Abstract: Study on damage mechanism of bridge is the important procedure which turns seismic damage investigation results into a practical technology. Some damage features of simply supported beam bridges which differ from the features in other earthquakes are shown in Wenchuan earthquake. The damage mechanism of pier and girder was simulated by FEM analysis and seismic table test. The results show that the seismic action of girder released by relative sliding between girder and bearing is why the damage of pier is reduced in Wenchuan earthquake. The displacement of girder is coordinated by continuous pavement , and the longitudinal displac&lnent is restrained by abutment , which reduces the risk of girder fell down. A complete seismic resistance system is formed by girder, pier, bearings , abutment , continuous pavement in simply supported beam bridges; the seismic action of girder is released and the risk of girder fell down is reduced by the system.

Key words: bridge engineering, simply supported beam bridges, design of seismic resistance, seismic damage of bridges , damage mechanism

摘要： 桥梁震害机理研究是将震害调查结果转化为实用技术的重要技术环节，汶川地震中简支梁桥表现出一些区别于其他地震的特点。采用数值模拟结合振动台试验的方法，揭示了桥墩震害和主梁震害的形成机理。结果表明，主梁与支座间的相对滑动释放了主梁的地震作用是汶川地震中桥墩震害少的主要原因；桥面连续协调了主梁位移，桥台约束了主梁的纵向位移是汶川地震中落梁少的主要原因。简支梁桥的主梁、桥墩、支座、桥台、桥面连续构成了一个完整的抗震系统，在释放主梁地震作用的同时，减小了落梁风险。

关键词: 桥梁工程, 简支梁桥, 抗震设计, 桥梁震害, 震害机理