The Analysis On Dynamic Responses Of Bridge Pier Due To Vehicle Impact

The impact between vehicle and pier is common,and the consequences are often more serious,so it is necessary to study the dynamic responses of pier affected by vehicles.This paper mainly uses finite element technology to analyze the responses of reinforced concrete bridge piers when subjected to vehicle collision.The finite element model of the bridge pier is established by using LS-PREPOST software that is very user-friendly to create LS-DYNA input file and produce the simulation results in graphic and text format.Three vehicle models are used to discuss the dynamic responses of the pier due to collision:a reduced model of Ford SUT（35,353 elements）,a detailed model of a Chevrolet C2500pickup（58,313 elements）developed by George Washington University and HGV heavy truck.The main work and conclusions are as follows:（1）The finite element model of pier is established by using LS-PREPOST.The pier considered fixed at the bottom end for any case,but two restraint conditions are considered for upper end,one is fixed,and another is hinged.The correctness of vehicle-bridge coupling model and the rationality of material constitutive are verified by the drop hammer test in[17]literature.The results show that the stress characteristics of concrete structure can be accurately simulated by selecting suitable material constitutive,contact algorithm and mesh size.（2）In order to compare the difference of the dynamic responses of the pier after the impact of the vehicle,many situations are considered.For hinged restraint condition,to consider the effect of superstructure on the dynamic responses of pier,the axial loads P0of 5%and 10%of the column’s axial compressive capacity are exerted,respectively.Where P0 are calculated according to the AASHTO-LRFD specification(9^th edition).The vehicle impact velocity is 60km/h,80km/h and 100km/h,and the vehicle weight is 8t,10t and 12t,respectively.The results show that the dynamic responses of pier for different boundary conditions are quite different,and it is not conservative to design the pier according to the result calculated without considering the axial compressive load due to superstructure load.The stress initialization is conducted by using implicit static dynamic relaxation,and it is unconservative to design the pier by the result calculated without considering preload effects.（3）Parameter analyses are carried out for vehicle and pier.Vehicle parameters are truck cargo stiffness,impact eccentricity and vehicle type.The pier parameters include pier diameter,pier height,pier section shape,longitudinal reinforcement ratio and stirrups spacing.The results show that:1)The local peak value of impact force caused by the stiffness of carriage cargo is affected by impact velocity.When the impact velocity is equal to 80km/h,increasing the cargo stiffness does not cause a significant increase in the local peak of impact force.However,when the velocity increases to 100km/h,the peak value of local impact force caused by increment of the cargo stiffness and vehicle weight becomes significant,and the effect of the increment of the vehicle weight is more significant.2)The impact effect of each vehicle collision eccentricity is very different because the impact effect will be different under each eccentric condition.3)The effects of C2500 pickup,F800 trucks and HGV heavy trucks on the dynamic responses of pier are different,and this difference is more obvious with the increase of impact velocity.4)The diameter of the pier directly affects the bearing capacity of the pier.Reducing the height of the pier,increasing the reinforcement ratio of the longitudinal reinforcement,and reducing the spacing of the stirrups can improve the bearing capacity of the pier.In addition,the failure modes of square and circular section piers are similar after impact,and the shear failure is mainly in the collision position.