Numerical Simulation Investigation On Local Failure Of Steel Box Girders Under Internal Blast Loading

The potential risks of bridges subjected to terror blast attack are increasing，butthere are few studies on the resisting blast of bridges. In this paper, the responses ofLarge-span cable supported bridges under terrorist bomb blast loading were investigatedwith numerical simulation; the local failure mechanisms of steel box girders underinternal suitecase bomb and vehicle bomb blast were emphasized. The main contentsand innovative work include:（1）Based on the Fluid-Solid coupling arithmetic method of ALE Multi-materialformulations, the experiments of rectangular metal tubes subjected to blast load andmetal boxes subjected to internal blast load were simulated with the nonlinear finiteelement software ANSYS/LS-DYNA. The results of the simulations were consistentwith experiments which demonstrated the feasibility and rationality of the simulationtechnology used in this paper. Meantime, the shock wave propagation inside the tube,the roof break process, and the collision process of fragment have been studied. Theimpect effects of steel-plate structures subjected to blast wave load, and the propagationlaw of the internal blast wave were achieved with the simulation method.（2）Using ALE fluid-structure coupling algorithm，a typical suitecase bomb(TNTequivalent23kg) detonated in four typical position inside the box girder wereconsidered, the failure mechanisms and the propagation law of the blast wave insidesteel box girders under blast loading were deeply analyzed through a great deal ofsimulations. The results show that: There are two failure modes of the girder’scomponents, large plastic deformation and rupture. The explode position has strongeffect on the box’s destruction, for a multi-box destruction will be caused if theexplosion take place at the juncture of two boxes, and diaphragm’s fragments may alsobe destructive to the box. A multi-impact effect is observed since the shock wave isrestricted by the box.（3）Types of vehicle bomb detonated in three typical position on the lower deckwere considered, the response process, failure mode, failure parameter and maininfluence factors of double deck steel truss box-shaped girders under blast loading weredeeply analyzed through simulations with ALE fluid-structure coupling algorithm. Theresults show that:1) The failure modes and damage parameters have a clear correlationwith the explosive TNT equivalent and position, and the explosive positions have strong effects on the damage degree of the steel truss.2) Stiffening ribs can restrict the crack inits vertical direction.3) The damage effects have been intensified by the restriction ofthe box-shaped girder.