ML20212L162

Structural Engineering Branch Position Re Plant Seismic Design

ML20212L162
Person / Time
Site:	05000000, Diablo Canyon
Issue date:	05/18/1976
From:	Sihweil I Office of Nuclear Reactor Regulation
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FOIA-86-391 NUDOCS 8608250234
Download: ML20212L162 (2)

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Enclosure No. 2 NUCLEAR REGULATORY C0tHISSION STRUCTURAL ENGINEERING BRANCH BRANCH POSITION ON THE SEISMIC DESIGN OF DIABLO CANYON 1.

The applicant will be asked to specify a magnitude 7.5 earthquake at the HOSGRI fault with horizontal spectra normalized to 0.75g Regulatory Guide 1.60 spectral shapes may be used. Use of the HOSGRI spectral shape will require further justification since it is believed that the HOSGRI spectral' shape was developed for lower magnitude earthquakes.

2.

A reduction in both horizontal and vertical response spectra will be permitted depending on the actual equivalent length of individual IFieW buildings. This reduction recognizes that ground motions are not synchronized under structures during earthquakes.

In other words, different points in the foundation base slab will not experience, the maximum free field ground potion,at the same time. The quiv-alent length of each individual structure will be equal to the square root of the building base slab area. The magnitude of the reduction factor shall be determined as the average of the value from the theoretical procedure given by Scanlan (see Reference) for a harmonic wave and the value determined using trie Pacoima Dam record obtained in the 1971 San Fernando earthquake. The harmonic wave in the Scanlan procedure will be assumed to have a frequency of 7 hertz.

3.

Where such reduction in response spectra is used, the applicant will be asked to appropriately account for additional tilting and torsion which may result from the nonsynchronized earthquake motions considered in item 2, above.

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4.

In reevaluating the capability of the plant structure, systems and components, inelastic behavior may be relied upon to absorb the ground motion energy. Where such a behavior is relied upon, a ductility ratio not exceeding 1.2 may be used in determining seismic loads and motions. Foreachparticul5rstructurewhere this ductility is relied upon, the applicant. will be asked to provide justification and bases for assuring that the increased strains and deformations will not affect the safety functions of the plant systems and structures. Th'is ductility ratio is permitted by the SEB staff for near-field earthquakes, such as those associated with the HOSGRI fault, which tend to have shorter duration.s of strong motion.

It is recognized that for short duration earthquakes, the use of elastic response spectra tends to produce overly conservative results.

5.

It was also decided that the a,nalytical work required to develop individual response spectra fo'r the various plant buildings will be performed by the applicant and a report will be requested thereafter. The SEB staff and Dr. Newmark will review this report and only thereafter will finalize the SER for release.

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Isa S. Sihweil, Chief Structural Engineering Branch Division of Systems Safety

Reference:

"Seisnic Nwe Effects on Soil Structure Interaction" by R. H.

Scanlon, 3rd 9fIRT Conference,1975