Analysis Of Fatigue Load Combination Effect On Cable-Stayed Bridge With Roads And Tracks In The Same Floor

Rail-cum-road bridge can be divided into two structural forms according to the distribution type of traffic lanes.One is two-tiered structure with roads and rails distributed separately,the other is parallel structure with roads and rails distributed on the same level.In recent years,the parallel structure has gradually begun to be used in the construction of bridges in China.Compare with two-tiered structure,the parallel structure has an advantages of low road elevation and better vision on road,which can save some construction cost and improve driving comfort.For bridge structures with different structural forms,the mechanical properties have a great difference comprehensive influenced by all factors when suffering the combined effect of road and rail traffic loads.In view of the fact that there is no domestically constructed parallel rail-cum-road cable-stayed steel bridge,and there is no special specification to guide the design.The structural mechanics response bearing two loads is not clear yet.Therefore,it is necessary to investigate the mechanical response characteristics and load combination method when suffering both two loads.The main work of this thesis includes:(1)The current development status on fatigue research of steel bridges is reviewed.The mechanism of fatigue damage on steel bridges is elaborated.The theory of fatigue damage analysis is described and the evaluation method of calculating linear cumulative fatigue damage is determined.(2)Provisions on fatigue load of highway steel bridges in four specifications which contains BS5400,Eurocode,AASHTO and JTGD64-2015 are comprehensive compared.The principle of formulating fatigue load spectrum was analyzed.The loading method of fatigue load was selected.(3)Full-bridge analysis model which based on Haikou Ruyi Island Cross-sea Bridge is established with Midas software.Structural mechanical responses bearing road and rail traffic loads are calculated.The mechanical properties of the bridge suffering two different loads are analyzed.(4)Based on the results of the full-bridge model analysis,a bridge segment is selected to establish a local analysis model with the finite element analysis software Ansys.Then,stress responses bearing road and rail traffic loads are calculated.Stress history of the local fatigue details is analyzed.Finally,fatigue effects are evaluated.(5)Suitable probabilistic model is selected to calculate the encountering probability of road and rail traffic loads.Fatigue cumulative damage caused by combination fatigue loads is calculated based on fatigue damage linear accumulation theory.Revise coefficient of combined fatigue load is got.(6)Based on the results of finite element calculations,the mechanical response characteristics of parallel rail-cum-road bridges bearing two traffic loads are obtained,and the loading method of fatigue load is determined.The method of calculating the fatigue correction coefficient based on the actual traffic volume is concluded.