Simply-supported bridges are vulnerable to surface fault rupture as evidenced by several fault-crossing bridges in the 1999 Chi-Chi earthquake. To investigate the seismic collapse mechanism of simply-supported bridges crossing the fault, across-fault ground motions are firstly simulated in the present study. In particular, based on a previously developed fault model of the 1999 Chi-Chi earthquake, broadband across-fault ground motions at six fault-crossing bridges are simulated using the hybrid deterministic-stochastic method, in which the low- and high-frequency components are computed using the deterministic Green’s function method and the stochastic finite-fault modeling method, respectively. The simulation results indicate that the hybrid deterministic-stochastic method can give reasonable predictions to the across-fault ground motions. Furthermore, utilizing the explicit dynamic finite element (FE) code LS-DYNA, behaviors of a three-span simply-supported bridge under a selected pair of across-fault ground motions are numerically simulated. Numerical results indicate that the structural responses and collapse mechanisms are dominated by the low-frequency ground motions. The large differential static offset across the fault is the main reason for the collapse of the simply-supported bridges. This study contributes understandings for the across-fault ground motions and the collapse mechanism of some bridges in the 1999 Chi-Chi earthquake.
Abstract.A high damping rubber bearing was designed and manufacturedin order to reduce the seismic response of the bridge structure. The experimental study on its mechanical properties was carried out. The results show: the horizontal equivalent damping ratio is 16.77% when the shear strain is 175%. If the shear strain is larger, the post yield stiffness will be smaller as well as the horizontal equivalent stiffness. However, the equivalent damping ratio and yield force will be larger. If the vertical compressive stress is greater meanwhile the loading frequency is faster, and number of repeated loading is smaller, the equivalent stiffness and the post yield stiffness will be larger as same as the equivalent damping ratio. Destruction didn't occur if the shear strain was no more than allowable shear strain (250%), and the ultimate shear strain was 350%. Compression destruction came when pressure stress was 10MPa. In the case of failure, the bearing was stable, but had large, nonrecoverable vertical and horizontal deformation. The study results can be used as the basis for shaking table test of seismic isolated continuous girder bridge with high damping rubber bearing and the reference for relative seismic isolated bridge design.
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