Research On Fatigue Characteristics And Fatigue Performance Improvement Of Steel Bridge Deck-longitudinal Rib Welded Joint

Under the repeated action of vehicle load,the welded joint between steel bridge panel and longitudinal rib joint is easy to produce fatigue cracks in the direction of deck plate thickness,among which,fatigue cracks at the weld root are not easy to detect at the inner side of steel box girder,hidden,difficult to maintain,which is not conducive to the long-term service of the bridge.Therefore,this paper was based on the numerical method combined with the theory of linear elastic fracture mechanics to carry out a study of the fatigue expansion behavior of cracks at the weld root of the welded joint between the steel bridge panel and the longitudinal rib connection.And on the basis of the existing research results to consider the weld root at the fatigue crack at different locations,as well as the geometric uncertainty of the initial crack and the complex stress field near the welded joint multiple influencing factors to further assess the fatigue performance of the welded joint,to provide support for the reasonable design of the construction details.The main research contents and results of this paper are as follows:(1)Analysis of the weld root at different starting crack location crack fatigue expansion behavior.First,based on the ANSYS software steady-state crack analysis method,to obtain the stress intensity factor influence line of the crack tip,to obtain the most unfavorable load location;then,proposed to consider the different crack initiation locations at the weld root,based on the ANSYS software extended finite element analysis method to simulate the fatigue expansion behavior of two kinds of cracks;and then based on the existing test model,for the obtained about the different initiation locations of the crack Finally,considering the initial crack geometry uncertainty,the effects of the initial angle effect and the initial depth effect on the fatigue expansion behavior of the crack at the "two tips" of the weld root inner crack were analyzed.The study shows that: the weld root inner crack compared to the outer crack,for the fatigue deterioration of the welded joint is smaller,when the initial crack exists on the outside of the weld root,the structural load capacity is reduced by 5.8% compared to the inner crack.(2)Consider the effect of complex stress environment on the fatigue expansion behavior of cracks at different crack initiation locations.Firstly,the complex stress field is decomposed into six basic stress models based on the principle of mechanical superposition;then,based on the extended finite element method of ANSYS software and combined with the basic models,the effects of tensile and bending stresses on the fatigue expansion behavior of cracks at different crack initiation locations are analyzed.It was found that both tensile and bending stresses at the steel bridge panel lead to crack expansion at the weld root;while the bending stresses at the longitudinal ribs have less influence,and the tensile stresses at the longitudinal ribs lead to the compressive stress concentration at the weld root.(3)Based on the fatigue performance assessment of welded joints under different forms of loading.First of all,taking into account the section model test force is clear,single mode,for this reason proposed to consider the effect of vertical load and horizontal tensile load,the two forms of load on the welded joint;then,by changing the deck plate thickness,weld size and weld penetration rate,to study the impact of different parameters on the fatigue performance of the welded joint,the study found that: vertical load,increasing the deck plate thickness can significantly improve Weld root stress amplitude,a reduction of 32.74%,but also can significantly improve the weld root fatigue cracking at the toe,while changing the weld size and penetration rate almost all can not improve the crack cracking;Finally,the crack expansion stage into short crack expansion stage and long crack expansion stage,combined with different forms of loading and different structural parameters,consider different forms of loading,changing a single structural parameters on the The effect of changing a single structural parameter on different stages of cracking under different forms of loading is considered,and it is learned that increasing the thickness of the steel bridge panel under vertical loading can significantly improve the cracking in different stages of cracking,while increasing the melt penetration rate only under horizontal loading can improve the fatigue cracking at the weld root and the cracking in the long cracking stage at the weld toe.In addition,when multiple failure modes are considered,the fatigue resistance deterioration of the structure is more severe compared to that of a single failure mode.