黏质粉土中在单向地震动输入下的低承台桩基动力响应特征分析

Analysis on Dynamic Responses Characteristic of Low Base Slab Pile Foundation under One-way Seismic Motion Input in Clayed Silt

针对均质黏质粉土场地中上部荷载一定而设计了五桩一承台的布桩方式,采用强震记录的El-Centro-NS波前30 s地震动加速度时程作为地震动输入时程,进行了单向地震动输入的数值模拟,揭示了动力响应的特征及机理。数值模拟研究表明:墩顶、墩底、桩顶的加速度峰值分别是输入加速度峰值的2倍、0.8倍和0.76倍,表明上部结构的运动效应受结构惯性力影响更大;地表结构物的结构尺寸、荷载对地震响应具有显著的影响;承台与承台侧土体对加速度具有一定的削减作用。承台底面土体沉降先随着地震动小幅度波动,之后随着地震动幅值的增大,沉降迅速放大。五桩一承台布桩方式下,五根桩加速度峰值自桩端向上先增大,至埋深25 m附近开始减小,至埋深13 m附近峰值加速度减小到最小,再向上加速度峰值又迅速放大。

The five-pile one-base-slab pile arrangement mode is designed for the upper load in the homogeneous clayed silt site. The 30 s seismic oscillation acceleration time history before the strong seismic records of El-Centro-NS wave taken as the seismic oscillation input time history is used to carry out the numerical simulation of one-way seismic oscillation input, and to reveal the characteristic and mechanism of dynamic response. The numerical simulation study shows that the acceleration peak of the pier top, pier bottom and pile top are separately 2 times, 0.8 times and 0.76 times of the input acceleration peak. The study shows that the motion effect of the superstructure is more affected by the structural inertia force, the structural size and load of the surface structure have a significant effect on the seismic response,and the base slab and its side soil have a certain role in the reduction on the value of acceleration. The settlement of subface soil of the base slab firstly has the fluctuation within a narrow range with the seismic oscillation, and then the settlement speeds up with the increment of the amplitude of the seismic oscillation. In the case of the five-pile one-base slab arrangement mode, the peak of five-pile acceleration increases from the pile end upwards, starts to decrease near the burial depth 25 m, and decreases to the minimum near the burial depth 13 m, and again increases rapidly upwards.