Bridges are a part of vital infrastructure, which should operate even after a disaster to keep emergency services running. There have been numerous bridge failures during major past earthquakes due to liquefaction. Among other categories of failures, mid span collapse (without the failure of abutments) of pile supported bridges founded in liquefiable deposits are still observed even in most recent earthquakes. This mechanism of collapse is attributed to the effects related to the differential elongation of natural period of the individual piers during liquefaction. A shake table investigation has been carried out in this study to verify mechanisms behind midspan collapse of pile supported bridges in liquefiable deposits. In this investigation, a typical pile supported bridge is scaled down, and its foundations pass through the liquefiable loose sandy soil and rest in a dense gravel layer. White noise motions of increasing acceleration magnitude have been applied to initiate progressive liquefaction and to characterize the dynamic features of the bridge. It has been found that as the liquefaction of the soil sets in, the natural frequency of individual bridge support is reduced, with the highest reduction occurring near the central spans. As a result, there is differential lateral displacement and bending moment demand on the piles. It has also been observed that for the central pile, the maximum bending moment in the pile will occur at a higher elevation, as compared to that of the interface of soils of varied stiffness, unlike the abutment piles. The practical implications of this research are also highlighted.

桥梁是重要基础设施的一部分，即使在灾难发生后桥梁也应运转，以保持应急服务的正常运行。在过去的大地震中，由于液化，桥梁多次失灵。在其他类型的破坏中，即使在最近的地震中，也仍然可以观察到在可液化沉积物中建立的桩支撑桥梁的中跨坍塌（无基台破坏）。坍塌的这种机制归因于与液化过程中各个墩的自然周期差异伸长有关的影响。在这项研究中，进行了振动台调查，以验证液化沉积物中桩基桥梁中跨倒塌的机理。在这项调查中，典型的桩支撑桥按比例缩小，其基础穿过可液化的疏松沙土，并停留在致密的砾石层中。已经应用了增加加速度幅度的白噪声运动来引发液化并表征桥梁的动力特性。已经发现，随着土壤液化的进行，单个桥梁支撑的固有频率会减少，其中最大的减少发生在中央跨度附近。结果，在桩上需要不同的横向位移和弯矩。还已经观察到，与基桩不同，对于中心桩，与刚度变化的土壤的界面相比，桩中的最大弯曲力矩将在更高的高度上发生。还强调了这项研究的实际意义。