Evaluation of Elastomeric Bridge Bearings for Seismic Design: Fid-Bau Portal

Evaluation of Elastomeric Bridge Bearings for Seismic Design

C. Ash / J. Schwartz / M. Aschheim / N. Hawkins / B. Gamble

Elastomeric bridge bearings have been used by various states in the mid-American region to accommodate thermal movement of bridge decks for over thirty years. Their potential role for mitigating damage in the infrequent but high consequence earthquakes that characterize the central United States is explored in this project. The potential protective role of conventional elastomeric bearings is critically influenced by material properties such as shear modulus, known to be temperature dependent. The degree of influence at low temperatures is determined through experimental studies. Slip characteristics of in-service aged and contaminated Teflon interfaces are determined. Full-scale bearings taken from existing bridges in addition to new bearing form the basis of these tests. Materials tests performed on the elastomer characterize the properties of aged bearings. The influence of these physical on possible bridge damage caused by earthquake ground shaking is assessed through computational simulations. A retrofit bearing with improved details for seismic isolation is designed and tested. An apparatus for testing the bearings was developed to simulate actual loading conditions. The apparatus provides a temperature-controlled chamber to allow for low temperature testing. Test protocols are developed to address the influence of testing parameters such a low temperature exposure and compressive stress. The prototype retrofit bearing design was also tested in this setup. The seismic response of a representative bridge is assessed by computational simulations conducted using the nonlinear analysis software DRAIN-2DX.