Research On Fatigue Life Evaluation And Reliability Based On Strain Energy In Deck-to-rib Joint Of Orthotropic Steel Deck

Welding residual stress and stochastic traffic load are primary causes of fatigue damage at deck-to-rib joints of orthotropic steel deck(OSD).The assessment of the time-varying fatigue damage at deck-to rib joints with consideration of welding residual stress and stochastic traffic,is the precondition to ensure the safety of bridge in the period of service.However,the solution of combining the welding residual stress and vehicle-induced stress is too difficult to consider the welding residual stress effectively in the present evaluation methods.To quantify the effect of welding residual stress on fatigue damage of structure,the fatigue performance and fatigue reliability of deck-to-rib joints are evaluated by the strain energy-based approach in this study,based on the superposition model of welding residual stress and vehicle-induced stress.(1)The mainly causes of fatigue cracks and and modals of fatigue failure of OSDs have been introduced in this part.The current researches on the properties of welding residual stress,fatigue assessment methods,fatigue reliability evaluation around the world have been summarized and analysed.Besides,the shortcomings and disadvantages in the present study have been expounded.Finally,the research objectives and contents of this study have been proposed.(2)Considering the influence of welding residual stress on deck-to-rib joints of OSD,the welding residual stress analysis model is established by the thermal elastic-to-plastic finite element method.The thermal elastic-to-plastic finite element model has been validated by the present testing data.Thus,the empirical formula on distribution of welding residual stress field has been proposed,and the parameters on empirical formula have been determined in the different plate thicknesses of deck and rib.(3)The welding residual stress is so large that the plastic region may appear after combination of the welding residual stress and vehicle-induced stress.The simplified coupling model of welding residual stress and vehicle-induced stress is advanced,based on the similar P-E method and elementary beam theory.And the proposed stress combination simplified model would have been verified by the finite element method.(4)Because the effect of welding residual stress on fatigue performance of OSD is quantified difficultly,the strain energy-based fatigue life assessment approach is developed.The strain energy-based fatigue strength evaluation curve is determined,with the effect of welding residual stress on fatigue damage.At last,the fatigue evaluation method and fatigue strength curve have been validated by the present testing data.(5)To quantify the effect of welding residual stress and stochastic traffic load on fatigue damage of OSD,the limited state equation and fatigue reliability evaluation model have been established,considering the combination effect of welding residual stress and stochastic traffic flow.And the effects of the growth of vehicle weight and traffic flow on fatigue reliability have been analyzed.(6)The statistical analysis of stochastic traffic flow of Junshan Yangtze Bridge has been carried out.Then,the typical fatigue load vehicles and fatigue load spectrum have been determined.Considering the effect of welding residual stress,the fatigue life and sthrength of the deck-to-rib joints have been evaluated by the proposed stress combination simplified model and strain energy-based fatigue life evaluation method,and the distribution on fatigue life of deck-to-rib joints has been predicted by the stochastic traffic flow.The fatigue reliability evaluation is conducted by the developed fatigue reliability evaluation model,and the influence laws of welding residual stress and stochastic traffic load on fatigue life have been analysed.