Dynamic Responses And Damage Assessment Method Of PC Box Girder Bridge Under Impact Of Over-height Vehicle

In recent years,with the rapid development of transportation infrastructure,the construction of grade separation transportation systems has become an important way to alleviate the traffic burden.However,the frequent occurrence of collision accidents such as over-height vehicles impacting the bridge superstructures has brought new challenges to the rapid development of transportation.Once a collision accident occurs,it will seriously affect the safety status and normal performance of the bridge structure.The design of bridge structures mainly considers vertical loads,while the lateral impact of vehicles on the bridges will inevitably affect the vertical load-bearing performance of the bridge structure.In order to ensure the safety of bridge structures,it is necessary to explore in-depth the damage and failure modes and dynamic responses of the bridge superstructure caused by over-height vehicle impact,and propose a damage assessment method to evaluate the damage state of the impacted bridge.The thesis is based on the National Natural Science Foundation of China Project "Research on damage mechanism and damage assessment method of prestressed concrete(PC)beams under over-height vehicle impact(51908049)".A combination of numerical simulation and theoretical analysis was used to study the dynamic response and damage assessment method of the superstructure of a prestressed concrete box girder bridge under over-height vehicle impact.In this paper,LS-DYNA software is used to establish a refined finite element model of the superstructure of a prestressed concrete box girder bridge impacted by an over-height vehicle.The accuracy and effectiveness of the finite element simulation techniques are verified by comparing the results with typical drop hammer impact tests on reinforced concrete(RC)beams and prestressed concrete beams.Subsequently,parametric research method is employed to examine the effects of different vehicle and bridge parameters on the damage modes and dynamic responses of prestressed concrete box girder bridge.Finally,a damage assessment method for PC box girder subjected to impact based on vertical residual bearing capacity is proposed.The main research contents and conclusions are as follows:(1)This paper provides a comprehensive overview of the current research status on damage modes and damage assessment methods for falling weight,pendulum impact,and overheight vehicle impact on bridge superstructure.The working principle,collision contact algorithm,and hourglass effect of explicit analysis method in finite element simulation of vehicle-bridge collisions are introduced in detail.(2)The finite element software LS-DYNA is used to simulate typical drop hammer impact tests on RC beams and PC beams,and the impact force time history curve,displacement time history curve,and crack development mode of the finite element simulation and test results are compared and analyzed.The validity and rationality of the finite element simulation parameters used in this paper,such as the material constitutive model,strain rate effect,collision contact algorithm,and boundary conditions are verified.(3)The effects of impact velocity,impact mass,impact angle,impact height,concrete strength,and prestress strength on the dynamic response of a prestressed concrete box girder bridge are investigated using the single variable method.Major dynamic response indicators such as impact damage process,impact force time history,midspan displacement time history are analyzed in depth.The results show that vehicle parameters have a significant impact on the damage of box girder bridges during impact,while the impact of bridge parameters is relatively small.Therefore,the vehicle parameters should be primarily considered in the collision resistance design of bridges.In addition,for the damage caused by vehicle lateral impact,the possibility of overall damage is low,and attention should be focused on local damage.(4)Combining a large number of finite element simulation results and statistical data analysis,a damage assessment method for PC box girder after impacts based on vertical residual bearing capacity is proposed.This method uses a damage index formula to classify the degree of damage and fits the mass-velocity(m-v)curves under different combinations of vehicle mass and speed combinations to quickly and effectively evaluate the damage level of PC girders.In addition,based on the principle of energy conservation,this paper proposes a calculation formula for predicting the maximum impact force,which can provide a reference for local damage assessment of PC girders.