make available to the public Service Section.

methods acceptable to the NRC sltal of implemenling specific parts of the Commission aeIgulations. to delineate techniques used by the Staff in Osalu The guides are issued in the following tIn broad divisions cling specific problems or postulated accidents, at to provide guidance to appli cents. Regulatory Guides ate not substitutes for regulations, and compliance i. Power Aeacti's 6 Products with them is talrequired Malhods and solutions dilflatent from those sat out in 2. Research and Test Reactors 7 Transportation the guides will be acceptable if they provide a basis for the findings requisite to I. Fuels and Materials Facilities 8. Occupational Health the issuance Ot continuance ofe permit or license by the Commission 4 Environmental and Siting S. Antitrust Review Comments and suggestions fo, improvements in these guides are encouraged 5 Materials end Plant Protection 10. General at alf times, and guides will be revised, as appropriate, to accommodate cam ments and to reflect new rnfotmation or esperiance However. comments on Copies of published guides may be obtained by written request indicating the this guide. if received within about two months after its issuance, will be par divisions desited to the U S Nuclear Regulatory Commilsion. Washington. D.C.

ticularle useful in evaluating the need foran early revision 20%6. Attention. Director, Office o0 Standards Development.

• account for possible dynamic interaction effects. Such equipmlent can be analyzed by combining the complete TABLE 1 equipment model with the model of the supporting structure and applying the proper excitation to the base SUGGESTED FREQUENCY INTERVALS FOR

• of the supporting structure. With this method, no sepa- CALCULATION OF RESPONSE SPECTRA

• rate equipment-support excitations need be generated because the equipment will be excited directly through Frequency the structure. It should be noted that a combined model Range Increment of the building and equipment must be formulated to (hertz) (hertz)

perform such an analysis.

0.2- 3.0 0.10

I. Floor Response Spectra 3.0- 3.6 0.15 The two horizontal and the vertical response spectra 3.6- 5.0 0.20

• can be computed from the time-history motions of the

• supporting structure at the various floors or other equip- 5.0- 8.0 0.25 ment-support locations of interest. The spectrum ordi-

. nates should be computed at frequency intervals 8.0- 15.0 0.50

sufficiently small to produce accurate response spectra (see Table 1 for guidance). Spectrum peaks normally 15.0- 18.0 1.0

would be expected to occur at the natural frequencies of the supporting structure. 18.0-22.0 2.0

2. Smoothing Floor Response Spectra and Broadening 22.0 - 34.0 3.0

Peaks To account for variations in the structural frequencies owing to -uncertainties in the material properties of the unsymmetric structures, the structural motion in a given

• structure and soil and to approximations in the modeling direction at a given location will contain contributions techniques used in seismic analysis, the computed floor from the vertical and the two horizontal excitations. In response spectra should be smoothed, and peaks asso- such cases, the contribution from each Individual ciated with each of the structural frequencies should be analysis will generate a response spectrum at a given broadened. One acceptable method for determining the location in each of the three directions. The ordinates amount of peak broadening associated with each of the of these three smoothed response spectra (with peaks structural frequencies is described below. broadened) for a given direction should be combined according to the SRSS criterion to predict the floor Let fj be the Jth mode structural frequency that is design response spectrum at the given location and for determined from the mathematical models. The varia- the given direction. In the case of symmetric structures, tion in each of the structural frequencies is determined there will be only one floor response spectrum in each of by evaluating the variation due to each significant para- the three directions. The smoothed versions of these meter such as the soil modulus, material density, etc. floor response spectra will be the floor design response The total frequency variation, +/-.eAfj, (see Figure 1) is spectra. In those cases in which the mathematical model then determined by taking the square root of the sum of is subjected simultaneously to the action of three spatial

• squares (SRSS) of a minimum variation of 0.05fj and the components of an earthquake, the three computed and individual frequency variations, A(Jn, as described in smoothed floor response spectra at a given level will be regulatory position 1. the floor design response spectra.

Figure 1 shows a sample of a smoothed floor response

C. REGULATORY POSITION

spectrum curve. Note that the broadened peak is bounded on each side by lines that are parallel to the The following procedures for smoothing the floor lines forming the original spectrum peak. response spectra (with peaks broadened) and combining the smoothed floor response spectra to obtain the floor

3. Floor Design Response Spectra design response spectra are acceptable to the NRC staff:

• Nuclear power plant facilities are designed for three- 1. To account for variations In the structural fre- component earthquakes, as indicated in Regulatory quencies owing to uncertainties in such parameters as Guide 1.60, "De.sign Response Spectra for Seismic the material properties of the structure and soil, Design of Nuclear Power Plants." When a structural damping values, soil-structure interaction techniques, seismic analysis is performed separately for each direc- and the approximations In the modeling techniques used tion (two horizontal and one vertical), and in the case of in seismic analysis, the computed floor response spectra

1.122-2

z

0

L-

t~J ILl VJ

.2 .3 .4 .5 .6 .7.8.91. 2. 3. 4. 5. 6. 7. 8.9.10. 20. 30. 40. 50.60.

COMPUTED FREQUENCY (CPS)

Figure 1 Response Spectrum Peak Broadening and Smoothing

irn froni the floor time-history motions should be given direction will be the smoothed floor response smoothed, and peaks associated with each of tihe struc- spd*trum for that direction.

tural frequencies should be broadened (see the sample in Figure 1) by a frequency, +Afj, where 3. When the mathematical model of the supporting structure is subjected simultaneously to the action of XP (Afn) ] three spatial components of an earthquake, the computed and smoothed response spectrum in a given Afj. [)=(0.05J)2 + X Wild 21 4o0.ofJ direction will be the floor design response spectrum in n=l that directiotn.

where /fJn denotes the variation in Jth mode fr

D. IMPLEMENTATION

quency, f., due to variation in parameter number n, and P is the number of significant parameters considered. A The purpose of this section is to piovide information value of 0.10fj should be used if the actual computed to applicants regarding the NRC staff's plans for using value of Afj is less than 0.10fj. If the above procedure this regulatory guide.

is not used, AfJ should be taken as 0.1 5fJ.

This guide reflects current NRC staff practice. There.

2. When the seismic analysis is performed separately fore, except in those cases in which tie applicant for each 6f the three directions, and in the case of un- proposes an acceptable alternative method for symmetric structures, the ordinates of the floor Oesign complying with specified portions of the Commission's response spectrum for a given direction should be regulations, the method described herein is being and obtained by combining the ordinates of the three will continue to be used in the evaluation of submittals smoothed floor response spectra for that direction for construction permit applications until this guide is according to the SRSS criterion. In the case of symme- revised as a result of suggestions from the public or addi- tric structures, the floor design response spectrum for a tional staff review.

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1.122-4