Study Of Pressure Distribution And Damage Effect For Concrete Bridges Subjected To Vehicle-mounted Blast Loads

In recent years,more and more explosion accidents such as the terrorist attack and car-bomb explosion have happened on the bridge structure,taking bad effects on the economy development of society and people's daily life.The study background of this paper is vehicle-mounted blast occurred on the deck of Fengxingpai Middle Bridge located in Jiangxi Province,the finite element software AUTODYN is used to simulate the damage process of reinforced concrete bridge under the car-bomb blast.This paper focuses on overpressure distribution and dynamic responses of the bridge deck under the car-bomb explosion as the Parameters change,which include carriage plate size,gap between the two bridges and guardrail.Based on the damage detection report of the existing bridge,numerical simulation of the RC bridge subjected to blast loading has been done.The main research work and conclusions are as follows:1.The overpressure distribution form on the deck is not sensitive to explosive quantity and detonating position.The peak overpressure load field is a ‘unimodal' and position of peak value is related to detonation position,which all appeared in the projection of detonation in the bridge deck.The difference is that the greater the amount of explosives,the high-pressure area more concentrated decay rate faster.2.The car bomb cannot be directly simulated by TNT,the floor of the vehicle which can block the propagation of blast shock waves should be considered in simulation as steel plate changes the pressure distribution.There are three functions of the steel plate under car-bomb explosion: the eliminating effect,Propagation delay and the circulation effect.The empirical formula of overpressure prediction in free air is not applicable.Based on the empirical formula and numerical simulation results,therefore the prediction formula of the peak overpressure under car-bomb explosion is proposed based on the Baker formula and numerical simulation results.3.The steel plate shows increasing blocking effect with the size increases in the range of H~2H(H is explosion height),overpressure values below the steel plate decay fastest in the range of 1.5H~1.8H.A new concept of the blast effect zone is first proposed in this paper,in which the loading distribution is divided as four effect zones: shock wave isolation zone,the zone of which can be determined by the size of steel plate;semi-free field zone;shock wave attenuation zone;shock wave attenuation zone shock wave strengthening zone;shock wave free field zone.4.The gap between two bridges is beneficial for the dissipation of blast load and decrease the attack to the bridge.With the gap increasing,the arrival time of peak overpressure increases while values of overpressure decreases gradually.when the space is more than 2 m,the effect of explosion to the other bridge could be ignored.5.Taking reinforced concrete guardrail,combined guardrail and beam column guardrailas as the research object,finite element analysis models are respectively set up,and various guardrail's impact on pressure field and damage degree are investigated.Reinforced concrete guardrail is hard to dissipate energy by deformation.It also block the Propagation of blast loads that the deck suffered more severely than the other two guardrail.The difference is that the space between the guardrail is more active for blast diffusion and consume more blast energy.6.Based on the damage detection report of the existing bridge and numerical simulation results,damage area of Fengxingpai Middle Bridge can be divided into three deformation types: shear,flexural-shear,and flexural,which are in good correspondence with typical load pressure line on the deck,further verify that steel plate should be considered in simulation.