刚性桩复合地基地震响应的拟静力简化计算方法

刚性桩复合地基在建筑结构中已得到广泛应用,但对其地震作用下的动力响应研究还不够充分。采用上海市《建筑抗震设计规程》8度罕遇地震的规范标准反应谱拟合生成人工地震波,以软土场地中的某10层钢筋混凝土框架结构为对象,将土体自由场变形和上部结构惯性力对桩身内力的影响分开考虑,提出一种拟静力简化计算方法,分析刚性桩复合地基的地震响应。并建立刚性桩复合地基-筏板-上部结构体系整体有限元模型,利用数值方法进行动力时程分析,验证了拟静力方法的合理性。进一步分别计算了自由场位移对桩基的作用、刚性桩复合地基-筏板-上部结构体系整体地震响应以及桩筏基础地震响应。结果表明:拟静力方法与数值方法较为吻合,复合地基的桩身内力和筏板底加速度峰值均小于桩筏基础,褥垫层对地震波具有滤过作用,显著减轻了地震的作用效应。

Pseudo-static Simplification Analysis of Rigid Pile Composite Foundation under Earthquake Action

Rigid pile composite foundation has been widely applied in structures. However, researches on seismic performance under earthquake loading are very inadequate. Referring to the code for seismic design of buildings, an artificial earthquake wave is generated by a standard response spectrum of rare earthquake with intensity 8. Via earthquake response of a ten-story reinforced concrete frame structure in soft ground, seismic performance of the rigid pile composite foundation is analyzed in this paper. Internal force of a pile is separately influenced by deformation of free-field response and the inertia force of super-structure. A pseudo-static simplification method is proposed based on the above assumption for this kind of foundation. Then numerical analysis method is used to establish a whole finite element model of a rigid pile composite foundation-raft-superstructure system and dynamic time-history analysis on the model is carried out to verify the pseudo-static method. The effect of free-field displacement on piles and seismic response of the whole finite element model are analyzed in this paper. Besides, seismic response of piled raft foundation and composite foundation under the same conditions is compared in this paper. It is shown that results of the pseudo-static method are close to those of the numerical analysis method. Internal forces and peak accelerations on the raft bottom of the composite foundation are all less than those of the piled raft foundation. The cushion has a filtering effect on seismic waves to reduce the impact of earthquakes.