承台型式对可液化场地桥梁桩-柱墩地震响应影响振动台试验

Effect of cap type on seismic responses of bridge pile-column pier in liquefiable ground by shaking table test

基于相同土层结构地基条件下,分别采用低承台群桩-独柱墩与高承台群桩-独柱墩结构,完成了两次可液化场地群桩-土-桥梁结构地震反应振动台试验,据此研究了承台型式对桥梁桩-柱墩地震反应的影响。研究表明,与高承台桩相比,可液化场地中低承台桩的抗震性能更优;地震中砂层尚未液化或液化不充分时,低承台更多表现出减弱桩尤其桩上段的加速度反应的作用,相反高承台更多起到放大桩的加速度作用,而高承台桩与低承台桩的峰值应变自下而上更多表现出逐渐增大趋势;即使砂层完全液化时,低承台桩的峰值应变自下而上仍以渐增为主;与低承台桩相比,高承台桩更有助于放大墩顶加速度、位移反应,对结构体系整体稳定性产生了不良影响;虽然低承台桩未出现严重破坏,但砂层中部桩的应变却很大,液化砂土-桩运动相互作用对桩的抗震性能影响不容忽视。

Two shaking table tests concerning seismic soil-pile group-bridge structure interaction in liquefiable ground with the same soil structure condition were completed to study the effect of cap type on the seismic response of bridge pile-column pier, adopting low-cap pile group-single column pier and elevated-cap pile group-single col- umn pier respectively. It showed from the tests that seismic performance of low-cap pile group was better than that of elevated-cap pile group. For low-cap pile group, the acceleration responses of the pile were more reduced, espe- cially in the upper pile parts when the sand layer was not liquefied or liquefied partly; however, for elevated-cap pile group the acceleration responses of the pile were amplified distinctly; moreover, the peak strains on both low- pile and elevated-cap pile tended to progressively increase bottom-up. Even though the sand layer was liquefied completely, the peak strains on the low-cap pile mainly revealed augmentation characteristic bottom-up; the elevat- ed-cap pile would be more helpful to amplify the acceleration and displacement responses of the pier top and had a disadvantageous impact on the stability of the whole test system. The strain of the pile in the middle of the sand lay- er was still very large, despite the serious damage to low-cap pile was not caused. So, seismic pile-soil interaction had remarkable effect on the seismic performance of the piles in liquefiable ground.