Abstract: The problem of the defection upwards of PC bridge appears frequently，and it is disadvantageous to the driving comfort.Based on the 1/4 models of motorcar.the mode1 of simple supported beam was used with constant moving load to simulate bridge vibration and the half sine curve was used to simulate the bridge floor longitudinal curve when bridge upwards formed.Two response equations of motorcar vibration are established，which are caused by bridge vibration as well as deflection upwards.Further more.these two influences on motorcar vibration arc analysed and compared in detail.A conclusion that the influence of bridge vibration to the motorcar vibration iS trivial compared with that of deflection is drawn.

Key words: defection upwards, bridge vibration, comfort, high speed travel, acceleration

摘要： 中小跨径的PC简支梁桥过度上拱现象经常出现对行车舒适性产生了不利的影响．基于1/4汽车模型，采用常 量力移动荷载模型模拟桥梁振动，以及半正弦曲线模拟桥梁上拱后所形成的桥面纵坡曲线，分别建立了由桥梁振动 和桥梁上拱引起的车辆振动响应方程，分析比较了以上2种情况对车辆振动的影响．得出桥梁振动相对于上拱度对 车辆振动的影响很小的结论．

关键词: 上拱度, 桥梁振动, 舒适度, 高速行驶, 加速度