Regulatory Guide 1.122
| ML13350A275 | |
| Person / Time | |
|---|---|
| Issue date: | 09/30/1976 |
| From: | NRC/OSD |
| To: | |
| References | |
| RG-1.122 | |
| Download: ML13350A275 (4) | |
U.S. NUCLEAR REGULATORY
COMMISSION
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
September
1976
A. INTRODUCTION
Criterion
2, "Design Bases for Protection Against Natural Phenomena," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50,"Licensing of Production and Utilization Facilities," re-quires, in part, that nuclear power plant structures, systems, and components important to safety be de-signed to withstand the effects of earthquakes without loss of capability to perform their safety functions.
Para-graph (a)(1) of Section VI, "Application to Engineering Design," of Appendix A, "Seismic and Geologic Siting Criteria for Nuclear Power Plants," to 10 CFR Part 100,"Reactor Site Criteria," requires, in part, that safety-related structures, systems, and components remain functional in the event of a Safe Shutdown Earthquake (SSE). It specifies the use of a suitable dynamic analysis as one method of ensuring that the structures, systems, and components can withstand the seismic loads.Similarly, paragraph (a)(2) of Section VI of the sarkl appendix requires, in part, that the structures, sy.i.ms, and components necessary for continued opezation""th- out undue risk to the health and ie remain functional in the event of an t~qratinrnBasis Earthquake (OBE). Again, the use of suit .d> .amic analysis is specified as one method of ensurt'iAiat the structures, systems, and nents can withstand the seismic loads.* This guide cri e ds acceptable to the NRC* staff for 4 l g tw ori ontal and one vertical floor design .o t various floors or other equip-ment-su locafs of interest from the time-history motions Iting from the dynamic analysis of the supporting cture. These floor design response spectra are needed for the dynamic analysis of the systems or equipment supported at various locations of the sup-porting structure.
B. DISCUSSION
Nuclear facility structures can be approximated by mathematical models to permit analysis of responses to earthquake motions. Because of the large number of degrees of freedom that would be necessaiy.
and the possible ill-conditioning of the resulting stfqiiess matrix if the complete plant were treated in a cal model, the plant is usually dvided intQ. several separate systems for analysis P.-Urs's-Thus itis usual that there arc one or more matheail models of sup-.,t" I, .= M;porting structures.
Each supporting structure normally supports one or rte systems or of equipment.
Also, different m"-.l structure may be required For these reasons, the mathen .Mo A used to generate the seismic excita-tion ..for s ects ent separate analyses of supported.syterZ,_.., -. eq~upment may not be suitable for the*t.Wed-Aoidized analyses of the supporting structure.
I'1ost equipment having a sr'all mass relative to that:of the supporting structure will 'lave negligible interac-tion effects on the support structu, -and will need to be included only in the mass distributicin of the mathemati- cal model for that structure.
For such equipment, a separate analysis will be performed using the floor design response spectra or time-history excitations at the equip-ment-support locations derived from the analysis of the supporting structure.
This guide addresses the acceptabil- ity and development of floor design response spectra only. Time-history motions that will give results comparable to the floor design response spectra are also acceptable.
There are, however, other major equipment systems such as the reactor coolant system whose stiffness, mass, and resulting frequency range should be considered for 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.
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 tal required 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.
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 equipment model with the model of the supporting structure and applying the proper excitation to the base* of the supporting structure.
With this method, no sepa-*rate equipment-support excitations need be generated because the equipment will be excited directly through the structure.
It should be noted that a combined model of the building and equipment must be formulated to perform such an analysis.I. Floor Response Spectra The two horizontal and the vertical response spectra* can be computed from the time-history motions of the* supporting structure at the various floors or other equip-ment-support locations of interest.
The spectrum ordi-.nates should be computed at frequency intervals sufficiently small to produce accurate response spectra (see Table 1 for guidance).
Spectrum peaks normally would be expected to occur at the natural frequencies of the supporting structure.
2. Smoothing Floor Response Spectra and Broadening Peaks To account for variations in the structural frequencies owing to -uncertainties in the material properties of the* structure and soil and to approximations in the modeling techniques used in seismic analysis, the computed floor response spectra should be smoothed, and peaks asso-ciated with each of the structural frequencies should be broadened.
One acceptable method for determining the amount of peak broadening associated with each of the structural frequencies is described below.Let fj be the Jth mode structural frequency that is determined from the mathematical models. The varia-tion in each of the structural frequencies is determined by evaluating the variation due to each significant para-meter such as the soil modulus, material density, etc.The total frequency variation, +/-.eAfj, (see Figure 1) is then determined by taking the square root of the sum of* squares (SRSS) of a minimum variation of 0.05fj and the individual frequency variations, A(Jn, as described in regulatory position 1.Figure 1 shows a sample of a smoothed floor response spectrum curve. Note that the broadened peak is bounded on each side by lines that are parallel to the lines forming the original spectrum peak.3. Floor Design Response Spectra* Nuclear power plant facilities are designed for three-component earthquakes, as indicated in Regulatory Guide 1.60, "De.sign Response Spectra for Seismic Design of Nuclear Power Plants." When a structural seismic analysis is performed separately for each direc-tion (two horizontal and one vertical), and in the case of TABLE 1 SUGGESTED
FREQUENCY
INTERVALS
FOR CALCULATION
OF RESPONSE SPECTRA Frequency Range Increment (hertz) (hertz)0.2- 3.0 0.10 3.0- 3.6 0.15 3.6- 5.0 0.20 5.0- 8.0 0.25 8.0- 15.0 0.50 15.0- 18.0 1.0 18.0-22.0
2.0 22.0 -34.0 3.0 unsymmetric structures, the structural motion in a given direction at a given location will contain contributions from the vertical and the two horizontal excitations.
In such cases, the contribution from each Individual analysis will generate a response spectrum at a given location in each of the three directions.
The ordinates of these three smoothed response spectra (with peaks broadened)
for a given direction should be combined according to the SRSS criterion to predict the floor design response spectrum at the given location and for the given direction.
In the case of symmetric structures, there will be only one floor response spectrum in each of the three directions.
The smoothed versions of these floor response spectra will be the floor design response spectra. In those cases in which the mathematical model is subjected simultaneously to the action of three spatial components of an earthquake, the three computed and smoothed floor response spectra at a given level will be the floor design response spectra.C. REGULATORY
POSITION The following procedures for smoothing the floor response spectra (with peaks broadened)
and combining the smoothed floor response spectra to obtain the floor design response spectra are acceptable to the NRC staff: 1. To account for variations In the structural fre-quencies owing to uncertainties in such parameters as the material properties of the structure and soil, damping values, soil-structure interaction techniques, and the approximations In the modeling techniques used 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.COMPUTED FREQUENCY (CPS)20. 30. 40. 50.60.Figure 1 Response Spectrum Peak Broadening and Smoothing irn froni the floor time-history motions should be smoothed, and peaks associated with each of tihe struc-tural frequencies should be broadened (see the sample in Figure 1) by a frequency, +Afj, where XP (Afn) ]Afj .[)=(0.05J)2
+ X Wild 2 1 4o0.ofJ n=l where /fJn denotes the variation in Jth mode fre.quency, f., due to variation in parameter number n, and P is the number of significant parameters considered.
A value of 0.10fj should be used if the actual computed value of Afj is less than 0.10fj. If the above procedure is not used, AfJ should be taken as 0.1 5fJ.2. When the seismic analysis is performed separately for each 6f the three directions, and in the case of un-symmetric structures, the ordinates of the floor Oesign response spectrum for a given direction should be obtained by combining the ordinates of the three smoothed floor response spectra for that direction according to the SRSS criterion.
In the case of symme-tric structures, the floor design response spectrum for a UNITED STATES NUCLEAR REGULATORY
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WASHINGTON, 0. C, 20555 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE. S300 given direction will be the smoothed floor responsefor that direction.
3. When the mathematical model of the supporting structure is subjected simultaneously to the action of three spatial components of an earthquake, the computed and smoothed response spectrum in a given direction will be the floor design response spectrum in that directiotn.
D. IMPLEMENTATION
The purpose of this section is to piovide information to applicants regarding the NRC staff's plans for using this regulatory guide.This guide reflects current NRC staff practice.
There.fore, except in those cases in which tie applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method described herein is being and will continue to be used in the evaluation of submittals for construction permit applications until this guide is revised as a result of suggestions from the public or addi-tional staff review.POSTAGE AND FEES PAID U.S. NUCLEAR REGULATORY
.r COMMISSION
-1.122-4