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

The potential risks of bridges subjected to terror blast attack are increasing,but there are few studies on the resisting blast of bridges. In this paper, the responses of steel box girders in Large-span cable supported bridges under vehicle bomb blast loading were investigated with numerical simulation; the local failure mechanisms of steel box girders were emphasized when vehicle bomb exploded on the deck. The main contents and innovative work include:(1)Based on the Fluid-Solid coupling arithmetic method of ALE Multi-material formulations, the experiments of metal thin plates subjected to blast load, stiffened metal plates subjected to blast load and metal tubes subjected to blast load were simulated with the nonlinear finite element software ANSYS/LS-DYNA. The results of the simulation were consistent with experiments which demonstrated the feasibility and rationality of the simulation technology used in this paper.(2)The blast shock wave diffraction and its influence to the response of horizontal flexible specimen were analyzed, the results showed if the scale distance and the size of flexible specimen were small, the influence of the diffraction should be considered. The influence of two weld models to the response of stiffened plates under blast loading were contrastively analyzed, the results show that weld model has little effect on the deformation process of failure modeⅠ(the final deflection error is less than 6%)and the rupture and tearing process,the critical charge of failure modeⅡ(less than 4%). The influence of element type and mesh size of shell element to the response of tube were analyzed, the results show that: the simulation results of solid element and shell element both meet the experimental results well, the error is about 10%; the range of reasonable mesh size was given.(3)Using ALE fluid-structure coupling algorithm,two types of vehicle bomb(TNT equivalent 100kg~500kg) detonated in three typical position on the deck were considered, the response process,failure mode,failure parameter and main influence factors of steel box girders under blast loading were deeply analyzed through a great deal of simulations. The results show that: The response process of steel box girders subjected to vehicle bomb blast load can be divided into three stages: deck crevassing, blast wave acting, fragment acting. The failure modes contain mode II(only the deck has rupture) and mode III (both the deck and the soleplate have rupture). The deck crevasse subjected to the blast wave,and the crevasse size is constrained by the clapboard and stiffening rib; the clapboards have out-plane displacement subjected to blast wave; the tears of soleplate are mainly subjected to the deck's fragments. The explosive position affect the crevasse size of deck, the transverse displacement of longitudinal clapboard significantly, the explosive equivalent affect tears area of soleplate and longitudinal displacement of bulkhead significantly.