Study On Axial Compression Behavior And Direct Strength Method Of Cold-formed Steel Channel Column With Web Holes

In order to facilitate the installation of plumbing,electrical facilities and auxiliary facilities in cold-formed steel(CFS)structures,CFS channel sections with web holes are also frequently used in building structures.But web holes have noticeable influence on the stability of CFS members.The Direct Strength Method(DSM)formulas for CFS members without or with web holes have been included in the current North American Specification for the Design of ColdFormed Steel Structural Members(AISI S100-16).However,the DSM formulas for CFS compression members with web holes are derived from the experimental datas under frictionbearing boundary conditions,and whether the formulas are suitable for axial compression members with web holes under pinned-pinned boundary conditions is still lacking the support of relevant test datas.Therefore,test and extensive finite element(FE)analyses of CFS columns with web holes on axial compression behaviour were conducted and the reliability of DSM formulas for CFS columns with web holes in AISI S100-16 was assessed in this study,which provides reference for practical engineering and revision of relevant specification.A total of 16 CFS channel columns with axial load were tested under pinned-pinned boundary conditions,including 8 CFS channel columns with industry-standard slotted web holes and the remaining 8 such channel columns without web holes.Two kinds of nominal lip widths were selected as 15 mm,30 mm and four kinds of nominal column lengths were selected as 600 mm,800 mm,1000 mm,1200 mm for CFS channel columns with or without web holes.The test results are shown that the lip widths and the web holes are significant influence factor on failure mode and ultimate capacity.Short-lip specimens failed mainly by distortional buckling and the slotted web holes caused the ultimate capacity to decrease slightly by 2.4% on average compared with specimens without web hols.Long-lip specimens failed by local buckling and the slotted web holes caused the ultimate capacity to decrease slightly by 6.4% on average compared with specimens without web hols.The FE software ANSYS was adopted to simulate the specimens and the simulation results show good agreement in terms of ultimate capacities,failure modes and load versus axial displacement curves with test results.It is reliable to analyze the axial compression behaviours of CFS channel columns with web holes under pinned-pinned boundary conditions using the ANSYS.On this basis,numerous FE parametric analyses were conducted by changing the parameters of FE models and the failure modes,the critical elastic buckling stresses and the ultimate capacities of members were obtained from FE parametric analyses,which lays a foundation for further study on the calculation method of critical elastic buckling stresses and DSM design formulas for CFS channel steel columns with web holes under pinned-pinned boundary conditions.According to the critical elastic buckling stresses of CFS channel axial compression columns with web holes under pinned-pinned boundary conditions obtained from FE parametric analyses,the accurateness of critical elastic distortional buckling stresses for such columns with web holes predicted by discounted-thickness method was verified,and the existing approximate calculation formulas of critical elastic local buckling stresses for such columns with web holes were revised.On the basis of the test results and the FE parametric analysis results,DSM formulas of AISI S100-16 for CFS channel axial compression columns with web holes were revised.DSM formulas for CFS channel axial compression columns with web holes under pinned-pinned boundary conditions were proposed,which were suitable for distortional buckling and local buckling respectively.