Vertical Earthquake Loads on Seismic Isolation Systems in Bridges
Publication: Journal of Structural Engineering
Volume 134, Issue 11
Abstract
An important consideration for the design of seismic isolation systems composed of elastomeric and lead–rubber bearings is the safety of individual bearings for maximum considered earthquake shaking. One assessment of bearing safety involves the calculation of the vertical (or axial) earthquake load on the individual seismic isolation bearings. This paper investigates the influence of vertical earthquake excitation on the response of a bridge isolated with low-damping rubber and lead–rubber bearings through earthquake simulation testing. Response data collected from the experimental program are used to determine the vertical load on the isolation system due to the vertical component of excitation. A comparison of the normalized vertical load data to the vertical base acceleration showed significant amplification of the vertical response for each simulation and configuration. Disaggregation of the axial load history showed the summation of maximum values from the vertical earthquake load and overturning moment overestimates the maximum axial load because these maximum values are unlikely to occur simultaneously. Additionally, a spectral analysis procedure using the unreduced vertical stiffness of the bearings was shown to provide a reasonable estimate of the vertical earthquake load.
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Acknowledgments
The writers gratefully acknowledge the financial support of the Multidisciplinary Center for Earthquake Engineering Research and the Federal Highway Administration through Task D1.5 of the Federal Highway Administration Contract No. DTFH 61-98-C-0094. The writers also wish to thank Dr. Amarnath Kasalanati of DIS Inc. for providing the model bearings used in this study. The opinions expressed in this paper are those of the writers and do not reflect the opinions of the Multidisciplinary Center for Earthquake Engineering Research or the Federal Highway Administration. No guarantee regarding the results, findings, and recommendations are offered by either the Multidisciplinary Center for Earthquake Engineering Research or the Federal Highway Administration.
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Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 134 • Issue 11 • November 2008
Pages: 1696 - 1704
Copyright
© 2008 ASCE.
History
Received: Dec 14, 2006
Accepted: Mar 21, 2008
Published online: Nov 1, 2008
Published in print: Nov 2008
Notes
Note. Associate Editor: Marvin W. Halling
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