Study On Welding Residual Stress Of Diaphragm-through Beam-column Joints And Its Effect On Ductile Fracture

In order to avoid brittle failure of steel structure beam-column joints,domestic and foreign efforts have been made in selecting suitable strength and toughness weld materials,improving welding technology,improving construction quality,and selecting ductile joints.These measures have indeed improved the seismic performance and plastic deformation capacity of the beam-column joints in varying degrees.However,under the action of strong earthquakes,such a node will produce a large cumulative plastic deformation of the steel.Some micro cracks or small defects will propagate under the driving of the deformation,which will also cause the node to crack.In order to improve the accuracy of the prediction of ductile fracture behavior,this paper made use of the existing pseudo-static tests of steel diaphragm-through beam-column joints,and used the finite element software ABAQUS to conduct welding simulation and pseudo-static finite element analysis successively.Based on the analysis of welding residual stress and strain fields,the cyclic loading was applied to the steel diaphragm-through beam-column joints,and the ductile fracture behavior of the joints was predicted by using the cyclic cavity expansion model(CVGM)in micro-mechanism.The main work and conclusions are as follows:1.According to the existing tests,the finite element model of welding was established by ABAQUS.According to the welding sequence,heat source model and welding thermal parameters,the DFLUX heat source subroutine was used to solve the welding temperature field of the model,and the welding stress and strain field of the model was solved by using the sequential coupling method.The results of welding residual stress analysis show that the larger welding residual stress is basically concentrated in the area where the butt weld and fillet weld are located,and the stress at both ends of the weld is higher than that in the middle area,which may become an inducement for cracking during subsequent loading.2.In the pseudo-static analysis of nodes,UMAT subroutine was used to calculate the cracking criterion for the elements in the analysis model,and the prediction results show that the cracking judgment results considering welding residual stress are close to the test results.Due to the introduction of the initial welding residual stress field,the stress and equivalent plastic strain values of the model with welding residual stress are larger than those of the model without welding residual stress,and the larger stress distribution area is more concentrated.3.The calculation of fracture index RI value show that the RI value of the model with welding residual stress is greater than that of the model without welding residual stress,and for the model with welding residual stress,the RI value of the area near the failure element is slightly greater than that of the surrounding elements.On the butt welds of the beam and column,the RI values of the middle region on each path are all smaller than those of the two ends.The validity of location prediction of failure element is further demonstrated.