United States Department of Transportation
i
Experimental investigation of the seismic response of bridge bearings.
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2013-05-01
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[PDF-4.90 MB]
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Abstract:The Illinois Department of Transportation (IDOT) commonly uses elastomeric bearings to accommodate thermal
deformations in bridges. These bearings also present an opportunity to achieve a structural response similar to isolation
during seismic events. IDOT has been developing an earthquake resisting system (ERS) to leverage the displacement
capacity available at typical bearings in order to provide seismic protection to substructures of typical bridges. The research
program described in this report was conducted to validate and calibrate IDOT’s current implementation of design practice for
the ERS, based on experiments conducted on typical full-size bearing specimens, as well as computational models capturing
full bridge response. The overall final report is divided into two volumes. This first volume describes the experimental program
and presents results and conclusions obtained from the bearing and retainer tests. The experiments described in this volume
provide data to characterize force-displacement relationships for common bearing types used in Illinois. The testing program
comprised approximately 60 individual tests on some 26 bearing assemblies and components (i.e., retainers). The testing
program included (1) Type I elastomeric bearings, consisting of a steel-reinforced elastomeric block vulcanized to a thick top
plate; (2) Type II elastomeric bearings, distinct from Type I bearings with a steel bottom plate vulcanized to the bottom of the
elastomeric block, and a flat sliding layer with polytetrafluoroethylene (PTFE) and stainless steel mating surfaces between the
elastomer and the superstructure; and (3) low-profile fixed bearings. Tests conducted to simulate transverse bridge motion
also included stiffened L-shaped retainers, consistent with standard IDOT practice. Tests were conducted using monotonic
and cyclic displacement protocols, at compression loads corresponding to a range of elastomer compression stresses from
200 to 800 psi. Peak displacements from initial position ranged from 7-1/2 in. to 12-1/2 in., depending on bearing size. Test
rates were generally quasi-static, but increased velocities up to 4 in./sec were used for bearings with PTFE and for a subset
of other elastomeric bearings. On the basis of all of the experimental findings, bearing fuse force capacities have been
determined, and appropriate shear stiffness and friction coefficient values for seismic response have been characterized and
bracketed.
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