Research On Fatigue Performance Of A New Type Of Upsetting U-rib Orthotropic Steel Bridge Deck

The main contradiction in the development of orthotropic steel bridge decks(OSDs)lies in the contradiction between good mechanical performance and high fatigue risk,where the rib-to-deck welded joints is one of the most prominent parts of fatigue disease.It has made great progress from the traditional OSDs itself to improve its fatigue performance,But the fatigue disease cases of this structural details are still emerging.On the basis of the traditional OSDs,improving the fatigue performance of the structure by innovating on the structure is the main way to promote the application of OSDs and its sustainable development.Taking the new type of upsetting U-rib OSDs as the research object,the following research work is carried out:(1)This thesis briefly introduces the development course of orthotropic steel bridge panel,the causes of fatigue problems and the basic theory and basic concepts of fatigue analysis.Introduce the research status of the new structure,and on this basis,a new type of upsetting U-rib OSDs is introduced,and its design concept is expounded.(2)The thesis presents a comprehensive introduction to the notch stress approach,elaborates the theoretical basis of the notch stress approach,summarizes the characteristics of the notch stress approach and the similarities and differences with the nominal stress approach and the hot stress approach.Some key factors influencing the use of notch stress approach are discussed:fatigue notch factors,S-N curve and how to solve notch stress.(3)The influence of the structural parameters of the orthotropic steel bridge deck on the notch stress and the fatigue notch factor is analyzed,The results show that increasing the thickness of the deck can effectively improve the stress concentration of the rib-to-deck welded joints.The thickness of the U-ribs is mainly reduced by the stress of weld toe at the U-ribs,and the opening angle to the stress of weld toe at the deck.While the increase in weld penetration will improve the stress concentration of the weld root.All above conclusions can be used to improve the fatigue performance of the steel bridge deck.(4)The fatigue data of the rib-to-deck welded joints extracted from the existing fatigue test are systematic re-analysis and converted to the notch stress.The results show that the notch stress fatigue data are located on the FAT 225 curve recommended by IIW,so the notch stress approach can be well applied in the fatigue evaluation of OSDs.(5)The fatigue life of the new type of upsetting U-rib OSDs is evaluated by notched stress approach,and the key problems are studied.The results show that the notch stress can be used as an effective evaluation index to determine the difference of the weld root or weld toe in fatigue performance.Relatively speaking,the welding root is more prone to crack.Compared with the traditional U-rib,the fatigue properties of weld toe at the new type of upsetting U-rib are substantially improved,but the improvement effect at the weld root is not obvious.