Abstract: The influence factors of vehicles impacting the bridges are complicated.At present，it rather dificult to solve the problem just by theory analysis.Before the analyzing method based on the probability theory accomplishing and the statistice work according on the coeficient finishing.it's better to adopt the experiment to reflect the results approxinately through expe- riential“impact coefficient”formula.In terms of a dynamic test upon a typical arch bridge，the imfluence factors that cause the exceptional impact coefficient are analyzed and discussed，the reasons why there is obvious diference between the measured value and standard one are discussed，with the hope to give some useful reference.

Key words: impact coefficient, dynamic response, dynamic performance

摘要： 影响车辆对桥梁冲击作用的因素复杂，目前要想通过理论分析的途径来解决这个问题还有一定的困难，在基 于概率论的分析方法以及对许多有关的参数进行统计等工作没有解决之前，不得不借助于实验的方法，通过经验的 “冲击系数”公式加以近似的反映．以一座典型拱桥的动载试验为基础，对造成该桥冲击系数异常的影响因素进行分 析，对实测值与规范值差异较大的原因进行了探讨，以供借鉴．

关键词: 冲击系数, 动力响应, 动力特性