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

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.