钢桁-混凝土组合结构梁桥连续破坏-倒塌动态行为研究

近年来交通荷载激增，桥梁构件破坏和整体结构倒塌时有发生，造成重大人员伤亡和经济损失。其中，相对其他形式结构桥梁，钢桁-混凝土组合结构桥梁冗余度较低，重载作用下构件的初始破坏易引发桥梁整体倒塌，故明确钢桁-混凝土组合梁桥连续倒塌机理和模式，对该类桥梁抗连续破坏-倒塌设计具有十分重要的理论和工程意义。因此依托钢桁-混凝土组合连续梁桥实体工程，采用能量法和显式动力学数值分析方法，对其构件重要性、破坏后剩余结构冗余度和倒塌动态行为开展研究。研究结果表明：最不利荷载作用下，钢桁-混凝土组合连续梁桥边跨正弯矩最大区域下弦杆破坏后剩余结构的最低冗余度为1.94，而边跨梁端支点附近腹杆破坏后剩余结构的最低冗余度为1.61。组合梁边跨正弯矩区下弦杆破坏后剩余结构遵循转动铰机制倒塌，破坏路径较长，结构整体倒塌前具有显著变形，最大竖向位移达到60.1 cm；组合梁支点区域腹杆破坏后剩余结构遵循滑移面机制倒塌，破坏路径极短，倒塌前整体结构无明显变形，最大竖向位移仅为9.1 cm，结构破坏呈明显脆性特征。腹杆失效所形成的滑移面倒塌机制对钢桁-混凝土组合结构梁桥极为危险，需重点设计预防。通过对钢桁-混凝土组合连续梁桥破坏路径的研究，探明了该类结构各构件的重要性分布特征和结构连续倒塌机制，为提高同类型桥梁抗破坏-倒塌性能提供理论依据和设计方法。

Research on the Progressive Failure-collapse Dynamic Behavior of Steel Truss-concrete Composite Bridge

The damages in bridge members and the collapses in entire structures usually happens, with the arises in the traffic, resulting heavy injures and economic losses. Compared to other bridge structural systems, the steel truss-concrete composite bridge is lack of redundancy, indicating that this type of bridge is venerable to the structural collapse caused by the initial failures in members under heavy traffic load. Thus, it is vitally important for the theory and engineering to determine the collapse mechanism and mode of steel truss bridge. This paper presents a study for member significance, damaged structure and dynamic collapse performances of a steel truss-concrete composite continuous beam bridge, using elastic energy and explicit dynamic numerical method. The results indicate that the minimum redundancy factor is 1.94 for the damaged bridge with failed lower chord in the area of the largest positive bending moment in side span, while the minimum factor is 1.61 for the damaged bridge with failed bar in the vicinity of the side support. The damaged bridge, with the failed lower chord in the area of positive bending moment, collapses following the mechanism of rotating hinge. This mechanism has long failure paths, with the maximum vertical displacement of 60.1 cm before the entire collapse. In contrast, the damaged bridge, with the failed bar in the vicinity of support, collapses following the mechanism of slip surface. Leading the critical brittle collapse, this mechanism has extremely short failure paths, with the merely maximum vertical displacement of 9.1 cm before the entire collapse. Thus, the mechanism of slip surface, caused by the failure in bars near supports, is the most critical for steel truss-concrete composite bridges, and is prevented by special design. This research, on the failure paths of steel truss-concrete composite bridge, investigates the member significance and collapse mechanism, providing the theoretical basis and design method for enhancing the resist performance for progressive failure-collapse in this type of bridges.