Study On Welding Detail Residual Stress Distribution And Its Effect On Fatigue Performance Of Orthotropic Steel Bridge Deck

In recent years,orthotropic steel deck has been widely used in steel bridge construction at home and abroad because of its advantages such as less consumables,light weight and good overall performance.However,as the main way of connecting structural parts in orthotropic steel bridge deck,welding inevitably causes certain welding defects(porosity,slag,crack,bite edge,etc.)in the weld and its adjacent area.Under the reload of vehicles,the fatigue problem of orthotropic steel bridge deck is very prominent.The specific fatigue details of orthotropic steel deck of a steel box girder section were studied in this thesis.The main research work was as follows:(1)This thesis introduced the development and application of orthotropic steel deck in the field of steel bridges at home and abroad,summarized the fatigue damage of bridges with orthotropic steel deck,and expounded the research status of welding residual stress of steel structure,multi-modal composite cracking of fatigue crack and fatigue cracking of orthotropic steel deck.The comprehensive analysis showed that there are still some limitations in the current research on orthotropic steel bridge deck.(2)Based on the finite element software ABAQUS,Segmental model of a steel box girder was established,the loading response of 9 transverse load cased and 46 longitudinal load cases are analyzed,and the most unfavorable load case of crack propagation at the weld between the top deck and the U rib and the opening of the diaphragm,which is the fatigue sensitive position of the steel deck,was defined.(3)ABAQUS subroutine was written based on FORTRAN language to simulate and analyze the temperature field and stress field during the welding process of steel bridge deck top deck and U rib,and obtained the residual stress values and distribution of corresponding welding details.(4)The basic concept of stress intensity factor and three common crack propagation criteria were discussed,and the existing prediction formulas of fatigue crack propagation were summarized.For Q345 q D steel commonly used in bridges,the fatigue crack growth test of compact tensile specimen(CT)was carried out based on flexibility method and Digital Image Correlation.The test data were fitted by least square method,and the material constants C and m related to fracture mechanics are determined.(5)The basic theory of evaluating fatigue crack growth life based on fracture mechanics was expounded.Based on the NASGRO formula of fracture mechanics,the effects of different initial crack sizes considering the influence of welding residual stress on the weld toe and weld root of deck and U-rib were studied through the finite element software ABAQUS and threedimensional fracture analysis software FRANC3 D.The fatigue crack propagation life at the diaphragm opening under the initial cracks with different sizes and fixed depth width ratio at different positions was analyzed.