Finite Element Analysis and Fatigue Damage Calculation of Welded Bridge –K Joint

Abstract

One of the most important deterioration mechanisms of steel bridges structures, which occur in service condition, is fatigue. In Nepal, numerous number of fatigue cracks has been recently reported to initiate in steel bridges in superstructures and even in sub structures. Such fatigue cracks may lead a significant influence to the traffic and even collapse of the bridges if the cracks are left to propagate. Repair and retrofitting works including investigation of fatigue mechanism for such fatigue damage are very urgent issues now. This is the research work about the finite element modeling and fatigue damage calculation of steel welded truss bridges. The Rapti Bridge of Nepal is taken as a typical case that was failed by buckling and retrofitted by welding technique.3D finite element model of Rapti bridges was created using the available SAP2000 software package. The result obtained from the linear analysis was used to find the most critical joint for fatigue damage. The analysis shows that the middle joint is the most critical joint for IRC class –A load. For the modeling of k- joint and calculation of fatigue damage the software package ANSYS Ver.10 was used. The micro model of the k joint was model using the elements available in software package. In the FE model, 3D 20 node tetrahedral solid elements, solid 95, was used for gusset plate and diagonal members. The weld nugget was model using a two node beam element BEAM 188. Contact and target elements, Targe170 and Conta175 were also created on the inner surfaces of the plates around the weld. The transient step loading analysis was done considering the effect of material non linearity. In the present study, numerical analysis was carried out to look into the performance of welded k- joint in axial loading with different weld radius. Strength of joint is increased with the increase of weld radius. The displacement along the longitudinal direction is decreased and the stress distribution is more uniform with the increases of weld radius. The stress life approach (S-N) curve was used to evaluate the cumulative fatigue damage. Based on the predicted stress and strain states fatigues life analysis were performed. The result of this study shows that the fatigue life of welded joint increases with the weld diameter. In this study, the weld radius 5mm has a lesser fatigue damage than the weld radius 3mm and 2mm.