Numerical And Experimental Study On The Welding Process Of Complex Steel Structures

Welding is one of the most widely utilized techniques nowadays in the fabrication and installation of steel structures during the construction process due to its strong adaptability,simplicity,and flexibility as well as low cost.However,residue stress caused by welding would reduce the structural stiffness and initiate structural distortions thus affecting the overall constructional quality and safety of the structures.Therefore,it is very important and meaningful to investigate and predict the impact of residual stresses and thus residual distortions on large-scale structures,which are connected through welding by numerical simulations and experimental studies.Firstly,the reasons that cause the residual stresses and the factors which affect the efficiency and accuracy of numerical simulation of welding are analyzed.It is known that,numerical simulation of welding can be hardly applied in the construction of large-scale steel structures due to significant time consumption,low efficiency and convergence difficulties.In order to resolve the above mentioned difficulties and from a higher efficiency point of view,a method based on heat generation rate simulation is proposed,which reduces the time consumption,avoids the weaknesses of many heat source models such as Gaussian model,and ensures both the calculation accuracy as well as its efficiency.Meanwhile,a technology of sub-structure analysis is introduced in thermal elastic-plastic analysis,which will further increase the calculation efficiency.Moreover,this simulation method is proved effective to quantitatively estimate the residual stresses and distortions of steel structures caused by welding through experimental studies.Digital image measurement system is used to measure the residual stresses and distortions caused by welding,under artificial speckle field protection.This method overcomes the difficulty of large-scale three-dimensional digital image measurement,and it can then be effectively used in the experiments of measuring the residual stresses and distortions of thick plates caused by welding.The experimental results indicate that this method is efficient and reliable to measure the residual stresses and distortions caused by welding.The numerical simulations of the welding process are validated through the experimental results of the residual stresses of the welded Q460 tubes with box section,which were conducted by Li et al.(2012).This proves that the numerical simulations used in this paper can be effectively adopted to calculate and analyze the residual stresses existed in realistic steel structures.The method based on heat generation rate simulation is applied in the on-site assembling and welding process of the giant transfer truss in Tianjin 117 project,and the giant column at the bottom level of China Bronze project in Beijing.In the former case,this paper discusses how the welding sequence of the web members affects the residual stresses of the transfer truss,while in the latter case,the impact of the thickness of the transverse stiffeners being placed inside the mega column on the distortions of the innerstiffened mega column caused by welding is analyzed.