考虑竖向地震动的中小跨径梁桥地震响应特征研究OA

The highway bridges with medium-small span play an important role in China's transportation network,especially in western mountainous areas,and are the main form of highway bridges because of the flexible design and convenient construction.However,this type of bridge is directly supported on the bearings,the horizontal fric-tional resistance of the bearings is sensitive to vertical reaction forces,making its seismic response susceptible to vertical seismic motion.In order to study the seismic performance of highway bridges with medium-small span in western China under vertical seismic motion,a nonlinear finite element model of a 3×30 m continuous beam bridge was established based on OpenSees software.65 sets of strong near-field seismic records were selected for nonlinear time history analysis.By comparing the horizontal seismic response of bridges under two working conditions,with and without considering vertical seismic response,the influence mechanism of vertical seismic motion on the hori-zontal seismic response of bridges was systematically studied.The research results indicate that vertical seismic mo-tion significantly increases the amplification effect of vertical seismic motion on the main beam,and the normalized mean of vertical seismic motion of the main beam is about 1.1.When the peak vertical ground acceleration is greater than 0.7g,under the action of dynamic axial force,the support cannot provide effective vertical support or the beared vertical loads far greater than the one under gravity conditions,thereby increasing the dual risk of falling beam and bridge pier collapse,seriously threatening the safety of the bridge.At the same time,the coupling effect of vertical seismic motion and horizontal seismic impulse will amplify the horizontal response and exacerbate the cu-mulative damage of the structure.This research result can provide important basis for seismic design of bridges with medium-small span,and indicate research directions for the seismic design.