水平地震力作用下桥梁结构-地基完全相互作用体系动力响应分析

Numerical analysis of seismic response of interaction system for bridge structure-pile-soil foundation under horizontal excitation

为探讨场地地基动力相互作用对桥梁结构的影响,通过建立桥梁结构-地基基础相互作用体系动力有限元数值模型,采用子空间迭代法提取自然频率与振型,用Newmark逐步积分方法求解材料非线性的动力平衡方程,在此基础上,针对水平地震力作用下桥梁结构-地基完全相互作用体系进行了动力固有特性和动力响应时程分析。计算分析表明:地震动沿河道中线从基岩传递到河底,场地土层对主频带内成分具有明显放大效应;场地中桩线和桥台线相较于河堤中线上具有更为明显的地震动加速度反应谱卓越平台,且呈现典型软土夹层场地滤波双峰特征;中桩和边桩弯矩时程极值沿深度均呈现先增大后减小的变化趋势。由于河堤场地中线土层侧移显著,同深度处中桩时程内弯矩极值明显高于边桩;软弱夹层场地地基相互作用对于桥梁结构地震动力响应具有显著影响,工程设计与计算中应加以考虑与重视。

In order to discuss the effect of dynamic interaction of soil foundation on bridge structure,numerical analysis is conducted based on the FE model of interaction system including bridge structure,piles and soil foundation under horizontal excitation using both the subspace iteration method to extract dynamic inherent characteristics and Newmark's step-by-step integration method for material nonlinearity.The computational results show that the soil layers have obvious amplification effect on the main frequency band of seismic excitation from bed rock.Furthermore,the frequency spectrum displays an obvious twin-peak feature.The extremums of bending moment for both middle pile and border pile firstly increase and then decrease with depth.Due to large lateral displacements at middle line of field,the extremums of bending moment of middle pile are higher than those of border pile at the same depth.It can be concluded that soft interlayer has significant effect on seismic response of interaction system of bridge structure and importance should be attached in engineering practice and design.