Research On Interactive Buckling Behavior Of Welded Section Steel Members Under Axial Compression

For the interactive buckling behavior of steel columns under axial compression, thedesign method provided in the current Chinese code for design of steel structures GB50017-2003is not completed. Instead of using the post buckling strength of plate, limitvalues of width-to-thickness ratios are set up to prevent the plate from local buckling,and the calculation equation of effective width is only recommended for the web withwidth-to-thickness ratio exceeding the limit values. However, the design methodconsidering the post buckling strength of plate is more appropriate which allows thedesign more flexible and increases the utilization of steel. With the increasing applicationof high strength steel in structures, the self-weight of structures is reduced, which leadsto the buckling behavior of axial compressed columns more critical. The current studieson the interactive buckling behavior and design methods in different codes weresummarized in the paper. An experimental program and parametric analysis werecarried out as well. The research works in this paper are as follows:(1)28welded section columns fabricated from Q235B and Q345B steel with athickness of6mm were tested. Two section types (I section and box section) wereincluded. Wide ranges of width-to-thickness ratios and slenderness were covered in theexperimental program. The material properties, geometricinitial imperfections, ultimatestrengths, load-displacement curves and load-strain curves were measured during thetest.(2) A finite element model with consideration of residual stress and initialgeometric imperfections was established. Validated by the test results summarized inthis paper, the finite element model was proved to be accurate enough to simulate theinteractive buckling behavior of welded section columns under axial compression.(3) With the validated finite element model, a parametric analysis was carried outto study the effects of residual stress, initial geometric imperfections and steel degrees.It is indicated that effects of initial imperfections could not be ignored and the bucklingstrength of columns made of high strength steel increased comparing with normalstrength steel because the effects of initial imperfections were less severe for highstrength steel columns. (4) A total of1008welded section columns were calculated by the finite elementmodel, which covered6steel degrees (fy=235MPa,345MPa,460MPa,550MPa,690MPa and960MPa). Comparing the parametric analysis results with current designmethods in different codes, modified formulae for the design of interactive buckling ofwelded section axial compressed columns were proposed in this paper. Furthermore, avalidation for the proposed formulae was implemented with the test results.