摘要
目前橋梁耐震規範主要是考慮斷層遠域自由場的地震特性，僅透過放大係數來考慮近斷層。然而近斷層擁有高速度脈衝、大殘餘位移的動力特性，因此有必要考慮這些特性對於橋梁受震行為的影響。而跨斷層橋梁由於斷層地表相對錯動導致斷層兩側支撐呈現不同，甚至完全相反的地面運動特徵，在數值模擬上必須採用多支承非同步輸入，計算橋梁模型在地震作用下的結構地震反應。本研究之目的在建立位移輸入法之多支承地震激勵輸入方式，用以探討跨斷層橋梁受地震作用之反應。首先以近斷層地震的加速度歷時經數值積分得到對應的位移歷時，利用位移輸入方式進行非線性動力歷時分析。考慮多支承在非同步輸入的情況下模擬跨斷層橋梁的地震反應，用以探討近斷層地震中殘餘位移與速度脈衝對橋梁受震反應的影響。並進一步比較橋面板支承形式、斷層穿越角度等對於跨斷層橋梁受震反應之影響。數值模擬結果顯示非同步輸入地震歷時會使橋梁結構產生局部較大變形與內力；同步輸入地震歷時則會使橋梁結構產生較大的絕對加速度。此外，本文就位移的分配方式區分為絕對錯位和相對錯位兩種，數值結果顯示在內力計算的部分，相對錯位與絕對錯位所得之最大值差異不大；但變形的部分，絕對錯位所得之最大值往往高於相對錯位所得之最大值。模擬同時顯示斷層水平角45度的作用下，對於柱底扭矩會產生較明顯的放大，但其餘物理量會小於斷層水平角90度的作用。最後，本文依橋面板與柱頂接合處不同的邊界條件，將橋型分為連續橋、簡支梁橋和構架橋等三種。構架橋與連續橋的最大歷時反應相當接近，簡支梁橋各項物理量的最大歷時反應相較於連續橋可能增大或減少。
並列摘要
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.
參考文獻
延伸閱讀
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