考虑邻梁碰撞的多跨长简支梁桥落梁震害分析

Seismic analysis of girders falling down in multi-span long simply supported bridges with adjacent pounding effects

以1976年唐山地震破坏的滦河桥为例,选择合适的地震波并以行波方式输入,利用时程分析法研究了邻梁碰撞对多跨长简支梁桥落梁震害的影响问题,得到了几点共性认识:①碰撞一般首先发生在近震源的桥台处,为几跨几乎同时发生的同向追赶碰撞,此类碰撞以行波方式向桥梁远端传递,并因伸缩缝宽度的累加作用而使碰撞逐渐减弱;②桥梁中部各跨因远离桥台,运动受约束较弱,加之受桥梁端部各跨的碰撞推顶作用,墩梁间将会发生更大的相对位移,易在强烈地震中首先发生落梁;③输入加速度峰值正、负不同,邻梁碰撞对全桥墩梁最大相对位移发生与分布的影响有很大不同。基于实际震害和纵桥向非线性地震反应分析,提出了近断层地震动可能是造成滦河桥落梁震害重要外因的新观点。

Seismic damage of girders falling down in Luan River Bridge during Tangshan earthquake in China in 1976 is studied using nonlinear time-history analysis, and attention is concentrated on the effects of pounding between adjacent girders induced by the seismic wave propagation effect. It is demonstrated that the pounding firstly occurs at the expansion joint on one abutment in the side of the bridge closing to the epicenter. Several bridge girders move towards the same direction and come into collision with each other. The pounding travels from the side of the bridge where it occurs to the mid-span of bridge, but the pounding force becomes smaller because of the accumulation of gap size. Girders at the middle of the bridge are far from abutments and can move relative freely, so the relative displacement of bridge girders to the piers increased by pounding may be large enough to cause damage of girders falling down at the mid-span firstly during severe earthquakes. Effects of pounding on the distributions of the maximum relative displacement of bridge girders to the piers along the global bridge strongly depend on that the peak value is negative or positive if the same one acceleration earthquake record is input. It is concluded that near-fault ground motion effects may cause the collapse of Luan River Bridge on the basis of earthquake damage investigation and global bridge structural damage analysis.