| Orthotropic steel bridge panels are widely used in deck systems of long-span cable-stayed Bridges and suspension Bridges.Under the action of heavy traffic flow,the roof has a lot of fatigue cracks.The crack of roof of steel bridge was repaired by rewelding with longitudinal ribbed through fatigue crack.The initial fillet weld of roof and longitudinal rib is simulated by finite element numerical modeling.According to the guide of DVS1709,the article realizes the repair process of roof-longitudinal rib rewelding.The fatigue life of roof after machining and rewelding was analyzed.Based on the thermoelastic-plastic finite element method,the heat source loading and cooling processes are numerically simulated,and the residual stress fields of different stages of roof and longitudinal rib machining,crack groove opening and rewelding repair are obtained by using the thermo-elastic plastic finite element method.The influence of residual stress of initial fillet weld of roof and longitudinal rib on residual stress field of rewelding repair is discussed.The most unfavorable loading point of roof-longitudinal rib was determined by moving loading,the service life of roof before and after rewelding was determined based on s-n data,and the local deformation amount of rewelding area was analyzed.The research contents and conclusions are summarized as follows:(1)The influence of temperature load and mechanical boundary constraint on welding residual stress was analyzed.After welding,the thermal insulation effect does not change the residual stress distribution trend in the section,but reduces the residual stress value.The strength of boundary constraint directly affects the welding residual stress of weld and motherplate.The stronger the boundary constraint,the greater the welding residual stress.(2)The residual stress on the lower surface of roof is higher than that on the upper surface of roof.There is a high stress gradient in the range of 30mm on both sides of the top plate fillet weld and 8mm on the longitudinal rib,which will become the"hot spot"area for fatigue crack.The longitudinal stress distribution of the roof is symmetrical"M"shape,and the longitudinal stress distribution of the longitudinal rib is symmetrical"L"shape.Compared with the single side welding of roof and longitudinal rib,the longitudinal stress on the upper surface of roof is reduced and the longitudinal stress on the outer surface of longitudinal rib is increased by using double-sided welding technology,and the area of 5mm near seam of longitudinal rib in double-sided welding will become a new"hot spot"distribution area.(3)The initial stress of fillet weld directly affects the residual stress after rewelding.The initial stresses of"over welding"and"virtual welding"are obviously different,but there is no significant difference in the distribution and value of residual stresses of rewelding under the influence of their respective initial stresses.Considering that the longitudinal stress under the influence of the initial stress is greater than that under the neglect of the initial stress,the width of the peak stress on the roof increases by 20%.After the roof was repaired by rewelding twice,the width of the transverse stress yield platform increased by 55%compared with that of the first rewelding.(4)Through moving loading,the A3 point of roof A1 was determined to be the fatigue vulnerable point.The fatigue service life of the roof after welding and forming is 1.42?10~7 times under the action of equivalent fatigue stress amplitude,while the fatigue service life of the roof after rewelding and repairing is reduced by11.34%.Under the action of external load,the local deformation of the rewelding zone increased significantly,and the length of the deformation zone was twice the length of the rewelding seam. |
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