桥墩高度对群桩承台系统动刚度的影响分析

对于服役桥梁,测试群桩承台桥墩系统的动刚度可以了解其健康状态,并可以作为推算静刚度及承载性能的依据。而当采用动刚度作为评估指标时,激振点和拾振点的选取应具备合理性,且不应忽视桥墩高度对动刚度值的影响。为分析上述问题,本文建立了三维动力有限元模型,施加瞬态激励以分析系统的竖向动刚度值,并考虑了激振点位于承台上和桥墩顶部2种情况。计算结果表明:2种激振点位情况下,在2.5 Hz频率下系统动刚度受桥墩高度变化影响小,计算结果稳定;当激振点位于承台上时,由于激振点和拾振点均不在结构对称中心上,因此当频率较高时(20 Hz左右),系统动刚度会受到自身模态的影响而发生阶跃式突变;当激振点位于墩顶中心时,随着桥墩高度的增加,在20 Hz频率下的系统动刚度降低。

Analysis for Influence of Pier Height on Dynamic Stiffness of Group Pile-cap System

For the existing bridges on service,the dynamic stiffness of the group pile-cap-pier system can be used to analyze its safety status,and can be used as the basis for calculating the static stiffness and bearing capacity.When the dynamic stiffness is used as the evaluation index,the selections of the excitation position and the test point should be reasonable,and the inf luence of the pier height on the dynamic stiffness value should not be neglected.In order to analyze the above problems,this paper established a 3 D dynamic f inite element model.The transient excitation was applied to analyze the values of vertical dynamic stiffness of the system.The excitation location on the cap and on top of the pier were considered.The results show that,in the conditions of two excitation positions,the inf luence of the pier height on dynamic stiffness at 2.5 Hz is small,and the calculation result is stable.If the excitation is applied on the cap,and when the frequency is relatively high(20 Hz or so),the system dynamic stiffness will be affected by the selfmode and the step-like mutation occurs,because the excitation position and the test point are not on the center of the structure.When the excitation is applied on the center of the pier top,with the increase of the pier height,the dynamic stiffness of the system at 20 Hz decreases.