Shear and Friction Response of Nonseismic Laminated Elastomeric Bridge Bearings Subject to Seismic Demands
Publication: Journal of Bridge Engineering
Volume 18, Issue 7
Abstract
Laminated elastomeric bridge bearings are commonly used in areas with low-to-moderate seismicity, although the applications are typically intended for service-level considerations such as thermal movements of the bridge superstructure. These components provide a potential source of displacement capacity frequently neglected in seismic design. An experimental program was carried out to evaluate the behavioral characteristics and performance of steel-reinforced, laminated elastomeric bearings, which had not been designed for seismic demands, as the primary quasi-isolation components for seismic events by permitting slip at the interface of the bearing and substructure. The rubber at the top of the bearing is vulcanized to a steel plate, which is bolted to the test frame to simulate a connection to the superstructure. At the base of the bearing, the elastomer directly contacts concrete representing the substructure, with no restraint of horizontal motion other than friction. The elastomeric bearings investigated during the experimental program displayed an approximately linear elastic response before sliding, with an initial friction coefficient in the range of 0.25–0.5 (at a shear strain between 125 and 250%) depending on combinations of the contact surface roughness, applied load, and bearing velocity. The friction coefficient decreased as a nonlinear function of the imposed vertical load. The maximum elastomer shear strain prior to sliding exhibited nonlinear increases with vertical load, resulting from the influence of the variable friction coefficient. Linear shear moduli were primarily influenced by the maximum shear strain imposed on the bearing, and showed shear stiffness reductions of approximately 40–50% following multiple, large displacement slip cycles, compared with 15–25% after reaching 50% shear strain. Multiple cycles of large displacement demands resulted in noticeable degradation in the friction coefficient over the duration of the tests. However, the bearings possessed a high degree of resiliency, considering that the specimens retained load-carrying capacity through total cumulative slip travel demands in the range of 3.5–4.5 m (140–180 in.).
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Acknowledgments
This paper is based on the results of ICT R27-70, Calibration and Refinement of Illinois’ Earthquake Resisting System Bridge Design Methodology (LaFave et al. 2013). ICT R27-70 was conducted in cooperation with the Illinois Center for Transportation (ICT), IDOT, Division of Highways, and the U.S. Department of Transportation, Federal Highway Administration (FHwA). The content of this paper reflects the view of the authors, who are responsible for the facts and the accuracy of the data presented herein. The content does not necessarily reflect the official views or policies of the ICT, IDOT, or FHwA. The authors would like to thank the members of the project Technical Review Panel, chaired by D. H. Tobias of the Illinois Department of Transportation, for their valuable assistance with this research.
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© 2013 American Society of Civil Engineers.
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Received: Aug 26, 2011
Accepted: Apr 24, 2012
Published online: Apr 26, 2012
Published in print: Jul 1, 2013
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