Performance evaluation of bridge seismic bearings based on in-situ quick-release tests

A nonlinear model-based system identification method is proposed, formulated, implemented, and applied to a three-span continuous base-isolated bridge. Transverse and rotational rigid-body motions of the bridge superstructure are formulated into two degrees-of-freedom dynamic governing equations. To model hysteretic behavior of lead-rubber bearings, the Menegotto-Pinto model is used. The proposed system identification procedures consist of two phases to lessen ill-conditioning of the given problem. It has been reported that the stiffness of deck joints located at two abutments contributes to the dynamic responses of the structure. However, the mechanical properties of the deck joints have not been investigated thoroughly for use in the identification procedures. The uncertain contribution of the deck joints is considered by treating deck joint stiffnesses as random variables. The identification, therefore, results in probability distributions and hypothesis testing is used to determine the closeness of identification results. The proposed method is applied to quick-release field experiments on the bridge to investigate aging and temperature dependent effects of leadrubber bearings. The results from system identification are compared with those from design guidelines for seismic isolation.