美国I-35W大桥连续垮塌过程研究

Study of Progressive Collapse of I-35 W Bridge in US

为研究美国I-35W大桥连续垮塌原因,基于我国钢结构设计规范,采用理论推导与有限元仿真结合的方法,对节点板和整体结构失效过程进行分析。首先根据实桥在运营和维修过程中的受载情况,对4种典型工况下,全桥模型中U10节点板抗拉、抗剪及局部稳定性进行分析,得到其破坏的原因和失效的过程;最后分析了U10节点板失效后全桥结构连续垮塌过程。结果表明:集中作用于U10节点板处的维修荷载是其破坏的直接外因;节点板抗剪强度不足是其失效内因。全桥连续垮塌过程为:U10节点板剪切破坏后节点连接杆件受力急剧变化,原设计受拉竖杆变为压杆,杆件失稳破坏,整个节点失去刚度,桥梁结构体系改变,无法继续按原设计承载,结构垮塌。

To study the causes of progressive collapse of the I-35 W Bridge in US, the method of combined use of theoretical derivation and finite element simulation was used, based on the Chinese steel structure design specification. The failure of gusset plates and the overall structure were analyzed. First, in the 4 typical loading cases, the tensioning and shearing performance and local stability of U10 gusset plates in the overall bridge model were analyzed, according to the load bearing behavior of the real bridge in operation and maintenance process, and the causes of the damage and failure were gained. Furthermore, the progressive collapse of the overall bridge structure after the failure of U10 gusset plates was analyzed. The results demonstrate that the maintenance loads concentrating on the UI@ gusset plates are the direct external cause of the damage, and the insufficient anti shearing strength of the gusset plates is the internal cause. The progressive collapse of the overall bridge experienced several stages. When the U10 gusset plates failed due to shearing damage, the forces carried by the linking members at the panel point dramatically changed, the original tensile vertical member turned to be the compressive member, leading to the instability damage of members. Then, the whole panel point lost stiffness, the structural system of the bridge changed and was unable to carry load according to the original design, as a result, the structure collapsed.