Research On Transient Responses And Damage Assessment Of Bridge Superstructure To Impacts

Under the background of rapid development of social economy and busy transportation,the use of various types of overpass bridges in the road network eased some traffic pressure,but with it,accidents of various super-high vehicles hitting the superstructure of the bridge appeared.Once the bridge collision accident happens,it will seriously affect the safety status and service performance of the bridge,and even cause the collapse of the bridge and serious casualties.Therefore,it is of great practical significance and application value to deeply study the dynamic response law and damage assessment method of bridges under vehicle impact.Vehicle-bridge collision process involves a large number of nonlinear factors,and the dynamic response of bridges is easily disturbed by many factors.Finite element method is an effective method to study collision problems.In this paper,a reinforced concrete simply supported T-beam bridge and a van truck are taken as examples,and the finite element software ABAQUS is used to model and calculate.The main work is as follows:(1)Summarize the typical vehicle-bridge collision accidents at home and abroad,the research status,and the relevant standards for the standard value of bridge collision force in Europe,the United States and China;The finite element calculation theory of collision system is introduced,and the hourglass effect and dynamic contact problems during the collision between vehicles and bridges are expounded.(2)Based on the constitutive model of concrete in Code for Design of Concrete Structures(GB50010-2010),the calculation method of damage factor in plastic damage model of concrete is given.The typical accident of vehicle-bridge collision is simulated by finite element method,and the time history curves of horizontal and vertical vehicle impact force are obtained.The dynamic response of bridge during vehicle impact is studied from the aspects of energy exchange,plastic damage of concrete,stress and displacement.Through analysis,it is found that the energy conversion between vehicles and bridges is severe in the early stage of impact process,and the equivalent stress is mainly distributed in the impact area,and develops to the constraint area of beam end bearings in the later stage.Bridge damage caused by vehicle impact is produced under the coupling action of various displacements and deformations.(3)The influence of vehicle speed,vehicle mass,vehicle superelevation,concrete strength grade,section reinforcement ratio and diaphragm arrangement position on the mechanical response and damage mode of the bridge is analyzed by using the control variable method.The results show that the impact force is most affected by the vehicle speed.The increase of vehicle mass and speed will aggravate the damage of bridge and advance the damage time of bridge;The difference of vehicle superelevation height will change the vehicle-bridge impact mode,and with the increase of superelevation height,the risk of impact on the inner beam will increase;Some factors,such as concrete strength grade,cross-section reinforcement ratio and the arrangement position of diaphragm,have influence on the local deformation of the bridge,but have little influence on the overall displacement of the bridge.(4)According to the law of overall damage and local damage of the impacted bridge,the quick detection content and evaluation standard of the simply supported beam bridge after being impacted by vehicles are put forward;This paper analyzes the influence of local damage of bridge on vertical stiffness after impact with different vehicle speeds and weights,and evaluates the damage grade of bridge in combination with codes.