深水桥梁群桩桁架组合基础抗震性能分析

首先研究了水下双桩系统按照同向、反向振型振动时的频率及动水压力变化规律，通过分析发现，水下相邻桩反向振动振型会增强作用于桩身的动水效应。据此提出群桩—桁架组合基础设计方案，通过桩间桁架，限制群桩间反向振动，提高基础刚度。以四桩群桩基础模型为试验对象，进行了普通群桩基础和3种组合基础方案在不同水深条件下的水池模态试验，研究了群桩—桁架组合基础的动力性能。然后，通过对四跨连续梁桥进行地震反应谱分析，全面评估了该新型基础的抗震性能。研究表明，经过合理设计的群桩—桁架组合基础可以改善并优化深水桥梁的地震响应。

Seismic Analysis of Pile Group truss Foundation for Deep water Bridges

The frequencies and the modal hydrodynamic pressure of the parallel and nonparallel vibration modes for a submerged two pile system are investigated first. The results show that the nonparallel vibration of the two pile system increases the hydrodynamic effect. The pile group truss foundation is developed to control the nonparallel vibration of piles and increase the stiffness by installing the truss braces between piles. The modal tests for a typical group foundation and three developed pile group truss foundation designs are carried out on a 4 pile foundation specimen to investigate the dynamic performances experimentally. The seismic performance of the pile group truss foundation is then assessed through seismic response spectrum analyses of a four span deep water bridge. The study shows that the properly designed pile group truss foundation improves and optimizes the seismic responses of the deep water bridges.