Influence of Mullins and hardening effects of seismic isolation rubber bearings on the seismic response

In the current Specifications for Highway Bridges of the Japan Road Association, a bilinear force- displacement relationship is recommended as the hysteresis loops of the seismic isolation rubber bearings for the dynamic structural analysis of seismically isolated bridges. However, it has been confirmed that the restoring force characteristics of the actual devices are different from the bilinear model due to the Mullins effect and the hardening phenomenon of the rubber under large shear strains. In this study, the effect of these two factors on the seismic response of a bridge is investigated through the dynamic analysis with the tri-linear double target model considering the factors. The parameters of the model are obtained from product test results of lead-plugged laminated rubber bearings and high-damping laminated rubber bearings.