Numerical study of the seismic performance and damage mitigation of steel-concrete composite rigid-frame bridge subjected to across-fault ground motions

The new steel-concrete composite rigid-frame bridge (SCCRFB) with concrete-filled double skin steel tube (CFDST) piers has been verified showing superior seismic performance, and a promising structural solution for bridge constructions near or above active faults. Previous experimental and numerical studies revealed that the damages of this bridge type under across-fault ground motions mainly concentrate on the two CFDST piers. This paper investigates the effectiveness of damage mitigation measures for the SCCRFB with CFDST piers by using numerical simulations. Three detailed three-dimensional (3D) finite element (FE) bridge models are developed by using the explicit FE code LS-DYNA, in which Model A represents a reference SCCRFB with CFDST piers, and Models B and C employ different stiffeners at the two ends of the CFDST piers aiming to mitigate the damages induced by the effect of across-fault ground movements. Two pairs of across-fault ground motions with thrust and strike-slip mechanisms are considered, and the influence of fling-step is parametrically investigated. Numerical results including structural damages and responses are presented and the damage mechanisms are analyzed. Numerical results indicate that the strengthening measure used in Model C can effectively restrain local buckling of the steel tubes under both types of across-fault ground motions and is a practical option for SCCRFB with CFDST piers to mitigate the potential fault-crossing hazard. This study provides useful references for the seismic design of SCCRFB with CFDST piers crossing active faults.