Research On Behavior Of Cold-formed Steel Built-up Box Section Short Columns Failed In Local Buckling

The cold-formed thin-walled steel(CFS)built-up box section column is the mainly structural member,which is composed of the single-limb C-section and the single-limb Usection connected by self-drilling screws.In this paper,the axial compression behavior of the CFS built-up columns subjected to local buckling was researched in detail by experiments and numerical analysis.The corresponding design method is proposed.The following work has been carried out in detail.Firstly,a series of axial compression specimens of CFS C-section,U-section and built-up box section columns were tested.The test specimen design,test loading system,test phenomenon record and data collection were described in detail,and the test results were analyzed in detail.Secondly,based on the finite element analysis software ABAQUS,the test specimens were simulated,and the simulation results were compared with the test results to verify the reliability of the finite element model.On this basis,the variable parameters analysis of three factors: height-thickness ratio,width-height ratio and screw spacing were carried out.The heightthickness ratio and the width-height ratio have a great influence on the ultimate bearing capacity of CFS built-up box section columns failed in local buckling.In addition,the width-height ratio is an important factor affecting the ultimate buckling mode of the specimens.The screw spacing has little effect on the ultimate bearing capacity of CFS built-up box section columns failed in local buckling.In addition,when the screw spacing is less or larger than the local critical buckling half--section,the ultimate bearing capacity of CFS built-up box section columns failed in local buckling decreases with the increase of screw spacing.Thirdly,in this paper,the ultimate bearing capacities obtained by the Chinese standard GB50018-2002 and the American standard AISI of the specimens were compared with the test results and the finite element results.The conclusions are drawn: the results are conservative obtained by the effective width method in Chinese standard GB50018-2002 and American standard AISI,however,the direct strength method can accurately estimate the bearing capacity of members,but it is unsafe.Finally,the computational model was proposed and the unknown combination coefficient in the model was obtained by variable parameter analysis in this paper.Based on the direct strength method,the design superposition method of CFS built-up box-section columns failed in local buckling was proposed.Subsequently,the calculation results obtained from the proposed method were compared with those of the Chinese and American standards,and the applicability and accuracy are verified.