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A study of the apparent change in the foundation response of a nine-story reinforced concrete building

Foutch, Douglas A. and Jennings, Paul C. (1978) A study of the apparent change in the foundation response of a nine-story reinforced concrete building. Bulletin of the Seismological Society of America, 68 (1). pp. 219-229. ISSN 0037-1106.

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Forced vibration tests of the Millikan Library building, a nine-story reinforced concrete shear-wall structure, were conducted in 1966 and 1967, before the San Fernando earthquake, and again in 1974. The measured foundation response of the structure reported for the two tests was significantly different: in the earlier tests, motion of the foundation in the N-S direction contributed only about 3 per cent to the total roof motion, whereas in the more recent tests almost 30 per cent of the roof motion was contributed by foundation compliance. A lengthening of the fundamental period of vibration of 11 per cent was also noted. The purpose of this study is to examine the indication that the foundation response of the structure may have changed because of the earthquake. To determine whether the observed changes in foundation response are consistent with the change in natural period, two analytical models of the Millikan Library building were developed. Both of these models include the effects of foundation compliance and one includes the effects of shear deformations in the walls of the structure. The results of these simple analyses show the changes of mode shape and period observed between the two tests to be consistent. From the analysis, and from an examination of what is thought to be minor earthquake damage at the ground floor level of the structure, the authors conclude that the most probable cause of the differences observed in the two tests is the loss of rotational and translational stiffness provided by retaining walls, concrete slabs and other stiff, but brittle elements.

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Additional Information:Copyright © 1978, by the Seismological Society of America. Manuscript received August 4, 1977. The authors wish to acknowledge the assistance of Mr. Raul Relles in conducting the tests and maintaining and operating the instrumentation systems. Financial support was supplied by the National Science Foundation under Grant ATA 74-19135, and by the Earthquake Research Affiliates of the California Institute of Technology.
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NSFATA 74-19135
Caltech Earthquake Research AffiliatesUNSPECIFIED
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Record Number:CaltechAUTHORS:20140812-132823758
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48412
Deposited By: George Porter
Deposited On:12 Aug 2014 21:57
Last Modified:13 Aug 2021 23:31

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