Regulatory Guide 1.122
| ML003739367 | |
| Person / Time | |
|---|---|
| Issue date: | 02/28/1978 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-1.122, Rev 1 | |
| Download: ML003739367 (4) | |
Revision 1 U.S. NUCLEAR REGULATORY
COMMISSION
February 1978 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
A. INTRODUCTION
Criterion
2, "Design Bases for Protection Against Natural Phenomena," of Appendix A, "General De sign Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Licensing of Production and Utilization Facilities," requires, in part, that nuclear power-plant structures, systems, and components important to safety be designed to withstand the effects of earth quakes without loss of capability to perform their safety functions.
Paragraph (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 struc tures, 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 same appendix requires, in part, that the structures, sys tems, and components necessary for continued opera tion without undue risk to the health and safety of the public remain functional in the event of an Operating Basis Earthquake (OBE). Again, the use of suitable dynamic analysis is specified as one method of ensur ing that the structures, systems, and components can withstand the seismic loads. This guide describes methods acceptable to the NRC staff for developing two horizontal and one ver tical floor design response spectra at various floors or other equipment-support locations of interest from the time-history motions resulting from the dynamic analysis of the supporting structure.
These floor de sign response spectra are needed for the dynamic analysis of the systems or equipment supported at various locations of the supporting structure.
The Advisory Committee on Reactor Safeguards has been -consulted concerning this guide and has concurred in ýthe regulatory position.
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 necessary and the possible ill-conditioning of the resulting stiffness matrix if the complete plant were treated in a single mathematical model, the plant is usually divided into several separate systems for analysis purposes.
Thus it is usual that there are one or more mathematical models of supporting structures.
Each supporting structure normally supports one or more systems or pieces of equipment.
Also, different models of the same structure may be required for different pur poses. For these reasons, the mathematical models used to generate the seismic excitation data for sub sequent separate analyses of supported systems or equipment may not be suitable for the detailed lo calized analyses of the supporting structure.
Most equipment having a small mass relative to that of the supporting structure will have negligible interaction effects on the support structure and will need to be included only in the mass distribution of the mathematical 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 equipment-support locations
- Lines indicate substantive changes from previous issu
e. USNRC REGULATORY
GUIDES Comments should be sent to the Secretary of the Commission, US. Nuclear Regu latory Commisston, Wash ington, D.C. 20555. Attention:
Docketing and Service Regulatory Guides are issued to describe and make available to the public methods Branch. acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate techniques used by the staff in evaluating specific problems The guides are issued in the following ten broad divisions or postulated accidents, or to provide guidance to applicants.
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1. Power Reactors 6. Products Methods and solutions different from those set out in the guides will be accept- 2. Research and Test Reactors 7. Transportation able if they provide a basis for the findings requisite to the issuance or continuance
3. Fuels and Materials Facilities
8. Occupational Health of a permit or license by the Commission.
4. Environmental and Siting 9. Antitrust Review, 5. Materials and Plant Protection
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or for place times, and guides will be revised, as appropriate, to accommodate comments and ment on an automatic distribution list for single copies of future guides in specific to reflect new information or experience.
This guide was revised as a result of divisions should be made in writing to the US. Nuclear Regulatory Commission, substantive comments received from the public and additional staff review. Washington, D.C. 20555, Attention:
Director, Division of Document Control.
derived from the analysis of the supporting structure.
This guide, addresses the acceptability and develop ment of floor design response spectra only. Time history motions that'WIill give results comparable to the floor design response spectra are also acceptable.
There are, however, other major equipment sys tems such as the reactor coolant system whose stiff ness, mass, and resulting frequency range should be considered for inclusion in the model of the support ing structure to account for possible dynamic interac tion effects. Such equipment 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 struc ture. With this method, no separate equipment support excitations need be generated because the equipment will be excited directly through the struc ture. It should be noted that a combined model of the building and equipment must be formulated to per form such an analysis.1. Floor Response Spectra The two horizontal and the vertical response spectra can be computed from the time-history mo tions of the supporting structure at the various floors or other equipment-support locations of interest.
It is important that the spectrum 'ordinates be computed at the natural frequencies of the supporting structure and at frequencies sufficiently close to produce accu rate response spectra (see Table 1 for guidance).
Spectrum peaks normally would be expected to occur at the natural frequencies of the supporting structure.
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 2. Smoothing Floor Response Spectra and Broadening Peaks To account for uncertainties in the structural fre quencies owing to uncertainties in the material prop erties of the structure and soil and to approximations in the modeling techniques used in seismic analysis, it is important that the computed floor response spectra be smoothed and peaks associated with each of the structural frequencies be broadened.
One ac ceptable method for determining the amount of peak broadening associated with each of the structural fre quencies 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 deter mined by evaluating the variation due to each signifi cant parameter such as the soil modulus, material density, etc. The total frequency variation, +/-tAfi, (see Fig. 1) is then determined by taking the square root of the sum of squares (SRSS) of a minimum var iation of 0.05fj and the individual frequency varia tions, Afin, as described in regulatory position 1. Figure 1 shows a sample of a smoothed floor re sponse 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 Regula tory Guide 1.60, "Design Response Spectra for Seismic Design of Nuclear Power Plants." When a structural seismic analysis is performed separately for each direction (two horizontal and one vertical), and in the case of 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 re sponse spectrum at a given location in each of the three directions.
It is important that the ordinates of these three response spectra for a given direction be combined according to the SRSS criterion and that the resulting response spectrum then be smoothed and the peaks broadened to predict the floor design re sponse spectrum at the location of interest and for the given direction.
In the case of symmetric structures, there will be only one significant floor response spec trum 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 statistically independent spatial components*
of an earthquake, the three computed and smoothed floor response spectra at a given loca tion will be the floor design response spectra.
C. REGULATORY
POSITION The following procedures for combining and smoothing the floor response spectra (with peaks broadened)
to obtain the smoothed floor design re sponse spectra are acceptable to the NRC staff. *See Regulatory Guide 1.92, "Combining Modal Responses and Spatial Components in Seismic Response Analysis." 1.122-2 I I I
.2 .3 .4 .5 .6 .7.8.91. 2. 3. 4. 5. 6. 7. 8.9.10. COMPUTED FREQUENCY (CPS) Figure 1 Response Spectrum Peak Broadening and Smoothing 20. 30. 40. 50.60..8.7 .6.5 .4.3 z 0 I-j L. <C..2 .1
1. When the seismic analysis is performed sepa rately for each of the three directions, and in the case of unsymmetric structures, the ordinates of the floor design response spectrum at the location of interest and for a given direction should be obtained by com bining the ordinates of the three floor response spectra for that direction according to the SRSS criterion.
The resulting response spectrum should be smoothed with peaks broadened.
In the case of sym metric structures, the floor design response spectrum for a given direction will be the smoothed floor re sponse spectrum for that direction.
2. To account for uncertainties in the structural frequencies 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 from the floor time-history motions should be smoothed, and peaks associated with each of the structural frequencies should be broadened (see the sample in Figure 1) by a frequency, __Afi, where Afj = (0.05fj)2 n Y (Afjn)2 4 0.If, n=l where Afjn denotes the variation in the Jth mode fre quency, fj, due to variation in parameter number n, and P is the number of significant parameters consid ered. A value of 0.1fj should be used if the actual computed value of Afj is less than O.1fj. If the above procedure is not used, Afj should be taken as 0. 15fj. 3. When the mathematical model of the supporting structure is subjected simultaneously to the action of three spatial components of an earthquake, the com puted response spectrum in a given direction with peaks broadened and smoothed will be the floor de sign response spectrum in that direction.
D. IMPLEMENTATION
The purpose of this section is to provide informa tion to applicants regarding the NRC staff's plans for using this regulatory guide. This guide reflects current NRC staff practice.
Therefore, except in those cases in which the appli cant proposes an acceptable alternative method for complying with specified portions of the Commis sion'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 additional staff review.1.122-4