索-桥动态相互作用及行波效应对斜拉桥地震反应的影响

Study on effects of travelling waves on the seismic responses of cable-stayed bridges in consideration of dynamic cable-deck interaction

主要研究斜拉桥地震响应中拉索与梁、塔动态相互作用和行波效应的影响,索-桥相互作用的影响是根据结构动力学中广义自由度的概念,把索的振型作为自由度来考虑,通过把索边界节点的位移和索局部振型位移叠加得到索的整体位移,行波效应是通过在不同支承点输入具有一定相位差的同一条地震动模拟。以一座斜拉桥为例进行了数值模拟和参数分析,结果表明考虑索-桥动态相互作用时,出现了很多频率密集分布的索桥耦合振动的振型,桥梁模态频率变化较小;在一致地震激励下考虑索-桥相互作用时,梁和塔地震响应有不同程度的增大,部分索的纵向位移增大,相应脉动索力也明显增大;行波效应引起梁某些截面处竖向位移和弯矩增大,塔的纵向位移和弯矩减小,索的位移和脉动索力减小。随着行波波速的减小,梁和塔纵向位移减小,梁竖向位移、梁和塔内力先增大后减小,呈周期性变化。

The dynamic cable interaction with the deck and towers as well as the travelling wave effect on the seismic responses of cable-stayed bridges is investigated in this paper.The influence of cable-deck interaction is incorporated based on the concept of generalized freedom,in which the modes of cable are treated as freedoms.The cable displacement is superposed by the boundary nodal displacement and the local modal displacement.The travelling wave effect is simulated by inputting the same earthquake wave with phase difference at every base support.Numerical simulation and parametric analysis are carried out in an example cable-stayed bridge.The results show that many densely distributed cable-deck couple modes appear when the cable-deck interaction is considered.The modal frequencies of the bridge change little.When the bridge is actuated by uniform excitation and cable-deck interaction is considered,the seismic responses of deck and tower,the longitudinal displacements of some cables and the corresponding dynamic cable tension increase.The travelling wave effect can induce the vertical displacements and the bending moments of girder to increase,the longitudinal displacements and the bending moment of tower to decrease,and the cable displacements and dynamic cable tensions to decrease.With the descending of wave velocity,the longitudinal displacements of girder and tower decrease,the girder vertical displacements decrease,the bending moments of girder and tower increase first and then decrease,which show periodic variation.