Fatigue Performance Of Large Span Suspension Bridges Based On Monitoring Data And Muti-scale Simulation Study Of Fatigue Performance Of Steel Bridge Panels

Modern suspension bridges are gradually developing in the direction of oversized spans with the advancement of technology and science.The orthotropic steel bridge panels are widely used in the main girder deck of large span and super span suspension bridges because of their many advantages,but their local structure is complex,there are many welds,and the stress concentration effect at the welding area is prominent,especially under the repeated action of external random traffic load,the fatigue problem is very significant.In the study of fatigue problems of steel bridge panels,multi-scale simulation is a common method,which can reduce the research cost and simulate the problems that are difficult to achieve in actual engineering compared with model experiments and real bridge monitoring,but the model accuracy and computational efficiency are also the key problems to be solved by multi-scale models.The main work and conclusions are as follows:(1)The fatigue cracking mechanism of orthotropic anisotropic steel bridge panels is introduced in an exhaustive manner.(1)The fatigue cracking mechanism of orthotropic anisotropic steel bridge panels is introduced in a comprehensive manner.The current state of research at home and abroad is systematically described and summarized in terms of fatigue assessment methods for steel bridge panels,random traffic loading,and multiscale simulation of structures;the shortcomings of current suspension bridge research are explained;the core of the thesis is introduced and the main research content and objectives of the thesis are determined based on the summary of the current state of research;(2)In order to make a reasonable assessment of the fatigue performance of orthotropic anisotropic steel bridge panels of suspension bridges,the results of stress amplitudes using all levels of grid size are compared and analyzed based on the extrapolation formula of the hot spot stress method.The study shows that the structural hot spot stress of the finite element model is influenced by the grid size,and the grid should be refined as much as possible under the premise of ensuring the calculation rate;(3)Based on the actual traffic vehicle monitoring data,the statistical analysis of the probability distribution characteristics of the traffic flow is carried out,and the traditional random traffic load model and the time-based multi-scale random traffic load model are established to reflect the actual traffic flow operation conditions.The results show that the timebased multiscale random traffic load model can reflect the effect of time change on random traffic load more intuitively,and the total traffic volume in the left half of a large span suspension bridge is significantly higher than the total traffic volume in the other direction.The traffic volume is more intensive between 10:00 a.m.and 2:00 p.m.,and the two types of fatigue structure details are also more likely to have higher amplitude stress responses during this time period;(4)A multi-scale model of suspension bridge structure was established based on the multipoint constraint method,and the full bridge model,standard girder segment model and fatigue structure detail model were established with girder rod unit,plate and shell unit and solid unit respectively;two types of random traffic load axial weight sequences were loaded onto the hot spot stress effect surface fitting formula in turn,and the stress response of the structure detail was calculated by the vehicle-induced load,so as to realize the typical fatigue structure detail fatigue damage analysis of steel bridge panels.The fatigue damage analysis of the details of the steel bridge panels was carried out.The results show that the fatigue life of the two types of random traffic loads shows that the time-based multi-scale random traffic load simulation method can calculate the fatigue life of the structure more accurately than the traditional random traffic simulation method,and the fatigue life of the two types of typical fatigue structural details are lower than the design fatigue life of the bridge.The fatigue life of the cross weld detail of the longitudinal ribs is lower than the fatigue life of the butt weld of the longitudinal rib inlay section,and there is a significant risk of cracking in the steel bridge panel.