Evaluation of Equivalent Linear Analysis Methods of Bridge Isolation

Various equivalent linear analysis methods for base-isolated regular bridges are compared and evaluated in this paper. The equivalent linear analysis models encompassed in the paper are those specified by the American Association of State Highway and Transportation Officials (AASHTO) and the Japanese Public Works Research Institute (JPWRI). In addition, an internally used model by the California Department of Transportation (CALTRANS) and a recently proposed model are also included. The comparison and evaluation are conducted to investigate the fidelity of various equivalent linear models in simulating the bilinear hysteretic bearings and the accuracy of the models in predicting the maximum seismic responses of the bearings. To perform the evaluation, a single degree of freedom (SDOF) system composed of a rigid block isolated by bilinear hysteretic bearings is subjected to 55 earthquake ground motions. The discrepancies of maximum seismic responses predicted by equivalent linear analysis methods and by inelastic analysis method are measured using root mean square (RMS) errors. The average of RMS errors over the 55 earthquake ground motions are compared and used to evaluate the formulations of equivalent linear analysis methods.