Seismic Isolation of Highway Bridges

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Seismic Isolation of Highway Bridges

by Ian G. Buckle,1 Michael C. Constantinou,2

Mirat Dicleli3 and Hamid Ghasemi4

Publication Date: August 21, 2006 Special Report MCEER-06-SP07

Task Number 094-D-3.1 FHWA Contract Number DTFH61-98-C-00094 Contract Officer's Technical Representative: W. Phillip Yen, Ph.D., P.E. HRDI-7 Senior Research Structural Engineer/Seismic Research Program Manager

Federal Highway Administration

1 Department of Civil and Environmental Engineering, University of Nevada Reno 2 Department of Civil, Structural and Environmental Engineering, University at

Buffalo, The State University of New York 3 Department of Engineering Sciences, Middle East Technical University 4 Turner Fairbanks Highway Research Center, Federal Highway Administration

MCEER University at Buffalo, The State University of New York Red Jacket Quadrangle, Buffalo, NY 14261 Phone: (716) 645-3391; Fax (716) 645-3399 E-mail: mceer@buffalo.edu; WWW Site:

EXECUTIVE SUMMARY

Seismic isolation is a response modification technique that reduces the effects of earthquakes on bridges and other structures. Isolation physically uncouples a bridge superstructure from the horizontal components of earthquake ground motion, leading to a substantial reduction in the forces generated by an earthquake. Improved performance is therefore possible for little or no extra cost, and older, seismically deficient bridges may not need strengthening if treated in this manner. Uncoupling is achieved by interposing mechanical devices with very low horizontal stiffness between the superstructure and substructure. These devices are called seismic isolation bearings or simply isolators. Thus, when an isolated bridge is subjected to an earthquake, the deformation occurs in the isolators rather than the substructure elements. This greatly reduces the seismic forces and displacements transmitted from the superstructure to the substructures. More than 200 bridges have been designed or retrofitted in the United States using seismic isolation in the last 20 years, and more than a thousand bridges around the world now use this cost- effective technique for seismic protection. This manual presents the principles of isolation for bridges, develops step-by step methods of analysis, explains material and design issues for elastomeric and sliding isolators, and gives detailed examples of their application to standard highway bridges. Design guidance is given for the lead-rubber isolator, the friction-pendulum isolator, and the Eradiquake isolator, all of which are found in use today in the United States. Guidance on the development of test specifications for these isolators is also given. This document is intended to supplement the Guide Specifications for Seismic Isolation Design published by the American Association of State Highway and Transportation Officials, Washington, DC, in 1999. Every attempt is made with the procedures, descriptions and examples presented herein, to be compatible with these specifications. It is not intended that this Manual replace the Guide Specifications, but should, instead, be read in conjunction with these Specifications.

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