Research On Dynamic Characteristics And Fatigue Performance Of Long Span Steel Concrete Composite Beam Suspension Bridge

At present,highway bridges are gradually developing towards the direction of large span and flexible stiffness,and the driving speed and weight is also gradually increasing.The problem of vehicle bridge coupling vibration effect of highway bridges is becoming increasingly prominent.Steel concrete composite beams have obvious advantages of large-span bridges and have broad application prospects in large-span bridges.As the main load-bearing component,the fatigue damage to steel concrete composite beams is crucial to evaluating the fatigue state of the entire bridge structure operation cycle.Therefore,this paper takes a steel-concrete composite beam suspension bridge as the research object,and studies its structural dynamic performance considering the vehicle bridge coupling effect and the fatigue performance of the steel-concrete composite beam segment of the bridge.The main research content and conclusions include:(1)Build a vehicle bridged coupling system.Establish vibration differential equations for vehicles and bridges separately,based on Nemak-β by combining Matlab language,a vehicle bridge coupling vibration system was constructed,and a tool for calculating the coupling effect of the vehicle bridge was obtained.Four types of road roughness parameters were generated,and relevant research variables were substituted to calculate the results of the vehicle bridge coupling.(2)Establish an overall model of the bridge.Using the parametric modeling method,based on the main cable shape finding theory,the pre deflection of suspension bridge is determined,and the main cable shape is obtained.The script of the overall bridge model is established in Python language,and the ABAQUS analysis software is used to run the script to generate the overall bridge model in the state of bridge completion.The static characteristics of the main cable and the bridge model as well as the natural frequency and mode of vibration of the bridge are analyzed in detail.The research shows that the maximum deflection value of the bridge can reach4 cm,and the maximum camber value can reach 2.348 cm at 1/4 and 3/4 of the main span.The vibration mode of the bridge is mainly vertical bending and torsion.The first and second frequencies of the suspension bridge are 0.101 Hz and 0.126 Hz respectively.There is no longitudinal drift in the first ten vibration modes,and it shows good stiffness performance in the longitudinal bridge.(3)Study the influence of changes in bridge structural parameters such as the stiffness of the main cable,main tower,and main beam on the natural frequency and main mode of vibration of the bridge.The research results indicate that the dynamic displacement of the main beam decreases with the increase of the tensile stiffness of the main cable,and the stress of the main cable in the span increases with the increase of the stiffness.The change in the tensile stiffness of the main cable mainly affects the frequency of the transverse and torsional modes and the vertical bending modes of the structure;The stiffness of the main tower mainly affects the vertical bending and torsional mode frequencies of the suspension bridge structure,and has a higher impact on the low order modal frequencies;The stiffness of the main beam mainly affects the transverse and vertical bending modal frequencies of the structure,and has a significant impact on the higher-order modal frequencies.Overall,the change in stiffness of the main beam has the greatest impact on the natural frequency of the bridge.(4)Study the effect of vehicle bridge coupling vibration on the dynamic characteristics of bridges.Using vehicle speed,weight,damping ratio,and road roughness as research parameters,analyze the effects of each parameter on the deflection,natural vibration frequency,and impact coefficient of the bridge structure.The research results indicate that under low vehicle speed conditions,the 1/8 span,1/4span,and 1/2 span sections of the secondary longitudinal beam exhibit relatively larger moment impact coefficients,while the impact coefficients of the 3/8 span section show a continuous increasing trend after the vehicle speed exceeds 80km/h;The dynamic displacement of the bridge increases with the increase of vehicle weight,and the displacement curve of the bridge under each vehicle weight is similar in shape;The deflection impact coefficient of the bridge decreases with the increase of damping ratio.Increasing damping can effectively reduce the vibration amplitude of the bridge beam,and the change curve of the impact coefficient also tends to be stable;As the unevenness of the bridge deck increases,the impact coefficients of each section of the main and secondary longitudinal beams increase.At the same level of unevenness of the bridge deck,the impact coefficients of 1/2 span are the highest,and the impact coefficients of 3/8 span are the lowest.At the same time,the impact coefficients between different sections gradually approach with the increase of unevenness of the bridge deck.(5)The fatigue damage of steel concrete composite beam segments was studied.Select the standard section of the bridge,determine the representative fatigue vehicle load,and conduct static and moving load analysis to determine the fatigue details of the standard section.Based on the linear fatigue damage theory based on S-N curve,calculate the fatigue damage degree and fatigue life under standard fatigue vehicle load,and analyze the impact of traffic growth on fatigue life.Research has shown that when the vehicle weight changes from 50 t to 100 t,the amount of fatigue damage within the same time period will increase by more than 5 times,and an increase in vehicle weight will reduce the fatigue life of the bridge structure;The fatigue damage of bridge structures increases with the increase of vehicle speed.When the vehicle speed is low,the increase rate of fatigue damage is faster,but the increase rate of damage slows down as the vehicle speed increases.