Dynamic Characteristics Analysis Of Damaged Beam Under Vehicle-Bridge Coupling

At present,a large number of bridges have been built in China.As the traffic volume increases year by year,the mechanical response of bridges under the action of vehicles has attracted the attention of scholars.Vehicle-bridge coupling vibration mainly studies the interaction between vehicle and bridge,and analyzes the mechanical response of beam under vehicle load.At present,the research on vehicle-bridge coupling is more extensive,and there are many factors that can be analyzed,such as bridge deck roughness,temperature field,wind load,seismic load,and beam fatigue damage.However,there are relatively few studies on the cracked beam under vehicle load,and the calculation conditions are not comprehensive.Therefore,based on the finite element theory,thesis calculates the stress intensity factor at the crack tip by setting cracks in the beam,and then obtains the crack propagation parameters,and considers different temperature gradients in the analysis.At the same time,the vertical deflection and vertical acceleration of three kinds of beams are calculated and the fatigue damage of key points of steel-concrete composite beams is analyzed.The main contents and conclusions of this thesis are as follows:1)The vehicle-bridge coupling motion equation is established and the corresponding finite element model is established.Three kinds of bridge models are established,which are single concrete box girder,multiple concrete T beams and steelconcrete composite beams.The vertical deflection,vertical acceleration and impact coefficient of the three girder bridges under vehicle load are calculated.The influence of vehicle speed,unevenness and vehicle weight on the mid-span vibration of the beam is analyzed.The results show that the vehicle weight has the greatest influence on the vertical deflection and vertical acceleration of the beam span.2)The stress intensity factor at the crack tip is calculated and the crack propagation parameters are evaluated.Cracks are set at the bottom of the middle span of the box girder and at the middle span and diaphragm of multiple concrete T-beams.The influence of crack angle,crack depth and vehicle speed on crack propagation parameters is analyzed.At the same time,the influence of temperature gradient on the stress intensity factor at the crack tip is considered.The results show that the type I stress intensity factor curve is similar to the mid-span vertical displacement time history curve,which reaches the peak when the vehicle passes through the mid-span;the type II stress intensity factor is hyperbolic.At the same time,when the temperature gradient is applied,as the amplitude of the temperature gradient increases,the bridge deck will produce upward arch deflection,resulting in a decrease in the vertical displacement value at the mid-span and a decrease in the type I tensile stress intensity factor at the crack tip.3)The fatigue damage of steel-concrete composite beams under vehicle load is analyzed.The Miner linear cumulative damage criterion is used to calculate the damage degree at key points.The results show that with the increase of roughness grade,the total number of stress cycles increases,and the damage increment also increases gradually.