Research On In-Plane Local-Overall Buckling Behavior Of Welded I-Section High Strength Steel Beam-Columns

Compared with ordinary strength steel,high strength steel is of both higher yield strength and ultimate strength,resulting in smaller section of members and lighter weight of structures under same stress condition,leading to less assumption of steel and energy as well as less pollution while not only meeting the architectural needs of function and form,but also realizing the benefit of economy and environment well.High strength steel has been applied to both domestic and overseas projects in recent years.Nevertheless,the permitted steel strength grade is only up to 420 MPa due to Code for Design of Steel Structures(GB 50017-2003),which hampers the nationwide dissemination of high strength steel,let alone fully exerts its advantages.Moreover,current domestic and overseas research concentrates on members under axial compression.Less research has been done on beam-columns,which is popular in engineering and vital to structure's safety.Under the circumstances,local and overall as well as local-overall buckling behavior of welded I-section high strength steel beam-columns,which are made of high strength steel without evident yield plateau such as Q550 and Q690,were investigated by means of theoretical derivation and numerical simulation.Besides,calculation formulas based on current research findings of high strength steel members under axial compression and beam-columns were proposed.Main contents of this paper are as follows.(1)Theory of local buckling behavior of welded I-section beam-columns was teased for the sake of calculation formula of width-thickness ratio's limit of elastic-plastic welded I-section high strength steel beam-columns' flanges.Elastic buckling coefficient of better accuracy was obtained via Matlab,which is a good warm-up for calculating buckling coefficient of elastic-plastic welded I-section high strength steel beam-columns' webs.(2)Constitutive model that reflects the characteristics of high strength steel,such as Q550 and Q690,was introduced into the theory of width-thickness ratio's limit of welded I-section high strength steel beam-columns' webs.Buckling coefficient as well as width-thickness ratio's limit of elastic-plastic welded I-section high strength steel beam-columns' webs was derived through precise theoretical derivation.(3)FEM(short for finite element method)models of welded I-section high strength steel beam-columns,which took material nonlinearity,geometric nonlinearity,initial geometric imperfection and residual stress into account,were set up and verified by data of existing tests.(4)Parametric analysis was conducted to investigate the in-plane overall and local-overall buckling behavior of welded I-section high strength steel beam-columns via numerical simulation based on the verified FEM model.320 FEM examples on in-plane overall buckling behavior and 384 FEM examples on local-overall buckling behavior of welded I-section high strength steel beam-columns were conducted in order to explore how different parameters influence the buckling behavior and ultimate bearing capacity of welded I-section high strength steel beam-columns.(5)According to the results of parametric analysis through numerical simulation,calculation formulas based on the correlation formula were proposed for overall and local-overall buckling behavior of welded I-section high strength steel beam-columns.