Influence Of Welding Initial Imperfections On Ultimate Strength Of Lateral Brace Of An Offshore Platform

Assessment of ultimate strength plays a really important role in design of ship and ocean structures.Welding residual stress and deformation has great influence on the ultimate strength of structures because of the widely use of welding technique in ship building progress.In this article,welding residual stress and deformation of a lateral brace of an offshore structure is studied based on thermal elasto-plastic finite element method(TEP FEM).On this foundation,axial compression ultimate strength of the lateral brace is computed by Riks method.Influence of welding sequence on welding-induced imperfection and ultimate strength of the lateral brace is studied.Besides,influence of welding-induced imperfection and lateral load on ultimate strength is discussed.The main works are as follows:(1)The research status of simulation of welding-induced imperfection is reviewed,as well as the ultimate strength of ship and ocean structures.Basic theory of sequential TEP FEM and Shell/solid molding is introduced,together with Riks method.(2)Three typical structures of the lateral brace are selected as study object.Influence of welding sequence on welding-induced imperfection is studied.Segmented moving heat source,temperature field's translation and Shell/solid modeling are adopted to improve simulation efficiency.The results show that the residual stress and deformation induced by welding transverse web firstly is smaller than welding longitudinal stiffeners firstly.(3)Ultimate strength of the lateral brace under different welding sequence is computed by Riks method in comparison to a lateral brace without welding-induced imperfection to study the influence of welding-induced imperfection and welding sequence on ultimate strength.The results demonstrate that welding-induced imperfection make lateral brace bulking more easily,whereas welding sequence has little effect on its ultimate strength.(4)Ultimate strength of the lateral brace with different hydrostatic pressure is researched based on the practical working condition of lateral brace.The results show that the ultimate strength increases along with the water depth increases.