Study On Fatigue Performance Of Steel Bridge Deck After Rewelding Repair

In recent years,orthotropic steel deck has become the preferred deck structure for large and medium span steel bridges due to its light weight,high strength and easy assembly construction.However,due to the influence of fatigue disease,the early construction of steel bridge deck has serious cracking problem.The RD welded joints between the top plate and the longitudinal rib of the diaphragms introduce a large amount of residual stress due to welding.In addition,these areas are also the fatigue hot spots of the steel bridge structure.Under the complex and changeable traffic load,RD welded joints become the concentrated source of fatigue cracks,which leads to the fatigue cracking of the orthotropic steel bridge deck after a period of operation.As one of the effective means of RD welded joints repair,rewelding repair has attracted people's attention in recent years.However,the research at home and abroad is mainly focused on the rewelding repair process,and there is a lack of research on the residual stress and post weld fatigue properties.And most of the fatigue studies ignore the effect of residual stress,which is difficult to accurately evaluate the fatigue performance of orthotropic steel bridge deck,and it is likely to lead to secondary cracking soon after re welding repair.In view of the various fatigue cracking modes that RD welded joints may exist,this paper studies the residual stress and fatigue properties of RD welded joints after rewelding repair.The main work and conclusions are as follows:(1)According to the German repair guideline DVS1709,and based on the thermoelastic-plastic theory,the welding temperature field and stress field during the initial welding and rewelding of RD welded joints machining were numerically simulated by using the thermal structural sequence coupling method.The reliability of the welding finite element simulation is verified by comparing the longitudinal residual stress test data of RD welded joints with the welding finite element simulation in this paper.The analysis of transverse residual stress which has great influence on fatigue shows that: compared with the initial welding,the distribution of transverse residual stress near the weld after re welding is more complex,and the peak values of transverse residual stress at the top welding toe(welding toe 1)and the top welding root(welding root 1)are 300.7mpa and 349.3mpa;according to the distribution of transverse residual stress along the panel thickness of initial welding and rewelding,the local distribution model of residual stress is proposed.(2)The results show that the equivalent structural stress method has a good grid insensitivity for fatigue performance prediction of RD welded joints.Without considering the influence of welding residual stress,a three-dimensional fine sub model of RD welded joints between two diaphragm sections is established.The equivalent structural stress time history curves of fatigue vulnerable parts are calculated by vehicle moving load.The results show that the weld toe 1,weld root 1 and longitudinal rib weld toe(weld toe 2)are mainly subjected to compressive stress cycle under typical load conditions.Under the three load cases,the equivalent structural stress amplitude of root1 is 39.6mpa,49.4mpa and 42.5mpa respectively,which is significantly larger than that of toe 1 and toe 2.According to the calculation of annual fatigue cumulative damage degree of fatigue vulnerable parts of RD welded joints by equivalent structural stress amplitude,it shows that the fatigue cracking mode of root 1 cracking along the roof is the dominant failure mode of rewelding RD welded joints.(3)The initial stress method is used to apply the residual stress to the fatigue sub model,and the fatigue loading analysis is carried out.The results show that compared with the case without considering the residual stress,the maximum stress amplitude of root 1 increases about 18% under the typical load condition after considering the residual stress.Based on miner's linear cumulative damage theory and principal S-N curve,the calculation of fatigue damage degree shows that root 1 is still the dominant cracking mode after considering residual stress,but the maximum annual fatigue damage degree of root 1 increases about 21.5% compared with that without considering residual stress under typical load conditions.(4)Considering the effect of residual stress,the fatigue loading of RD welded joints after initial welding is calculated.The results show that the annual damage degrees of root 1 under typical load cases are respectively.Compared with the fatigue performance after initial welding,the dominant fatigue failure mode of root 1 does not transfer after rewelding,but the maximum annual cumulative fatigue damage of root 1increases by about 17.4%.It is proved that the introduction of new residual stress in rewelding repair will further reduce the fatigue performance of RD welded joints,and accelerate the fatigue deterioration process of RD welded joints under vehicle cyclic load.