Research On Design Method Of Cold-formed Steel SHS And RHS Beam-column Members

The cross section type of steel tube is mainly square hollow sections(SHS)and rectangular hollow sections(RHS).Cold-formed steel hollow sections tube are preferred in some applications as they are easier and less energy consuming to fabricate when compared to hot-rolled steel and built-up steel sections.At present,the research on cold-formed square and rectangular hollow sections is mainly focused on the local buckling of mild steel column at home.while the research on mild steel abroad is more ripe,mainly focused on the local buckling of high strength steel columns and beam-columns members.The research on the overall stability of cold-formed steel SHS and RHS members at home and abroad needs to be supplemented.In addition,for such nonlinear materials as cold-formed steel,the design methods based on ideal elastic-plastic theory in most current codes have been proved to be unreasonable,ignoring the strain hardening properties of the materials.At the same time,previous studies have shown that the applicability of the current code for the design of high strength steel remains to be studied.Current design codes employ interaction curves for the design of beam-column structural members.with the shape of the interaction curve defined by interaction factors,and the end points taken as the member strengths under the individual loading conditions.However,comparisons between these established design methods and experimental and numerical results have generally indicated significant disparities,as well as scatter,in the prediction of beam-column capacities.These deficiencies promote the study of this paper.In this paper,the finite element model of cold-formed steel SHS and RHS tube members considering initial geometric imperfections is established by using finite element software.After comparing with the collected experimental data to verify the accuracy of the finite element model,the design method of overall stability bearing capacity of cold-formed steel SHS and RHS beam-column members with different strength(355Mpa～1100Mpa)is studied systematically.The main results are as follows:The suggested value of global geometric imperfections(1/1000 of the length of the member)、the local geometric imperfections(a/200,a is the larger value of the effective width of different plates)and the suggested imperfection factorα_c associated with the yield strength of the material,are given.A proposed formula for the design of stable bearing capacity of cold-formed steel SHS and RHS beam-column members is presented;The recommended limit value of the member non-dimensional slendernessλ_n(λ_n is 0.1)is given for short column members;Continuous Strength Method(CSM)is extended to the design of the stable bearing capacity of cold-formed steel SHS and RHS beam members,CSM is was used to determine the bending moment capacities.Based on the finite element numerical results and these more accurate end points,the design formula of the interaction factors related to the steel yield strength is proposed.By comparing the finite element results and the collected test data,the accuracy of the calculation results of the Chinese、European and American codes and the recommended formulas were assessed.The results show that for the design of the stable bearing capacity of cold-formed steel SHS and RHS beam-column members,the proposed formula provide more accurate and consistent prediction of the ultimate bearing capacity.