Recommendations for 

Resolution of 

Public Comments 

on USI A-40, 

“Seismic Design Criteria”

Office of Nuclear Regulatory Research 

NUREG/CR-5347 

BNL-NUREG-52191 
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Recommendations for 

Resolution of 

Public Comments 

on USI A-40, 

“Seismic Design Criteria” 

Manuscript Completed: February 1989 

Date Published: May 1989 

Prepared by 

A.J. Philippacopoulos 

Brookhaven National Laboratory 

Upton, NY 11973 

NRC Job Code A3981 

Office of Nuclear Regulatory Research 

NUREG/CR-5347 

BNL-NUREG-52191 

ABSTRACT

In June 1988 the Nuclear Regulatory Commission (NRC) issued for public

comment the proposed Revision 2 of the Standard Review Plan (SRP) Sections

2.5.2, 3.7.1, 3.7.2 and 3.7.3. Comments were received fron six organiza- tions. Brookhaven National laboratory (BNL) was requested by NRC to provide

expert consultation in the seismic and soil-structure interaction areas for

the review and resolution of these comments. For this purpose, a panel of

consultants was established to assist BNL with the review and evaluation of

the public cowments. This review was carried out during the period of October

1988 through January 1989. Many of the suggestions given in the public

comments were found to be significant and a number of modifications to

appropriate SRP sections are recommended. Other public comments were found to

have no impact on the proposed Revision 2 of the SRP. Major changes are

recommended to the SRP sections dealing with a) Power Spectral Density (PSD)

and ground motion requirements and b) soil-structure interaction requirements. This report contains specific recommendations to NRC for resolution of

the public comments made on the proposed Revision 2 of the SRP.

iii

EXECUTIVE SUMMARY

In June 1988, the U.S. Nuclear Regulatory Commission (NRC) issued for

public review and comment a proposed Revision 2 to the Standard Review Plan

(SRP) sections dealing with seismic design criteria (Federal Register, June 1,

1988). These sections are:

Section 2.5.2: Vibratory Ground Motion

Section 3.7.1: Seismic Design Parameters

Section 3.7.2: Seismic System Analysis

Section 3.7.3: Seismic Subsystem Analysis

In response to this, NRC received comments from several organizations.

Brookhaven National Laboratory (BNL) was requested to assist the NRC in

resolving these public coouients. This effort was supported by the Engineering

Issues Branch, Division of Safety Issue Resolution of the Office of Nuclear

Regulatory Research. As part of this effort, a consulting panel was formed

(Dr. R.P. Kennedy, Prof. C.J. Costantino, Prof. M. Shinozuka,

Dr. J.D. Stevenson and Prof. A.S. Veletsos) which was headed by

Dr. A.J. Philippacopoulos. The review and evaluation of the public comments

was initiated during October 1988 and was completed in January 1989.

As a result of this review, BNL and its consultants recommended major

changes on the proposed Revision 2 to the SRP sections mentioned above. The

recommended changes particularly affect the SRP areas dealing with a) ground

motion requirements and b) soil-structure interaction requirements. BNL and

its consultants strongly believe that the recommended changes will advance the

licensing process in view of the developments in the seismic area over the

last two decades and on the other hand they will provide an improved accountability of conservatism in the seismic design review process. In addition, it

is strongly recommended that future research in the seismic area focus on a)

development of PSD criteria for other than Regulatory Guide 1.60 design

spectra and b) investigation of the spatial variation of free-field ground

motions.

This report presents recommendations to the Nuclear Regulatory Commission

(NRC) for resolution of the public comments on the proposed Revision 2 of the

Standard Review Plan (SRP) specific sections mentioned above. In Section 1 we

provide background material related to the review of the public comments by

BNL and its consultants. In Section 2 we present a summary of the public

comments on the proposed Revision 2 of the SRP Sections 2.5.2, 3.7.1, 3.7.2

and 3.7.3. In Section 3 we provide an analysis of the pertinent issues and we

present the basis of our recommendations. Finally, in Section 4 we present a

summary of modifications to pertinent areas of the proposed Revision 2 of the

SRP. BNL and its consultants strongly recommend that these modifications be

implemented by the NRC.

v

TABLE OF CONTENTS

Page

ABSTRACT ..................... ........... .......... .. . . . . iii

EXECUTIVE SUMMARPY ............................................. v

ACKNOWLEDGMENT ................................................. ix

1.0 INTRODUCTION .......... . ...... .......................... 1

2.0 PUBLIC COMMENTS ON PROPOSED SRP REVISION 2 ................. 4

2.1 Sargent and Lundy Engineers .......................... 4

2.2 Westinghouse Electric Corporation ....... ....... 5

2.3 Stevenson & Associates ............ ......... o........ 6

2.4 Duke Power Company ................................ 6

2.5 General Electric Company .o...... ......... ... 6

2.6 Electric Power Research Institute ....... .... 7

3.0 PROPOSED RESOLUTIONS OF PUBLIC COMMENTS ... 0... .......... 9

3.1 Input Ground Motion Requirement ........ ... 10

3.1.1 Power Spectral Density Requirements ........... 10

3.1.1.1 Power Requirements for Design Time

Histories ....... o........ ..... 10

3.1.1.2 PSD Criteria of Proposed SRP

Revision 2 .... ................... 12

3.1.1.3 Minimum PSD Requirements ............ 13

-3.1.1.4 Power Requirements for Multiple Time

History Analyses .................... 13

3.1.1.5 Concluding Remarks on PSD Issue ...... 14

3.1.2 Duration of Input Design Time Histories ....... 14

3.1.3 Number of Time Histories for Multiple Time

History Analyses . .......... .......... .... 15

3.1.4 Ratio of Vertical to Horizontal Ground Design

Response Spectra ................. . ..... . o..... 16

3.2 Soil-Structure Interaction Requirements .............. 18

3.2.1 Justification of Fixed-Base Analysis ......... 18

3.2.2 Enveloping Requirement of Alternate 1 ........ 19

3.2.3 Variation of Soil Properties for SSI Analysis 19

3.2.4 Limit on Soil Damping of Hysteretic Type ...... 20

3.2.5 Limit on Reduction of Ground Motion with

Embedment ................................. ... 21

3.2.6 Limit on Modal Composite Damping ............... 25

3.2.7 Alternate 1 and 2 Requirements ......... 25

vii
TABLE, OF CONTENTS

(Continued)

3.3 Other

3.3.1

3.3.2

3.3.3

Issues .. .......... .... ....... .. ....... ...... ,...

Requirements for Modal Combination ............

Correlation of Damping and Stress Levels ......

Greater Use of Professional Society Consensus

Standards .....................................

4.0 RECOMMENDATIONS ..............................

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

APPENDIX E

COMMENTS ON PROPOSED REVISIONS TO STANDARD

REVIEW PLAN SEISMIC P"ISIONS BY R.P. KENNEDY

RECOMMENDED MINIMUM POWER SPECTRAL DENSITY

FUNCTIONS OMPATIBLE WITH NBC REGULATORY GUIDE

1.60 RESPONSE SPECTRUM BY R.P. KENNEDY AND

M. SHINOZUKA .. .......... ............ ........

COMMENTS ON PROPOSED REVISIONS TO STANDARD

REVIEW PLAN SEISMIC PROVISIONS BY J.D. STEVENSON

COMMENTS ON PROPOSED REVISIONS TO NRC STANDARD

REVIEW PLAN BY A.S. VELETSOS ..................

COMMENTS ON PROPOSED REVISIONS TO SEISMIC

SPECIFICATIONS OF THE US NRC STANDARD REVIEW

P LAN BY C.J. COSTANTINOo .......................

Page

27

27

27

27

28

31

A-I

B-I

C-I

D-1

E-1

viii
ACKNsflEDGMENrS

The author wishes to acknowledge the significant contributions of the

consultants, C.J. Costantino, R.P. Kennedy, M. Shinozuka, J.D. Stevenson,

A.S. Veletsos under the tight time frame available to carry out this work.

N. Chokshi, Probabilistic Risk Assessment Branch, Division of Systems

Research, Office of Nuclear Regulatory Research, was very effective in

communicating technical issues between the Review Team and the NRC staff. His

contribution is greatly appreciated. Special thanks go to S.K. Shaukat,

Engineering Issues Branch, Division of Safety Issue Resolution, Office of

Nuclear Regulatory Research, for the management direction he has provided for

this project. Thanks also go to Ms. Mary Ann Drapkin for her secretarial

support in preparing this report.

ix
1.0 INTRODUCTION

During the first quarter of 1988, the Nuclear Regulatory Commission (NRC)

prepared a Revision 2 to the NUREG-0800 (Ref. 1) Standard Review Plan (SRP)

Sections 2.5.2 (Vibratory Ground Motion), 3.7.1 (Seismic Design Parameters),

3.7.2 (Seismic System Analysis) and 3.7.3 (Seismic Subsystem Analysis). The

Revision 2 to the SRP was a result of many years' work carried out by the NRC

and the nuclear industry on the Unresolved Safety Issues (USI) A-40: "Seismic

Design Criteria." The background material related to NRC's efforts for

resolving the A-40 issues is described by Shaukat, Chokshi and Anderson in

NUREG-1233 (Ref. 2).

In June 1988, the proposed Revision 2 of the above mentioned sections of

the SRP was issued by NRC for public review and comments. Around August 1988,

comments were received from:

a) Sargent and Lundy Engineers (Ref. 3)

b) Westinghouse Electric Corporation (Ref. 4)

c) Stevenson and Associates (Ref. 5)

d) Duke Power Company (Ref. 6) and

e) General Electric Company (Ref. 7)

In October 1988, additional comments were provided by the Electric Power

Research Institute (Ref. 8).

In September 1988, Brookhaven National Laboratory (BNL) as a contractor

to the NRC was requested to assist the staff in resolving the public conments

from the above six organizations. Specifically the project entitled:

"Resolution of Public Comments for USI A-40 - Seismic Design Criteria" was

issued to BNL with the following objectives:

1) Provide expert consultation in the seismic and soil-structure

interaction areas for the review and resolution of the public

comnmnts on USI A-40 "Seismic Design Criteria."

2) Provide reconmendations for possible modifications to the proposed

revisions of the SRP Sections 2.5.2, 3.7.1, 3.7.2 and 3.7.3 and,

3) Investigate specific issues related to:

a) Power Spectral Density (PSD) function, and

b) Soil-Structure Interaction (SSI).'

The above project was sponsored by the Engineering Issues Branch, Division of

Safety Issue Resolution of the Office of Nuclear Regulatory Research. The NRC

Project Manager was S.K. Shaukat, Engineering Issues Branch, Division of

Safety Issue Resolution, Office of Nuclear Regulatory Research. Technical

direction has been provided by N. Chokshi, Probabilistic Risk Assessment

Branch, Division of Systems Research, Office of Nuclear Regulatory Research.

1
In order to accomplish the above objectives, a consulting panel was

established in October 1988. The activities of the consulting panel were

directed by Dr. A.J. Philippacopoulos of BNL. The members of the consulting

panel were:

- Prof. C.J. Costantino, City University of New York - Dr. R.P. Kennedy, Structural Mechanics Consulting, Inc.

- Prof. M. Shinozuka, Princeton University - Dr. J.D. Stevenson, Stevenson and Associates

- Prof. A.S. Veletsos, Rice University

The responsibility of the consulting panel was to perform a detailed

evaluation of all public comments and to draw conclusions with regard to their

possible impact on the proposed Revision 2 of the SRP Sections 2.5.2, 3.7.1,

3.7.2 and 3.7.3. For those cases in which such an impact was identified,

specific recommendations are made for resolving the issue.

The review and evaluation of the public comments received by the six

organizations mentioned above, was initiated during October 1988 and was

completed on January 1989. The work accomplished during this period went far

beyond the expected work requirements under this project. This was due to a

major effort which was undertaken in order to resolve several issues

associated with the public comments on the Power Spectral Density (PSD)

requirement. Prof. M. Shinozuka and Dr. R.P. Kennedy carried out a detailed

evaluation of various aspects related to the PSD issue. Numerical data were

generated and several alternatives were considered. The results of this work

are described in Appendix B. The effort by Prof. M. Shinozuka and

Dr. R.P. Kennedy was extremely important in reaching consensus on the PSD

issue.

The work conducted under this project for the resolution of public

comments on SRP Revision 2 can be categorized into three phases. Phase I of

the work reflects the preliminary stage of the review of public comments in

which the major issues were identified. Phase II of the work was associated

with the main portion of the review from which resolutions were prepared for

most of the public comments except those related to the PSD requirement.

Finally, Phase III of the work was devoted to efforts for resolving the PSD

issue and reaching a consensus on the definition of the target PSD for Reg.

Guide 1.60 type spectra. The above three phases of the work under this

project were carried out during the period of October 1988 through January

1989. During this period, the consulting panel met twice. Members of the NRC

staff attended both meetings.

A kick-off meeting was held at the White Flint North Building in

Rockville, MD (October 6, 1988). The purpose of this meeting was to:

- Discuss the objectives of the work for BNL and its consultants.

- Discuss the approach for accomplishing the objectives.

2
- Give a preliminary assessment of the public comments to NRC.

The second and most significant meeting under this program was held on

December 16, 1988 at the Nicholson Lane South Building in Rockville, MD.

During this meeting recommendations for resolution of the public comments were

presented to NRC. These comments were categorized as follows:

-Comments on Power Spectra Density (PSD) and seismic input requirements.

- Comments associated with proposed limits on various aspects of soilstructure interaction.

- Comments on modal combination and damping requirements.

Following the December 16, 1988 meeting, the work under this project was

focused on the following items:

a) Preparation of Consultant Reports.

b) Efforts by M. Shinozuka and R.P. Kennedy to reach a consensus on the

PSD issue.

The above two activities were completed by the end of January 1989. Finally,

it should be mentioned that BNL and its consultants considered the majority of

the public comments to be valid and, in addition, to have made significant

impact on the seismic design process. In view of this, a set of modifications

to the SRP Sections 2.5.2, 3.7.1, 3.7.2 and 3.7.3 are recommended. These are

presented in Sections 3.0 and 4.0 of this report.

3
2.0 PUBLIC COMMENTS ON PROPOSED SRP REVISION 2

The following is a selective summary of the public comments received by

the NRC on the proposed Revision 2 of the SRP (Refs. 3-8).

2.1 Sargent and Lundy Engineers

- The differences between SSE and OBE should be clarified in the SRP.

- The vertical input should be defined as 2/3 of the horizontal.

- The following comments were made with regards to the PSD requirement:

a) The 15% requirement in amplitude drop below the

target PSD could force unnecessary conservatism.

b) The target PSD above 10 Hz is questionable.

c) The parameters defining the target PSD should be

further examined in view of actual records.

d) The frequency window of 0.05 Hz is questionable.

A maximum frequency interval of 0.2 Hz with 25 second

duration is recommended.

e) The units of the PSD parameters should be consistent.

SRP should state that the proposed PSD is a two-sided one.

f) Two target PSD's should be specified for the horizontal

and vertical analysis respectively.

- The requirement of minimum 5 time histories for multiple time history

analysis is too high.

- The use of ASCE Standard 4-86 (Section 3.1.2.2, p. 10) damping

requirement which correlates stress levels with damping values is

recommended.

- The use of ASCE Standard 4-86 (Section 3.3.1.1, p. 25) definition of

rock-like foundations is recommended.

- The requirement of enveloping the SSI results from half-space and

finite boundary methods should be deleted.

- SRP should not require a limitation of hysteretic soil damping to 5%.

- Combination of modal responses according to ASCE Standard 4-86 is more

appropriate and should be permitted.

- Item b on p. 3.7.2-11 of SRP should be deleted.

4
- Arbitrary limit on reduction of motion at foundation level should not

be imposed.

- Limitation of total soil damping (material plus radiation) is not

consistent with actual phenomena.

- The shear modulus and damping should be limited to the values associated with strains which are consistent with those observed during

earthquakes.

2.2 Westinghouse Electric Corporation

- Multiple time history analyses are not always needed. The required

minimum of 5 sets "is unrealistic and unwarranted."

- PSD requirements will place added burden on the industry. They should

not be imposed at this time for various reasons.

- more definitive acceptance criteria should be given with respect to

the duration of the seismic input, i.e.,

a) Minimum strong motion duration of 6 seconds.

b) Total duration of 10-15 seconds.

Choice of shorter durations with appropriate justification should be

allowed.

- On the subject of high frequency nude combinations Westinghouse pointed

out four references related to:

a) Envelope seismic spectra analyses

b) Seismic multi-spectra analyses

- On the subject of modal combinations, Westinghouse suggested that the

procedures of Reg. GWide 1.92 are over conservative. SRP should be

changed to include the algebraic sum method as per NUREG-1061 (Vol., 4).

- Westinghouse agrees with the SRP provision regarding a maximum 40%

reduction of the surface free-field motion to the corresponding motion

at the foundation level. Westinghouse-suggested that this limitation

will account for uncertainties due to wave type, angle of incidence and

soil non-linearity. Furthermore, it is pointed out that this

suggestion is in agreement with provisions given in ASCE Standard 4-86.

- Westinghouse agrees with the recommendation of the Senior Seismic

Review Team (SSRT) regarding limits imposed on radiation damping.

Specifically, frequency-independent radiation damping obtained from

5
standard formulas should be limited to 75%. When layered soil profiles

are of interest then the radiation damping should be the same with that

computed with acceptable computer codes.

- Westinghouse suggested that when modal damping is used in SSI calculations in conjunction with modal superposition, the composite modal

damping should be limited to 20%. It was further recommend that for

higher composite damping, the direct integration method be used.

- Westinghouse recommended that the enveloping of the results of

different SSI methods should be dropped.

2.3 Stevenson & Associates

- The proposed Revision 2 of SRP does not reflect the results contained

in NUREGC-1061 Vols. 1-5 which are specifically related to seismic

design of piping.

- The proposed Revision 2 of SRP does not reflect contents of available

standards such as:

a) ASME Boiler and Pressure Vessel Code Section III

Appendix N, "Dynamic Analysis Methods."

b) ANSI/ASCE Standard 1-82, "N-725 Guidelines for Design

and Analysis Nuclear Safety Related Earth Structures."

c) ASCE Standard 4-86, "Seismic Analyses of Safety Related

Nuclear Structures."

2.4 Duke Power Company

- Duke Power Company agrees with the use of site-specific spectra. They

recommend that certain spectra be allowed for application to a number

of sites for consistency with standard power plant design.

- Duke Power Company pointed out that it was not possible to investigate

the PSD requirement since one of the references given in the SRP (Ref.

12) was not available at the time of their review.

- Duke power recommended that the backfit analyses for above ground tanks

(rigid versus flexible wall assumption) be done using realistic

allowable stresses (rather than code allowable) and by considering

yielding for worst case type loads.

2.5 General Electric Company

- The 15% acceptance criterion for meeting the target PSD is unrealistic.

GE recommended that the computed PSD at the major amplified frequency

range of interest should reasonably envelope the target PSD.

6
- The cumulative PSD may be a more accurate measurement of energy than

the conventional PSD.

- The 5% limit for hysteretic soil damping is too low. A 15% limit has

been recommended in NUREG/CR-1161.

- Distinction of Alternates 1 and 2 in SSI analysis seems inadequate.

Any state-of-the-art analyses should be acceptable provided that major

uncertainties are accounted for.

- The vertical ground spectra should be 2/3 of the horizontal over the

entire frequency range. This definition is consistent with recommendations of NUREG/CR-1161.

- A realistic limit for the reduction of the free-field with depth should

be established by looking into more recorded earthquake data.

- No limit on radiation damping is needed provided that layering effects

are properly incorporated into the analysis. When a layered halfspace

is represented by a uniform halfspace having average properties then,

the radiation damping may be over estimated. This can be improved by

using refined methods.

- The following limits on soil moduli are agreeable to GE:

a) Shear modulus reduction with strain should be limited

to 40% of the low-strain value.

b) Hysteretic damping increase with strain should be

limited to 15%. This limit has been proposed in

NUREG/CR-II61.

- GE recommended that the requirement of enveloping the results from the

two SSI methods be deleted. Instead, any method should be acceptable

provided that variations in soil properties are accounted for.

2.6 Electric Power Research Institute

- The OBE should not control the design and should be left with utilities

to define.

- Although the use of various alternative approaches are encouraged in

the design process, some of the restrictions imposed on the more

realistic methods defeat the purpose of their use.

- The definition of the control motion either at the surface or at an

outcrop is a major advance in the proposed SRP.

- More definitive guidelines are needed especially for Alternate 2

approach in SSI.

7
- Guidelines for establishing the importance of high frequency modes are

needed.

- The extensive requirements associated with Alternate 2 SSI analysis may

defeat the purpose of site-specific analyses.

- In the design of above ground tanks, soil-structure interaction

criteria are required.

- The 40% limit on the reduction of free-field at the foundation level is

not clear. Some Lotung data show even larger reductions. EPRI will

provide specific recommendations on the amount of reduction with depth

after completion of ongoing studies dealing with the Lotung data.

- EPRI is currently conducting additional tests (field and laboratory

tests) to determine soil properties and their variation with strain in

view of the results obtained in the blind predictions with Lotung

data. When these efforts are completed EPRI will provide specific

comments with regard to limitations on soil damping for SSI analysis.

8
3.0 PROPOSED RESOLUTIONS OF PUBLIC COMMENTS

The review of public comments was carried out by first examining all

public comments contained in Refs. 3-8. Subsequently, it was focused on those

comments which were judged to be more important in terms of impact on Sections

2.5.2, 3.7.1, 3.7.2 and 3.7.3 of the proposed SRP Revision 2. These comments

were classified conveniently into the following three categories:

o Comments on input ground motion requirements.

o Comments on soil-structure interaction requirements.

o Comments on other issues.

Discussions and recommendations for their resolution are presented in Sections

3.1, 3.2 and 3.3 respectively of this report. The recommendations given in

these sections are products of a) the reviews carried out by the consultants

and described in the reports attached here to as Appendices A thru E; b)

discussions between BNL and its consultants; and c) meetings between BNL, its

consultants and the NRC staff. It should be realized that these

recommendations involve some level of judgment resulting from the fact that

the current state-of-the-art does not permit a complete resolution of certain

issues. It is to be expected that refinements may be justified in these areas

based on future research. Therefore, it is recommended that a mechanism be

established for reviewing the SRP at some regular intervals (perhaps every

five years).

9
3.1 Input Ground Motion Requirement

3.1.1 Power Spectral Density Requirements

The public comments reflect a strong response with respect to the PSD

requirements described in the proposed SRP Revision 2 (SRP Section 3.7.1,

Subsection I: Areas of Review, Item ib: Design Time History, p. 3.7.1-4 and

Subsection II: Acceptance Criteria, Item ib: Design Time History, p. 3.7.1-8

through 3.7.1-11). It is the common understanding in the present review that

the NRC's intent for requiring a PSD check on the design time history is to

ensure that an adequate power distribution exists in the design time history

throughout the frequency range of interest. Prior to implementing PSD

requirements into the SRP, the usual procedure was to demonstrate that the

design time history produces response spectra which closely match the design

response spectra for all damping values employed in the analysis and over the

frequency range of interest. The public comments made on the proposed PSD

requirement ranged from clarification type to those expressing strong

reservations regarding the target PSD function given on page 3.7.1-11 of the

SRP Revision 2. Our review of public conmments focused particularly into the

PSD related ones and an intensive effort was made during the time frame of

this review to provide recommendations for possible resolution of this issue.

Specific aspects of this review are described in the following subsections.

3.1.1.1 Power Requirements for Design Time Histories

As indicated above, the understanding of the proposed SRP Revision 2 PSD

requirement is that it was intended to provide power criteria for the design

input time histories used to perform seismic evaluations so that possible

power deficiencies are prevented. It should be made clear though at this

point that in order to accomplish this objective, the PSD approach is not the

only way but perhaps a convenient one. A more practical approach for implementation in the design practice is to provide criteria for preventing potential power deficiency at the response spectrum level. Specifically, another

way for identifying lack of power in a design time history is to look at the

low damped response spectra produced by this time history. It is realized

that a response spectrum does not provide a direct definition of the input

power since part of the latter is dissipated in the form of viscous damping

which is conventionally employed for computing response spectra. On the other

hand, low damped response spectra allow for more accessible information

regarding the frequency distribution of the input power thus facilitating

exercise of judgment. There is, however, a need for specific criteria.

In order to implement power requirements through response spectra, one

needs to define how close the response spectra produced by the time history in

question should match the corresponding design response spectra. Specifiically, the following items have to be addressed:

o What is the permissible frequency window for the damping considered?

10
o What is the permissible amplitude difference at this window

as well as in adjacent frequencies? (Lower power within a

frequency window can be picked up by adjacent frequencies.)

In Appendix A it is suggested that possible answers to these questions are:

o Frequency window: ± 20% centered at any spectral frequency.

o Allowable differences: maximum 20% by average above the

design spectrum within any frequency window and 10% maximum

dip below the design spectrum at any frequency.

In Appendix A it is cautioned, however, that although the above seem to be

reasonable values, the subject needs further investigation. On the other

hand, in Appendix D it is suggested that the above requirements may not be

difficult to implement if real time histories are employed to generate

spectrum consistent time histories. Finally, in Appendix E, it is recommended

that PSD criteria should not be required in the proposed SRP Revision 2 if the

following two conditions in terms of response spectra are satisfied:

1. That the design time history satisfies the enveloping

criteria for response spectra associated with equipment

damping of 2% or less, whether the response spectra used

in the analyses are of the broad-banded generic type (such

as those of Reg. Guide 1.60) or site-specific.

2. That the enveloping criteria be defined as follows:

o no more than five points of the calculated spectrum

fall below, and no more than 10% below the target

spectrum

o the calculated spectrum does not exceed the target

spectrum by more than 50% at any frequency

o the calculated spectrum lies at or above the target

spectrum at all calculated structural frequencies of

interest, and

o the calculated spectrum satisfies the specific frequency

requirements of the current SRP.

In view of the above, it appears that although at this time qualitative

descriptions are available, a more quantitative basis is required for

implementing a power requirement through the response spectrum approach.

It is reccmLended, however, that the discussions on this subject given in

Appendices D and E be also considered by the NRC.

Turning now to a PSD approach for expressing power requirements on the

design time history, the following items must be addressed:

11
a) Form of the target PSD function.

b) Criteria to meet the target PSD.

These two items have been addressed in the PSD requirements of the proposed

Revision 2 of the SRP. However, both the target. PSD as well as the criteria

to me-et the target PSD were questioned in the public comments. The following

sections provide suggestions for resolution of the public comments on the

proposed PSD criteria.

3.1.1.2 PSD Criteria of Proposed SIRP Revision 2

The proposed SPR Revision 2 specifies that (p. 3.7.1-11):

"... Further, the computed PSD at no frequency should drop below 15 percent of

the target value.

s1 + 4E g 2 ( / g)2

[1 - (W/W g)2]2 +4 4•g2 (W/wg)2

with So = 1,100 in2 /secs3 (this value corresponds to a peak acceleration of

1g), wg = 10.66 rad/sec and-Eg = 0.9793 .... "

The above requirements are based on the preliminary study reported in

Ref. 12. In the latter studyi the Kanai-Tajimi spectral density function was

employed to produce ground acceleration time histories compatible with the

Reg. Guide 1.60 design spectra. The response spectra produced by the time

histories obtained from the above target PSD satisfy the Reg. Guide 1.60

requirements simply in the sense that they envelop conservatively the

corresponding Reg. Guide 1.60 design spectra. This enveloping is associated

with relatively large differences from a design standpoint especially at

higher spectral frequencies (above 10 cps) where the response spectra produced

from the target PSD lie much above the Reg. Guide 1.60 spectra. This may

cause the following problem: If one starts with a time history having

response spectra which match closely the Reg. Guide 1.60 spectra, then in

order to satisfy the proposed target PSD requirements the time history may be

forced with unnecessary conservatism beyond that embodied in the design

spectra.

Specifically, a design time history which matches closely the design

response spectra has to be subsequently modified so that its PSD meets a

target PSD which in turn produces response spectra that are excessively conservative as compared to the design response spectra. In this awkward

situation, the PSD requirement controls the design time history instead of the

design response spectra controlling the time history. The fundamental role of

the design response spectra is thus violated. This inconsistency which could

force design response spectra is thus violated. This inconsistency which

could force unnecessary conservatism is perhaps the main source of reaction in

the public comments.

12
In order to resolve this issue it is reconvended that the PSD requirements of the SRP Revision 2 be replaced with minimum PSD requirements.

Minimum implies that they preserve the level of conservatism associated with

the definition of the design time history through the design response spectra.

Ideally, a minimum PSD requirement should reflect the same level of compatibility in terms of design response spectra to that of the design time history

to the design response spectra. Practically speaking, a minimum PSD requirement must basically maintain the conservatism associated with design response

spectra without artifically imposing additional one. In this context, the

design response spectra are still the primary acceptance criteria while the

PSD requirement is a secondary one which can be used to guard against unwanted

(in terms of response) power dips in the input time history.

3.1.1.3 Minimum PSD Requirements

As part of the present review of public comments on the proposed

Revision 2 of the SRP, Kennedy prepared initially the PSD requirement which is

described in Appendix A (item 2: Earthquake Ground Motion Power Requirements). This requirement was developed on the basis of observations on the

cumulative power spectral density functions of seven time histories (one

synthetic of the Reg. Guide 1.60 type and six recorded earthquakes). The

numerical results and the comparative plots which are presented in Appendix A

demonstrate the consistency of minimum type PSD requirement and point out

clearly the need for modifying the proposed Revision 2 to the SRP on this

issue. Following this initial work, Kennedy and Shinozuka developed jointly a

minimum PSD requirement for Reg. Guide 1.60 spectra (Appendix B). The

procedure for developing this requirement is essentially similar to that

proposed in Ref. 12 without the use of the Kamai-Tajimi PSD function as a

target function. Pertinent details and definitions are presented in Appendix

B and are not reproduced here.

The minimum PSD requirements proposed here by Kennedy-Shinozuka appear to

be much more consistent than the PSD requirements of the proposed SRP Revision

2 (p. 3.7.1-10 and 3.7.1-11). It is recommended that the PSD requirements of

the SRP Revision 2 be replaced with the minimum PSD requirements presented in

the Appendix B of this report. This will help greatly in resolving the public

comments on this issue.

3.1.1.4 Power Requirements for Multiple Time History Analysis

For the multiple time history seismic analysis option, the following

suggestions were made by the consulting panel:

o The PSD provision of the proposed SRP Revision 2 (p. 3.7.1-11)

regarding multiple time histories should be retained

(Appendix A).

13
o The PSD requirement should be applied only when multiple

artificial time histories are used. It is not needed when

multiple real or modified real ground motion histories are

used (Appendix D).

o The average of the individual PSD's should satisfy the target

PSD (Appendix E).

It is logical to assume that the risk of missing power in the design

input decreases with increasing number of time histories. Generally speaking,

there is a sense of repetition when imposing a PSD check on a multiple time

history seismic analysis. Perhaps, requiring a PSD check only when artificial

time histories are employed in the multiple time history analysis could be a

reasonable compromise.

3.1.1.5 Concluding Remarks on PSD Issue

First of all, it is reconmmended that the PSD criteria (target PSD

function as well as requirements to meet the target PSD) of the proposed SRP

Revision 2 be replaced with the minimum PSD criteria given in Appendix B of

this report. The SRP should also clarify that the design response spectra are

the primary acceptance criteria while the PSD requirement is a secondary one.

Secondly, it is recommended that the following items be considered by the NRC:

o PSD requirements for other types of generic broadbanded design spectra.

o PSD requirements for both horizontal and vertical

cases should be specified.

o PSD requirements for site-specific spectra.

o The purpose of PSDIfunctions in seismic analysis should

be clarified. Should PSD representations of input

motion be also used in conjunction with other aspects

of seismic analysis?

o The case of implementing power requirements directly at

the level of the response spectrum should be further

investigated.

3.1.2 Duration of Input Design Time Histories

In the public comments a suggestion was made to have explicit acceptance

criteria in the proposed SRP Revision 2 for defining the duration of design

time histories. Specifically, Westinghouse suggested the following:

14
o Total duration: 10-15 seconds

o Strong motion duration: 6 seconds (minimum)

o Acceptance of shorter time histories with proper justification.

Based on our review of this subject, the following recommendation is made:

o Strong motion duration: Minimum: 6 seconds

Maximum: 15 seconds

o Total duration: 10-25 seconds

Shorter or longer durations should also be accepted on a case-by-case basis.

3.1.3 Number of Time Histories for Multiple Time History Analyses

The requirement of a minimum five time histories which is specified in

the proposed SRP Revision 2 (Section 3.7.1, p. 3.7.1-11) for the case of

multiple time history analysis was questioned in the public comments. Sargent

and Lundy suggested that this requirement be reduced to three time histories.

On the other hand, Westinghouse suggested that "it is unrealistic, and

unwarranted, to use five sets of time histories to perform a seismic

analysis."

The recommendations made by the consulting panel on this subject are:

o Kennedy recommended (Appendix A) that the provisions of the

ASCE Standard 4-86 (Ref. 9, Section 2.3.1, p. 7, commentary

Section 2.3.1, p. 45) are preferable to the response spectra

and minimum number provision of the proposed SRP Revision 2.

o Veletsos considers the proposed SRP Revision 2 requirement of

minimum five time histories as "quite reasonable" while the

ASCE Standard 4-86 provision on this matter as "inappropriate"

(Appendix D, p. 5). He recommends that the minimum number of

time histories may be reduced to four but no less than four.

From an overall prospective, the minimum number of time histories to be

used in the multiple time history analyses:

o Should not be high enough to discourage the use of the

multiple time history option.

o Should not be low enough so that the use of the multiple

time history analyses option is unwarranted.

In making a decision on an acceptable minimum number of time histories

for the multiple time history option of seismic analysis one needs to further

consider how these time histories are required to match the design response

15
spectra. According to the proposed SRP Revision 2, the acceptance criterion

is "... if the average (or other appropriate statistical measure such as MSD)

response spectra generated from these time histories envelope the design

response spectra ." (p. 3.7.1-11). The following clarification with respect

to this criterion is suggested (Appendix D):

If a collection of artificial, real or modified real ground

motion histories is used, the response spectra for the

individual records need not separately match the design

spectrum, but the spectrum for the ensemble of records

corresponding to the mean plus one standard deviation (MSD)

level of non-exceedance must match it. The response values

considered for design in this option must be those associated

with the MSD level of non-exceedance. Alternatively, one may

initially adjust the intensities of the ground motion records

so that the mean of their response spectra matches the design

spectrum, and work with the mean values of the resulting

responses. In either case, the match should hold over the

entire range of frequencies and damping values of interest.

In addition, the PSD requirements to be imposed (if any) for the multiple

time history option should be also factored into the decision for a minimum

number of time histories. The provisions on the proposed SRP Revision 2call

for a power check based on an average PSD function. As indicated in Section

3.1.1.4, no consensus was reached here with respect to this item. In general,

it appears that there is somehow a repetition in approach when imposing PSID

requirements for a multiple time history analysis.

In view of the above, it is recommended that the minimum number of time

histories required to perform a multiple time history seismic analysis be

reduced from five to four. At this time, there is no sufficient basis for

further reduction.

3.1.4 Ratio of Vertical to Horizontal Ground Design Response Spectra

The proposed Revision 2 of the SRP Section 3.7.1 has deleted the 2/3

acceptance criteria regarding the definition of the vertical design input from

the corresponding horizontal (p. 3.7.1-8 of Ref. 1). Comments received by

Sargent and Lundy as well as by General Electric suggest that the 2/3

provision for defining the vertical component of the ground motion be accepted

in the SRP. Although the consensus reached from the review of the public

comments is in agreement with this suggestion, a limitation of the rule for

certain applications is recomnmended. Specifically, it is judged that the 2/3

acceptance criteria be applicable only to epicentral distances of 10 Km or

more. For smaller epicentral distances the vertical component can exceed the

horizontal. In such cases the 2/3 provision may lead to unconservative

results and should be avoided. Instead, the definition of the vertical

component should be subjected to a review on a case-by case basis.

16
It is recognized that the 2/3 rule for defining the vertical ground

design spectra from the corresponding horizontal has been a subject of many

discussions in the past. In view of the recent Revision 2 of the SRP Section

2.5.2, however, it is appropriate not to allow for this rule when the horizontal ground response spectrum is defined according to the provisions of

Item 1 of Subsection 2.5.2.6 of the SRP. Specifically, if a site-specific

approach is employed for deriving the horizontal ground design spectrum then

the same process should be employed for deriving the vertical ground design

spectrum without resorting to the 2/3 scaling approach.

In summary, the following recommendations are made with respect to the

ratio of vertical to horizontal design response spectra.

- The vertical ground design spectrum should be taken as 2/3 of

the horizontal over the complete frequency range of interest

provided that the epicentral distance of the design earthquake

is more than 10 Km. For smaller epicentral distances the

definition of the vertical ground design spectrum should be

reviewed and accepted on a case-by-case basis.

- The 2/3 scaling rule should not be permitted for cases in

which the horizontal ground design spectrum is generated using

the site-specific approach described in Item 1 of SRP Subsection 2.5.2.6. In such cases, the same procedure should

be followed for generating both the horizontal as well as the

corresponding vertical ground design spectra.

17
3.2 Soil-Structure Interaction Requirements

3.2.1 Justification of Fixed-Base Analysis

The following specifications are given in the proposed SRP Revision 2

concerning the justification for performing a fixed-base analysis:

p. 3.7.2-9

"For sites where SSI effects are considered insignificant and

fixed base analyses of structures are performed, bases and

justification for not performing SSI analyses are reviewed on

a case-by-case basis."

and

p. 3.7.2-10

"For structures supported on rock, a fixed base assumption is

acceptable. A comparison of interaction frequencies and the

fixed base frequencies can be used to justify the fixed base

assumption."

In response to request for public comments, Sargent and Lundy suggested

that the provisions of the ASCE Standard 4-86 (Ref. 9) could be used as one

acceptable basis for justification of a fixed-base analysis. These provisions

are:

3.3.1.1 Fixed-Base Analysis - A fixed-base support may be

assumed in modeling plant structures for seismic response

analysis when the site soil conditions are rock-like beneath

the foundation. A rock-like foundation is defined by a shear

wave velocity of 3,500 ft/sec (1,100 m/sec) or greater at a

shear strain of 10-3 percent or smaller when considering

preloaded soil conditions due to the structure.

The suggestions provided by Sargent and Lundy on this matter are found

generally acceptable. Specifically, the following are recommended:

o The ASCE Standard 4-86 definition of rock-like materials

be adopted in the proposed SRP Revision 2.

o Acceptability of fixed-base assumption should be primarily

addressed by comparison of interaction and fixed-base

frequencies.

o Justification of the fixed-base assumption of the ASCE

Standard 4-86 be acceptable by the proposed SRP Revision 2

as an option for cases in which the fixed-base structural

frequencies are 10 cps or less.

18
3.2.2 Enveloping Requirement of Alternate 1

The proposed SRP Revision 2 (Section 3.7.2, p. 3.7.2-9) requires the

enveloping of the results frcm the two SSI methods.

o In the review efforts of Task Action Plan A-40 (Ref. 10)

it was recommended that the enveloping of the two methods

should not be required.

o In the SSI Workshop (Ref. 11) it was recommended that

this enveloping requirement be dropped.

o In the public comments by Sargent and Lundy, Westinghouse,

General Electric and EPRI, it is recommended that this

requirement be deleted from the proposed SRP Revision 2.

o In the present review of the public comments on the proposed SRP Revision 2, it is unanimously recommended that

this requirement be deleted from the proposed SRP Revision 2.

The skepticism in the regulatory community which led years ago to this

requirement has been recognized. There is really no longer a need for this

requirement.

3.2.3 Variation of Soil Properties for SSI Analysis

Sargent and Lundy suggested that the low strain values mentioned in Item

2, p. 3.7.2-12 of the proposed SRP Revision 2 be defined. This is a valid

point and it is further related to Item 4 on the same page, concerning

requirements for variations in soil properties for SSI analysis.

Soil properties are usually handled in the SSI analysis by either of the

following approaches:

o The shear stress and the material damping are computed

iteratively through the use of appropriate shear modulus

(G) versus shear strain (y) and damping (8) versus shear

strain (y) curves (e.g., SHAKE, FLUSH). In this case a

set of such curves are entered into the SSI calculation.

o The soil is represented as a linear viscoelastic material

(i.e., CLASSI or similar solutions which are based on

continuum models). In this case, a single set of shear

modulus and damping are entered into the analysis (i.e.,

G, 8 are taken as constants).

In the second of the above approaches, however, some representative values of

(G, 8) in terms of shear strain should be employed in the analysis. These

values should be defined according to the effective shear strains (taken

usually as 65% of corresponding maximum values) obtained in the soil profile

through the free-field analysis of the design ground motion. It is

19
recomunended that this clarification be made on page 3.7.2-11 of the proposed

SRP Revision 2 so that the provisions are not interpreted as not allowing for

any reduction of the shear modulus at seismic strain levels (p. 18 Appendix

A).

With respect to the variation in soil properties, the following

clarifications are given (Appendix E).

o Definition of best estimate, upper and lower bound cases:

The upper bound shear modulus at low strain can be

taken as twice the best-estimate value while the lower

bound shear modulus can be defined as one-half this value,

provided that this range of variability suitably encompasses

the scatter typically found in the field program. The

average shear modulus degradation (G/Gmax vs peak shear

strain) and hysteretic damping ratio (D vs peak shear strain)

curves, as defined in ASCE Standard 4-86 can be determined

from the laboratory testing program, together with typical

data available for similar soils. These curves can then be

used in the iterative pseudo-linear analyses to determine

shear moduli and hysteretic damping ratios compatible with

the effective shear strains computed in the free-field for the

input seismic motions for all soil layers for each of the

three cases of interest. These properties can then be used

directly in the SSI computational model.

o Criteria for the lower and upper cases:

First, the lower bound shear moduli should not be less than

the moduli required for an acceptable foundation design, that

is, lead to static settlements much greater than considered

acceptable for normal foundation design. Secondly, the upper

bound shear moduli should not be less than the best estimate

shear moduli defined at low strain (Gmax defined at 10-4

percent effective shear strain) for all soils.

3.2.4 Limit on Soil Damping of Hysteretic Type

The Revision 2 of the SRP states that the internal soil damping of the

hysteretic type is "not expected to exceed about 5% of critical" (SRP Section

3.7.2, p. 3.7.2-12). Public comments made with respect to this limitation

suggest that the value of 5% is too low and should be increased to 15% which

was also recomnended in Ref. 10. The maximum value of 15% is also found to be

acceptable in the present review and it is recommended that the provision 2 on

page 3.7.2-12 of the SRP be changed to allow for a 15% limit on the material

(hysteretic) soil damping in place of the current 5% requirement.

It is further recommended that a definition of the hysteretic soil

damping be provided in the SRP to avoid confusion with regard to the 15%

value. According to the published literature on the SSI subject, the

20
material soil damping for hysteretic behavior can be expressed in terms of the

specific loss factor A W/W as

1 AW wG

47r W 2G - (I)

and

tan6 =%1 1 AW 

2ir W G (II)

G = shear modulus

G' = shear viscosity

w = circular frequency

Note that tan6 = 2a

Any of the above two relationships i.e., (I) or (II) can be used in the

SRP to define material attenuation relationships for hysteretic soil

behavior. It must be made clear, however, that the recommended 15% limit on

the hysteretic type soil damping implies that a must be equal or less than

0.15 or tan6 must be equal or less than 0.30.

3.2.5 Limit on Reduction of Ground Motion with Embedment

The reduction of ground design motion for embedded structures received

special attention in the public comments. Four out of the six organizations

which provided comments to NRC on the Revision 2 of the SRP expressed

different opinions on this subject. A brief description follows:

- Sargent and Lundy suggested that arbitrary limits on the

reduction should not be imposed.

- Westinghouse agrees with provisions 3.3.1.2(b) of the ASCE

Standard 4-86 (Ref. 9) which states that:

"'Variation of amplitude and frequencies content

with depth may be considered for partially embedded

structures. The spectral amplitude of the acceleration

response spectra in the free-field at the foundation

depth shall be not less than 60% of the corresponding

design response spectra at the finish grade in the freefield."

- General Electric suggested that a realistic limit on the

allowable reduction should be established by looking into

more data.

- EPRI suggested that the limit of 40% reduction of the translational ground motion is not clear. They are currently

investigating this issue using the Lotung data and are

expecting to provide final recommendations at the completion

of the work.

21
looking back at the ef fort under Task Action Plan A-40 for resolving this

issue in late seventies, it was made clear at that time that the review team

was dealing with a co~ntroversial subject and no consensus could be reached

(p. 20 of Ref. 10). In the present work this subject was reconsidered in view

of the public commuents on the proposed Revision 2 of the SRP * The consulting

panel conducted a detailed review of the comm~ents made by General Electric,

EPRI, Sargent and Luindy and Westinghouse on this subject. Specifically, the

following issues were considered:

o Should a limit on the reduction with embedment be required?

o If so, then: - What is the amrount of allowable reduction?

- What is the form of the reduction?

The following views were expressed by the consulting panel:

o The spectral amplitude of the acceleration response spectra

in the free-field at the foundation depth shall not be less

than 60% of the corresponding design response spectra at

the finish grade in the free-field. [Section 3.3.1.2(b) of

ASCE Standard 4-861. This recommrendation is discussed in

Appendix A (p. A-19) of this report.

o The reduced motion should not be less than 70-75% of the

corresponding surface motion and should not be permitted

if rotational components are ignored. The reduction should

refer to the horizontal comuponent of the foundation input

motion. This recommnendation is discussed in Appendix D

.(p. D-11) of this report.

o A limit on the reduction is not generally needed. If a*

limit of the reduction is to be imposed, then the reduced

motion should be limited to 60% of the design ground motion.

This recommendation is discussed in Appendix E (p. E-11) of

this report.

It is clear from the above that no consensus among the members of the

consulting panel was reached With respect to the reduction of motion with

embedment. As indicated previously, a similar conclusion on this subject was

also obtained in Ref. 10. There are, however, the following differences:

First, among other options, the case of not limiting the reduction with

embedment was considered in the present review. Specifically, it is recommended in Appendix E (p. E-11) that if the kinematic and inertial aspects of

the SSI process are properly addressed in the analyses, then there is no need

to place a limit on the reduction.

Secondly, while the range of the allowable reduction is the same with

that of Ref. 10, specifically 25-40%, the proposed options with respect to the

form of the reduction are:

22
1) The reduction should refer to the difference between the surface

motion arnd the corresponding motion in the free-field at the

foundation level.

2) The reduction should refer to the difference between the foundation

input motion for a surface supported structure and the corresponding

foundation input motion of the embedded structure.

Based on the above, the options proposed here with respect to the form of the

reduction are only two. as comnpared to the three cases given in Ref . 10. The

case of -reduction with respect to the foundation mat was unanimously rejected

at the SSI Workshop (Ref. 11).

Perhaps the main source of the continuing confusion on this matter is

because we are still having difficulties in expressing this reduction through

the direct and the substructure approaches used in the S51 analysis. In the

direct approach, one starts with a free-field analysis to define the input at

the base of the finite element model of a soil-structure system. Subsequently, this input is applied at the base of this miodel and the SSI response

is computed. On the other hand, in the substructure approach, the concept of

foundation input motion is used. The latter is the response of the rigid

foundation in absence of the superstructure to the free-field motion. Since,

given a design ground motion, the form of the excitation applied to the

soil-structure system is different in the two methods, it is logical to

require that the form of the allowable reduction be suitable for both

methods. It appears that the recommrendation given in Appendix A is more

suitable for the direct method (it can be also applied to the substructure

method) while the recommuendation given in Appendix D is more suitable for the

substructure method. Allowable reduction criteria expressed in terms of the

foundation input motion could not be easily implemented in the direct method,

since the foundation input motion is not computed in the latter method. It

is, however, implicitly included in the SSI analysis.

Now, if the percentage of the allowable reduction of the translational

component of the foundation input motion could be somehow "equivalent" to the

percentage of the allowable reduction in the free-field at the foundation

level then the puzzle would be solved. This brings up the following question:

Is it more appropriate to place a limit on the free-field motion at the

foundation level or on the foundation input motion? one may argue that there

is a better handle of the subject when dealing with the foundation input

motion. The latter is more representative to what actually is seen by the

structure and gives very useful information for appraising the SSI effect. On

the other hand, the foundation input motion is related to the free field.

Specifically, the former is the response of the massless foundation in absence

of the superstructure due to the latter. Consequently, if an exercise of

judgment is made for limiting the horizontal component of the foundation input

motion, this judgment can also be expressed in terms of reduction of the

free-field at the foundation level., The above analogy, however, is not that

straightforward.

23
What is happening in between is that in order to compute the foundation input

motion certain assumptions have to be made regarding the nature of the seismic

waves in the free-field. In several published studies the foundation input

motion has been computed for different foundation configurations .and wave

types. The general effect is that the free-field is basically filtered for

wavelengths which are comparable to the foundation geometry (higher dimensionless frequencies). The resulting foundation input motion has translational

components which are generally lower than the free-field as well as rotational

(rocking and torsional) components. Nonvertically incident P, SV and Rayleigh

waves produce a rocking component while SH waves produce a torsional component. Similar results were obtained in recent, more advanced, treatments of

this problem using noncoherent motions. The main problem, however, still

remains that we do not yet know enough about the combination of wave trains in

a real earthquake environment. In order to guard against potential unconservatism due to insufficient knowledge of the precise character of the seismic

waves, it is more reasonable to impose a limit on the amount of reduction with

respect to the foundation input notion rather than in the free-field at the

foundation level. On the other hand, while free-field motions can be directly

measured (recorded data are available at depths below the surface), this is

not quite clear for the case of foundation input motions.

Finally, if an allowable reduction with embedment is to be specified with

respect to either free-field at foundation level or translational component of

the foundation input motion, then some clarification should be made in terms

of the soil property variation. Specifically, does the reduction refer to the

difference of the surface spectra and the envelope (best estimate, lower bound

and upper bound) of the free-field spectra at the foundation level?

Similarly, does the reduction refer to the difference of the surface spectra

and the envelope (best estimate, lower bound and upper bound) of the translational spectra of the foundation input motion? If it is not the envelope or

say some average for that matter, then do we require that the allowable

reduction be applied to each case (best estimate, lower bound and upper

bound)? Whatever the criteria are, however, the level of uncertainty which is

addressed through them should be adequately identified. At the present time

this is not quite clear.

Recognizing the uncertainties associated with this subject, a reasonable

compromize can be made as follows:

o Reduction of the translational components of the ground motion

with embedment should be permitted in SSI analyses provided

that the relevant rotational components are accounted for.

This is supported by physical considerations of the problem

as well as by recorded data.

o At this time, it is appropriate to impose a limit on the

reduction of the ground motion with embedment. This will

guard against the uncertainties discussed previously in this

section.

24
o The reduction should refer to the difference between the

surface translational motion and the corresponding motion

in the free-field at the foundation level. This form of

reduction has primarily two advantages: a) the reduction can

be conveniently applied to both the direct as well as the

substructure methods of SSI analysis and b) the reduction can

be directly measured with field data.

o The amount of reduction should be reasonably taken in the

range of 30-40%, with the 30% limit being considered as very

conservative.

o The reduction should refer to the envelope (best

estimate, lower bound and upper bound cases) of the

free-field spectra at the foundation level.

In conclusion, the following criteria are recommended at this time with

respect to the variation of ground motion with embedment:

The translational components of the free-field motion at the foundation

level should not be less than 60% of the corresponding surface motion. This

provision should be: a) allowed only when the associated rotational components are accounted for and b) applied in terms of the envelope of the best

estimate, lower and upper bound soil property variation cases.

3.2.6 Limit on Modal Composite Damping

Westinghouse suggested that the composite modal damping used in an SSI

analysis, which is based on modal superposition be limited to 20%. This

suggestion is acceptable and it is recommended that the proposed SRP Revision

2 incorporate the 20 percent limit in Section 3.7.2 as follows:

P. 3.7.2-18 add after "...complex eigenvectors":

o The use of composite modal damping for computing the response

of systems with non-classical modes may lead to unconservative

results. The composite modal damping used in conjunction

with modal SSI analysis should be limited to 20 percent.

o When the composite modal damping exceeds 20 percent, then

generally acceptable methods are a) time domain analysis using

complex modes/frequencies (complex eigenvalue problem)

b) frequency domain analysis or c) direct integration of

uncoupled equation of motion.

3.2.7 Alternate 1 and 2 Requirements

During the December 16, 1988 meeting, the Alternate 1 and 2 approaches of

SSI analysis, which are described in Section 3.7.2 of the proposed SRP

25
Revision 2, were further considered in view of the public comments. These

alternates were proposed at the SSI Workshop (Ref. 11). Specifically,

the SSI analysis procedures were categorized as follows: Alternate 1 which is

associated with enveloping requirements and it is based on broad-banded design

ground response spectra and Alternate 2 which is associated with detailed

state-of-the-art analysis using site-specific ground motion investigations.

Following the SSI Workshop, however, certain changes have been made in

the seismological areas of the SRP. Specifically, Section 2.5.2 of the

proposed SRP Revision 2 has embodied the general philosophy of the Alternate 1

and 2 criteria into the definition of the vibratory ground motion. Specifically, it appears that the requirements of Alternate 1 are reflected in

Section 2.5.2.6 of the proposed SRP Revision 2 through the broad-banded design

response spectra (Item 3, p. 2.5.2-13) while the requirements of Alternate 2

are reflected in the same section by the detailed site-specific ground motion

investigations (Item 1, p. 2.5.2-12). Consequently, it is no longer necessary

to include this distinction in Section 3.7.2.

Based on these observations, it is recommended that the distinction of

Alternate 1 and 2 procedures of SSI analysis be deleted fran Section 3.7.2 of

the proposed SRP Revision 2. This recognizes that alternative ground motion

options are to be included in Section 2.5.2 of the SRP.

26
3.3 Other Issues

3.3.1 Requirements for Modal Combination

In the public comments (Sargent and Lundy, Westinghouse) it was suggested

that the acceptance criteria on modal combination of the proposed SRP Revision

2 should allow for algebraic sum method. Specifically, the proposed SRP

Revision 2 refers to Reg. Guide 1.92 which in turn does not permit the use of

the algebraic sum method.

This suggestion was found unanimously acceptable by the present review of

public comments. Specifically, it is concluded that there is adequate basis

in support of the algebraic sum method as an acceptable method to perform

modal combination. It is further recommended that a resolution of this issue'

be made by modifying appropriately Reg. Guide 1.92 to reflect the

acceptability of the algebraic sun method. The proposed SRFP Revision 2 should

be issued with the condition that the Reg. Guide 1.92 be revised accordingly.

3.3.2 Correlation of Damping and Stress Levels

The following paragraph was added in the proposed SRP Revision 2

(p. 3.7.1-12):

"In addition, a demonstration of the correlation between

stress levels and damping values will be required and

reviewed for compliance with regulatory position C.3 of

Reg. Guide 1.61."

Public comments suggest that more reasonable requirements are provided in item

3.1.2.2 of the ASCE Standard 4-86 (p. 10, Ref. 9) which should be used in

place of the above.

This suggestion was considered in the present review of public comments

and was found acceptable. Accordingly, it is recommended that the provision

3.1.2.2 of ASCE Standard 4-86 be considered in the proposed SRP Revision 2 as

acceptable criteria for demonstrating correlation between stress levels and

damping values.

3.3.3 Greater Use of Professional Society Consensus Standards

As a result of the review of the public comments, it is strongly recommended that the proposed SRP Revision 2 should make reference to available

standards of professional societies and other organizations.

27
4.0 RECOMMENDATIONS

The recommendations given in Section 3.0 are summarized here for

convenience as follows:

(I): Input Ground Motion Requirements

" It is recommended that the PSD criteria (form of target PSD

as well as the 15% requirement to meet the target PSD) of

the proposed SRP Revision 2 be replaced with the minimum PSD

requirements given in the Appendix B of this report. Furthermore, it should be made clear in the SRP that the design

response spectra are the primary acceptance criteria while

the PSD requirements are secondary.

o It is recommended that the following items be further

considered by the NRC:

- PSD requirements for other types of generic

design spectra.

- PSD requirements for horizontal/vertical components.

- PSD requirements for site-specific input spectra.

- Should PSD representations of the seismic input be

also used in other aspects of seismic analysis?

o It is recommended that criteria on the duration of input

design time histories be implemented in the SRP as follows:

- Total duration: 10-25 seconds

- Strong motion duration: Minimum = 6 seconds

Maximum = 15 seconds

A provision should be made for acceptance of other durations on a

case-by-case basis.

o It is recommended that the current SRW requirement of

minimum 5 time histories for multiple time history analysis

be reduced at the present time to 4. Further reduction

should be done only after additional investigation of this

subject.

o It is recommiended that the vertical design spectra be

taken as 2/3 of the corresponding horizontal over the

complete frequency of interest. The 2/3 rule should not

be permitted in the following cases:

28
o Small epicentral distances (e.g., less than

10-15 km).

o When the horizontal design spectrum is obtained

through the site-specific approach given in

item 1 of SRP Section 2.5.2.6.

(II): Soil-Structure Interaction Requirements

o It is recommended that the definition of rock-like materials

per ASCE Standard 4-86 be adopted in the SRP.

o It is recommended that the ASCE Standard 4-86 provision for

fixed-base assumption be accepted in the SRP for fixed-base

frequencies of 10 cps or less.

o It is recommuended that the enveloping requirement of results

from different SSI methods be deleted from the SRP.

o It is recommended that the following clarifications/criteria

be given in the SRP with regard to soil properly variations:

o The shear modulus and the soil damping of hysteretic

type used in the SSI analysis should be compatible

with the effective shear strains (65% of corresponding

peak values) associated with the free-field analysis

of the design ground motion.

o The low strain 4best estimate shear modulus should be

defined at 10- percent shear strain. The low and

upper bound shear moduli at low strain should be

defined as half and twice this value respectively.

o The lower bound shear moduli should not be less

than those required for an acceptable foundation

design.

o The upper bound shear moduli should not drop at any

shear strain below the value of the best estimate at

low strain.

o It is recommended that the current 5% limit on soil damping

of hysteretic type be changed to 15%. Furthermore, the

ASCE Standard 4-86 definition of hysteretic damping or

other equivalent be specified in the SRP.

o The translational components of the free-field motion at

the foundation level should not be less than 60% of the

corresponding surface motion. This provision should be:

a) allowed only when the associated rotational components

29
are accounted for and b) applied in terms of the envelope

of the best estimate, lower and] upper bound soil property

variation cases.

" It is recomme~nded that when modal superposition is used in

the SSI analysis, the modal damping be limited to 20%.

If the comrposite modal damping is higher than 20%, then

acceptable methods should be; a) time domain analysis

based on solution of complex eigenvalue problem b) frequency

domain analysis or c) direct integration.

o It is recommended that alternate 1 and] 2 procedures of SSI

analysis be deleted from SRP Section 3.7.2 and their design

philosophy be associated with the specification of the

vibratory ground motion (Section 2.5.2).

(III): other Issues

" It is recommuended that the algebraic sum method in modal

combination be accepted in the SRP by appropriately

revising Reg. Guide 1.92 to that effect.

" It is recommended that the provisions of the ASCE Standard

4-86 on correlation of damping with stress levels be an

acceptable procedure in the SRP.

o It is recommended that the SWP make reference to available

standards of professional societies and other organizations.

It should be realized that these recommendations involve some level of

judgment resulting from the fact that the current state-of-the-art does not

permit a complete resolution of certain issues. It is to be expected that

refinements may be justified in these areas based on future research. Therefore it is recommended that a mechanism be established for reviewing the SRi'

at some regular intervals (perhaps every five years).

Finally, it is strongly recommended that the following subjects be

considered by the NBC for future research: a) development of PSD criteria for

other than reg. Guide 1.60 spectra and b) investigation of spatial variations

of free-field motions.

30
5.0 REFERENCES

1. Proposed Revision 2 to Standard Review Plan, Sections 2.5.2, 3.7.1, 3.7.2

and 3.7.3, U.S. Nuclear Regulatory Comnission (53 FR 20038; June 1, 1988).

2. NUREG-1233, "Regulatory Analyses for USI A-40, Seismic Design Criteria,

Draft Report for Comment," S.K. Shaukat, N.C. Chokshi, N.R. Anderson,

U.S. Nuclear Regulatory Commission, April 1988.

3. Sargent and Lundy Engineers: Conmnents on Proposed Revision 2 to Sections

2.5.2, 3.7.1, 3.7.2, 3.7.3 of NLJREG-0800 (SRP) and questions on SoilStructure Interaction. Letter from B.A. Erler to R. Baer, NRC dated

July 29, 1988.

4. Westinghouse Comments on the Proposed Resolution for Unresolved Safety

Issue (USI) A-40, "Seismic Design Criteria." Letter from W.J. Johnson to

R. Baer, NRC dated July 20, 1988.

5. Stevenson & Associates Comments. Letter to R. Baer, NRC dated July 25,

1988.

6. Duke Power Company Comments: NRC Proposed Resolution for USI A-40

"Seismic Design Criteria." Letter from H.B. Tucker to R. Baer, NRC dated

July 25, 1988.

7. General Electric Company: Comments on Proposed Revision 2 to SRP

Sections 2.5.2, 3.7.1, and 3.7.2, and Comments on Questions Related to

the Lotung SSI Experiment. Letter from R. Mitchell to R. Baer, NRC dated

August 1, 1988.

8. Electric Power Research Institute: Comuents on Proposed Revision 2 to

Sections 2.5.2, 3.7.1, 3.7.2 and 3.7.3 of NUREG-0800, Standard Review

Plan, Draft NUREG-1233 and on the Specific Questions Related to the

Lotung Soil-Structure Interaction Experiment. Letter from J.C. Stepp to

R. Baer, NRC dated October 4, 1988.

9. ASCE Standard 4-86: Seismic Analysis of Safety-Related Nuclear

Structures and Commentary on Standard for Seismic Analysis of Safety

Related Nuclear Structures, ASCE, September 1986.

10. NUREG/CR-1161: "Recommended Revisions to Nuclear Regulatory Commission

Seismic Design Criteria," D.W. Coats, May 1980.

11. NUREG/CP-0054: "Proceedings of the Workshop on Soil-Structure

Interaction," H.L. Graves, A.J. Philippacopoulos, eds., June 1986.

12. NUREG/CR-3509: "Power Spectral Density Functions Compatible with NRC

Regulatory Guide 1.60 Response Spectra," M. Shinozuka, T. Machio,

E.F. Samaras, June 1988.

31
APPENDIX A

COMMENTS ON PROPOSED REVISIONS

TO STANDARD REVIEW PLAN

SEISMIC PROVISIONS

Prepared for

Brookhaven National Laboratory

by

R. P. KENNEDY

JANUARY 1989
1. Introduction

Around May 1988, the U.S. Nuclear Regulatory Commission (NRC)

issued Proposed Revision 2 to Sections 2.5.2, 3.7.1, 3.7.2, and

3.7.3 of their Standard Review Plan, NUREG-0800 (1) for public

review and comment. Prior to August 30, 1988, comments (2) had

been received from five organizations (Sargent & Lundy, Westinghouse, Stevenson & Associates, Duke Power Company, and General

Electric). As a contractor to the U.S. Nuclear Regulatory Commission, Brookhaven National Laboratory has been requested to

assist the NRC in resolving these public comments. As part of

this effort, Brookhaven has formed a panel of consultants in the

field of seismic analysis and design of nuclear power plants to

review these public comments and to recommend resolutions. I am

one member of this panel.

I have carefully reviewed each of the public comments contained

in Reference (2). The comments are all of excellent quality and

each points to areas of the Proposed Revision 2 (1) where improvements should be made. These comments can be broken down

into the following topic areas:

* Earthquake Ground Motion Power Requirements--SRP Section

3.7.1 (Seismic Design Parameters), Subsection II (Acceptance Criteria), Item lb (Design Time History), pages

3.7.1-10 and 11.

* Time History Strong Motion Duration and Time Envelope

Function Requirements--SRP Section 2.5.2 (Vibratory Ground

Motion), Subsection II (Acceptance Criteria), page 2.5.2-14.

A-I
" Ratio of Vertical to Horizontal Ground Motion Requirements-- SRP Section 3.7.1, Subsection II, Item la (Design

Response Spectra), page 3.7.1-8.

" Multiple Time-History Requirements--SRP Section 3.7.1,

Subsection II, Item lb, page 3.7.1-11.

" Soil-Structure Interaction Requirements--SRP Section 3.7.2

(Seismic System Analysis), Subsection II (Acceptance

Criteria), Item 4 (Soil-Structure Interaction), pages

3.7.2-9 through 12.

" Dampinq Requirements--SRP Section 3.7.1, Subsection II,

Item 2 (Percentage of Critical Damping Values), page

3.7.1-12.

" Modal Combination Requirements--SRP Section 3.7.2, Subsection II, Item 7 (Combination of Modal Responses), page

3.7.2-16.

* Greater Use of Professional Society Consensus Standards--

General comment on all sections.

Based upon my review of the public comments (2) plus my own

considerations, I make specific recommendations for each of the

affected sections of the Proposed Revision 2 (1) in the following

sections of this brief report.

2. Earthquake Ground Motion Power Requirements

Prior to the proposed revision, the Standard Review Plan (SRP)

had no explicit requirements for the design earthquake ground

motion power throughout the frequency range of interest. All

that was required was that the design ground motion time history

produce a response spectrum which essentially envelopes the

A- 2
design earthquake response spectrum at corresponding damping

levels. As an extreme example, a 0.6 Hz steady-state single

frequency sinusoidal 0.85g ground motion will totally envelope

the R.G. 1.60 Spectrum for a 0.2g earthquake. Theoretically,

this 0.85g sinusoidal ground motion could be used to generate

floor spectra and for equipment design and qualification because

it envelopes the required design response spectrum for a 0.2g

SSE. However, all nuclear power plant civil structures (2 Hz and

higher frequency) would respond in a cyclic pseudo-static manner

to such a low frequency sinusoidal input motion, because this

input motion has no power in the frequency range of 2 Hz or

higher. Thus, there would be no resonant amplification of this

input motion by the civil structures, so that equipment mounted

in such structures would only be subjected to this input motion

without amplification. Floor spectra generated from such an

input would be much less than that generated by broad-frequency

content earthquake ground motion at the structure's resonant

frequencies and at higher frequencies, even though the input

ground motion response spectrum enveloped the design earthquake

response spectrum at all frequencies. Such an extreme and obvious example would never be allowed in practice, even though it

might be argued that it meets the existing Standard Review Plan

requirements. However, to a lesser extent, this same reduction

in floor spectra occurs even with broad frequency input time

histories when such time histories are significantly deficient in

power over a frequency band of about ±20% centered on any of the

important structure natural frequencies. Thus, for a.7 Hz structure, floor spectra can be severely underestimated when an input

motion deficient in power over the 5.6 to 8.4 Hz range is used as

input, even though it has excess power at other frequencies so

that its response spectrum envelopes the required earthquake

design spectrum at all frequencies. Within my experience, this

latter situation has occurred in a few instances within the

nuclear industry. Therefore, I fully support proposed revisions

to the Standard Review Plan which place broad frequency power

requirements on design earthquake ground motion time histories.

A-3
There are at least two methods to ensure adequate power throughout the frequency range of interest. One method would be to

require the input motion time history to produce a low damped

(2% damping) response spectrum that closely matches the design

response spectrum over the entire frequency range. In this way,

excess power over one frequency range would not be allowed to

mask a deficiency in power within another frequency range, since

the response spectrum in the frequency range of excess power

would greatly exceed the design response spectrum. An input time

history that produces an input response spectrum which closely

matches the design response spectrum at low damping over the

entire frequency range from 0.4 to 33 Hz must contain power

throughout this frequency range consistent with that of the

design response spectrum. However, how close this match must be

over the entire frequency range is not clear. Furthermore, the

difficulty of achieving a close match at all frequencies has not

been fully investigated. Probably it would be sufficient to

require that the input motion produce low damped spectral accelerations which do not average more than 20% above the design

response spectrum over any ±20% frequency band width (i.e., 4 to

6 Hz band width for 5 Hz) and do not dip more than 10% below the

design response spectrum at any frequency (current requirement).

However, this requirement may be difficult to meet.

A second approach is to directly define the minimum power

requirements as a function of frequency. I prefer this approach

because it directly defines the minimum power requirements within

various frequency ranges. This approach has been proposed in the

revision to the Standard Review Plan in which the average PowerSpectral-Density (PSD), So(w), over any 0.15 Hz frequency band

between 0.2 Hz and 34 Hz be at least 85% of the following target

value:

.= S 1 + 3.836 (w/wg)2 (2.1)

0 M-0 (W/g)2]2 + 3.836 (w/wg)2

A-4
with So = 1,100 in 2 /sec 3 for a peak acceleration, A, of Ig, and

wg = 10.66 rad/sec. For other peak accelerations, the factor So

is scaled proportional to A2 . I support the idea of establishing

minimum PSD requirements. However, I have several concerns with

regard to Equation (2.1).

First, for earthquake time histories, the reported values for a

PSD can vary widely depending upon the exact formulation used to

compute the PSD. Each of the following three factors must be

defined with regard to Equation (2.1):

1. Either a one-sided or a two-sided PSD can be specified.

It should be clearly specified that Equation (2.1)

represents a one sided PSD.

2. Even specifying that Equation (2.1) is a one-sided PSD

is insufficient. Different relationships between the

one-sided PSD and Fourier Amplitude IF(w) I exist

between common textbooks and within existing practice.

The one-sided PSD is specified as either

SO(W) = (2.2a)

271 TD

or

G ~2 I F(w) I2(22) GO (W) = W (2.2b) TD

where TD is the strong motion duration over which F(w)

is evaluated. The relationship between these two

different definitions of the one-sided PSD is

SO(M) = GO(w) (2.2c) 2 T

Throughout this brief report, I will use the symbols

SO(w) and GO(w) to distinguish between those two

A-5
definitions. I don't care which definition is used.

However, the Standard Review Plan should clearly

specify which relationship between PSD and Fourier

Amplitude (Equation (2.2a) or Equation (2.2b)) is being

used. The coefficient So in Equation (2.1) is based

upon the PSD being defined by Equation (2.2a). If

Equation (2.2b) is preferred, then So = 1,100 in 2 /sec 3

should be replaced by Go = 6,900 in2/sec3 in Equation

(2.1).

3. For earthquake time histories, some people determine

the Fourier Amplitude over the entire duration of the

record, while others determine the Fourier Amplitude

only over the strong motion duration within which the

power is near maximum. Whichever duration is used, the

same duration should be used in the denominator of

Equations (2.2). If the power is nearly stationary, it

is irrelevant which duration is used to determine the

Fourier Amplitude, so long as this same duration is

used in Equations (2.2). However, for most actual

records, the power is only stationary over the duration

of strong motion, TD, during which the power is near

maximum. This strong motion duration is discussed

further in the next section. Over a longer duration,

the average power is less. Equation (2.1) was

developed so as to be applicable during the time of

maximum power. When a PSD is developed from an input

motion time history for comparison with Equation (2.1),

the actual PSD should be based on using the duration of

near maximum power. Otherwise excess conservatism can

be introduced by the comparison.

However, even beyond the need for additional clarification, I

have other reservations about Equation (2.1). In my opinion,

the Design Ground Motion should be primarily defined by the

Design Response Spectrum. The PSD requirement is a secondary

A- 6
requirement which is simply used to prevent a severe deficiency

of power over any frequency range. The PSD requirement should

not be used to add additional conservatism beyond that contained

in the Design Response Spectrum. Any ground, motion time history

which produces a response spectrum that closely fits the Design

Response Spectrum should be able to pass the PSD requirement.

However, this situation will not be the case with the PSD

requirement given by Equation (2.1). Reference (a) presents

results for seven artificial time histories (Nos. 1-3, 6, and 8-

10) which have PSD levels similar to those expressed by Equation

(2.1). Figure 1 shows a representative example PSD from one of

these time histories (jagged line) versus the Equation (2.1) PSD

requirement (smooth solid line). Figure .2 shows the response

spectrum from this PSD versus the R.G. 1.60 Response Spectrum.

In every case, the PSDs fall below Equation (2.1) and appear to

average about 90% of the required PSD below about 6 Hz and even

less at higher frequencies. Even so, the resultant response

spectra are consistently higher than the R.G. 1.60 Response

Spectrum. Below 6 Hz, the exceedance appears to average about

20% and is much greater at high frequencies (about 70% at 30 Hz).

Thus, the Equation (2.1) PSD requirement will add additional

conservatism beyond that contained in the R.G. 1.60 Spectrum,

particularly at higher frequencies.

Reference (4) studied the engineering characterization of ground

motion. It concluded that the Cumulative PSD as defined by:

Cum GO(W) = foGO(W) dw (2.3)

is an important descriptor of the ground motion. In particular,

if one defines fl 0 , f 5 0 , and f 9 0 as the frequencies below which

10%, 50%, and 90% of the cumulative power occurs, then fl 0 ' f 5 0 '

and f 9 0 were found to be very important descriptors of the ground

motion. Table 1 reports Cum GO(w), fl 0 , f 5 0 1 and f 9 0 for an

artificial time history which produced a Response Spectrum which

A-7
very closely fits the R.G. 1.60 Spectrum plus 6 actual earthquake

ground motion records (Olympic, Taft, El Centro No. 12, Pacoima

Dam, Hollywood Storage Lot, and El Centro No. 5) which produced

both elastic and inelastic response very similar to that produced

by the artificial time history when scaled to an effective acceleration, ADE. This effective acceleration, ADE, and actual(peak

ground acceleration, A, are also given in Table 1. Lastly, a

Scaled Cum GO(60) appropriate for comparison with a ig R.G. 1.60

Spectrum is obtained from:

Scaled Gum G ON) . 2 (Cum G O(M)) (2.4)

Figure 3 presents plots of the Cum PSD for each of these seven

records, as reproduced from Reference (4). All seven of these

records have similar characteristics, which accounts for the

similarity in elastic and inelastic response produced by these

records. These characteristics are:

1. Negligible power above about 12 Hz (see slope of

Cumulative PSD curves in Figure 3)

2. Scaled Cumulative PSD between 0.49g2 and 0.71g 2 for an

effective peak acceleration of 1.0g

3. fl 0 between 0.55 and 1.20 Hz; f 5 0 between 2.15 and

3.30 Hz; f 9 0 between 5.50 and 7.90 Hz

Reference (4) also showed that the effective acceleration, ADE,

at which the R.G. 1.60 Spectrum needed to be anchored to produce

linear and nonlinear responses similar to those from the six

actual records could be accurately estimated from:

ADE1 = Kp ARMS

A-8
where ARMS is the root-mean-square acceleration and Kp is a mean

peak factor as defined in Reference (4). For the artificial time

history, Kp was 3.04 and ranged from 3.21 for the longest time

history (Olympia) to 2.71 for the shortest (El Centro #5), with

an average of 2.98 for the six actual records. Thus, a Kp value

of 3.0 is a reasonable average for these seven records.

In turn, the RMS acceleration is related to the cumulative PSD

by:

A2MS = Cum S

A2 Cum GOM()

RMS 2 7

depending upon whether the PSD is defined by Equation (2.1a) or

(2.1b). For an ADE = 1.0g and Kp = 3.0, the ARMs should be 0.33g

and

Cum SO(w) = 0.11g 2

Cum GO(w) = 0.70g 2

Thus, for a 1.0g R.G. 1.60 Response Spectrum, the Cum GO(w)

should not exceed 0.70g 2 . To prevent the PSD requirements from

generally controlling and to enable the R.G. 1.60 Response

Spectrum to generally control, I recommend that the Cum GO(w) be

established at about 0.63g 2 , which is midway within the range

presented in Table 1 for the seven time histories presented.

Also presented in Table 1 are the Scaled Cumulative PSD, fl 0 '

f50, and f 9 0 values corresponding to the PSD being defined by

Equation (2.1). Since Table 1 is in terms of Cum GO(w), a Go

value of 6,900 in 2 /sec 3 is used in Equation 2.1 in lieu of the So

value of 1,100 in 2 /sec 3 - One should note that the Scaled

Cumulative PSD from Equation 2.1, when put on a common basis, is

approximately three times as great as for the seven records

A-9
presented in Table 1. In addition, f 9 0 is 17.0 Hz, which is out

of line with f 9 0 of about 6.6 Hz for the seven records studied.

Table 2 compares the cumulative power predicted over various

frequency ranges from Equation (2.1) with that given by the

artificial R.G. 1.60 time history studied in Reference (4).

Below 6.55 Hz, the power given by Equation (2.1) needs to be

reduced by a factor of about 2.50, while above 6.55 Hz the

cumulative power produced by Equation 2.1 is about 7.0 times

too great.

Based upon a review of the Cumulative PSD plots presented in

Figure 3 and the power characteristics given in Table 1, I

recommend the following revised PSD requirements. From 0.4 Hz

to 15 Hz, the average one-sided PSD over any ±20% frequency band

width centered on a frequency f (i.e., 4 to 6 Hz band width for

f = 5.0 Hz) computed over the strong motion duration should

exceed:

0.4 Hz to 15.0 Hz

GO(f) Ž 20,000 in 2 (f)-2.1 < 3,500 in 2 (2.5)

sec 3 sec 3

and Cum Go 0.63g2

for a 1.0g peak ground acceleration with GO(f) scaled proportional to the square of the peak ground acceleration for other

ground accelerations. Note that Equation (2.5) is consistent

with the one-sided PSD being defined by Equation (2.2b). If it

is decided that the one-sided PSD should be defined by Equation

(2.2a) as is the case for Equation (2.1), then Equation (2.5)

should be converted as defined by Equation (2.2c). Equation

(2.5) is much more consistent with the Cumulative PSD results

for all seven time histories reported in Table 1land shown in

Figure 3. As shown by Tables 1 and 2, Equation (2.5) produces a

Cumulative PSD within each frequency band approximately 85% of

A-10
that obtained from the artificial R.G. 1.60 time history. It

also produces the same f1 0, f 5 0 , and f 9 0 frequencies as does the

artificial time history. Table 3 compares SO(f) from Equation

(2.5) after being converted using Equation (2.2c) with SO(f) from

Equation (2.1). My recommendation differs from the proposed SRP

in the following ways:

1. No power requirements exist for frequencies below 0.4

Hz. Power below this frequency is immaterial to the

seismic performance of nuclear power plant structures

and equipment. Furthermore, the requirements of

Equation (2.5) become excessively conservative below

about 0.4 Hz, since most of the earthquake records show

a substantial power dropoff below about this frequency.

2. No power requirements exist for frequencies above 15 Hz.

All seven studied records which produce Response Spectra

similar to the R.G. 1.60 Spectrum have negligible power

above about 12 Hz. Equation (2.5) becomes excessively

conservative above about 12 to 15 Hz. The R.G. 1.60

Spectrum can be accurately matched by ground motion

records which contain essentially no power above about

15 Hz, and such records are representative of the actual

earthquake records upon which the R.G. 1.60 Spectrum is

based.

3. The average power over a ±20% frequency band width is

compared to Equation (2.5) as opposed to comparing the

average power over a 0.15 Hz band width with 85% of the

power from Equation (2.1). Actual PSD plots have substantial peaks and valleys. In my opinion, it is the

average power over a frequency band which is the important ground motion characteristic and not a very narrow

(0.15 Hz), but deep valley. It is very difficult to

produce a smooth PSD at frequencies above about 5 Hz

(see Figure 1), and a requirement that a narrow 0.15 Hz

A-1I
wide valley exceed a target PSD will produce excessive

conservatism at higher frequencies..

4. The Equation (2.5) one-sided PSD ranges from 46% at

0.4 Hz to 21% at 15 Hz of the Equation (2.1) PSD.

5. The one-sided PSD requirement specified by Equation (2.5)

introduces no excess conservatism in the design response

spectrum. The R.G. 1.60 artificial time history used in

Reference (4) meets the PSD requirements of Equation

(2.5) throughout the frequency range of 0.4 to 15 Hz.

The six actual records given in Table 1 can be Fourier

Amplitude adjusted (retaining their Fourier Phase

Spectra) to produce a smooth R.G. 1.60 Response Spectrum

while meeting the PSD requirements of Equation (2.5).

The PSD limits defined by Equation (2.5) are appropriate when the

required response spectrum is that defined by R.G. 1.60. When a

different required response spectrum shape is specified, the PSD

limits must be correspondingly adjusted. For instance, with a

NUREG/CR-0098 median rock site spectrum shape, the specified PSD

limits should be only 60% of those specified by Equation (2.5)

over the entire frequency range because of the lesser amplifications with this spectrum shape. Alternately, if a spectrum shape

with a substantially enriched high frequency content and lesser

lower frequency content were specified such as those currently

being considered for the east, the PSD limits should be enriched

for the higher frequencies and reduced for lower frequencies.

3. Time History Strong Motion Duration and Envelope Function

In addition to specifying the characteristics of input motion in'

terms of a required response spectrum plus minimal PSD provisions, some requirements on strong motion duration and/or a

time-envelope function should be specified which are consistent

A-12
with earthquake ground motion records from'which the required

response spectrum was developed. Reference (4) suggests that the

strong motion duration, TD, of an input motion time history should

be defined as the time over which the power is near its maximum.

In turn, the power is simply the slope of a cumulative energy plot

where cumulative energy E(t at the time, tI is given by:

t11

ti

E(t 1~I {A2 f (t) dt (3.1)

0-

where A(t) is the acceleration at time t. Figure 5 shows a

cumulative energy plot from a representative time history.

All seven time histories listed in Table 1 produce cumulative

energy plots similar to that shown in Figure 5. For most time

histories, Reference (4) recommends that the strong motion duration, TD (duration of near maximum power) can be defined by:

TD = T 0 . 7 5 - T0 . 0 5 (3.2)

where T0 . 7 5 and T0 . 0 5 are the times at which 75% and 5%, respectively, of the cumulative energy are reached. For the time

history shown in Figure 5 (El Centro #12), this strong motion

duration is 9.6 seconds. For the six actual records listed in

Table 1 which produce spectra similar to the R.G. 1.60 response

spectrum, TD ranges from 3.4 to 15.6 seconds. In my opinion,

time histories consistent with the R.G. 1.60 response spectrum

should have strong motion duration based upon Equation (3.2) of

5.0 to 16.0 seconds.

The use of strong motion duration in excess of 16 seconds can

lead to either of the following unrealistic anomalies:

1. The high frequency power can be concentrated near the

start of the record with the low frequency power concentrated near the end of the record. In this way the high

A-13
and low frequency modes of a 5% or more damped structure

will not combine because the high frequency response is

damped out before the low frequency response becomes

strong. Thus, combined response can be severely

unconservatively biased.

2. Alternately, if random phasing is used for all Fourier

harmonics, then modes have an increased probability of

coming into essentially worst-case phasing (absolute sum

combination) at some time as strong motion durations are

increased to very long times. Thus, combined responses

can be severely overestimated when excessively long

strong motion durations are used.

When strong motion durations of 20 seconds or longer are used,

combined responses of multi-mode systems can be either severely

overestimated or severely underestimated, depending upon how the

phasing of different Fourier harmonics is handled. To avoid these

problems, the use of artificial time histories with strong motion

durations in excess of about 16 seconds should not be allowed.

One method to develop an artificial input time history for use in

design is to first choose an actual earthquake time history which

produces a response spectrum shape close to the required response

spectrum shape (such as the R.G. 1.60 response spectrum shape)

and an appropriate strong motion duration. Then the Fourier

phase spectrum from this time history is retained and the Fourier

amplitudes are adjusted, frequency by frequency, until the

resulting response spectrum closely envelopes the required

response spectrum. When this method is used, it is unnecessary

to define a time-envelope function (Figure 4). I prefer this

approach because the resultant artificial time history is assured

of being like that produced by an earthquake except that the

resulting response spectrum is smooth. Many records have an

appropriate strong motion duration, TD, as defined by Equation

(3.1) and spectrum shape so that they may be used as the "seed"

A-14
record in this approach when the required response spectrum is

either defined by R.G. 1.60 or NUREG/CR-0098. Among these are the

first five actual records defined in Table 1. The only problem

with the sixth reco-rd (El Centro #5) is that its strong motion

duration is only 3.4 seconds, which might be undesirably short.

Alternately, one might start with a random Fourier phase spectrum. When this is done, it is also necessary to establish a

deterministic time-envelope function such as that shown in Figure 4. With this method, one must specify a time of maximum

power, tm, a rise time, tr, and a decay time, td. Reference (4)

showed that both peak elastic and inelastic responses are primarily determined by the portion of the time-history record

at which the power is near its maximum. Therefore, the strong

motion duration, TD, is only slightly greater than tm when a

Figure 4 envelope function is used. Thus, to achieve a strong

motion duration between 5 and 16 seconds, tm should be specified

between 4 and 15 seconds. The rise and decay time durations are

relatively unimportant but should typically be taken to be about

1/7 and 5/7 of tm, respectively. Use of tm durations longer than

about 15 seconds, or total durations longer than about 28 seconds,

should not be allowed because such long durations can lead to the

previously enumerated anomalies. Also, tm durations much less

than 4 seconds are inconsistent with a R.G. 1.60 response spectrum

shape.

4. Ratio of Vertical to Horizontal Ground Motions

I note that all guidance has been removed from SRP Section 3.7.1

(Seismic Design Parameters), Subsection II (Acceptance Criteria),

Item la (Design Response Spectra) on the recommended relationship

between vertical and horizontal response spectra, and that no

guidance has been added to Section 2.5.2 (Vibratory Ground

Motion) on this subject when site-specific response spectra are

not developed. In my opinion, this deletion leaves an obvious

A- 15
deficiency. I concur with Sargent & Lundy and General Electric

(2) that in most cases the provisions of Section 2.2.2.2 of the

ASCE Standard 4-86, "Seismic Analysis of Safety Related Nuclear

Structures" (5), should be permitted. These provisions state that

the vertical spectra should be taken as two-thirds of the

horizontal spectra throughout the entire frequency range. In my

judgment, such a provision is reasonable except when the design

earthquake has an epicentral distance less than about 10

kilometers. In this latter case, the vertical spectra are

likely to exceed two-thirds of the horizontal spectra at frequencies of about 8 Hz and greater, and need special

consideration.

5. Requirements for Use of Multiple Time Histories

Multiple time history analysis should be strongly encouraged. In

my opinion, the requirement that when multiple time history

analyses are performed, "as a minimum, five time histories should

be used for analysis," as stated on page 3.7.1-11 of Section

3.7.1 of Ref. (1), will discourage the use of multiple time

history analyses (for instance, see both the Sargent & Lundy and

the Westinghouse comments). I recognize that this requirement

was recommended by the Task Action Plan A-40 Seismic Consultants

to Lawrence Livermore Laboratory (of which 'I was a member) back

in 1979, as documented in Reference (6). However, since that

time considerable discussion on this subject occurred in the

ASCE Working Group on Seismic Analysis of Safety Related Nuclear

Structures, of which I was Chairman. In 1986, the consensus of

this Working Group was published in the ASCE Standard 4-86 (5).

I believe that the provisions of Section 2.3.1 of Reference (5)

and the corresponding Commentary Section C.2.3.1 on the subject

of multiple time history requirements are preferable to the

response spectra and minimum number provisions contained on page

3.7.1-11 of Reference (1). The PSD provision on page 3.7.1-11

should be retained. This change will provide greater

A- 16
flexibility, will encourage the use of multiple time histories,

and will answer the objections of both Sargent & Lundy and

Westinghouse (See Reference 2).

6. Soil-Structure Interaction Requirements

A number of public comments (2) were made to the proposed

revisions (1) to Section 3.7.2, Subsection II, Item 4 (SoilStructure Interaction), pages 3.7.2-9 through 12.

6.1 Fixed-Base Analysis

I concur with Sargent & Lundy (2) in their recommendation that

the provisions of Section 3.3.1.1 of the ASCE Standard 4-86 (5)

can be used to define when a fixed-base analysis is adequate.

The sentence additions to pages 3.7.2-9 and 10 of Reference (1)

recommended at the top of page 3 of the Sargent & Lundy letter. is

an acceptible way to incorporate these provisions.

6.2 Requirements for Two Methods of Analysis Under Alternate 1

Under Alternate 1 for Soil-Structure Interaction, page 3.7.2-9 of

SRP 3.7.2 (1) requires that both half-spare and finite boundary

methods be used to perform the soil-structure interaction

analysis. I concur with the comments of Sargent & Lundy,

Westinghouse, and General Electric in Reference (2) that this

requirement is no longer necessary, imposes a severe penalty in

some cases, and should be deleted.

6.3 Limits on Stiffness Reduction with Increased Strain and

Material (Hysteretic) Damping

I strongly believe that there is considerable uncertainty as to

how much the shear modulus of soils reduces when subjected to

high seismic strains. However, the provision 2 on page 3.7.2-12

A- 17
of SRP 3.7.2 (1) does not seem to allow for any reduction in

shear modulus even for the best-estimate shear modulus at seismic

strain levels. If I have interpreted this provision correctly, I

believe it will lead to too stiff of soil modeling, since provision 4 requires that lower bound and upper bound soil moduli

generally be taken as one-half and twice the best-estimate soil

modulus. If the best-estimate shear modulus is taken as the

low-strain value, then the lower bound would only be reduced to

half of the low-strain value and the upper bound would be twice

the best-estimate low-strain value. By this approach, both the

lower bound and upper bound shear moduli will be too stiff.

The best-estimate shear modulus under seismic strains should be

allowed to be reduced for increased strains in accordance with

the best available geotechnical evidence. However, a lower limit

should be placed on the upper bound shear modulus to be used in

SSI analyses. The upper bound shear modulus at seismic strains

should not be allowed to be taken as less than 80% or 90% of the

best-estimated low-strain (i0-3 to 10-4) shear modulus. This

restriction adequately guards against uncertainty as to how much

the shear modulus of soils reduces at high seismic strains.

The limit of provision 2 on page 3.7.2-12 of SRP 3.7.2 (1), that

material (hysteretic) damping is not expected to exceed about 5%

of critical, is too restrictive. A 15% limit, as recommended in

Reference (6), is more appropriate.

6.4 Vertical Spatial Variation of Ground Motion

Considerable uncertainty exists with regard to the vertical

spatial variation of ground motion. When the design control

motion is defined at the free ground surface (as it generally

should be), and the ground motion at the foundation level for a

partially embedded structure is obtained by deconvolution of the

free ground surface motion, a limit should be imposed on how much

the ground motion is allowed to be reduced with depth. In

A- 18
recognition of the uncertainty in vertical spatial variation of

ground motion, the ASCE Standard 4-86 (5) states in Section

3.3.1.2(b) that "the spectral amplitude of the acceleration

response spectra in the free field at the foundation depth shall

be not less than 60% of the corresponding design response spectra

at the finish grade in the free field." I concur with

Westinghouse (2), that. this limit should be imposed in SRP

Section 3.7.2, Subsection II, Item 4 (Soil-Structure

Interaction).

7. Damping Requirements

Paragraph 2 on page 3.7.1-12 of SRP Section 3.7.1, Subsection II,

Item 2 (Percentage of Critical Damping Values) of Reference (1)

defines the correlation between stress levels and damping values.

I concur with the Sargent & Lundy comment on the bottom of page 2

of their letter (2), that the requirements for correlation

between damping values and stress levels defined in Section

3.1.2.2 of ASCE 4-86 (5) are more reasonable and should be

substituted.

8. Modal Combination Requirements

On page 3.7.2-16, Item 7 (Combination of Modal Responses) of SRP

Section 3.7.2, Subsection II (1) refers to Reference (7) for the

combination of closely spaced modes. I concur with the comment

of both Sargent & Lundy and Westinghouse (2) that requirements of

Reference (7) for closely spaced modes are overly conservative

and that Reference (7) should be revised to allow the algebraic

sum of closely spaced modal responses in accordance with Equation

(3200-16) of ASCE 4-86 (5) and the recommendations of References

(6) and (8).

A-19
9. Greater Use of Professional Society Consensus Standards

In my opinion, it is highly desirable to encourage the development of professional consensus standards such as ASCE 4-86 (5)

and ASME Appendix N (9). These standards were developed through

the voluntary contribution of many hours of effort by professionals in the field and have undergone substantial consensus review.

When the Nuclear Regulatory Commission neither acknowledges these

standards nor adapts their provisions whenever possible, it is

highly discouraging to the development and updating of such

standards. I strongly concur with the comments of Dr. John

Stevenson (2) in this regard and recommend the incorporation of

his Insert A. In addition, I believe the Standard Review Plan

should reference those standards and adapt their provisions

wherever possible. Otherwise, these voluntary efforts will

simply disappear.

References

(1) Proposed Revision 2 to Standard Review Plan, Sections 2.5.2,

3.7.1-3.7.3, NUREG-0800, U.S. Nuclear Regulatory Commission,

May 1988.

(2) Public Comments on Proposed Revision 2 to Sections 2.5.2,

3.7.1-3.7.3 ofoStandard Review Plan, July 1988.

(3) Shinozuka, M., Mochio, T., and Samaras, E. F., "Power

Spectral Density Functions Compatible With NRC Regulatory

Guide 1.60 Response Spectra," NUREG/CR-3509, U.S. Nuclear

Regulatory Commission, March 1984.

(4) Kennedy, R. P., et al., "Engineering Characterization of

Ground Motion--Task I," NUREG/CR-3805 Vol. 1, U.S. Nuclear

Regulatory Commission, February 1984.

(5) "Seismic Analysis of Safety-Related Nuclear Structures,"

ASCE Standard 4-86, September 1986.

(6) Coats, D. W., "Recommended Revisions to Nuclear Regulatory

Commission Seismic Design Criteria," NUREG/CR-1161, U.S.

Nuclear Regulatory Commission, December 1979.

(7) Regulatory Guide 1.92, "Combining Modal Responses and

Spatial Components in Seismic Response Analysis."

A-20
(8) "Report of the U.S. Nuclear Regulatory Commission Piping

Review committee," Vo. 4, NUREG-1061, September 1984.

(9) ASME Boiler and Pressure Vessel Code, Section III, Appendix

N, "Dynamic Analysis Methods," 1986.

A-21
TABLE 1

POWER CHARACTERISTICS OF R.G. 1.60 TYPE

GROUND MOTION (FROM REFERENCE 4)

Effec- Scaled

Peak tive Cumu- CumuAccel- Accel- lative lative

Record eration eration GO(W GO(w) f0 f50 f 90

A (g) ADE (g) (g) 2 (g) 2 (Hz) (Hz) (Hz)

Artificial 0.20 0.20 2.70 x 10- 2 0.675 0.60 2.15 6.55

Olympia 0.281 0.219 2.35 x 10- 2 0.490 1.20 3.05 6.10

Taft 0.180 0.149 1.58 x 10- 2 0.712 1.10 2.70 5.50

El Centro #12 0.142 0.128 1.12 x 10-2 0.684 0.55 3.05 7.50

Pacoima Dam 1.170 0.856 0.445 0.607 0.75 2.60 6.70

Hollywood Storage 0.211 0.233 3.41 x 10-2 0.628 0.75 3.30 7.90

El Centro #5 0.530 0.471 0.138 0.622 0.80 2.75 6.75

E:qn (2.1) 1.00 1.00 2.010 2.010 0.62 2.93 17.0

Zqn (2.5) 1.00 1.00 0.578 0.572 0.59 2.16 6.57

A-22
TABLE 2

COMPARISON OF CUMULATIVE POWER OVER

VARIOUS FREQUENCY RANGES

Cumulative Power Go (g 2 ) for 1.0 Peak Acceleration

Below 0.6 Hz 2.15 Hz Above

Record 0.6 Hz to 2.15 Hz to 6.55 Hz 6.55 Hz

Artificial R.G. 1.60 0.068 0.270 0.270 0.068

Equation (2.1) 0.194 0.583 0.721 0.501

Ratio Artificial 0.35 0.46 0.37 0.14

Eqn (2.1)

Equation (2.5) 0.059* 0.229 0.232 - 0.058**

Ratio Artificial 1.14 1.18 1.16 1.16

Eqn (2.5)

* Conservatively assumes that G from 0

Go from 0.4 to 0.6 Hz.

** Conservatively assumes no power above

to 0.4 Hz averages half

15 Hz.

of required

A-23
TABLE 3

COMPARISON OF RECOMMENDED

PSD REQUIREMENTS

Frequency (Hz) Freuecy (in2/sec•) l"5)Eq21)______ (in2/sec Eqn 21) ) Egn Eqn (2.5) (2.1) PSD PSD

0.4 557 1,208 0.46

1.7 557 1,386 0.40

3.0 317 865 0.37

6.5 63 259 0.24

8.4 36 162 0.22

10.0 25 116 0.22

15.0 11 53 0.21

20.0 0 30 0

A-24
3

10

4io

U S 10

0-

10

10-1 --

10- 11100 100

Fig. 1 Spectral Density Functions (Initial, Actual

(From Reference 3)

9.

f (Hz) P

10

and Lower Bound); Parameter Set No. 2
in/sec

3 iii

10

10

4.1

0

NRC RG 160

E

o3E

x

101

100 9

Fig. 2 Velocity Spectrum; 'Parameter Set No. 2

(From Reference 3)
C=

* U

C,

C2

Cý

Olympia

.,00 4 . 00 86.00 12.00 16.00 FREQUENCY (CPS) 20.00 2Y. 00

C - C,

rJ

*

so

C

* 1'.s

*

C - a

LI ~

C

uI*.O0 m.ocI J2.00 6.00

Taft

RO.0O ~.uu

0

C,

b" coo 4,.00 a'. 0C FREQUENCY (CPS) 2 .00 2.4.0

(a) T6> 9 sec.

FIGURE 3. CUMULATIVE SPECTRAL DENSITY FUNCTIONS OF EFFECTIVE

ACCELEROGRAM SEGMENT DEFINED BY T6 = Tm - T.05

(Reproduced from Ref. 4)

A-27
-- El Centro

a No. 12 C,

;I C

oo 0 W.0 ' 8.0 1,2.0 1,6i.00. 2-'. 00 2k 00 ... .. REQUENCY (CPS)

~Artificial

31200 Ja. 0a 210. o0 2.4. ;0 FRQEC ( CPS)

(a) T6> 9 sec.

.(Continued)

FIGURE 3 (Cont. ). CUMULATIVE SPECTRAL DENSITY FUNCTIONS OF EFFECTIVE ACCELEROGRAM SEGMENT DEFINED BY T6 = Tm - T .05 (Reproduced from Ref. 4)

A-28
*1~ 8

a

0'

a * -.

* r..

~ a

C-,..

LI:

a

S

HollvwoQd

Storage

".00 4.4O0 8.00 7i2.00

FREQUENCY

16.00

(CpS)

20.00 2U. 00

Cb) 2.5 sec6T6)•9 sec.

FIGURE 3 (Cont.). CUMULATIVE SPECTRAL DENSITY FUNCTIONS OF EFFECTIVE

ACCELEROGRAM SEGMENT DEFINED BY T6 = Tm - T.O5

(Reproduced from Ref. 4)

A-29
(b) 2.5 seciTD49 sec.

(Conti nued)

FIGURE 3 (Cont.). CUMULATIVE SPECTRAL DENSITY FUNCTIONS OF EFFECTIVE

ACCELEROGRAM SEGMENT DEFINED BY TO = Tm - T.05

(Reproduced from Ref. 4)

A-30
)(t)

1.0

V i t

tr - tm td

Figure 4. Deterministic Envelope Function

A-31
00.

im 0

0.-

F U 0

'N:

0 -

I,O

FI aE5

li0fillffilliffill, 

J. 111,111111,17q

15.0 20.0

TIME (SECS)

15.0 20.0

TIME ISECS)

ACCELEROGRAM AND CORRESPONDING CUMULATIVE ENERGY FOR THE

EL CENTRO, ARRAY NO. 12, IMPERIAL VALLEY 2979 (140) RECORD

(From Ref. 4)

A-32
'P%. Robert P. Kennedy

Structural Mechanics Consulting, Inc.

18971 Villa Terrace, Yorba Linda, CA 92686 * (714) 777-2163.

February 18, 1989

Dr. A. J. Philippacopoulos

Brookhaven National Laboratories

Bldg. 129

Upton, NY 11973

Re: Comments on Proposed Revisions to Standard Review Plan

Seismic Provisions

Dear Mike:

Enclosed are the original copies for incorporation into your

report of my report on the subject material and the report by

Professor Shinozuka and myself on PSD functions compatible with

R.G. 1.60.

Very truly yours,

Robert P. Kennedy

cc. Prof. Shinozuka

A-33
APPENDIX B

RECOMMENDED MINIMUM POWER SPECTRAL

DENSITY FUNCTIONS COMPATIBLE

WITH NRC REGULATORY GUIDE

1.60 RESPONSE SPECTRUM

Prepared for

Brookhaven National Laboratory

by

R. P. KENNEDY

R.P.K. STRUCTURAL MECHANICS CONSULTING

M. SHINOZUKA

PRINCETON UNIVERSITY

JANUARY 1989
1. Introduction

Around May 1988, the U.S. Nuclear Regulatory Commission (NRC)

issued Proposed Revision 2 to Sections 2.5.2, 3.7.1, 3.7.2, and

3.7.3 of their Standard Review Plan, NUREG-0800 (1) for public

review and comment. One of the proposed revisions was the

introduction of the following Power Spectral Density (PSD)

requirement to Section 3.7.1:

In addition to the response spectra enveloping requirement,

the use of single time history will also be justified by

demonstrating sufficient energy at the frequencies of

interest through the generation of PSD function which is

greater than some specified values throughout the frequency

range of significance, from 0.24 Hz to 34 Hz. For the cases

where the design response spectra correspond to those of

RG 1.60 spectra, the underlying stationary process of the

artificial time history (representing horizontal component

of the earthquake) must possess a power spectral density

which is, generally, not less than the following target

spectral density So(w) Kanai-Tajimi form throughout the

frequency range between 0.2 Hz and 34 Hz. Reference (2)

contains details of the basis for the staff recommendation.

The spectral values should be computed at frequency intervals no greater than 0.05 Hz. The smoothing of the PSD

function is acceptable, if it is performed by means of the

moving average method involving three successive frequency

points (wi_, wi and wi+l) with the average values plotted

at wi. Further, the computed PSD at no frequency should

drop below 15 percent of the target value.

1 + 4& (W/Wg) 2 (PSD 1)

SO(W) = so2 ()

[i1 - (W/Wg) 2] + 4C2 (W/W ) 2

with So = 1,100 in 2 /secs 3 (this value corresponds to a peak

acceleration of ig), wg = 10.66 rad/sec and ýg = 0.9793.

B-I
Such an artificial time history, having satisfied both the

response spectrum and power spectral requirements, may be

used as a representative seismic input for design purposes

after being properly scaled (Reference 2). The above target

PSD function is one acceptable form to demonstrate sufficient energy content in the frequency range of interest.

Other forms may be used, if justified. For the cases

where design response spectra do not correspond to RG 1.60

spectra, the target PSD function corresponding to the design

response spectra and the demonstration of adequate energy in

the frequency range of the interest are reviewed on a caseby-case basis.

At the outset, it should be clearly noted that Equation (1) represents a one-sided PSD which is related to the Fourier Amplitude

i F(w) I by:

2 1 F(M)

O(W) 2f TD (2)

where TD is the strong motion duration over which F () is

evaluated. This duration TD represents the duration of near

maximum and nearly stationary power of an acceleration time

history record. For an artificial time history with a

deterministic time envelope function such as that shown in

Figure 1:

TD = tm (3)

For an actual earthquake time history, TD represents the duration

over which the slope (power) of a cumulative energy plot is

nearly constant and near maximum where cumulative energy E(tl)

at the time t, is given by:

t1

E(tl) = A2(t) dt (4)

0

B-2
where A(t) is the acceleration at time t. Figure 2 shows a

cumulative energy plot from a representative time history. For

the record shown in Figure 2, power is nearly constant and near

maximum from about 6.4 seconds to 16 seconds for a duration TD of

about 9.4 seconds.

Alternative and more sophisticated definitions exist within the

literature for the PSD and for the duration TD over which it is

to be evaluated. Throughout this brief report the definitions

presented in the previous paragraph are used.

Reference (3) recommends that the Design Ground Motion should be

primarily defined by the Design Response Spectrum. The PSD

requirement is a secondary requirement which is simply used to

prevent a severe deficiency of power over any frequency range.

The PSD requirement should not be used to add additional

conservatism beyond that contained in the Design Response

Spectrum. Most ground motion time histories which produce a

response spectrum that closely fits the Design Response Spectrum

should be able to pass the PSD requirement.

The PSD defined by Equation (1) was initially recommended in

Reference (2) as being compatible with the RG 1.60 Response

Spectrum. However, in Reference--(2)---it was recommended for use

in generating artificial time histories which produced response

spectra which conservatively enveloped the RG 1.60 Response

Spectrum. As such, it was never intended by its authors to

represent a minimum PSD requirement. Equation (1) is not

compatible with the goal recommended by Reference (3) that the

Design Ground Motion should be primarily defined by the Design

Response Spectrum and that the PSD requirement should be a

secondary requirement used to prevent a severe deficiency of

power over any frequency range. In fact, the PSD requirement of

Equation (1) will introduce additional conservatism beyond that

contained in the RG 1.60 Response Spectrum at all frequencies,

B- 3
but particularly so above about 10 Hz, as was clearly illustrated

by the results presented in Ref. (2).

Cumulative PSD plots and other power characteristics of a number

of actual earthquake ground motion records have been presented in

Reference (4). It concluded that the Cumulative PSD as defined

by:

W

Cum S 0 ( = So() dw (5)

0

is an important descriptor of the ground motion. In particular,

if one defines fl0' f 5 0 1 and f 9 0 as the frequencies below which

10%, 50%, and 90% of the cumulative power occurs, then f 1 0 , f 5 0 '

and f 9 0 were found to be very important descriptors of the ground

motion. Table 1 reports fl 0 , f 5 0 , and f90 for an artificial time

history that produced a response spectrum which very closely fits

the RG 1.60 Spectrum plus 6 actual earthquake ground motion

records (Olympic, Taft, El Centro No. 12, Pacoima Dam, Hollywood

Storage Lot, and El Centro No. 5) which produced both elastic and

inelastic response very similar to that produced by the

artificial time history.

Based upon a review of the Cumulative PSD plots and the power

characteristics given in Reference (4), Reference (3) recommended

that the minimum PSD requirements compatible with the RG 1.60

Response Spectrum should be as follows. From 0.4 Hz to 15 Hz,

for a 1.0g peak ground acceleration, the average one-sided PSD

over any ±20% frequency band width centered on a frequency f

(i.e., 4 to 6 Hz band width for f = 5.0 Hz) computed over the

strong motion duration should exceed:

B-4
0.4 Hz to 2.3 Hz

S 5 5 7in2 0O(W) SQ~w)Ž ~'sec 5 3 3

(PSD 2)

2.3 Hz to 15 Hz (6)

S0(•)Ž 3183 in2 (f)-2.1

sec 3

where f - 2T"

Table 2 compares the minimum PSD requirements from Equation (6)

with the conservative envelope requirements from Equation (1).

The two requirements differ by a ratio of 2.2 at 0.4 Hz to 4.8 at

15 Hz.

Because of this large difference, Mr. Nilesh Chokshi and Mr.

Klalid Shaukat of the NRC Staff requested that we present a

mutually agreeable minimum Power Spectral Density (PSD) Function

compatible with the NRC Regulatory Guide 1.60 Response Spectrum.

A time history based upon this minimum PSD requirement should

produce a response spectrum which lies close to, but generally

below, the RG 1.60 Response Spectrum.

2. Development of Minimum PSD Requirement

The process followed in developing a recommended minimum Power

Spectral Density (PSD) requirement compatible with the RG 1.60

Response Spectrum was as follows:

1. Starting with a candidate PSD function, a deterministic

time envelope function (Figure 1) and a randomly

selected set of phase relationships generate an

artificial time history.

B-5
2. From this artificial time history, produce the 2% damped

response spectrum and compare with the 2% damped RG 1.60

Response Spectrum.

3. Repeat this process until the resultant response

spectrum lies close to, but generally below, the RG 1.60

Response Spectrum for frequencies between about 0.4 Hz

and 20 Hz. The response spectrum below 0.4 Hz is of

little interest for stiff nuclear power plant structures

and so a match below this frequency was not considered

to be of interest. The response spectrum above about

20 Hz for the RG 1.60 Response Spectrum shape is

primarily controlled by the peak acceleration of the

resultant time history. In turn, this peak acceleration

is insensitive to the shape of the PSD function.

Artificially high peak accelerations can be removed from

the resultant time history by either "clipping" or

"fractional folding," as described in Reference (2),

with little or no effect on-the smoothed PSD function

averaged over any ±20% frequency band, as will be shown.

Thus, response spectrum fitting above about 20 Hz was

not a prime consideration in selecting the minimum PSD

requirement.

Two time-envelope functions of the type shown in Figure 1 were

used for this brief study. They were:

Time Function A I Function B

tr (sec.) 5.0 1.4

tm (sec.) 10.24 10.24

td (sec.) 5.0 7.0

B-6
Function A has a symmetric rise and decay time, while Function B

has an asymmetric rapid rise time and much slower decay time,

similar to many actual earthquake ground motion records. Both

have the same maximum power duration, tm, of 10.24 seconds, which

is sufficiently long so that the ground motion can be treated as

stationary, at least within the frequency range of interest

(0.4 Hz to 40 Hz). It will be shown that time histories generated using Envelope Functions A and B both produce essentially

the same response spectra so that tr and td are of little significance. Low (2%) damped response spectra will increase slightly

with increasing maximum power duration tm and will decrease

slightly with decreasing tm. However, so long as tm exceeds

about 4 seconds, these differences will be small at frequencies

in excess of about 1 Hz.

Given a candidate PSD function, So(w), and a time-envelope

function, g(t)' as shown in Figure 1, an artificial ground

acceleration time history, ZO(t), can be generated from:

20(t) = gmt)ý0(t) (7)

N

= 2 k-i(t) k So(wk)Aw cos (wkt + ) (8)

with

wk = kAw, Aw = wu/N (9)

and ýk representing a sequence of independent realizations of the

random variable (D uniformly distributed between 0 and 27. The

quantity wu in Equation (9) is the largest natural frequency

value considered in this study;

Lu = NAw = 1,000 rad/sec (N = 1,630) (10)

Figure 3 compares the 2% damped pseudo-relative velocity (PSRV)

response spectrum generated from an artificial time history

corresponding to the PSD function defined by Equation (1) (PSD 1)

and time Envelope Function A with the 2% damped RG 1.60 Response

Spectrum anchored at 1.0g. Figure 4 makes a similar comparison

B-7
for the PSD function defined by Equation (6) (PSD 2). Note that

PSD 1 produces a response spectrum that exceeds the RG 1.60

Response Spectrum by approximately a factor of 1.3 from 1.5 Hz

to 10 Hz with greater exceedance at both lower and higher frequencies. Therefore establishing PSD 1 as a minimum requirement

would produce greater conservatism than is embedded within the RG

1.60 Response Spectrum. On the other hand, PSD 2 produces a

response spectrum which averages only about 70% of the RG 1.60

Response Spectrum between about 2.5 Hz and 12 Hz while being a

bit high at frequencies below about 0.8 Hz.

Using the results obtained for PSD 1 and PSD 2, one can quickly

narrow in on a recommended PSD which will produce a response

spectrum close to the RG 1.60 Response Spectrum at all frequencies between about 0.4 Hz and 20 Hz. From about 2.5 Hz to

about 9.0 Hz, the minimum required PSD should lie about 25% to

30% of the difference between PSD 1 and PSD 2 above PSD 2. At

about 1.2 Hz, the minimum required PSD should approach PSD 2 and

be less than PSD 2 below this frequency. Similarly, at about

15 Hz, the required PSD should approach PSD 2 and should drop off

very rapidly at higher frequencies. Based upon these observations and several trials, the following minimum PSD requirement

was developed:

Less Than 2.5 Hz

SO(w) = 650 inch2 /sec 3 (f/2.5 Hz)0" 2

2.5 Hz to 9.0 Hz

SO(w) = 650 inch2 /sec 3 (2.5 Hz/f)1" 8

9.0 Hz to 16.0 Hz (PSD 3)

SO(w) = 64.8 inch2 /sec 3 (9.0 Hz/f) 3 (11)

Greater Than 16 Hz

SO(w) 11.5 inch2/sec3 (16.0 ( Hz/f) 8

where f = w/2n.

B-8
The PSD requirement defined for PSD 3 by Equation (11) is shown

in Figure 5 while the relative cumulative power for PSD 3 is

shown in Figures 6 and 7. The fl 0 , f50' and f 9 0 frequencies are

about 0.7 Hz, 2.6 Hz, and 8.1 Hz, respectively, as noted in

Table 1. The fl 0 and f5 0 frequencies are consistent with those

obtained for the broad frequency content ground motion records

also listed in Table 1, while f 9 0 is only slightly higher than

the highest f 9 0 listed for the actual records in Table 1. If

anything, PSD 3 may be slightly too broad in its high frequency

content. However, a slight error in this direction is prudent

for stiff nuclear plant structures.

Figure 8 presents the 2% damped PSRV response spectrum obtained

from a time history based on PSD 3 and time Envelope Function A

and compares this response spectrum with a 2% damped RG 1.60

Response Spectrum anchored at 1.0g. Figure 9 presents the same

results for PSD 3 coupled with the time Envelope Function B.

Note that the response spectra in Figures 8 and 9 are essentially

identical, indicating the lack of importance of the specified

rise time, tr, and decay time, td. Note the excellent fit of the

PSRV response spectrum generated from the PSD 3 requirements to

the RG 1.60 Response Spectrum at all frequencies between about

0.25 Hz and about 23 Hz. With the exception of a couple of

narrow spikes and a couple of narrow valleys, the PSRV response

spectrum generated for the time history based on PSD 3 lies

between 80% and 110% of the RG 1.60 Response Spectrum from

0.25 Hz to 23 Hz.

Figures 10 and 11 present the time histories obtained using PSD 3

and Envelope Functions A and B, respectively. Note the single

high acceleration spike to approximately 520 inch/sec 2 , which is

approximately 35% greater than the desired 1.0g (386 in/sec 2 ).

When a smooth PSD function and random phasing are specified, it

is common to get at least one high frequency acceleration spike

which exceeds the target peak ground acceleration (in this case,

1.0g). It is this high acceleration spike which causes the PSRV

B-9
response spectra in Figures 8 and 9 to exceed the 1.0g RG 1.60

Response Spectrum at frequencies above about 23 Hz. The simplest

solution is to either "clip" or "fractionally fold" the high peak

acceleration at the target peak ground acceleration (1.0g) as

recommended in Reference (2). When either "clipping" or

"fractional folding" is done, the resulting PSD will only

slightly be changed. However, the resulting response spectrum

will closely match the RG 1.60 Response Spectrum at all

frequencies.

Figure 12 shows the resulting PSD obtained when the time history

shown in Figure 10 based on PSD 3 has the one peak which exceeds

1.0g clipped at 1.0g. Figures 13 and 14 show the 2% damped PSRV

response spectrum obtained when the time histories are clipped at

1.0g. Note that the exceedances of the RG 1.60 Response Spectrum

above 23 Hz have now disappeared.

3. Recommended Power Spectral Density Requirement

For an RG 1.60 Response Spectrum anchored to 1.0g, the following

minimum PSD requirement should be specified in the Standard

Review Plan. For other peak accelerations, this PSD requirement

should be scaled by~the square of the peak acceleration. From

0.3 Hz to 24 Hz, the average one-sided PSD defined by Equation

(2) over a ±20% frequency band width centered on any frequency f

(i.e., 4 to 6 Hz band width for f = 5.0 Hz) computed over the

strong motion duration should exceed 80% of PSD 3 as defined by

Equation (11). The power above 24 Hz for PSD 3 is so low as to

.be inconsequential so that checks above 24 Hz are unnecessary.

Similarly, power below 0.3 Hz has no influence on stiff nuclear

plant facilities so that checks below 0.3 Hz are unnecessary.

This minimum check is set at 80% of PSD 3 so as to be sufficiently high to prevent a deficiency of power over any broad

frequency band, but sufficiently low that this requirement

introduces no additional conservatism over that already embodied

B-10
in the RG 1.60 Response Spectrum. A time history can meet this

minimum PSD requirement and still produce a response spectrum

that lies below the RG 1.60 Response Spectrum at all frequencies.

To produce a response spectrum that accurately fits the 2%

damped, I.0g, RG 1.60 Response Spectrum at all frequencies above

0.25 Hz, we recommend the use of PSD 3 as defined by Equation

(11) with the resulting time history being clipped at ±1.0g.

To produce a response spectrum that conservatively envelopes the

1.0g RG 1.60 Response Spectrum at 2% damping and greater, we

recommend the use of a PSD set at 130% of PSD 3 defined by

Equation (11) with the resulting time history being clipped at

±1.0g. Following this recommendation will result in a response

spectrum 14.0% greater than that shown in Figure 13 at

frequencies less than about 23 Hz and equal to that shown at

frequencies greater than about 33 Hz.

References

(1) Proposed Revision 2 to Standard Review Plan, Sections 2.5.2,

3.7.1-3.7.3, NUREG-0800, U.S. Nuclear Regulatory Commission,

May 1988.

(2) Shinozuka, M., Mochio, T., and Samaras, E. F., "Power

Spectral Density Functions Compatible With NRC Regulatory

Guide 1.60 Response Spectra," NUREG/CR-3509, U.S. Nuclear

Regulatory Commission, March 1984.

(3) Kennedy, R. P., "Comments on Proposed Revisions to Standard

Review Plan Seismic Provisions," Brookhaven National

Laboratory, January 1989.

(4) Kennedy, R. P., et al., "Engineering Characterization of

Ground Motion--Task I," NUREG/CR-3805 Vol. 1, U.S. Nuclear

Regulatory Commission, February 1984.

B-I1
TABLE 1

FREQUENCY CHARACTERISTICS OF RG 1.60 TYPE

GROUND MOTION (FROM REFERENCE 4)

Frequencies

Record fl 0 f 5 0 f 9 0

(Hz) (Hz) (Hz)

Artificial 0.60 2.15 6.55

Olympia 1.20 3.05 6.10

Taft 1.10 2.70 5.50

El Centro #12 0.55 3.05 7.50

Pacoima Dam 0.75 2.60 6.70

Hollywood Storage 0.75 3.30 7.90

El Centro #5 0.80 2.75 6.75

PSD 1 0.62 2.93 17.0

PSD 2 0.59 2.16 6.57

PSD 3 0.69 2.64 8.13

B-12
TABLE 2

COMPARISON OF PSD REQUIREMENTS

Frequency Som() Som() SO(w)

(in 2 /sec 3 ) (in 2 /sec 3 ) (in 2 /sec 3 )

(Hz) PSD 1 PSD 2 PSD 3

0.4 1,208 557 451

1.7 1,386 557 602

3.0 865 317 468

6.5 259 63 116

8.4 162 36 73

10.0 116 25 47

15.0 53 11 14

20.0 30 0 2

B- 13
)

1.0

h tr tm td

Figure--l-.- Deterministic Envelope Function

B-14
U,

a

a

aj

0

5r4-)

0

a

0

0

15.0 20.0

TIME (SECS)

U

0

0. 0

F .O

Figure 2.

15.0 20.0

TIME ISECS)

ACCELEROGRAM AND

EL CENTRO, ARRAY

(From Ref. 4)

CORRESPONDING CUMULATIVE ENERGY FOR THE

NO. 12, IMPERIAL VALLEY 1979 (140) RECORD

B-15
RESPONSE SPECTRUM

1.00 +03

S-4

-.4

-4

-4

-4

Q

1.00 +02

1.00 +01

1.00 +00 -

1.00 -01 1.00 +00 1.00 +01

FREQUENCY - HZ

1.00 +02

Figure 3. 2% DAMPED PSEUDO RELATIVE VELOCITY RESPONSE SPECTRUM

ASSOCIATED WITH PSDI AND ENVELOPE FUNCTION A COMPARED

TO RG 1.60

B-16
RESPONSE SPECTRUM

0

C-4

z

cc

04

1.00 +03

1.00 +02

1.00 +01

1.00 +00

2.00 -01

Figure 4. 2%

1.00 +00 1.00 +01

FREQUENCY - HZ

1.00 +02

AS•

TO

DAMPED PSEUDO RELATIVE VELOCITY RESPONSE SPECTRUM

SOCIATED WITH PSD2 AND ENVELOPE FUNCTION A COMPARED

RG 1.60

B-17
POWER SPECTRUM

1.00 +0 -

1.00 +03

a 1.00 +02

(A

C4,-J

,,, 1.00 +01

1. C0 +00

1.00 -01

1.00 -01

I I I I ITI1~ T~1 1 I i1I1J I I ~

I I I t.,,,,I i,,ii,,i I I I I I I @ I| " i .... • I I i I i

I I ii . I I I I I I I I I I I J-lJ

1.00 +00 1.00 +01 1.00 +02 1.00 +03

FREQUENCY - RAD / SEC

RECOMMENDED MINIMUM POWER SPECTRAL DENSITY REQUIREMENT

(PSD3)

Figure 5.

B- 18
1. 00

0.90

0.80

Uj :3 0.70

C)

Lii

ý: 0.60

0.-

w 0.30

r Of,

0.20

0.10

0.00 vI I I I I I I

0.00 +00 5.00 +00 1.00 +01 1.50 +01 2.00 +01 2.50 +01

FREQUENCY (Hz)

Figure 6. RELATIVE CUMULATIVE POWER FOR PSD3

B-19
0.90

.80-

0.70

, 0.60

U-]

c- 0.50 --J

= 0.30

LU

0.20

0.10

0.00

0.00 +00 2.00 +00 41.00 +00 6.00 +00 8.00 +00 1.00 +01

FREQUENCY (Hz)

Figure 7. ALTERNATE PLOTTING OF RELATIVE CUMULATIVE POWER

FOR PSD3

B-20
RESPONSE SPECTRUM

0o

U)

w

a0

1.00 +03

1.00 +02

1.00 +01

1.00 +00

1.00 -01

ýýo ',mAI-C2.

1.00 +00 1.00 +01

FREQUENCY - HZ

1.00 +02

Figure 8. 2% DAMPED PSEUDO RELATIVE VELOCITY RESPONSE SPECTRUM

ASSOCIATED WITH PSD3 AND ENVELOPE FUNCTION A COMPARED

TO RG 1.60

B-21
RESPONSE SPECTRUM

1.00 +03 Artificial

z

E---

C)

0

0

rU)

OD

1.00 +02

1.00 +01

.... Art if icial

Time History

-RG 1.60

| I I - I I I I Ii i i I I

1.00 +00 -

1.00 -01 1.00 +00 1.00 +01 1.00 +02

FREQUENCY - HZ

Figure 9. 2% DAMPED PSEUDO RELATIVE VELOCITY RESPONSE SPECTRUM

ASSOCIATED WITH PSD3 AND ENVELOPE FUNCTION B COMPARED

TO RG 1.60

B-22
in/sec2

c.J

U

w

C

0

ILU

-J

LU

(-)

800.00

600.00 -

400.00 -

200.00 -

0.00

-200.00

-400.00

-600.00

-800.00

0.00 +00 5.12 +00 1.02 +01 1.5q +01

TIME (sec)

2.05 +01

sec

Figure 10. TIME HISTORY OBTAINED FROM PSD3 AND ENVELOPE

FUNCTION A

B-23
in/sec2

W

C)

LUJ

-J

LU

CD)

800. 00

600.00

400. 00

200. 00

0.00

-200.00

-q00.00

-600.00

-800S.00

0.00 +00 5.12 +00 1.02 +01 1.54 +01

TIME (sec)

2.05 +01

sec

Figure 11. TIME HISTORY OBTAINED FROM PSD3 AND ENVELOPE

FUNCTION B

B-24
POWER SPECTRUM

in 2 /sec 3

1.00 +04 -

1.00 +03

1.00 +02

1.00 +01

1.00 +00

1.00 -01

1.00 -01

I I I IIiIIj I I I 111111

I I I 111.11 I I I iitil

Clipped

-- Non-Clipped

I I I IIlull I, I I I lII II

1 1.00 +00 1.00 +01 1.00 +02 1.00 +03

FREQUENCY - RAD / SEC

Figure 12. PSD OBTAINED FROM CLIPPED VERSUS NON-CLIPPED TIME

HISTORIES

B-25
RESPONSE SPECTRUM

1.00 +03

U)

1/1

z

E0

0

m-.-

1.00 +02

1.00 +01

1.00 +00 , 1.00 -01 1.00 +00 1.00 +o -

FREQUENCY - HZ

1.00 +02

Figure 13. 2% DAMPED PSEUDO RELATIVE VELOCITY RESPONSE SPECTRUM

OBTAINED FROM PSD3 AND ENVELOPE FUNCTION A WITH

TIME HISTORY CFTP=ED AT 1.Og

B-26
RESPONSE SPECTRUM

1.00 +03

E-)

0

0:

U)

1.00 +02

1.00 +01

1.00 +00 1

1.00 -01 1.00 +00 1.00 +01 1.00 +02

FREQUENCY - HZ

Figure 14. 2% DAMPED PSEUDO RELATIVE VELOCITY RESPONSE SPECTRUM

OBTAINED FROM PSD3 AND ENVELOPE FUNCTION B WITH

TIME HISTORY CN"PPED AT 1.Og

B-27
Robert P. Kennedy

Structural Mechanics Consulting, Inc.

18971 Villa Terrace, Yorba Linda, CA 92686 * (714) 777-21663

February 18, 1989

Dr. A. J. Philippacopoulos

Brookhaven National Laboratories

Bldg. 129

Upton, NY 11973

Re: Comments on Proposed Revisions to Standard Review Plan

Seismic Provisions

Dear Mike:

Enclosed are the original copies for incorporation into your

report of my report on the subject material and the report by

Professor Shinozuka and myself on PSD functions compatible with

R.G. 1.60.

Very truly yours,

Robert P. Kennedy

cc. Prof. Shinozuka

B-28
88C1 516

0503G

APPENDIX C

COMMENTS ON PROPOSED REVISIONS

TO STANDARD REVIEW PLAN

SEISMIC PROVISIONS

PREPARED FOR

Brookhaven National Laboratory

Building 129

Upton, NY 11973

ALtn: A. J. Philippacopoulos

March 29, 1989'•

by

J.D. Stevenson

Stevenson and Associates

9217 Midwest Avenue

Cleveland, OH 44125

(216) 587-3805
88C1 516

0503G-10

TABLE OF CONTENTS

Page

1.0 INTRODUCTION ......................................... 1

2.0 REVIEW OF PUBLIC COMMENTS TO PROPOSED ................. .

CHANGES TO THE STANDARD REVIEW PLAN SECTION 3.7.3

2.1 Suggested Modification to Change to ................... .

SRP 3.7.3.11.12, Buried Piping Conduit and Tunnels.

Proposed by Sargent and Lundy and 3.D. Stevenson

2.2 Suggested Changes to SRP Section ..................... 3

3.7.3.11.1 Seismic Analysis Methods in Response

to 3.D. Stevenson General Comment Concerning Use

of Industry Standards

2.3 Suggested Changes to SRP Section 3.7.3.11.3 ......... 4

Procedures Used for Analytical Modeling in

Response to J.D. Stevenson General Comment

Concerning Use of Industry Standards

2.4 Suggest Change to SRP 3.7.3.11.14,.....................5

Method for Seismic Analysis of Above Ground

Tanks, in Response to J.D. Stevenson General

Comment Concerning the Use of Industry Standards

2.5 Add References to SRP Sections 3.7.2 ................. 6

and 3.7.3 to Accommodate Reconmended Changes

Contained in Sections 2.1 - 2.4

3.0 GENERAL REVIEW OF PUBLIC COMMENTS TO PROPOSED ........ 6

CHANGES TO THE STANDARD REVIEW PLAN SECTIONS 2.2.5,

3.7.1 AND 3.7.2

3.1 Time History Strong Motion Duration and .............. 7

Envelop Function

3.2 Damping Requirements ................................. 7

C-i
TABLE OF CONTENTS (Continued)

Page

ATTACHMENT 1

Table I

Recommendations for Future ....................

Revisions of Sections of the Standard Review

Plan Dealing with Seismic Design and

Evaluation of Nuclear Power Plants

Summary of Technical Areas Related .............

to Seismic Design Requiring Further

NRC Design Criteria Development

8

9

Table 1 References .......................................... 11

ATTACHMENT 2 Comments Concerning the Application ........... 12

of PSD Functions to the Generation

of Design Basis Response Spectra -

C-ii
88C1 516

0503G

1.0 INTRODUCTION

Around May 1988, the U.S. Nuclear Regulatory Commission (NRC) issued Proposed

Revision 2 to sections 2.5.2, 3.7.1, 3.7.2, and 3.7.3 of their Standard Review

Plan, NUREG-0800 for public review and conment. Prior to August 30, 1988,

comments had been received from five organizations (Sargent & Lundy,

Westinghouse, Stevenson and Associates, Duke Power Company, and General

Electric). As a contractor to the U.S. Nuclear Regulatory Commission,

Brookhaven National Laboratory has been requested to assist the NRC in

resolving these public comments. As part of this effort, Brookhaven has

formed a panel of consultants in the field of seismic analysis and design of

nuclear power plants to review these public comments and to recommend

resolutions. The comments contained in this report are the result of my

serving as a member of that panel.

This report in Section 2.0 is meant to document the changes to the proposed

text of SRP Section 3.7.3 based on the detailed review performed by Stevenson

and Associates (J.0. Stevenson) of the public comments relative to proposed

changes to the Standard Review Plan Section 3.7.3. In Section 3.0 is

contained J.0. Stevenson's general review comments concerning public comments

to proposed changes to the Standard Review Plan Sections 2.2.5, 3.7.1 and

3.7.2. In several cases specific sections of the ASCE Standard 4-86 are

recommended for incorporation into the revised SRP by reference. In

Attachment 1 to this report J.0. Stevenson has identified a number of areas

that in his opinion should be the subject a continuing effort on the part of

the NRC to improve and rationalize the SRP sections devoted to seismic design

and analysis. In Attachment 2 to this report are contained comments relative

to the use of a PSD function in the generation of Design Basis Response

Spectra.

2.0 REVIEW OF PUBLIC COMMENTS TO PROPOSED CHANGES TO THE STANDARD REVIEW PLAN

SECTION 3.7.3

2.1 Suggested Modification to Change to SRP 3.7.3.11.12, Buried Piping

Conduit and Tunnels, Proposed by Sargent and Lundy and J.D. Stevenson

1. Reason for Proposed Change

Sargent and Lundy has proposed the addition of another reference to Item

12 Subsection II to Section 3.7.3 concerning acceptance criteria for

buried piping conduit and tunnels.

Stevenson and Associates has proposed the use of industry standards by

reference where possible in the proposed changes to the S.R.P.

C-i
2. Discussion

The reference proposed by S&L is contained in the list of references of

the commentary (Ref. 3.5-4) to ASCE Standard ASCE 4-86, "Seismic Analysis

of Safety-Related Nuclear Structures and Commentary of Standard for

Seismic Analysis of Safety Related Nuclear Structures," ASCE September

1986.

ASCE Standard 4-86, Section 3.5.2 presents in detail design procedures

and acceptance criteria to be used in seismic design and analysis of

Category I Buried Piping, Conduits and Tunnels. It has been stated NRC

policy to use existing industry standards by reference in Regulatory

Guides and Standard Review Plans where the industry standard is

acceptable in total.- Where there is any disagreement on the part of the

NRC Staff as to the content of such standards, these disagreements should

be identified and published In the appropriate Regulatory Guide or

Standard Review Plan. In my review of the text of the proposed change to

SRP Section 3.7.3 II 12, to incorporate the ASCE 4-86 Standard by

reference I see no conflict between the industry position and the current

NRC Staff position.

3. Recommendation

It is recommended that a-change be- made to the currently proposed SRP

Section 3.7.3.11.12 as follows:

812. Category I Buried Piping. Conduits, and-Tunnels

For Category..I buried piping, conduits, tunnels, and auxiliary systems,

the following items should be considered in the analysis:

(a) Two types of ground-shaking-induced loadings must be considered

for design.

(i) Relative- deformati-o-ns-j-m--sed by seismic waves traveling

through the surrounding soil or by differential

deformations between-the soil and anchor points.

(ii) Lateral earth pressures and ground water effects acting on

structures.

(b) The effects of static resistance of the surrounding soil on

piping deformations or displacements, differential movements of

piping anchors, bent geometry and curvature changes, etc.,

should be adequately considered. Procedures utilizing the

principles of the theory of structures on elastic foundations

are acceptable.

(c) When applicable, the effects due to local soil settlements,

soil arching, etc., should also be considered in the analysis.

C-2
(d) Actual methods used for determining the design parameters,

methods of analysis and acceptance criteria associated with

seismically induced transient relative deformations are

reviewed and accepted on a case-by-case basis. Additional

information, for guidance purposes only, can be found in

Analysis Standards and Commentary Sections 3.5.2 of Ref. 7."

All other text in the currently proposed SRP Section 3.7.3.11.12 text is to be

deleted.

2.2 Suggested Changes to SRP Section 3.7.3.11.1 Seismic Analysis Methods in

Response to J.D. Stevenson General Comment Concerning Use of Industry

Standards

1. Statement of Proposed Change

Stevenson and Associates has proposed use of references to industry

standards where available and appropriate instead of detailed "how to"

text in the SRP.

2. Discussion

The ASME Boiler and Pressure Vessel Code Section III explicitly permits

the use of plastic, limit or inelastic analysis (e.g. NB 3213.21, NB

3213.22, NB 3228, NB 3653.6, NF 3340, A-9000, F-1321.4, F-1321.5,

F-1321.6, F-1321.7, F-1322.1, F-1340). Since subsystem components

constructed to the requirements of the ASME BPVC Section III can be

designed using other than linear elastic analysis, this permitted

exception to elastic analysis should be so stated in the SRP.

3. Recommendation

It is recommended that a change be made to the proposed SRP Section

3.7.3.11.1 as follows:

"l. Seismic Analysis Methods

The acceptance criteria provided in SRP Section 3.7.2 Subsection 11.1

are applicable."

change to:

'1. Seismic Analysis Methods

The acceptance criteria provided in SRP Section 3.7.2 Subsection II.1 are

applicable. In the design and analysis of subsystem components,

non-linear analysis is acceptable consistent with the provisions of

applicable Codes and Standards (e.g. Ref. 8) subject to review on a

case-by-case basis."

C-3
2.3 Suggested Changes to SRP Section 3.7.3.11.3. Procedures Used for

Analytical Modeling in Response to 3.D. Stevenson General Comment

Concerning Use of Industry Standards

1. Statement of Proposed Change

Stevenson and Associates has proposed use of references to industry

standards where available and appropriate instead of detailed "how to"

text In the SRP.

2. Discussion

Section 3.1.7 of the ASCE Standard 4-86 contains specific dynamic

coupling criteria which is more detailed than the proposed SRP text.

3. Recommendation

It is recommended that the proposed changed SRP text in Section

3.7.2.II.3.b which is referenced in Section 3.7.3.11.3 reference the ASCE

Standard as follows:

current text:

9b. Decoupling Criteria for Subsystems

It can be shown, in general, that frequencies of systems and subsystems

have negligible effect on the error due to decoupling. It can be shown

that the mass ratio, Rm, and the frequency ration, Rf, govern the

results wherelRm and Rf are defined as:

Rm Total mass of the supported subsystem

lotal mass of the supporting system

Rf Fundamental frequency of the supported subsystem

Dominant frequency of *the support motion

The following criteria are acceptable:

(I) If Rm < 0.01, decoupling can be done for any Rf.

(ii) If 0.01 < Rm S 0., decouplIng can be done if 0.8 > Rf > 1.25

(Ill) If Rm > 0.1, an approximate model of the subsystem should be included

in the primary system model.

If the subsystem is rigid compared to the supporting system, and also is

rigidly connected to the supporting system, it is sufficient to include only

the mass of the subsystem at the support point in the .primary system model.

On the other hand, in case of a subsystem supported by very flexible

connections, e.g., pipe supported by hanger, the subsystem need not be

included in the primary model. In most cases the equipment and components,

C-4
which come under the definition of subsystems, are analyzed (or tested) as a

decoupled system from the primary structure and the seismic input for the

former is obtained by the analysis of the latter. One important exception to

this procedures is the reactor coolant system, which is considered a subsystem

but is usually analyzed using a coupled model of the reactor coolant system

and primary structure."

change to:

ub. Decoupling Criteria for Subsystems

If the subsystem is rigid compared to the supporting system, and also is

rigidly connected to the supporting system, it is sufficient to include only

the mass of the subsystem at the support point in the primary system model.

On the other hand, in case of a subsystem supported by very flexible

connections, e.g., pipe supported by hanger, the subsystem need not be

included in the primary model. In most cases the equipment and components,

which come under the definition of subsystems, are analyzed (or tested) as a

decoupled system from the primary structure and the seismic input for the

former is obtained by the analysis of the latter. One important exception to

this procedures is the reactor coolant system, which is considered a subsystem

but is usually analyzed using a coupled model of the reactor coolant system

and primary structure.

To determine whether or not dynamic coupling of systems and subsystems is

significant, hence, must be considered in analytical modeling, the criteria

contained in Section 3.1.7 of Ref. 7 is acceptable."

2.4 Suggested Change to SRP 3.7.3.11.14, Methods for Seismic Analysis of

Above Ground Tanks, In Response to Stevenson and Associates Comment

Concerning the Use of Industry Standards'

1. Reason for Proposed Change

Stevenson and Associates has proposed use of references to industry

standards where available and appropriate instead of detailed "how to"

text in the SRP.

2. Discussion

The ASCE Standard 4-86 in Sections 3.5.4 of the Analysis Standards and

Commentary has specific design procedures, analysis method and

acceptance criteria applicable to-seismic analysis of vertical above

ground tanks. The ASCE Standards 4-86 provides significantly more

detail and guidance than does the current SRP text.

3. Recommendations

Delete the current proposed text of SRP Section 3.7.3.11.14 and replace

with the following:

"14. Methods for Seismic Anialvsis of Above Ground Tanks

C-5
Most aboveground fluid-containing vertical tanks do not warrant

sophisticated, finite element, fluid-structure interaction analyses for

seismic loading. However, the commonly used alternative of analyzing

such tanks by the "Housner-method" (Ref. 4) may be inadequate in some

cases. The major problem is that direct application of this method is

consistent with the assumption that the combined fluid-tank system in

the horizontal impulsive mode is sufficiently rigid to justify the

assumption of a rigid tank. For the case of flat bottomed tanks

mounted directly on their base, or tanks with very stiff skirt

supports, the assumption leads to the usage of a spectral acceleration

equal to the zero-period base acceleration. Recent evaluation

techniques (Refs. 5 and 6) have shown that for typical tank designs the

frequency for this fundamental horizontal impulsive mode of the tank

shell and contained fluid is generally between 2 and 20 Hz. Within

this regime, the spectral acceleration is typically far greater than

the zero-period acceleration. Thus, the assumption of a rigid tank

could lead to inadequate design loadings. The SSI effects are also

very horizontal and vertical motions.

The acceptance criteria, modeling and analytical procedures contained

in Analyses Standards and Comnentary of Sections 3.5.4 of Ref. 7 are

acceptable."

2.5 Add References to SRP Sections 3.7.2 and 3.7.3 to Accommodate

Recommended Chanqes Contained in Sections 2.1 - 2.4.

The following reference should be added to SRP Section 3.7.2.VI, References on

pages 3.7.2 - 23.

7. ASCE Standard, ASCE 4-86 "Seismic Analysis of Safety Related Nuclear

Structures and Commentary on Standard for Seismic Analysis of Safety

Related Nuclear Structures," American Society of Civil Engineers,

September 1986.

The following references should be added to SRP Section 3.7.3.VI, References

on pages 3.7.3 - 12.

7. ASCE Standard, ASCE 4-86 "Seismic Analysis of Safety Related Nuclear

Structures and Commentary on Standard for Seismic Analysis of Safety

Related Nuclear Structures," American Society of Civil Engineers,

September 1986.

8. ASME BPVC Section I11, "Rules for Construction of Nuclear Power Plant

Components," American Society of Mechanical Engineers Boiler and

Pressure Vessel Code, July 1986.

3.0 GENERAL REVIEW OF PUBLIC COMMENTS TO PROPOSED CHANGES TO THE STANDARD

REVIEW PLAN SECTIONS 2.2.5, 3.7.1 and 3.7.2.

I have reviewed the comments from the organizations listed in Section 1.0 of

this report as well as the draft comments on Proposed Revisions to Standard

Review Plan Seismic Provisions prepared for Brookhaven National Laboratory by

R.P. Kennedy dated December 1988. I concur with Dr. Kennedy's recommendations

with some additional clarification as suggested in this Section.

C- 6
3.1 Time History Stronq Motion Duration and Envelop Function

I concur with Dr. Kennedy's comments regarding time history strong motion

duration. However, I would recommend a specific time history strong motion

duration criteria as currently contained in industry standards be stated as

being acceptable to the NRC. Kennedy has recommended a time history strong

motion duration of between 5.0 and 16.0 seconds to be compatible with the R.G.

1.60 Spectra. Subparagraph N1212.2, Duration of Time History of Appendix N to

Section III of the ASME Boiler and Pressure Vessel Code recommends a minimum

strong motion duration of 6.0 seconds. Based on Kennedy's recommendation and

that contained in the ASME Code, it is recommended that the SRP Section

3.7.1.11.1.b. be modified to include a time history strong motion duration,

tD within the range of 6.0 < tD < 16.0 seconds.

3.2 Damping Requirements

Dr. Kennedy has recommended use of ASCE Standard 4-86 Section 3.1.2.2 proposed

by Sargent and Lundy and Kennedy to define damping requirements as a function

of stress level. I concur with the recommended use of Stress Level 2 damping

valves to generate floor response spectra be limited to cases where concrete

stress is greater than 50 percent of ultimate strength of concrete and also

greater than 50 percent of yield stress in the steel.

C-7
88C1 516

0503G-9

ATTACHMENT 1

Recommendations for Future Revisions of Sections

of the Standard Review Plan Dealing with

Seismic Design and Evaluation of Nuclear Power Plants

There have been a number of NRC staff recommendations, consultant reports and

NRC research reports which have made recommendations concerning changes to NRC

seismic design requirements covered by SRP Sections 2.2.5, 3.7.1, 3.7.2 and

3.7.3. Many if not most of these recommendations are not contained in the

current proposed changes to the SRP Sections 2.2.5, 3.7.1, 3.7.2 and 3.7.3.

In my opinion a number of technical areas covered by SRP Sections 2.2.5 and

3.7 still require NRC Staff review to develop more consistent, rational and

realistic seismic design and evaluation requirements for structural systems

and subsystems.

It must be understood that "conservative" design for inertia seismic loads

which is the focus of current NRC seismic design and evaluation requirements

covered in SRP Sections 2.2.5 and 3.7 does not necessarily lead to

"conservative" overall design.

In general optimum design of elevated temperature, high energy structural

subsystems tries to minimize the amount of restraint in such systems in order

to minimize stress induced in the system by restraint of free end displacement

caused by thermal expansion, support motions and water and steam hammmer and

sudden valve operation effects. Conservative design for seismic inertia

effects tends to increase restraint hence overall operating stress levels in

such systems.

In addition conservatively high seismic loads on structural systems

(buildings) require use of structural joints designed to transfer large

loads. This discourages use of ductile joint details because of the resultant

congestion (e.g. ACI 318 Appendix A). Earthquake response experience shows

ductile joint detailing to be very effective and necessary to resist

significant structural damage in strong motion earthquakes.

In Table 1 is presented a list of technical areas suggested actions and

associated references which should receive continued NRC Staff review to

improve the seismic and overall design basis of nuclear power plant systems

and subsystems.

C-8
88C1 516

0505G

Table I - Summary of Technical Areas Related to Seismic Design Requiring

Further NRC Design Criteria Development

Area

1. Modify (Increase) Seismic

Damping Values Used in

Design of Subsystems

(Piping)

Action Reference

1, 2, 3

2. Decouple OBE from

SSE and Eliminate

the OBE as a Design

Requirement for Low

Seismicity Sites

3. Use of a Median or

Uniform Hazard Spectra

Rather than Variable Mean

Plus One Standard Deviation

Design Response Spectra

4. Permit Limited Amounts

of Inelastic Response of

Systems and Subsystems

a) Increase Pipe Damping

Values to ASME Code Case N-411

b) Minimize Caveats Associated with

Use of ASME CC N-411

c) Increase Damping for Heavily

Insulated Pipe

a) Change or Clarify Wording of

1OCFR 100 Appendix A to Permit

Decoupling of OBE from SSE

b) Eliminate OBE as a Design Basis

for Low Seismicity Sites SSE

PGA < O.15g

a) R.G. 1.60 Contains a Variable

Design Margins as a Function of

Frequency with a Median Value

Defined at the High Frequency

Limit (33Hz) and Mean Plus One

Standard Deviation Defined in the

Amplified Frequency Range 2-10 Hz

b) Item 1 under SRP 2.5.2.6 Requires

Generation of Mean Plus Standard

Deviation (84 Percentile) Spectra.

Item 5 under SRP 2.5.2.6 Requires

Generation of Uniform Hazard

Spectra at Various Probability

Levels. NRC Should Permit

Use of a UHS instead of 84th

Percentile Spectra at a Probability

Level Acceptable to NRC.

1, 4

5

a) Consultants have Recommended 5, 6

Allowing Limited Amounts of

Non-linear Response Behavior

(Global Ductility > 1.0) in seismic design of

Systems as a Function of Importance

to Safety

b) Add Additional Constraints Based on

Ductility Capabilities of Systems

C-9
Table-1 - Summary of Technical Areas Related to Seismic Design Requiring

Further NRC Design Criteria Development (Continued)

Area

5. Permit Balanced Seismic

Design such that Seismic

Capacities of Subsystems

are Not Required to be

Significantly Greater than

the Structural System that

Houses or Supports Them.

6. Reconcile Results of

Recent Seismic Tests of

Subsystem (Piping Systems)

to Insure Rational Seismic

Design Margins are Being

Required.

7. Use of Bounding or

Threshold Damage Seismic

Spectra to Design Safety

Related and Evaluate

Class 2 (2 over 1 Issue)

to Assure They Do Not

Fail and Endanger Class 1

Components in Their

Proximity

8. Redefinition of High

Frequency Induced Seismic

Inertia Stresses as

Secondary

9. Permit Use of Vibration

Acceptance Criteria in

Terms of Velocity or

Displacement to Be

Applied to Seismic Design

Adequacy

Action Reference

c) Provide Explicit Global Ductility

Limits for Systems and Subsystems as a Function

of Importance to Safety and Ductility

Capabilities.

a) Institute a Design Margin

Review to Compare Seismic

Capabilities of Subsystems to the

System Housing or Supporting Them.

a) Consider Changes in Ductility and

Damping Parameters to Assure Rational

Seismic Design Margins (e.g. 1.5-2.0

against failure for the SSE) Are Being

Maintained.

a) Recent Comprehensive Experience

Data on the Behavior of Structural

Systems and Subsystems in Strong

Motion Earthquake and in Tests

Indicate That There Are Threshold

Spectral Values before Damage

Results. Use of These Threshold

Damage Spectra Together with Layout

and Detailing Caveats Should Be

Permitted in Design of Certain Types

and Classes of Systems and Subsystems.

b) Threshold Damage Spectra Procedures

Should Be Allowed in the Evaluation

Class 2 Subsystems to Insure They

Do Not Fail Under Seismic Loads.

a) Permit Limited Application of ASME

Code Cases N451 and N462 and to

Components Other Than Piping

b) Seismic Induced Loads above About

10 Hz Tend to Be Displacement

Limited Hence Develop Secondary

Stresses.

a) Permit the Application of

ANSI/ASME 0M3-1982 Criteria Limits

for Vibration Be Extended to Include

High Stress Low Cycle Conditions

Associated with Earthquake Response

7

8,9

10

C-i0
88C1 516

0505G-3

TABLE 1 REFERENCES

(1) Seismic Design Task Group "Report of the U.S. Nuclear Regulatory

Commission Piping Review Committee - Summary Piping Review Committee

Conclusions and Recommendations," NUREG-1061 Vol. 5 U.S. Nuclear

Regulatory Commission, April 1985.

(2) PVRC Committee, "Technical Position on Damping Values for Piping -

Interim Summary Report," WRC Bulletin 300, Welding Research Council,

December 1984.

(3) Bitner, J.L. et. al. "Technical Position on Damping Values for

Insulated Pipe - Summary Report," WRC Bulletin 316, Welding Research

Council, July 1986.

(4) Seismic Design Task Group "Report of the U.S. Nuclear Regulatory

Commission Piping Review CommiLtee - Evaluation of Seismic Design -A

Review of Seismic Design Requirements for Nuclear Power Plant Piping,"

NUREG-1061 Vol. 2 U.S. Nuclear Regulatory Commission, April 1985.

(5) Newmark, N.M, and Hall, W.J. "Development of Criteria for Seismic

Review of Selected Nuclear Power Plants," NUREG/CR 0098, U.S. Nuclear

Regulatory Commission, May 1978.

(6) Coats, D.W., "Recommended Revisions to Nuclear Regulatory Commission

Seismic Design Criteria," NUREG/CR 1161 Lawrence Livermore Laboratory,

May 1980.

(7) Senior Seismic Review and Advisory Panel (SSRAP) "Use of Seismic

Experience and Test Data to Show Ruggedness of Equipment in Nuclear

Power Plants," (Draft) Seismic Qualification Utility Group and USNRC,

August 1988.

(8) ASME Boiler and Pressure Vessel Code Case N-451 "Alternate Rules for

Analysis of Piping Under Seismic Loading, Class 1, 1987.

(9) ASME Boiler and Pressure Vessel Code Case N-462, "Alternate Rules for

Analysis of Piping Under Seismic Loading, Class 2 and 3," 1983.

(10) ANSI/ASME OM3-1982, "Requirements for Preoperational and Initial

Start-up Vibration Testing of Nuclear Power Plant Piping Systems,"

ASME, 1982.

C-1 1
88C1 516

0539G

ATTACHMENT 2

Comments Concerning the Application of PSD Functions

to the Generation of Design Basis Response Spectra

Comment 1 - High Frequency Power of the Target PSD Is Too High

The Kanai-Tajlmi Power Spectral Density (PSO) function form has a shape

identical to the response of a single resonance system due to a white noise

input. This is true in general at a specific site.

Nuclear Regulatory Guide 1.60 response spectra, on the other hand, are

enveloped from an ensemble of response spectra at various sites. The

enveloped response spectrum has a much broader energy content than any single

site. Trying to fit a single Kanai-Tajimi form to the PSO consistent with NRC

1.60 spectra, event though it fits well at the low frequency end where most of

the power lies, results in the use of high damping value.

The PSD at the high frequency end, in this case greater than about 10 Hz,

decays must slower than typical single site PSOs due to the large damping

value. A more sophisticated function form or some attenuation function should

be applied to the high frequency power.

Comment 2 - Comparison of PSD

To compare the PSO of a time history to the target PS, the Procedure

recommended in the proposed revision, calculating at frequency spacing of 0.05

Hz and perform a three point moving average, is very difficult, if not

impossible, to achieve. Due to the statistical error in the PSD estimate, the

PSD will still be very spiky after the moving average.

From random vibration theory, the standard deviation of the raw PSD estimate

is approximately equal to the mean value. After the three point moving, the

ratio of standard deviation to mean, or the normalized random error, will be

reduced to about 0.6, which is still too high to compare with the smooth

target curve.

A more. reasonable approach, which is also consistent with the previous section

in the Standard Review Plan, is to compare the area under the calculated PSD

and the target PSD at the same frequency intervals as the response spectrum

comparison, whether it is from Table 3.7.1-1 or based on 10% spacing ratios.

The acceptance criteria can be set up the same way, that "no more than five

points of the spectra obtained from the time history should fall below, and no

more than 10% below the target PSD."

C-12
The comparison of areas under the PSD, which becomes the Power Spectrum (PS),

is well established in the industry to compare the effect of noise and

vibrations.

C-13
A5"f

S "IT"j N"-EN S() N! & .S( )C L-\I 1.4s

a structural-m-ecJhanic~al co-ni,ult irig, ei'igiheerering firri-i

9217 Midwest Avenue * Clcveland, Ohio 44125 (21,) - * ... .; S • * .I x (2)6) 58-2215

88C 1516

0506G

February 13, 1989

Dr. A. 3. Philippacopoulos

Brookhaven National Laboratory

Building 129

Upton, NY 11973

Dear Mike:

Per our conversation on 8 February 1989, please find aitached hereto my report

containing my comments on proposed revisions to the Standard Review Plan

seismic provisions. Specific recommended changes to the text of the proposed

changes to the SRP are contained in Sections 2.0 and 3.0 of my report. I have

also described in Attachment 1 to my report technical areas where I believe

still require further NRC regulatory definition. In Attachment 2 are comments

concerning the use of power spectral density functions in the generation of

design response spectra discussed in SRP Section 3.7.1.1.1.b.

Please advise if you require any clarification of the material sent.

Sincerely,

John D. Stevenson

President

JDS:ss

Enclosures

C-14
APPENDIX D

COW4ENTS ON PROPOSED REVISIONS TO NRC STANDARD REVIEW PLAN

by

A. S. Veletsos

Prepared for

Brookhaven National Laboratory

Upton, Long Island, New York

January 1989
INTRODUCTION

The objectives of this report are:

1. To respond to the public comments concerning the U.S. Nuclear Regulatory

Commission's Proposed Revision 2 for Sections 2.5.2, 3.7.1, 3.7.2 and

3.7.3 of their Standard Review Plan (SRP) on Seismic Design Criteria

(Refs. 1 and 2); and

2. To comment on selected sections of the proposed revisions for which

clarifications and minor adjustment are deemed to be desirable.

The subject matters addressed, along with the relevant sections of the SRP,

are identified in the headings of the following sections. The comments

are presented in the order of the sections to which they refer rather than

the order of their importance.

SECTION 2.5.2 VIBRATORY GROUND MOTION

Definition of SSE and OBE, p. 2.5.2-1

I concur with the view expressed by Sargent and Lundy to the effect that

the definitions for the Safe Shutdown Earthquake (SSE) and the Operating

Basis Earthquake (OBE) presented on p. 2.5.2-1 are not clear. On the other

hand, I do not subscribe to the view that the requirements for the SSE

should be liberalized.

The following changes in wording may alleviate the reservations expressed:

"The Safe Shutdown Earthquake is the maximum credible earthquake

which would induce the most severe ground motion at the plant

site. This earthquake is determined from evaluations of the maximum earthquake potential for the site, giving due regard to the

regional and local geology, seismisity, and characteristics of

the subsurface materials involved. Safety related structures,

systems and components are designed to remain functional under

this earthquake."

"The Operating Basis Earthquake defines the class of earthquakes

which can reasonably be expected to affect the plant during its

operating life. Those elements of the power plant which are

D- I
necessary for its continuous operation without undue risk to the

health or safety of the public are designed to remain functional

under the ground motions induced by this event."

In Sect. 2.5.2.7 of the SRP, the return period for the OBE is indicated

to be "of the order of hundreds of years," whereas Sect. 3.7.3.I.B.2 requires that at least "five operating basis earthquakes" be assumed during

the plant life. Are the two requirements consistent? Also, is there any

correlation between the number of earthquakes referred to above and the

minimum number of ground motion histories specified for purposes of dynamic

analysis? I would think not.

Maximum Earthquake Potential, pp. 2.5.2-6 to 7

In recognition of the fact that the most severe ground motion for systems

with different natural frequencies may be induced by different earthquakes,

the last paragraph on p. 2.5.2-7 has been revised to refer to several

earthquakes rather than a single one. For the same reason, the end of the

first paragraph of Sect. 2.5.2.4 should be modified to read "...when the

earthquake or earthquakes which would produce the maximum...have been

determined."

Safe Shutdown Earthquake, pp. 2.5.2-12 to 14

1. The ground motion for the design earthquake in the SRP is specified indirectly in terms of a response spectrum rather than directly in terms

of ground motion histories. In the most sophisticated of the recommended procedures, the design response spectrum is determined from analyses

of a collection of appropriate ground motion records for the site. However, no guidance is given as to the minimum number of records required

in this approach. It is recommended that this number be specified, or

that, as a minimum, a statement be included to the effect that the number of ground motion records considered should be sufficiently large

such that the resulting spectrum is reasonably broad banded and properly

reflects the uncertainties of the problem.

2. It is not clear if the use of a reasonably large collection of appropriate earthquake ground motion records, as contrasted to the use of

D-2
a design spectrum, constitutes an acceptable basis for design. If this

is indeed acceptable, then what should the minimum number of records

be? If the required number is no smaller than that needed in the design

spectrum approach, then clearly this is not a distinct option.

3. Item 2 at the top of p. 2.5.2-13 refers to the case in which the available set of ground motion records is not sufficiently large to determine

the site-specific design spectrum. The requirements of this option require clarification. Incidentally, the recommended adjustments should

provide for the effects of magnitude and epicentral distance in addition

to those of fault mechanism, propagation path and local site conditions.

SECTION 3.7.1 SEISMIC DESIGN PARAMETERS

Use of Single and Multiple Time Histories, pp. 3.7.1-3 and 4

The objections to the use of multiple ground motion histories expressed

in the public comments appear to have stemmed, in part, from a lack of

clarity in the SRP of precisely what is intended in this regard.

Following discussions of this matter with Dr. Nilesh Choksi of NRC, I believe that the intent of the proposed provisions can more appropriately

be stated as follows:

. If a single artificial, real or modified real ground motion history is employed, itsresponse spectrum must match or exceed the

design spectrum over the entire range of frequencies and damping

values which are of interest. In addition, the ground motion

history must satisfy the power spectral density (PSD) requirement

examined in a later section of this report. The spectrum matching or enveloping requirements are identified on p. 3.7.1-10 of

the SRP.

. If a collection of artificial, real or modified real ground motion histories is used, the response spectra for the individual

records need not separately match the design spectrum, but the

spectrum for the ensemble of records corresponding to the mean

plus one standard deviation (MSD) level of non-exceedance must

D-3
match it. The response values considered for design in this option must be those associated with the MSD level of non-exceedance. Alternatively, one may initially adjust the intensities

of the ground motion records so that the mean of their response

spectra matches the design spectrum, and work with the mean

values of the resulting responses. In either case, the match

should hold over the entire range of frequencies and damping

values of interest.

Inasmuch as the power content at different frequencies for the

collection of real or modified real time histories can be expected to be representative of those deemed to be appropriate for

the site, it is my view that the PSD requirement need not be imposed when multiple histories are used. Expressed differently,

implementation of the PSD provision is recommended only for

single artificial, real or modified real histories and for multiple artificial histories.

Only multiple real or modified real ground motion histories are

appropriate for inelastic and other nonlinear analyses. In this

connection, the word 'appropriate' in the third line from the

bottom on p. 3.7.1-4 of the SRP should be changed to 'required'.

In general, I regard the use of multiple ground motion histories to be preferable to the use of a single history, and the use of real histories to

be preferable to that of artificial- ones. Consequently, I strongly favor

options which would encourage the use of multiple real or modified real

histories. The proposed relaxation of the PSD requirement, along with the

clarification of the requirements on target response spectra which has been

presented, should provide a reasonably strong incentive for the more extended use of such input motions, and should dilute the objections to the

use of such motions expressed in the public comments.

With regard to the minimum number of ground motion histories that should

be employed in the implementation of the multiple history option, I consider the proposed number of five to be quite reasonable. However, if in

the opinion of the other members of the Review Panel this number is still

likely to discourage the use of this option, I would concur to having the

D-4
number reduced to four, but would deem a further reduction to be inadvisable. In particular, I consider the multiple history option of the ASCE

Standard 4-86 (Ref. 3) to be inappropriate, as it effectively permits the

use of as few as two ground motion histories. The recommended minimum number of records should also govern all nonlinear response analyses.

Relationship Between Vertical and Horizontal Ground Motions and the Associated Response Spectra, p. 3.7.1-8

According to Item 1 on p. 2.5.2-12 of the proposed SRP, the design response

spectrum for the vertical component of ground shaking should be determined

from appropriate ground motion histories in a manner analogous to that used

in the development of the corresponding spectrum for horizontal shaking.

However, the relationship between vertical and horizontal design response

spectra, previously specified on p. 3.7.1-8, has been deleted, and no

acceptance criterion is specified in this regard in the revised SRP. I

concur with the public comments to the effect that this deletion is undesirable.

In the deleted section, the vertical component of the design acceleration

is taken as 2/3 of the horizontal component, and the design spectrum for

vertical motion is taken as 2/3 of the spectrum for horizontal motion for

all frequencies of interest. I consider this relationship to be generally

reasonable, and recommend that its use be permitted for those cases in

which the horizontal design spectrum is determined by the procedures specified in Items 2 and 3 on p. 2.5.2-13. However, the appropriateness of this

rule must be justified for relatively small epicentral distances. When

the design spectrum for horizontal motion is determined by the approach

outlined in Item 1, then the spectrum for vertical motion should be determined, as presently proposed, by statistical analysis of relevant ground

motion records.

PSD Requirement, pp. 3.7.1-10 to 12

The intent of the proposed PSD requirement is to ensure that the ground

motion histories employed in the analysis have adequate power in the frequency ranges of interest. The need for such requirements has clearly been

D-5
described by Dr. Kennedy (Ref. 4) and need not be reemphasized here. The

questions requiring evaluation are whether the recommended provisions represent the most desirable means of attaining the desired objective, and

whether -they are sufficiently rational and well founded for adoption at

this time.

As indicated by Dr. Kennedy, the desired objective could be achieved by

imposing stricter requirements on the response spectrum that the ground

motion histories must satisfy. In particular, the response spectra of the

ground motions for small amounts of damping (of the order of 2 percent of

the critical value) may be required to match closely and at closely spaced

frequency intervals the corresponding design spectrum. Such a requirement

would not be particularly difficult to implement if one were to start with

real ground motion histories for which the relevant response spectra are

reasonable approximations of the target spectrum. Furthermore, inasmuch

as this requirement is consistent with the use of the response spectrum

concept as a design basis, it is preferable, in my view, to an approach

based on a fundamentally different (the PSD) concept.

There is, of course, nothing wrong with the PSD approach provided it is

calibrated to yield practically the same results as those obtained from

the response spectrum approach. However, this calibration does not appear

to have been implemented to date, and I am not convinced that it can be

implemented readily in design applications. Under the circumstances, I

question the advisability of adopting the proposed PSD requirement at this

time. This view is in agreement with that expressed by Westinghouse on

this matter (Ref. 2).

The following facts are noted in further support of this view:

. The PSD function specified on p. 3.7.1-11 is meant to be compatible with

response spectra of the type presented in R.G. 1.60, but is clearly not

compatible with all other site-specific response spectra permitted in

the SRP.

- The discussions of the Review Panel in the December 1988 meeting raised

serious doubts about the appropriateness of the coefficient S in the

proposed PSD function, as well as about the shape of this function at

D-6
high frequencies. These uncertainties may be resolved, however, as a

result of studies now in progress.

- The operations involved in the determination of the PSD function corresponding to a specified response spectrum are generally delicate, and

there are many opportunities for getting the wrong interrelationship

between the two functions.

The requirement near the top of p. 3.7.1-11 to the effect that the computed

PSD does not fall at any frequency by more than 15 percent below the target

function is considered unrealistic by General Electric Company (Ref. 2).

While I tend to agree with this assessment, I feel that this issue requires

further study. Incidentally, in view of the almost erratic nature of the

PSD functions for real earthquakes, it may be preferable to select the

coefficient S0 in the target PSD so that it may be related to the mean of

the computed PSD rather than to its lowest 15 percent level.

As previously indicated, I feel that the PSD requirement need not be imposed when the analysis is based on multiple real time histories, even if

it is adopted for other cases.

SECTION 3.7.2 SEISMIC SYSTEM ANALYSIS

Soil-Structure Interaction Methodology, pp. 3.7.2-8 to 14

Two different acceptance criteria are specified for soil-structure interaction (SSI) analyses, depending essentially on how the design ground

motion is prescribed. Alternate 1 is required for those cases in which

the design ground motion is defined either by a broad-banded response

spectrum of the type presented in R.G. 1.60, or by some other standardized

spectrum determined from estimates of the maximum ground acceleration,

velocity and displacement for the site and the application of appropriate

amplification factors (as indicated in Item 3, p. 2.5.2-13 of the SRP).

Alternate 2 is determined from detailed, site-specific investigations,

essentially in the manner specified in Item 1, p. 2.5.2-12.

In Alternate 1, one is required to use both the direct and substructuring

methods of analysis, and to envelope the results obtained by the two

D-7
methods. There is no requirement for detailed parametric or sensitivity

studies for this case. By contrast, in Alternate 2, one is allowed to use

any state-of-the-art method of analysis and, through detailed parametric

studies, is required to assess the sensitivity of the computed responses.

The difference in the requirements for the state-of-the-art analyses referred to in Alternate 2 and those referred to in Alternate 1 is not clear.

Neither is the rationale for requiring detailed parametric studies for

Alternate 2 but not for Alternate 1. Finally, the requirement for enveloping the results of the direct and substructuring methods of analysis specified for Alternate 1 is not justified in my view.

When properly implemented, both the direct and substructuring methods of

analysis, or any other rational approach for that matter, will yield essentially the same results. When improperly implemented, the individual solutions may, of course, be significantly in error, and their envelope may

be no better than their component solutions.

The greatest uncertainties in SSI analyses in my view relate to the idealization of the structure-foundation system and its supporting medium,

rather than to the method used to analyze the idealized system. In recognition of this fact, the following recommendations are made:

- Delete reference to the two alternates, recognizing that the

design ground motion may, as indicated in Section 2.5.2.6, be

specified either by a standardized response spectrum or by a

site-specific spectrum.

. Permit use of either the direct or substructuring method of

analysis, without any enveloping requirement.

- Ensure that the structure-foundation-soil system is properly

modeled, and that detailed parametric studies are made to

assess the sensitivity of the calculated responses to the

numerous uncertainties involved and to bound the solutions.

Special reference need be made in this regard to the merits

of simple techniques with which the effects of the primary

parameters may be evaluated readily and cost-effectively in

design.

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- Ensure that the analysis of the idealized system is implemented

properly by enforcing the relevant provisions of the SRP. In

this connection, I do not concur with Sargent & Lundy in their

recommendation that item b on p. 3.7.2-11 be deleted. On the

contrary, I feel that this item should be presented as item

a.

In general, I concur with the position expressed by General Electric

(Ref. 2) to the effect that "as long as the major uncertainties associated

with SSI effects are properly considered in the analysis, any

state-of-the-art approach shall be acceptable". I further concur with the

view expressed on page 14 of Ref. 5 that "in view of the large

uncertainties, it is not clear that complex, expensive calculations are

justified or necessary to develop a soundly engineered design".

Acceptability of Fixed-Base Analysis, p. 3.7.2-10

The SSI effects depend on the relative stiffnesses of the structure and

the supporting medium involved rather than on the absolute stiffness of

the latter. Accordingly, I believe that the acceptability of the fixedbase analysis should not be expressed solely in terms of the shear wave

velocity of the supporting medium, as recommended by Sargent & Lundy

(Ref. 2), although their recommendation is likely to yield satisfactory

results for many practical cases. However, I do agree with the view that,

if reference is made in the SRP to rock and rock-like materials, these

terms must be defined.

It is my recommendation that the last paragraph in Item ii on p. 3.7.2-10

be modified as follows:

"For structures supported on rock or rock-like materials, a

fixed-base assumption may be acceptable. Such materials are

defined by a shear wave velocity of 3,500 ft/sec or greater at

a shear strain of 10-3 percent or smaller [when considering

preloaded soil conditions due to the structure (?)]. A

comparison of the fundamental natural frequencies of the

fixed-base and interacting structures can be used to justify the

fixed-base assumption."

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It might also be desirable to specify the maximum change in frequencies

that would be acceptable in this option. A reduction limited to 5 percent

of the fixed-base natural frequency value appears to be reasonable.

In the December 1988 meeting of the Review Panel, Dr. Kennedy suggested

that the fixed-base analysis be considered to be acceptable when the shear

wave velocity of the supporting medium is 3,500 ft/sec and the fundamental

fixed-base natural frequency of the system is 10 cps or less. This provision would be equally satisfactory in my view, but I wish to stress that

there is no special difficulty in evaluating the fundamental natural frequency of an interacting system when its corresponding fixed-base frequency

is known (see, for example, Ref. 6).

Limits for Soil Parameters, p. 3.7.2-12

I believe that the best-estimate values for the shear modulus of the soil

should be those corresponding to the strain levels associated with the design earthquake. These strains may be determined from analyses of the

seismic wave propagation under free-field conditions, or by some other

appropriately substantiated approach. However, the best-estimate values

should probably be no less than a prescribed percentage, say 40 percent,

of those corresponding to strain values of the order of 10-3 percent or

less. The specified variations in soil properties should be measured with

respect to the best-estimate values.

With regard to the maximum acceptable value of soil material damping, I

believe that the limit of 5 percent of critical specified in the SRP is

too low, and recommend that it be increased to 15 percent of the critical

value. It should be recalled that this percentage is only one-half as

large as the value of the tans factor frequently used in SSI studies.

The recommendations of this section are consistent with those presented

on p. 15 of Ref. 5.

Variation of Ground Motion with Depth, p. 3.7.2-14

Because of the multitude of uncertainties involved in the evaluation of

the variation of the ground motion with depth, I believe that there should

D-10
be a limit on the magnitude of the maximum reduction that may be permitted

due to embedment. I do not subscribe to. the view that such a limit is unnecessary in view of the requirement of varying the soil properties over

specified ranges. The latter requirement does not provide for the uncertainties relating to the nature and composition of the seismic waves and

their modes of propagation, or the manner in which the nonlinear action

of the soil is approximated.

The value of the maximum reduction from the surface motion that may be permitted has been a subject of considerable controversy over the years (see,

for example, p. 20 of Ref. 5), and no unanimity of opinion is expected

among the membership of the Review Panel. The proposed reduction of 40

percent, which is the same as that permitted in the ASCE Standard (Ref. 3)

is too high in my view, and should preferably be limited to a value of no

more than 25 or 30 percent.

Such a reduction should refer to the horizontal component of foundation

input motion (i.e., the motion that the massless foundation would experience at the level of embedment compared to that at the surface), and should

be permitted only when account is taken of the associated rocking and torsional modes of vibration. If the rotational components of motion are

ignored, no reduction should be permitted in the horizontal component.

Damping and Modal Combination Requirements, pp. 3.7.1-12 and 16

I concur with the views expressed by Dr. Kennedy on these issues (see Sections 7 and 8 of Ref. 4).

Appendix A, p. 3.7.2-24

1. The notation in this Appendix is highly confusing, and I feel that it

should be revised. Considering that the quantities Fi and Ki are dimensionless and do not represent forces or stiffnesses, I recommend that

they be replaced by di and ei. I further suggest that the symbols m

and M be changed to n and N, respectively, to avoid possible confusion

with the mass of the system, and that the participation factor for the

nth mode be denoted by cn. With these revisions, the three equations

of the section become:

D-11
N

di = 1 Cn n i

n=1

in which n =the order of the mode under consideration,

i ij

and

P. = ZPA x Mi x ei

2. The following expression should be given for the participation factor:

{4€n}{1}

fon

}n [m]{on}

in which {I = the nth natural mode of the system. It may be recalled

that these factors refer to displacements and do not involve the circular natural frequencies of the system as multipliers.

Greater Use of Professional Society Consensus Standards

While I strongly concur with Dr. J. Stevenson's recommendation (Ref. 2)

of making reference to relevant standards of professional societies and

other organizations, I believe that such reference should be limited only

to those sections of the standards with which NRC finds itself in

agreement, and there should be no impression created of a blanket approval

for these documents. I would also be concerned about creating the

impression that the proposed SRP is not reasonably up-to-date. In this

regard, I question the advisability of incorporating Dr. Stevenson's Insert

A in its proposed form.

SECTION 3.7.3 SEISMIC SUBSYSTEM ANALYSIS

Analysis of Above Ground Tanks, pp. 3.7.3-2 and 7 to 9

The following revisions are recommended:

1. On p. 3.7.3-2, change the sentence under Item 12 to read:

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"For Category ..... methods which consider the effects of

hydrodynamic forces, tank flexibility, soil-structure and other

pertinent factors are reviewed."

Basically, I suggest referring to the SSI effects at the end, because

they are generally the least important of the factors enumerated and

because there is no guidance given in the SRP for their consideration.

2. On p. 3.7.3-7 change the last three sentences of Item 14 to read:

"For the-ease-eo flat bottomed ..... acceleration. Recent

studies (Refs. ) have shown ..... contained fluid is such that

the spectral acceleration may be significantly greater ..... "

3. On p. 3.7.3-8, change the last sentence in the first paragraph to

"The SSI effect may also be very important for .......

It may be recalled that the SSI effects are more likely to reduce rather

than increase the response.

4. On p. 3.7.3-8 Item b, change the first two sentences to the following:

"The fundamental natural frequency for the horizontal impulsive

mode of vibration of the tank-fluid system must be evaluated

giving due consideration to the flexibility of the supporting

medium. It is unacceptable to assume a rigid tank unless the

assumption can be justified. The horizontal impulsive-mode

spectral acceleration Sal is then determined using this frequency and the appropriate damping for the tank-liquid system.

Alternatively, the maximum spectral acceleration corresponding

to the relevant damping may be used."

Note that no reference is made in this proposal to uplifting. While

it is true that uplifting will tend to increase the effective period

of the system, this change represents only one aspect of such action,

and the magnitude of the change cannot adequately be quantified at this

stage. Should it be deemed advisable to refer to uplifting, the first

sentence of the proposed section in Item 4 above may be modified to conclude as follows:

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" -.. giving due consideration to the flexibility of the supporting medium and to any uplifting tendencies for the tank."

5. Revise Item c on p. 3.7.3-8 to permit consideration of the additional

system damping associated with soil-structure interaction, subject, of

course, to properly substantiated analyses.

6. At the top of p. 3.7.3-9, delete the last sentence at the end of the

first paragraph.

7. Revise Item i on p. 3.7.3-9 to read:

"The tank foundation ..... seismic forces imposed on it. The

forces include ..... as well as the axial tank shell forces

resulting from M0 (caution: not Mb).

8. While Ref. 6 on p. 3.7.3-12 might be retained for its historical interest, Ref. 5 on p. 3.7.3-11 should be replaced by the following more

recent and more readily accessible references:

- A. S. Veletsos and J. Y. Yang, "Earthquake Response of Liquid Storage

Tanks," Advances in Civil Engineering Through Engineering Mechanics,

Proceedings of the Engineering Mechanics Division Specialty Conference, ASCE, Raleigh, North Carolina, 1977, pp. 1-24

. M. A. Haroun and G. W. Housner, "Seismic Design of Liquid Storage

Tanks," Journal of the Technical Councils, ASCE, Vol. 107, No. TC1,

1981, pp. 191-207

- A. S. Veletsos, "Seismic Response and Design of Liquid Storage Tanks,"

Guidelines for the Seismic Design of Oil and Gas Pipeline Systems,

Technical Council on Lifeline Earthquake Engineering, ASCE, 1984, pp.

255-370 and 443-461

Consideration may also be given to referring to the following recent

contribution on SSI effects:

A. S. Veletsos and Y. Tang, "Soil-Structure Interaction Effects for

Laterally Excited Liquid-Storage Tanks," to appear as an EPRI Technical Report, Palo Alto, California, 1989.

D- 14
No reference is made in the SRP to the effects of the vertical component

of ground shaking. This omission should be rectified by the addition of

the following statements:

"The maximum hoop forces in the tank wall must be evaluated with

due regard for the contribution of the vertical component of

ground shaking. The beneficial effects of soil-structure interaction may be considered in this evaluation."

Following is a list of references on these topics:

. M. A. Haroun and M. A. Tayel, "Axisymmetrical Vibrations of Tanks--Numerical," Journal of Engineering, Mechanics Division, ASCE, Vol. 111, No.

3, 1985, pp. 329-345.

- A. S. Veletsos and Y. Tang, "Dynamics of Vertically Excited Liquid Storage Tanks," Journal of Structural Engineering, ASCE, Vol. 112, No. 6,

1986, pp. 1228-1246.

- A. S. Veletsos and Y. Tang, "Interaction Effects in Vertically Excited

Steel Tanks," Dynamic Response of Structures, G. C. Hart and R. B.

Nelson, Editors, ASCE, 1986, pp. 636-643.

D- 15
REFERENCES

1. Proposed Revision 2 to Standard Review Plan, Sections 2.5.2,

3.7.1-3.7.3, NUREG-0800, U. S. Nuclear Regulatory Commission, May 1988.

2. Public Comments on Proposed Revision to Sections 2.5.2, 3.7.1-3.7.3 of

Standard Review Plan, July 1988.

3. "Seismic Analysis of Safety-Related Nuclear Structures and Commentary,"

ASCE Standard 4-86, September 1986.

4. Kennedy, R. P., "Comments on Proposed Revisions to Standard Review Plan

Seismic Provisions," Prepared for Brookhaven National Laboratory, Preliminary Draft, December 1988.

5. Coats, D. W., "Recommended Revisions to Nuclear Regulatory Commission

Seismic Design Criteria," NUREG/CR-1161, U. S. Nuclear Regulatory Commission, December 1979, Reprinted April 1988.

6. Veletsos, A. S. "Dynamics of Structure-Foundation Systems," Structural

and Geotechnical Mechanics, W. J. Hall, editor, Prentice-Hall, Inc.,

Englewood Cliffs, N. J., 1977, pp. 333-361.

7. Shaukat, S. K., Chokshi, N. C. and Anderson, N. R., "Regulatory Analysis

for USI A-40, Seismic Design Criteria, Draft Report for Comment,"

NUREG-1233, U. S. Nuclear Regulatory Commission, April 1988.

D-16
A. S. VELETSOS

BROWN & ROOT PROFESSOR * DEPARTMENT OF CIVIL ENGINEERING,

RICE UNIVERSITY e HOUSTON, TEXAS 77001 * (713) 527-8101, EXT. 2388

CONSULTANT * 5211 PAISLEY 0 HOUSTON, TEXAS 77096 e (713) 729-4348

February 20, 1989

Dr. A. J. Phillippacopoulos

Brookhaven National Laboratory

Department of Nuclear Energy

Building 129

Upton, Long Island, New York 11973

Dear Mike:

This concerns the originals of my report to you on the USI A-40 Project.

Please replace the cover sheet and pages 7, 9 and 10 of the originals which

accompanied my letter to you of January 30 with the corresponding pages

enclosed herewith. After reviewing the material that you sent me recently,

I have decided to make no other changes at this time.

Sincerely,

A. S. Veletsos

ASV:rm

Enc osures

D-17
APPENDIX E

COMMENTS ON PROPOSED REVISIONS

TO SEISMIC SPECIFICATIONS OF THE

US NRC STANDARD REVIEW PLAN

by

C. J. Costantino

prepared for

Brookhaven National Laboratory

January, 1989
1. INTRODUCTION

Recently, the U.S. Nuclear Regulatory Commission (NRC) issued a proposed revision

(Revision 2) to the Standard Review Plan (NUREG - 0800) for public comments. These revisions are

associated with Sections 2.5.2, 3.7.1, 3.7.2 and 3.7.3, which present requirements for the seismic

design of nuclear power plants. Comments to these proposed revisions were received from six

organizations active in the nuclear industry. In August 1988, a Consulting Panel was formed under the

direction of Brookhaven National Laboratory to assist the NRC in resolving the issues brought up by

these public comments. As a member of this panel of consultants, I have prepared this report which

describes my evaluation of these comments as well as a summary of my position on many of the issues

associated with the proposed revisions to the SRP.

The comments that follow can be organized into three primary areas of activity typically

associated with the seismic response analyses performed by the industry, namely:

(a) definition of the seismic input motions used in the seismic response analyses of nuclear

facilities;

(b) requirements for seismic response analyses to be performed which suitably incorporate

soil/structure interaction effects;

(c) details of the structural response analyses performed to assess both primary structural

and subsystem dynamic response.

A description of my comments on the above items are presented in the following paragraphs.

2. PSD REQUIREMENTS FOR SEISMIC INPUT MOTIONS

The proposed Revision 2 to Section 3.7.1 of the SRP has added a requirement to judge

acceptability of artificial accelerograms to be used In seismic response and SSI analyses. This new

iiF- I
criterion requires that the Power Spectral Density (PSD) of the acceleration time history satisfy

certain target PSD criteria. Prior to this revision, the requirements on input accelerograms

concerned enveloping from above the broad-banded Regulatory Guide 1.60 (R. G. 1.60) ground

response spectra. Some arguments in support of the newly added PSD requirements make use of

extreme examples of relatively simple input motions which formally envelop the R.G. 1.60 criteria

but which may yield deficient responses of subsystems at frequencies of interest in reactor systems.

However, there are two points to be made regarding this argument. Firstly, the extreme

examples make use of sinusoidal input motions which do not look like typical accellerograms and

therefore would not be accepted in the course of conventional reviews associated with licensing

applications. Secondly, at low equipment damping ratios (2% or less), there is no significant

difference between the spectrum approach and the PSD criteria (once the definition of the PSD is

completely specified). Both are expressions of the Fourier components of the input motions and both

strive to enforce adequate representation of the input motion over the entire frequency band of

interest. For all practical purposes, they lead to the same conclusions as far as safety of nuclear

structures is concerned.

Therefore, I recommend that a PSD criteria n=t be required in the revised SRP, provided that

the Applicant satisfies two conditions, namely:

1. that the design time history satisfies the enveloping criteria for response spectra

associated with equipment damping of 2% or less, whether the response spectra used in

the analyses are of the broad-banded generic type (such as those of R.G. 1.60) or site

specific;

2. that the enveloping criteria be defined as follows:

a) no more than five points of the calculated spectrum fall below, and no more than

10% below the target spectrum,

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(b) the calculated spectrum does not exceed the target spectrum by more than 50% at

any frequency,

(c) the calculated spectrum lies at or above the target spectrum at all calculated

structural frequencies of interest, and

(d) the calculated spectrum satisfies the specific frequency requirements of the

current SRP.

If these requirements are included in the SRP, the need for an added PSD requirement is, in my

opinion, not required to demonstrate adequacy of any artificial time history to be used in a seismic

response calculation. The structural frequencies of interest mentioned above are to include all

frequencies of both the primary and secondary components of the system, and include the effects of SSI

on these frequencies.

If, however, the analyst chooses to select a target design response spectrum at higher levels of

damping (greater than 2%) from which artificial time histories are to be generated, then a

corresponding target PSD criteria should be required to show that the input accelerogram contains

adequate power at all frequencies of interest. For the broad-banded spectra specified by R.G. 1.60, I

recommend that the procedures which have been developed by M. Shinozuka and R. Kennedy (Ref 1) as

part of this Panel's activity be used as a specification of the target PSD, which is suitably compatible

with the target design response spectrum. To eliminate any ambiguity in the calculations, the specific

definitions of the PSD, its method of calculation and the generation of the corresponding time history

should be specified in the SRP.

I do not agree with the suggestion that a Cumulative Power Spectral Density function be used

in place of the convential PSD. Since the Cumulative PSD is the integral of the PSD, gaps in power at

specific frequencies tend to be masked and seem to me to violate the original intent of the PSD criteria

which has been added to the Revision 2 of the SRP. In addition, computation of cumulative PSD's from

E-3
actual digitized records should be held suspect at the higher frequencies of interest (above 15 hz)

since the digitization process itself may have eliminated adequate measures of the power at these

frequencies (Refs. 3 and 4).

Guidelines for developing corresponding target PSD requirements for other types of design

ground response spectra to be used in the seismic evaluations, either broad-banded or site specific,

should be described in the SRP. It is important that sufficient effort be undertaken to develop PSD

target functions compatible with the target response spectra to allow for a meaningful comparison to

both criteria. Suitable smoothing processes as used in Ref. 2 should be included in the descriptions.

For any case where both target PSD and ground response spectra criteria are specified to

generate a design input motion, I recommend that the following procedure be employed to judge the

adequacy of the generated time history. First, the computed ground response spectra should satisfy the

four specific criteria listed above for the definition of enveloping criteria. Secondly, the computed

PSD of the artificial time history should on the average envelop the target PSD over the entire

frequency range of interest from 0.4 hz to 33 hz and should not be less than 85% of the target at all

the structural frequencies of interest (as previously defined). In applying this last criterion, the

comparison should be made using average values computed over a frequency band of + 15% at each

structural frequency.

3. DURATION OF ARTIFICIAL TIME HISTORY

I agree with the comments presented at the various panel sessions that a specific

recommendation should be made in the SRP concerning ground motion duration requirements. For

linear structural response analyses, the total duration of the accelerogram should be long enough such

that adequate representation of the Fourier components (or PSD) at low frequency be included in the

E-4
time history. To adequately match spectra at 0.4 hz requires total time duration of the ground motion

of between 15 and 25 seconds. The suggestion made that a corresponding duration criteria be specified

in terms of strong motion duration, based on computation of cumulative energy in the pulse as a

function of time, is equivalent. However the duration is specified, it should be adequately tied to the

definition of the PSD computation which is dependent on the definition of duration.

The upper bound on potential duration is more questionable. For nonlinear analyses, which

may be associated with liquefaction and/or yielding structural response, it seems to me that more care

should be taken in defining adequate duration. Firstly, duration should be incorporated in the

seismicity study as described in SRP Section 2.5.2 from which the anticipated acceleration levels and

earthquake magnitudes are determined. In the calculation of the nonlinear response, a primary topic of

interest should be the sensitivity of the specific response to the (strong motion) duration.

Specification of exceedingly long pulse durations can lead to overly conservative results. However, if

the characteristics of the nonlinear response changes significantly for total durations slightly longer

than say 25 seconds, engineering judgement must be incorporated to protect the system from such

occurrences. Although I agree that the maximum total duration (rise, stationary, and decay portions)

of 25 seconds is reasonable, I recommend that the revised SRP should make provision for such

evaluations on a case by case basis.

4. VERTICAL SPECIFICATION OF GROUND MOTION

It is my opinion that the SRP should be clear on the specification of compatible vertical time

histories which should be used in conjunction with horizontal motion definitions, whether using R.G.

1.60 criteria as well as site specific horizontal motions. In Ref. 5, it is recommended that a simple I

scaling of the horizontal spectra (by a factor of 2/3) across the entire frequency band be allowed for

the definition of the vertical spectra. This procedure has the obvious advantage of simply scaling the

E-5
horizontal time history to obtain the compatible vertical history. Such a recommendation may be

appropriate for sites located well away from the fault. However, whenever the primary causative fault

lies within 10 to 15 km of the site, such a simple scaling would not be appropriate, especially for

higher frequencies. For site independent analyses as defined in R.G. 1.60, amplification functions for

horizontal and vertical design spectra are not the same at all frequencies.

I recommend that the revised SRP contain a clear specification for the definition of vertical

motions for all cases, whether they be for site independent R.G. 1.60 or for site specific evaluations.

This definition should be specified in the seismicity studies associated with Section 2.5.2. For most

cases, this will lead to a separate development of vertical time histories which must be made in

conjunction with the development of horizontal motions. In addition, potential estimates of variability

of time phasing between the arrival of vertical and horizontal strong motions should be incorporated

in the description of acceptable analyses. For evaluation of linear responses, this phasing is probably

not too significant. However, for nonlinear effects at the higher acceleration levels, the phasing could

have significant influence on the magnitudes of computed response.

5. NUMBER OF INPUT MOTIONS

If the specification of the input motions discussed above are satisfied, that is, the pulse is

chosen to closely match both the target response spectrum and the target PSD, as described above, then

the requirement to use multiple time histories in the structural response analyses is not necessary.

The primary purpose of the use of multiple time histories in response studies is to ensure that all

frequencies of interest are adequately excited. If any one record was deficient at any one frequency, the

possibility was that the other records used would not have gaps at the same frequency. With the use of

the new criteria for specification of the input motion, the potential for such gaps in energy content is

no longer of concern for practical applications.

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If more emphasis is placed on closely matching the target spectra when developing input

criteria motions, the need for multiple histories reduces. The only variability that would be

incorporated in the response calculations with multiple time histories, all of which satisfy the new

criteria, would be in the definition of the phasing of the Fourier components of the records. If it is

shown that over the frequency range of from 0.4 to 33 hz the phase angles of the components are

uniformly distributed over the interval 0 to 2H1, it is my opinion that the potential for clustering of

the response is minimal and the need for multiple records is eliminated. In developing time histories

which satisfy the new criteria, initial records obtained from actual seismic records can be used! to

"seed" the computation. The artificial records so developed would then satisfy the above requirement.

I therefore recommend that the SRP include the following options in the seismic response

evaluations:

a. If the analyst chooses to use multiple time histories, the envelope spectra produced from all

the time histories should satisfy the target response spectra enveloping criteria, and the

average of the PSD's of the individual records should also satisfy the target PSD criteria

described above. I agree with the previous recommendation that a minimum of five such

records be considered.

b. If the analyst chooses to use a single time history to perform his seismic evaluation, then the

response spectrum and PSD calculated from this single record should satisfy the criteria

described above.

6. SOIL-STRUCTURE INTERACTION

Various modifications have been suggested in the public comments for the revised SRP which

are the result of the advances that have been made in recent years in SSI analysis, both as to

E--7
computational ability as well as to our understanding of the basic phenomena. However, significant

uncertainty in specific response of both the soil and structure will always exist so that we must

temper our understanding with realistic judgements which, in turn, will lead to "suitable" safety in

the design. The following subsections summarize my comments in these various areas associated with

the SSI analysis.

A. Alternate Methods of Analysis

In the Summer of 1986, at the workshop held on SSI in Washington, a relatively broad

concensus of the computational community arrived at a definition of two separate alternatives for the

analyses that may be performed to determine seismic response, one associated with a

non-site-specific study using the broad-banded R.G. 1.60 (or equivalent) spectra definition, and the

second associated with detailed site-specific evaluations of site seismicity. The basic intent of the

approach was to allow the analyst the choice of (a) using broad-banded criteria, or (b) expending

more time and effort to reduce the degree of uncertainty in input specification. In this second

alternative, the gain achieved is the potential for a more narrow-banded spectra to define input

motions.

However, the current proposed revision to the SRP associates this option in alternatives with

the specific SSI analysis used in the response calculation. In my opinion, the alternative input option

should be placed in Section 2.5.2, and be associated with the description of the applicable input spectra

and/or motion histories to be used in the calculations. Section 3.7.2 is intended to describe acceptable

methods of SSI analyses, which is a specific technical discussion uncoupled from the specification of

input motions.

E-8
B. Soil - Structure Interaction Analyses

The primary emphasis of the SRP should be to ensure that proper methods of SSI analysis be

utilized which adequately account for the various phenomena involved, such as, radiation and

hysteretic damping effects, frequency dependent impedance effects, depth of burial consequences, etc.

Various methods of analysis, whether called lumped parameter or half space or finite boundary

methods or the three-step approach or substructuring, etc., all can be acceptable provided they are

properly applied. In the past, this was not always the case, which in turn led to the conservative

enveloping criteria now in effect. All the methods of analysis require detailed evaluation of range of

acceptability, all are relatively complex to apply, and all can lead to correct results. However, if not

properly applied or evaluated, they can lead to grossly erroneous results. I agree with the comments

made by A. Veletsos time and again that more emphasis should be placed on simplified studies to allow

for prediction of the range of potential influences of various aspects of the phenomena, as well as

describing the bounds on the results that will be anticipated from the complex analyses.

If a proper SSI analysis is performed, suitably accounting for the effects important in a

particular problem, no specific concern should be raised as to specification of the criteria motion. In

general, this motion is specified at the ground surface (or at some rock outcrop, or rock interface).

However described, the analysis performed should be compatible with the specification, and all

phenomena associated with the interaction process accounted for and accepted. There is no need to limit

any reductions obtained for the process, except as the need requires to account for those aspects of the

problem not known or treated adequately.

Thus, if a complete SSI analysis is performed, properly accountingn for all effects due to

kinematic and inertial interaction for an embedded structure, with the criteria ground motion

specified at the ground surface or hypothetical outcrop, there is in my opinion no need to limit the

E-9
degree of reduction in the foundation level inputs. This assumes, however, that suitable variability in

soil properties, wave specification, etc, is considered. If, however, the SSI analysis is deficient, as say

by first performing a vertical motion variation calculation (a la SHAKE) and using this reduced

motion as input to the foundation level, then I would favor a limit to the allowable reduction since the

complete SSI effect is not properly included in the analysis. I would then suggest that this reduction be

limited to 40% of the criteria input spectrum.

C. Compatible Soil Properties For SSI Analyses

A variety of issues can be discussed under this general topic heading. In the SRP, it is not clear

how the definition of the "best estimate" soil properties should be incorporated in the analyses. It is

my opinion that the pseudo linear approach, assuming upward propagating shear waves, should be used

to characterize both the shear modulus and damping variation of the soil column compatible with

available experimental soil data. The degradation of soil modulus and increase of soil damping with

strain should include both the results from site test data as well as the mass of data accumulated over

the years. The "best estimate" SSI analyses should then be performed with these strain compatible

soil properties, adequately accounting for the effects of soil layering, depth of burial, etc.

Liquefaction, uplift and potential sidewall separation are obviously evaluated from other detailed

nonlinear studies.

To account for variability in soil properties in the analyses, I would recommend that the range

of properties used in the SSI study be varied from 1/2 to 2 times these "best estimate" values, unless

the analyst can show that a reduced degree of variability is appropriate. It has been my experience

over the years in testing of soils that such a range of variability is not uncommon in foundation

studies. The results at Lotung, Taiwan, even though sampling and testing was carefully controlled, in

my opinion demonstrate the validity of this argument.

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For all analyses performed for the upper and lower bound soil variation cases, the shear

moduli and hysteretic damping ratio used in the SSI analyses should both be compatible with the peak

strains calculated from the free-field analysis for the given seismic input accelerogram. This, in

turn, can be expected to lead to calculations with high shear modulus and low damping ratio and vice

versa. Specifically, I recommend that the upper bound, best-estimate and lower bound cases be

defined as follows. The low strain shear modulus (Gmax), for each soil, should be determined for the

best-estimate case based on the results of the field geophysical testing program. The upper bound

shear modulus at low strain can then be defined as twice this best-estimate value while the lower

bound shear modulus can be defined as one-half this value, provided that this range of variability

suitably encompasses the scatter typically found in the field program. Then, average shear modulus

degradation (G/Gmax vs peak shear strain) and hysteretic damping ratio (D vs peak shear strain)

curves, as defined in Ref. 5, can be determined from the laboratory testing program, together with

typical data available for similar soils. These curves can then be used in the iterative pseudo-linear

analyses to determine shear moduli and hysteretic damping ratios compatible with the peak shear

strains computed in the free-field for the input seismic criteria motions for all soil layers for each

of the three cases of interest. These properties can then be used directly in the SSI computational

model.

I would recommend that the final shear moduli results be limited by the following criteria.

First, the lower bound shear moduli should not be less than the moduli required for an acceptable

foundation design, that is, lead to static settlements much greater than considered acceptable for

normal foundation design. Secondly, the upper bound shear moduli should not be less than the best

estimate shear moduli defined at low strain (Gmax defined at 10-4 percent peak shear strain) for all

soils.

Finally, the limit stated in Section 3.7.2 that hysteretic soil damping should not exceed 5%

appears to be too conservative. I would recommend that this value be set at 15%, as suggested in the

public comments.

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7. REFERBENCES

1. R. P. Kennedy and M. Shinozuka, "Recommended Minimum Power Spectral Density Functions

Compatible With NRC Regulatory Guide 1.60 Response Spectrum", Appendix B January 1989.

2. M. Shinozuka, T. Mochio, E. Samaras, "Power Spectral Density Functions Compatible with NRC RG

1.60 Response Spectra", NUREG/CR-3509, March 1984.

3. R.P. Kennedy, et al, "Engineering Characterization of Ground Motion - Task I" NUREG/CR-3805,

volume 1, USNRC, February 1984

4. D.W. Coates, "Recommended Revisions to Nuclear Regulatory Commission Seismic Design

Criteria", NUREG/CR-1161, Lawrence Livermore Laboratory, May 1980

5. ASCE Standard 4-86, "Seismic Analysis of Safety Related Nuclear Structures" Sept 1986.

E-12
THE CITY COLLEGE OF NEW YORK

CONVENT AVENUE AT 140TH STREET

NEW YORK, N.Y. 10031

SCHOOL OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

Telephone: (212) 690-8145

February 23, 1989

Dr. A. J. Philippacopoulos

Structural Analysis Division

Department of Nuclear Energy

Brookhaven National Laboratory

Upton, New York 11973

Re: Report on Proposed Revisions to the US NRC Standard Review Plan

Dear Mike:

Please find enclosed my final report on the subject modifications to the Standard

Review Plan. If you have any questions, please do not hesitate to contact me.

Sincerely yours

Carl J. Costantino

E-13
4NRC FORM 335

12841

INRCM 1102.

3.01. 3202

SEE INSTRUCTIONS ON THE nTEVE

U.S. NUCL EAR rEGULAOIWIN COMMISSIONI

BIBLIOGRAPHIC DATA SH-EEIT

I PlEPON1 NUMBER IAA#-V-dLUV TIC, odor Vol Noe. ,I*,,v

NUREfl/CR-5347

BNL---NUREG-52 191 RIS

2. TITLE AND SUbTITLE

Recommendations for Resolution of Public Comments on

USI A-40, "Seismic Design Criteria"

3 LEAVE BLANK

S. AUTHORIS)

A. J. Philippacopoulos

4. DATE REPORT COMPLETED

LIONI H VYEAR

February I989 6. DATE REPORT ISSUED

MONTH I YEAR

June I 1989

2. PERFORMING ORGANIZATION NAME AND MAILING ADDRESS 111&ued2,p Code) 8. PROJECT.'TASK,'NORK UNIT NUMBER

Brookhaven National Laboratory 9 FINOR GRANT NUMBER

Upton, NY 11973

A3981

10. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS IIncludeZp Cod.) ,II. TYPE Of REPORT

Division of Safety Issue Resolution Technical

Office of Nuclear Regulatory Research .PERIOD COVERED 11,.0..,-.j

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555

12. SUPPLEMENTARY NOTES

13. ABSTRACT 1200 wordo O!eu

In June 1988 the Nutlear Regulatory Commission (NRC) issued for public

comment the proposed Revision 2 of the Standard Review Plan (SRP) Sections

2.5.2, 3.7.1, 3.7.2 and 3.7.3. Comments were received from six organizations. Brookhaven National Laboratory (BNL) was requested by NRC to provide

expert consultation in the seismic and soil-structure interaction areas for

the review and resolution of these comments. For this purpose, a panel of

consultants was established to assist BNL with the review and evaluation of

the public comments. This review was carried out during the period of October

1988 through January 1989. Many of the suggestions given in the public

comments were found to be significant and a number of modifications to

appropriate SRP sections are recommended. Other public comments were found to

have no impact on the proposed Revision 2 of the SRP. Major changes are

recommended to the SRP sections dealing with (a) Power Spectral Density (PSD)

and ground motion requirements and (b) soil-structure interaction requirements. This report contains specific recommendations to NRC for resolution of

the public comments made on the 'proposed Revision 2 of the SRP.

14 DOCUMENT ANALYSIS- . KEYWORDSDESCRIPTORS IS AVAILABILITY

STATEMENT

Criteria for seismic design of nuclear plants. Unlimited

16 SECURITYCLASS•fICATION

M714 0"e)

b IDENTIFIERS.OPEN ENDED TERMS Unclassified

Unclassified

I) NULIAER Of PAGES

IS PAIC(

0 U.LS.GOVERNMENT PRINTING OFF ICE:1989-241-59 :00992