研究结论：(1)纵梁腹板水平裂纹系被硬物划伤所致，纵梁端截而处的腹板下部竖向裂纹是疲劳引起的。(2)下平纵联节点板呈现的层状撕裂是由于材质不合格及冶炼时层间夹碴引起的。(3)桥梁上的腐蚀凹面是列车上的污物掉落在桥上长期腐蚀的结果。(4)现行采用的在裂纹部位粘贴钢板加固纵梁的方法，改变了纵梁的内力分布，改善了纵梁的应力水平，使钢桥满足了承载能力的要求。

Research conclusions:(1) The horizontal crack on the web plate of longitudinal beam is caused by damage by hard matter and the bottom vertical crack on the web plate in end section of longitudinal beam is caused by fatigue. (2) The bedded crack on low plain longitudinal node plate is caused by rejected steel quality and slag inclusion in interlayer while smelting. (3) The etched concave surface on cross beam is caused by long-time erosion of sewage on the bridge dropping from train.(4 ) The internal force distribution of longitudinal beam is changed and stress level of longitudinal beam is improved by adopting the method of pasting steel plate on crack position for reinforcing longitudinal beam. In this way, the bridge can meet the requirement of bearing capacity.