超大跨斜拉桥群桩基础多点振动台试验

Multi-shaking-table Test of Pile Group Foundation Under Super-long-span Cable-stayed Bridge

为研究一致激励条件下大跨度桥梁群桩基础的地震响应,以一座试设计斜拉桥(全长2 672m,主跨1 400m)为原型,设计了1/70的桩-土-桥梁结构全桥物理模型,基于该全桥模型开展群桩基础振动台试验研究。采用微粒混凝土和铁丝制作钢筋混凝土主塔和桥墩,C40混凝土和6mm螺纹钢制作桩基础和承台,质量比为3∶1的砂子和木屑模拟土体。模型包含8组群桩基础,分别支撑过渡墩、辅助墩和主塔。地震波采用人工波Acce100,自然地震波El Centro,Mexico City和Chi-Chi,以研究不同卓越频率地震波输入对大跨度桥梁群桩基础的影响。分析群桩基础的地震反应规律,包括不同桥墩处桩基础的桩身加速度、位移和弯矩。结果表明:因不同位置处群桩基础振动特性不同,相同地震动经各群桩基础传递至过渡墩、辅助墩和主塔底部,产生不同变化,导致不同桥墩或主塔处输入上部结构的激励不同;支撑辅助墩和主塔的群桩基础,桩顶加速度和相对位移随着输入地震波加速度峰值的增加而增加,但峰值加速度放大系数降低。4种地震波中Chi-Chi波引起的各群桩基础桩顶相对位移和桩顶弯矩响应最大;输入地震动为Mexico City波时,过渡墩处的群桩基础桩顶相对位移、加速度峰值放大系数大于辅助墩处群桩基础的相对位移和放大系数,输入地震动为其他3种地震波时,结果相反。

To investigate the seismic response of pile groups supporting long-span cable-stayed bridge under uniform excitations, a series of shaking table tests were carried out considering the seismic soil-pile-structure interaction （SSPSI） based on a 1/70 scaled model of an assumed prototype （a cable-stayed bridge with the length of pylons and piers were fabricated of micro-concrete made of C40 concrete and rebar with the diameter sand and sawdust with the mass ratio of 3 ： 1. 2 672 m and a main span of 1 400 m）. The and iron wire. The piles and pile-caps were of 6mm. The natural soil was simulated by The scaled model included 8 groups of pile foundation supporting transition piers, auxiliary piers and pylons, respectively. Four types of seismic waves, namely, artificial seismic wave Accel00, natural waves El Centro, Mexico City and Chi-Chi, were employed to investigate the impact of input waves with different predominant frequencies on the seismic response of the pile group foundation. The seismic response of pile group foundation supporting piers and pylons, including pile accelerations, displacements and moments, were highlighted. The results show that on account of the different vibration characteristics of pile group supporting piers or pylons, the same ground motions are transmitted differently to the bottom of transition piers, auxiliary piers and pylons, by dint of the pile group foundation. Seismic waves are changed differently by pile groups at different locations, and the excitations input to superstructure from the bottom of piers or pylons are different. With the peak acceleration of input waves growing, acceleration and relative displacement at pile head for pile groups supporting auxiliary piers and pylons increase, but amplification ratios of peak acceleration decrease. Among the four seismic waves, relative displacement and bending moments at pile head of each pile group caused by Chi-Chi are the largest. The relative displacement and amplification ratios of peak acceleration at the head of pile groups supporting transition piers are larger than that of pile groups supporting auxiliary piers under the Mexico City excitation. However, the opposite results will he acquired under the other 3 types of excitations.