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:	02/28/1978
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RG-1.122, Rev 1
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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

analysis of the systems or equipment supported at Criterion 2, "Design Bases for Protection Against various locations of the supporting structure. The Natural Phenomena," of Appendix A, "General De Advisory Committee on Reactor Safeguards has been sign Criteria for Nuclear Power Plants," to 10 CFR -consulted concerning this guide and has concurred in Part 50, "Licensing of Production and Utilization ýthe regulatory position.

Facilities," requires, in part, that nuclear power-plant structures, systems, and components important to

B. DISCUSSION

safety be designed to withstand the effects of earth Nuclear facility structures can be approximated by quakes without loss of capability to perform their mathematical models to permit analysis of responses safety functions. Paragraph (a)(1) of Section VI, to earthquake motions. Because of the large number

"Application to Engineering Design," of Appendix of degrees of freedom that would be necessary and A, "Seismic and Geologic Siting Criteria for Nuclear the possible ill-conditioning of the resulting stiffness Power Plants," to 10 CFR Part 100, "Reactor Site matrix if the complete plant were treated in a single Criteria," requires, in part, that safety-related struc mathematical model, the plant is usually divided into tures, systems, and components remain functional in several separate systems for analysis purposes. Thus the event of a Safe Shutdown Earthquake (SSE). It it is usual that there are one or more mathematical specifies the use of a suitable dynamic analysis as models of supporting structures. Each supporting one method of ensuring that the structures, systems, structure normally supports one or more systems or and components can withstand the seismic loads. pieces of equipment. Also, different models of the Similarly, paragraph (a)(2) of Section VI of the same same structure may be required for different pur appendix requires, in part, that the structures, sys poses. For these reasons, the mathematical models tems, and components necessary for continued opera used to generate the seismic excitation data for sub tion without undue risk to the health and safety of the sequent separate analyses of supported systems or public remain functional in the event of an Operating equipment may not be suitable for the detailed lo Basis Earthquake (OBE). Again, the use of suitable calized analyses of the supporting structure.

dynamic analysis is specified as one method of ensur ing that the structures, systems, and components can Most equipment having a small mass relative to withstand the seismic loads. that of the supporting structure will have negligible interaction effects on the support structure and will This guide describes methods acceptable to the need to be included only in the mass distribution of NRC staff for developing two horizontal and one ver the mathematical model for that structure. For such tical floor design response spectra at various floors or equipment, a separate analysis will be performed other equipment-support locations of interest from using the floor design response spectra or time the time-history motions resulting from the dynamic history excitations at the equipment-support locations analysis of the supporting structure. These floor de sign response spectra are needed for the dynamic

• Lines indicate substantive changes from previous issue.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, US. Nuclear Regu Regulatory Guides are issued to describe and make available to the public latory Commisston, Wash ington, D.C. 20555. Attention: Docketing and Service 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. Regulatory are not substitutes for regulations, and compliance with them is Guides not required. 1. Power Reactors 6.

Methods and solutions different from those set out in the guides will Products 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.

5. Environmental and Siting Materials and Plant 9. Antitrust Review, Protection

10. General Comments and suggestions for improvements in these guides are encouraged at all Requests for single copies of issued guides (which may be reproduced)

times, and guides will be revised, as appropriate, to accommodate comments or for place and ment on an automatic distribution list for single copies of future guides to reflect new information or experience. This guide was revised as in specific a result of divisions should be made in writing to the US. Nuclear Regulatory substantive comments received from the public and additional staff Commission, review. Washington, D.C. 20555, Attention: Director, Division of Document Control.

derived from the analysis of the supporting structure. of the structural frequencies be broadened. One ac This guide, addresses the acceptability and develop ceptable method for determining the amount of peak ment of floor design response spectra only. Time broadening associated with each of the structural fre history motions that'WIill give results comparable to quencies is described below.

the floor design response spectra are also acceptable. Let fj be the Jth mode structural frequency that is There are, however, other major equipment sys determined from the mathematical models. The varia tems such as the reactor coolant system whose stiff tion in each of the structural frequencies is deter ness, mass, and resulting frequency range should be mined by evaluating the variation due to each signifi considered for inclusion in the model of the support cant parameter such as the soil modulus, material ing structure to account for possible dynamic interac density, etc. The total frequency variation, +/-tAfi, tion effects. Such equipment can be analyzed by (see Fig. 1) is then determined by taking the square combining the complete equipment model with the root of the sum of squares (SRSS) of a minimum var model of the supporting structure and applying the iation of 0.05fj and the individual frequency varia proper excitation to the base of the supporting struc tions, Afin, as described in regulatory position 1.

ture. With this method, no separate equipment Figure 1 shows a sample of a smoothed floor re support excitations need be generated because the sponse spectrum curve. Note that the broadened peak equipment will be excited directly through the struc is bounded on each side by lines that are parallel to ture. It should be noted that a combined model of the the lines forming the original spectrum peak.

building and equipment must be formulated to per form such an analysis. 3. Floor Design Response Spectra

1. Floor Response Spectra Nuclear power plant facilities are designed for three-component earthquakes, as indicated in Regula The two horizontal and the vertical response tory Guide 1.60, "Design Response Spectra for spectra can be computed from the time-history mo Seismic Design of Nuclear Power Plants." When a tions of the supporting structure at the various floors structural seismic analysis is performed separately for or other equipment-support locations of interest. It is each direction (two horizontal and one vertical), and important that the spectrum 'ordinates be computed at in the case of unsymmetric structures, the structural the natural frequencies of the supporting structure I and at frequencies sufficiently close to produce accu rate response spectra (see Table 1 for guidance).

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 Spectrum peaks normally would be expected to occur from each individual analysis will generate a re at the natural frequencies of the supporting structure.

sponse spectrum at a given location in each of the TABLE 1 three directions. It is important that the ordinates of these three response spectra for a given direction be SUGGESTED FREQUENCY INTERVALS FOR combined according to the SRSS criterion and that CALCULATION OF RESPONSE SPECTRA the resulting response spectrum then be smoothed and the peaks broadened to predict the floor design re Frequency sponse spectrum at the location of interest and for the Range Increment given direction. In the case of symmetric structures, (hertz) (hertz)

there will be only one significant floor response spec trum in each of the three direction

s. The smoothed

0.2- 3.0 0.10

versions of these floor response spectra will be the

3.0- 3.6 0.15 floor design response spectra. In those cases in which

3.6- 5.0 0.20

the mathematical model is subjected simultaneously

5.0- 8.0 0.25 to the action of three statistically independent spatial

8.0-15.0 0.50

components* of an earthquake, the three computed

15.0-18.0 1.0

and smoothed floor response spectra at a given loca

18.0-22.0 2.0 tion will be the floor design response spectra.

22.0-34.0 3.0

C. REGULATORY POSITION

2. Smoothing Floor Response Spectra and The following procedures for combining and Broadening Peaks smoothing the floor response spectra (with peaks To account for uncertainties in the structural fre broadened) to obtain the smoothed floor design re quencies owing to uncertainties in the material prop sponse spectra are acceptable to the NRC staff.

erties of the structure and soil and to approximations in the modeling techniques used in seismic analysis,

• See Regulatory Guide 1.92, "Combining Modal Responses and it is important that the computed floor response Spatial Components in Seismic Response Analysis."

spectra be smoothed and peaks associated with each

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COMPUTED FREQUENCY (CPS)

Figure 1 Response Spectrum Peak Broadening and Smoothing

1. When the seismic analysis is performed sepa where Afjn denotes the variation in the Jth mode fre rately for each of the three directions, and in the case quency, fj, due to variation in parameter number n, of unsymmetric structures, the ordinates of the floor and P is the number of significant parameters consid design response spectrum at the location of interest ered. A value of 0.1fj should be used if the actual and for a given direction should be obtained by com computed value of Afj is less than O.1fj. If the above bining the ordinates of the three floor response procedure is not used, Afj should be taken as 0. 15fj.

spectra for that direction according to the SRSS 3. When the mathematical model of the supporting criterion. The resulting response spectrum should be structure is subjected simultaneously to the action of smoothed with peaks broadened. In the case of sym three spatial components of an earthquake, the com metric structures, the floor design response spectrum puted response spectrum in a given direction with for a given direction will be the smoothed floor re peaks broadened and smoothed will be the floor de sponse spectrum for that direction. sign response spectrum in that direction.

2. To account for uncertainties in the structural

D. IMPLEMENTATION

frequencies owing to uncertainties in such parameters as the material properties of the structure and soil, The purpose of this section is to provide informa damping values, soil-structure interaction techniques, tion to applicants regarding the NRC staff's plans for and the approximations in the modeling techniques using this regulatory guide.

used in seismic analysis, the computed floor response This guide reflects current NRC staff practice.

spectra from the floor time-history motions should be Therefore, except in those cases in which the appli smoothed, and peaks associated with each of the cant proposes an acceptable alternative method for structural frequencies should be broadened (see the complying with specified portions of the Commis sample in Figure 1) by a frequency, __Afi, where sion's regulations, the method described herein is being and will continue to be used in the evaluation of submittals for construction permit applications Afj = (0.05fj) 2 nY (Afjn)2 4 0.If, until this guide is revised as a result of suggestions n=l from the public or additional staff review.

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