| The bridges play an important status and role in transportation,social economy and military.Accidents of serious damage to bridge structures caused by the explosion of vehicles carrying hazardous chemicals are frequent at home and abroad,the vulnerability of bridges to explosion cannot be ignored.Thus the dynamic response and failure mechanism of bridge structures under blast load need to be studied urgently.Based on the ANSYS/LS-DYNA explicit dynamics finite element analysis software,the prestressed concrete simply supported small box girder structure is taken as the research obj ect,and the dynamic response and failure mechanism under blast load are studied.The main research work and conclusions can be obtained as follows:(1)The ALE multi-material fluid-solid coupling method is used to numerically simulate the explosion in free air and the explosion test of existing reinforced concrete beams.The numerical simulation results of the overpressure peak are consistent with the calculation results of the empirical formula.The error of the numerical simulation result of the mid-span displacement of the reinforced concrete beam is 3.6%,which proves the rationality and accuracy of the methods used in the numerical simulation.(2)Considering the interaction between the blast shock waves and the bridge structure,a finite element model for calculating the blast load of the bridge deck is established,and a formula for calculating the peak overpressure of the blast shock waves suitable for the blast above the bridge deck is proposed,which reveal the propagation law of the blast shock waves on the bridge deck and the peak overpressure distribution characteristics.The results show that the bridge deck has an enhancement effect on the blast shock waves,and the enhancement degree decreases rapidly with the increase of the distance from the blast center.The peak overpressure on the bridge deck can increase by approximately 2.9 times.(3)A numerical simulation analysis method for the dynamic response and failure mechanism of the prestressed concrete simply supported small box girders under blast load is established.The deformation process and failure mode of the prestressed small box girders under blast load are clarified,and the response law of the displacement,velocity,acceleration and other parameters of the girders is obtained.The results show that when the TNT equivalent is 200 kg,a rectangular break appear on the top deck of the box girder,and the break is mainly concentrated near the blast center,which is a local failure.There is a negative correlation between the damage degree of the girder and the distance from the blast center.The greater the distance from the blast center,the lighter the damage and the smaller the dynamic response peak value of each parameter.(4)Based on the finite element model of small prestressed concrete box girders,the effects of TNT equivalent,longitudinal blast locations,transverse blast locations,degree of prestress losses and steel plates of vehicles on the dynamic response and failure mode of small box girders are analyzed.The results show that with the increase of the TNT equivalent,the failure mode of the small box girders gradually change from overall bending failure to local shear failure;under the condition of the same proportional distance,the blast at the fulcrum position and above the wet-joint caused less damage to the girders than at other positions;when the prestress loss degree is less than 30%of the tension control stress,it can be considered that it does not affect the anti-blast performance of the girders;the steel plate with a thickness of 2 cm can effectively reduce the destructive effect of the blast shock waves on the girders. |
