基于振动台试验的桩基动力特性的研究

基于支盘桩-土-框架结构动力相互作用的振动台模型试验,采用大型有限元分析软件Marc对支盘桩和直杆桩体系的抗震性能进行了分析和研究。数值计算结果表明：在X单向和X、Z双向地震波激励下,框架结构顶层加速度时程曲线与试验曲线吻合较好。研究结果表明：在地震作用下,建筑物的摇摆使支盘桩承受交替变化的拉压荷载,支盘上部土体中的拉“应力泡”随着结构顶层侧移的增大而不断增大,说明上拔力主要是通过支盘传递的,支盘有效地耗散了部分地震能量,减小了上部结构的摆幅,有效的防止结构因过度倾斜而出现的整体倾覆;支盘桩的抗拔力由桩侧摩阻力和桩盘的端阻力组成,随着动荷载的增大端阻力所占的比重也增大,支盘成为传递荷载的主要途径。而直杆桩的抗拔力只靠桩侧摩阻力来提供,其抗拔力远小于支盘桩,且在X-Z双向地震波激励下表现的更为突出。研究结果为进一步揭示桩基抗拔和抗震机理提供了新的技术手段和依据,并在防灾减灾方面具有重要的理论和现实意义

Study on the dynamic characteristics of pile foundation based on shaking table test

Based on shaking table test of the dynamic interaction of squeezed disk pile - soil - frame structure, using large-scale finite element analysis software MARC, the seismic performance of squeezed disk pile and straight pile system are analyzed and researched. Numerical calculational results show that under excitation of the X-way and X, Z two-way seismic wave, at the top of framework structure, time-history curves of acceleration is in good agreement with the experimental curve. The research results show that: In the earthquake, squeezed disk pile bear alternating tension and compression loads because of the building swing, which result in the pull "stress bubble" in disk-upper soil grow with the displacement increase of the structure top, it explains that the uplift force is mainly transmitted through the disks that effectively dissipate some of the seismic energy, reduce swing of the upper structure, prevent whole capsize because of excessive tilt of structure; Anti-pulling force of the squeezed disk pile is from side friction resistance of the pile and end resistance of the disks which become the main way to transfer loads with the dynamic load increases. Anti-pulling force of straight pile that is far smaller than the disk pile is alone provided by friction resistance of its pile shaft, which is more prominent under excitation of the X, Z two-way seismic wave. The results provide a new technical means and basis for uplift and seismic mechanism, and have important theoretical and practical significance in preventive disaster.