以一座IV级航道预应力砼梁桥为例，对其受船撞后的病害进行了现场调查，建立了双层梁单元仿真模型，通过激活与钝化双层单元边界条件的方法，模拟船撞桥后桥梁结构边界条件的变化，对受损梁结构进行了力学分析，为受损梁应急处理决策提供了理论依据。调查及分析结果表明，结构虽然出现了开裂等病害，但受损结构临时加固后仍具有一定的安全富裕度，梁体置换前可维持半封闭车道通行，这一结果与实际情况相符。“,”Based on double-layer beam finite element method(FEM),this paper focuses on the damage and the structure safety of bridges damaged by ship. Taking a pre-stressed concrete beam over class IV channel as the example,this study carried out the field investigation after it was collided by a ship. A 3D FEM model with dou-ble-layer beam elements is developed to simulate the change of boundary condition after the collision and con-duct the mechanical behavior by using activation and conduct inactivation methods. The results present a theo-retical basis for emergency response decision making. According to the investigation and analysis,though with cracks on the beam,the damaged bridge structure is still safe with certain margin after temporary fixation,and can be open to traffic in half before the replacement of girders,which is in correspondence with the reality. In conclusion,the double-layer beam method is sound for analyzing the bridge damaged by ship.