Bi-directional testing, modeling, and system response of seismically isolated bridges

Using a rigid-block model with isolation bearings, a series of tests were conducted on an earthquake simulator to investigate the bi-directional characteristics of isolation bearings. The coupled plasticity model is used to characterize the bi-directional behavior of the bearings. The results show that both the lead-rubber (LR) and high-damping rubber (HDR) bearings exhibit bi-directional coupled behavior, which can be simulated by the circular yield surface of the plasticity model at a fixed cyclic strain level.; An improved model, based on the bounding surface theory, was developed to represent the bi-directional behavior of LR bearings. Compared with experimental data, the improved model, using only four independent parameters, can accurately simulate the strain-dependent properties under uni- and bi-directional displacement histories.; The adequacy of mathematical models for the LR bearings was examined using the experimental data of the rigid-block model subjected to various bi-directional ground motions. The results show that the improved coupled model can accurately simulate the behavior of LR bearings subjected to bi-directional ground motions.; Using the bi-directional model of bearing behavior, a parametric study was performed to investigate the effect of pier flexibility, and distributions of stiffness and bearing strength on response of five different one- and two-span isolated bridge systems subjected to bi-directional earthquake shaking. It was observed that the vibration period based on the equivalent pier stiffness, which corresponds to the sum of the flexibility of the pier stiffness and the second-slope bearing stiffness, is useful for characterizing the response of isolated bridges. (Abstract shortened by UMI.)...