多点激励下桩-土-斜拉桥全模型振动台试验研究

大跨斜拉桥的自振频率和阻尼低以及空间尺度大，其地震响应受桩基础、场地土特性和地震动空间效应的影响较大。然而，由于试验条件和技术所限，目前尚缺乏相关的全模型振动台试验研究。以一座试设计主跨1400m超大跨斜拉桥为原型，设计和制作了一座几何相似比为1/70且包括上部结构、桩基础和场地土等在内的试验模型，通过振动台试验研究了多点激励对桩-土-斜拉桥全模型地震响应的影响及其规律。试验结果表明：纵向多点激励使一侧主塔的纵向位移、一侧主塔和桥墩的纵向桩-土-结构相互作用效果以及主跨一侧竖向位移增大，而另一侧减小；横向多点激励使一侧主塔的横向位移和一侧桥墩的横向桩-土-结构相互作用效果增大，另一侧减小，但使两侧主塔的横向桩-土-结构相互作用效果和主跨两侧横向位移响应均增大；桩-土-结构相互作用对斜拉桥的加速度响应产生不利影响。基于上述结果，大跨斜拉桥的抗震设计或性能评估应考虑多点激励和桩-土-结构相互作用的影响。

Shaking table test on a pile-soil-cable-stayed bridge full model under multi-support excitations

 Seismic responses of long-span cable-stayed bridges may be significantly affected by the properties of the pile foundation and site soil as well as the spatial effect of ground motion because the long-span cable-stayed bridge has low natural frequencies, structural damping and large spatial scale. However, there are few experimental studies on the full model of a long-span cable-stayed bridge composed of the superstructure, pile foundation and site soil due to the limitations of shaking table testing facilities and technology. A complete model of 1/70-scaled cable-stayed bridge, composed of superstructure, pile foundations and site soil, was designed and fabricated according to a preliminary design of long-span cable-stayed bridge with main span of 1400 m. The full model was tested on the shaking table to study the mechanism associated with the seismic responses of the long-span cable-stayed bridge under uniform and multi-support excitations. Experimental results show that the longitudinal displacement response of the main tower, the longitudinal pile-soil-structure interaction effects of the main tower and piers, and the vertical displacement response of the main span in one side of the full model increase when being subjected to longitudinal multi-support excitations, while the corresponding seismic responses in other side decrease. The transverse displacement response of the main tower and the transverse pile-soil-structure interaction effects of the piers in one side increase when being subjected to transverse multi-support excitations, whereas the corresponding seismic responses in other side reduce. However, the transverse pile-soil-structure interaction effects of the towers and the transverse displacement of the main span in both sides increase for transverse multi-support excitations. Moreover, it is found that the pile-soil-structure interaction has adverse influences on the acceleration response of the cable-stayed bridge. Therefore, it is suggested that the multi-support excitations and pile-soil-structure interaction should be considered when conducting performance evaluation and seismic analyses on long-span cable-stayed bridges.