Research On “BBearing Capacity Unit” Superposition Method Of Cold-formed Double-limb Closed-section Built-up Short Columns

Cold-formed thin-walled steel(CFS)double-limb closed-section built-up short column,which is composed of single C-shaped and U-shaped basic members connected and pieced by self-tapping screws,is widely concerned by scholars at home and abroad for its good mechanical performance.Most scholars mainly study it from the Angle of bearing capacity and obtain certain results.However,the calculation method of the ultimate bearing capacity of national standards is still in its infancy,so that it can only be estimated conservatively in the practical engineering application without scientific and effective guidance.Taking CFS double-limb closed-section built-up short column as the research object,this paper creatively proposes a universal bearing capacity design method,"superposition method based on bearing capacity unit",considering the correlation of the split-section plate group,the stability of the screw split-section plate,and the influence of the mechanical properties of the whole member.A total of 36 specimens were designed to study the bearing capacity of the double-limb closed-section built-up short column divided into two types of bearing capacity units.The effects of the short limb members on the compression performance of the middle and long limb members of the split column were investigated.Finally,numerical analysis was carried out with finite element software to explore the mechanical properties of the two types of bearing capacity elements under local buckling failure mode.On this basis,the correctness and feasibility of the superposition method of bearing capacity elements proposed by our research group were verified.The main research contents of this paper are as follows:(1)The axial compression performance tests were carried out on 36 closed-section built-up short column bearing capacity units.The effects of section size,screw spacing and specimen length on the mechanical performance,deformation characteristics and failure mode of closed box section bearing capacity units of double limbs were studied.(2)With the help of ABAQUS finite element analysis software,the mechanical performance and ultimate bearing capacity of the two types of bearing capacity units were simulated and analyzed,and the comparative test results were used to verify the rationality of the finite element model.On this basis,the variable parameter analysis of the two kinds of bearing capacity units is carried out,and the influence law of section height to thickness ratio and screw spacing on the ultimate bearing capacity of local buckling is revealed.(3)Based on the results of test and finite element analysis,nonlinear regression analysis was carried out on the proposed calculation model to obtain the local buckling capacity curves of the two types of bearing capacity units.After verification of the test data,the calculation formula of the local buckling ultimate capacity in the superposition method of bearing capacity units was finally obtained.The test specimens were calculated according to the bearing capacity calculation method stipulated in the Chinese code GB50018-2002 and the American code AISI,and compared with the calculation results presented in this paper,to verify the applicability and accuracy of the calculation method presented in this paper for the ultimate bearing capacity calculation of CFS double-limb closed-section built-up short column.