落石撞击下双柱式RC梁桥的倒塌破坏分析

Collapse Analysis of Double-column RC Girder Bridge Under Rockfall Impact

针对山区梁桥面临落石撞击的威胁,利用LS-DYNA软件开展了落石撞击下典型双柱式RC梁桥倒塌破坏的精细化数值仿真分析。首先建立了落石撞击下考虑桩-土相互作用和钢筋-混凝土黏结滑移关系的原型梁桥有限元模型;其次基于双柱式RC桥墩水平撞击试验,验证了选取的材料本构、网格尺寸、接触算法及其参数的可靠性;进一步模拟重现了汶川彻底关断桥事故,并分析了落石撞击下梁桥的倒塌过程;最后讨论了落石质量、撞击速度和高度对梁桥动态响应和损伤破坏的影响。结果表明:梁桥的倒塌破坏过程可依次分为被撞墩柱破坏、相邻墩柱破坏和上部结构坠落,其中被撞墩柱破坏是造成梁桥倒塌的主要因素;忽略桩-土相互作用和钢筋-混凝土黏结滑移关系造成墩柱截面响应预测结果偏小,高估梁桥的抗落石撞击性能;落石质量和撞击速度对被撞墩柱动态响应和梁桥整体损伤程度的影响显著,而撞击高度的影响相对较小。

Aiming at the serious threat of rockfall impacting girder bridges in mountainous area,refined numerical simulations on the collapse of a typical double-column reinforced concrete(RC)girder bridge under rockfall impact were performed by the software LS-DYNA.Firstly,the finite element(FE)model of a prototype girder bridge under rockfall impact was established with considering the pile-soil interaction and bond-slip relationship between reinforcement and concrete.Then,the reliability of adopted material constitutive model,mesh size,contact algorithm and their parameters was validated by comparing with a horizontal impact test on double-column RC bridge pier.Furthermore,Wenchuan Chediguan Bridge Collapse Accident was numerically reproduced,and the collapse process of the girder bridge under rockfall impact was analyzed.Finally,the influence of rockfall mass,impact velocity and impact height on the dynamic responses and damage of girder bridge was discussed.The results show that:the collapse process of girder bridge under rockfall impact can be divided into impacted pier destruction,adjacent pier destruction and girder falling,in which the impacted pier destruction is he critical factor;neglecting the pile-soil interaction and bond-slip relationship between reinforcement and concrete,results in the smaller predicted cross-section responses of piers,and thus overestimates the rockfall impact resistance of girder bridge;compared with the impact height,rockfall mass and impact velocity have a more significant influence on the dynamic responses of impacted pier and overall damage degree of girder bridge.