Seismic Performance of Crossing-fault Bridges

• Main Authors: YI-CHE HO, 何宜哲
• Other Authors: JIN-GUO ZHENG
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/kf38wq

碩士 === 中原大學 === 土木工程研究所 === 107 === The seismic design code for highway bridges mainly considers the characteristics of far field ground motions. The influences of near-fault earthquakes are taken into account only by the magnification factors in the design codes. However, the characteristics of the near-fault ground motions include high velocity impulse, large ratio of PGA/PGV and large residual displacements, which may result in different failure mechanisms. As a result, it is necessary to consider the effects of these dynamic characteristic of near-fault earthquakes on the seismic responses of bridges. Cross-fault bridges which are subjected to different ground motions at opposite sides of the fault line suffer more attacks in earthquakes. In this study, the seismic responses of cross-fault bridges are simulated with the multiple-excitation method and solved by nonlinear dynamic time history analyses. The displacement time history of each excitation is obtained by integrating the acceleration time history of a near-fault ground motion. The influences of the velocity impulse and residual displacements of near-fault earthquakes on the seismic responses of cross-fault bridges are discussed. In addition, the effects of the boundary conditions of the bridge deck and the angle between the bridge and fault line on the seismic responses of cross-fault bridges are also elaborated here. Numerical results demonstrate that the multiple-excitation simulation obtained larger local deformation and internal forces. On the other hand, the single-excitation simulation obtained larger absolute acceleration. Moreover, the ground displacements from integration are further divided into absolute displacements and relative displacements, which are assigned to the ground motions at opposite sides of the fault line. Numerical results show that there are no obvious differences on internal forces between these two displacement distributions. However, the absolute displacement generates larger member deformation. Moreover, the torsions at the bottom of bridge columns are magnified when the fault angle is 45°. Finally, the influences of different boundary conditions between bridge slabs and columns on the seismic responses are investigated. The seismic responses of rigid connections are similar to those of pin connections while the seismic responses of simply supported bridges have different characteristics.