Prediction And Control Of Welding Residual Stress In Building Steel Structures By Means Of Finite Element Method

The stress caused by welding determine the initial stress of building steel structures and it will affect the safety and stability of structures.Meanwhile,due to the relatively thick steel plate used in the high-rise building steel structure,the stress in welding process is larger because of structural constraint.Lamellar tearing will be promoted by the stress generated in welding process,and fatigue strength will be reduced and even brittle fracture will be led by welding residual stress.Due to enlargement and complication of steel structure,now the analysis to initial stress is mostly qualitative instead of quantitative.It has been the focus of researching how to effectively control the state of initial stress,avoid excessive stress concentration,and lighten welding deformation so as to improve assembly accuracy.Firstly,the welding residual stress and deformation in the most typical T-joint of Q390 thick plate in steel structure were calculated with three different finite element software: ABAQUS,MARC and SYSWELD,which were compared with the experimental results.According to the results of residual stress and deformation measured by experiments,MARC software has more advantages considering the balance of calculation accuracy and efficiency of three different finite element software.Therefore,this paper chooses the MARC software to carry on the follow-up research.Based on the platform of MARC,a thermal-elastic-plastic FEM considering creep effect was developed to simulate the processes of TIG remelting and post-weld heat treatment(PWHT)of Q345 plate joint.The effect of PWHT on elimination of welding residual stress was mainly studied.Meanwhile,the experimental results were used to verify the calculation results.The results show that the peak value of welding residual stress can be reduced by 70%-80% by PWHT.Considering only creep effect of holding,the calculation efficiency can be increased by about 10 times while ensuring accuracy.For large structures which are not suitable for heat treatment,in order to control the welding residual stress and deformation,the butt joints with different grooves of 35°+8,25°+8 and 25°+5 were taken as research objects,and the effects of different groove angles and gaps on residual stress and deformation were discussed.The results indicate that by reducing groove angle and gap,the consumption of filler metal,welding deformation and high tensile welding residual stress area can be significantly reduced,but the peak value of welding residual stress has little effect.In addition,combined with the phenomenon of lamellar tearing easily occurring in the welding of thick steel plates,this paper took the 70 mm thick Q390 rolled steel corner joint as research object,and based on the results of FEM,the causes of lamellar tearing were discussed from the mechanical point of view.The effects of groove design,welding sequence and low strength cladding on the stress distribution in thickness direction were studied,which provided a basis for controlling stress by improving welding process and reducing the tendency of lamellar tearing.The results show that the predicted location of lamellar tearing by FEM is in good agreement with actual;From the perspective of stress,it can be inferred that lamellar tearing may be caused by the stress in welding process at the temperature of about 260 ?,rather than the welding residual stress.Lamellar tearing tendency of thick plate can be reduced to a certain extent by optimizing groove form,welding sequence and overlaying low-strength cladding.Finally,the welding residual stress distribution of large-scale complex column-beam structure in domestic building steel structure was predicted by using the FEM of 3D model and instantaneous heat source developed in this paper,which can provide some theoretical reference and guidance for the safety evaluation and structural optimization of the whole structure in engineering practice.In this paper,by simulating the TIG remelting welding and PWHT process of Q345 steel,the mechanism of relieving welding residual stress by PWHT is clarified based on numerical simulation;the effects of different groove forms on welding deformation and residual stress are studied by using 3D model and moving heat source;and the effects of mechanical factors on lamellar tearing during thick plate welding are discussed by using 2D plane strain model.The distribution characteristics of welding residual stresses in steel structures with complex shapes were calculated by using 3D model and instantaneous heat source.The research results not only enrich the theoretical basis of welding structure to a certain extent,but also have high engineering application value for the design and production of welding structure.