Study On Fatigue Life And Reliability Of Steel Deck Welding Details Based On Random Vehicle

With the continuous development of our country society and economy,more and more extra large span,large span bridges have been applied,at the same time,taking into account the need to China's steel industry production digest capacity and upgrade transformation,the government is promoting the use of steel structure bridge in extra large span,large span even middle and small span bridges.At present,the orthotropic steel deck,which has the advantages of small weight,large steel utilization,strong bearing capacity,convenient construction and various structural forms,has been widely used as the deck form of large and long-span bridges.However,a large number of engineering examples also show that the welding details of complex structure,welding defects appear easily in the process of welding,the repeated traffic loads,fatigue cracks are easy to occur at the weld joint.The damage phenomenon has become the main failure type of orthotropic steel bridge deck.This paper is supported by the national"973"project"basic theory research on safety design and evaluation of extra large span bridges?2015CB057700?"and the natural science foundation of China?51378081,5130807151308073?,based on WIM?weighing in motion?data of a highway girder suspension bridge,the probability distribution characteristics of random vehicle parameters were analyzed.Based on the concept of constrained stress zone,a trans-scale model for fatigue crack propagation was established.The fatigue life and fatigue reliability analysis of orthotropic steel bridge deck welds were carried out by using S-N curve method,linear elastic fracture mechanics method and trans-scale model.The main research contents are as follows:?1?Based on the concept of constrained stress zone,the expression ofK_micro^macro and K^macro were fitted by the finite element method,based on the Paris crack growth model,a semi elliptical surfaces crack trans-scale growth model was established in 3D conditions.The fatigue failure behavior of orthotropic steel bridge panel weld is described by fatigue crack cross-scale expansion model.As the fatigue test data have great divergence,the numerical simulation results show that the microscopic effect has a great influence on the fatigue life.?2?The probability distribution characteristics of parameters of the fatigue limit state equation based on S-N curve and linear elastic fracture mechanics method were discussed.On this basis,the probability distribution characteristics of the parameters in the fatigue limit state equation based on the trans-scale model for fatigue crack propagation were discussed,and the specific values of the parameters were given.According to the macroscopic crack as a random parameter of fatigue reliability calculation,the problem of macroscopic crack existing in traditional s-n curve and linear elastic fracture mechanics theory is solved.?3?Based on the measured data of WIM,the probability distribution characteristics of random vehicle parameters were analyzed,and a simulation program of random loads was worked out.Choose t-copulas connect function as a link function,correlation degree of every vehicle axle load and related characteristics are described,can be a very good the nonparametric kernel density estimation-copulas connect construction method can accurately describe the joint distribution of vehicle axle load.?4?Analyzed the road table temperature stress of the welded details of orthotropic steel bridge panel,namely fatigue analysis,should consider road table temperature on the influence of stress amplitude,don't consider the effect on the transverse distribution coefficient.?5?Taking the axle load correlation and pavement surface temperature as the change factors,the statistical analysis of the daily equivalent stress amplitude was carried out in four cases.Considering the effect of pavement temperature,the daily equivalent stress amplitude probability distribution character is more multi peaks.The daily equivalent stress amplitude mean considering the correlation between axle loads is larger than the daily equivalent stress amplitude mean without considering the correlation between axle loads.?6?Discusses the use of BS5400 and s-n curve of Eurocode 3 specification analysis of fatigue cumulative damage and life of differences,it is concluded that the UK the fatigue cumulative damage of BS5400 specifications of Eurocode 3 specification than Europe's fatigue cumulative damage in severe cases,the fatigue life is shorter;the initial size of different welding defects has a great influence on fatigue cumulative damage and fatigue life,when the initial depth of welding defects reaches 2mm,the fatigue life of the bridge is close to the design period;In the analysis of fatigue cumulative damage and fatigue life,the correlation of axle load and pavement temperature should be taken into consideration,otherwise the result will be unsafe.?7?Based on the traditional fatigue theory,the theory of linear elastic fracture mechanics and fatigue crack propagation across a scale model of the fatigue limit state equation,it is concluded that with the increase of initial share macro welding defects,the fatigue failure probability is also rapidly increasing,the fatigue reliability index will reduce rapidly.Therefore,reducing the occupation rate of the initial macro welding defects will effectively reduce the fatigue failure probability in the process of engineering implementation;the fatigue failure probability considering the axle load correlation and the road surface temperature is greater than the fatigue failure probability considering only the axle load correlation,considering only the pavement temperature and both unconsidering.The fatigue failure probability considering axle load correlation is bigger than the fatigue failure probability considering the pavement temperature,the fatigue failure probability is more sensitive to the axle load correlation.