Study Of Blast Loads Action Effect For Prestressed Concrete Bridges

With the development of highway and bridge construction,explosion accidents of bridge caused by the warfare and accidents become more and more frequent.The dynamic response and damage study of bridge structure under blast loads become more and more important day by day.Domestic and foreign scholars have do much anti-detonation research about reinforced concrete structure,but the anti-detonation research about prestressed concrete structure at the present is almost black.Moreover with the development of prestressing technique,prestressed concrete structures have been widely used in the field of civil engineering. Therefore,it is quiet necessary to corry out the study of blast loads action effect for prestressed concrete bridges. Aiming at the propagation rules of explosive shock wave and the dynamic response of concrete beams under blast loads,the following work has been done by numerical simulation in this paper:1.The production principle of explosive shock wave and its propagation and reflection law are analysed detailedly.Besides,the mass,momentum and energy conservation three important laws in the effect process between explosion production and medium are inferred,and the explosion total equations have been derived ultimately.2.The important characteristic parameters of blast loads have been analysed. Nonlinear explicit dynamic finite element analysis software AUTODYN has been used to simulate the peak overpressure and positive time of explosive shock wave in the air.The mesh size will affect numerical simulation results;At the same time,the simulation results have been compared with experiential formula value,and a reasonable expression which is useful to descrip the relationship between overpressure peak of shock wave and scale distance has been summed.3.The inherent frequency,natural vibration,static displacement and maximum dynamic displacement of monolithic concrete beam have been calculated by simplifying blast loads to linear declined triangular loads,which is based on simplified single degree of freedom system analytical method.Meanwhile.theoretical derivation and structural characteristic analysis of bridge deck structure have been done through the small bending theory of thin plate.4.The dynamic response and failure modes of reinforced concrete beams under blast loads have been researched.The upper and lower explosion of beams have simulated to analyse anti-detonation perfomance of reinforced concrete beams by changing parameters of scale distance,setting protective components,reinforcement ratio,stirrup ratio and section types.And pointed out that the changes of different parameters will affect the failure modes of reinforced concrete beams.5.According to explosion simulation related conclusions of reinforced concrete beam,the prestressed concrete beam models have been established. The upper and lower explosion of beams have simulated by changing parameters of scale distance and setting protective components,and compared its reponse and failure models with relevant reinforced concrete beams.It is concluded that action effect of prestressed concrete beams is unsatisfactory about upper explosion,and anti-detonation perfomance of prestressed concrete beams is poor.Meanwhile,the impact action effect of prestressed concrete beams is more obvious than reinforced concrete beams,and its anti-detonation perfomance is stronger than reinforced concrete beams.These research results can provide reference for predicting the deformation and damage mode of bridge structures under blast loads,meanwhile,it can provide theoretical basis for antiknock design and comprehensive protection of bridge structure...