Study On Calculation Method Of Axial Compression Performance And Bearing Capacity Of Cold-formed Thin-wall G-Shape Double-limbs Built-up Open-section Columns

At present,although a series of research work have been carried out on the stability of cold-formed thin-walled steel built-up members at home and abroad,it was mainly aimed at the research work of non-complex lipped channel steel composite columns.The research results of complex crimped G-shaped steel split columns are still relatively few.Moreover,the calculation method of the existing specification for the bearing capacity of the split column was mainly based on the research of the non-complexed lipped member,and its applicability to the stability design of the cold-formed thin-walled G-shaped steel double-limb open built-up column is also to be verified.In this paper,the axial compression performance and ultimate bearing capacity of cold-formed G-shaped steel double-limb open built-up columns were studied by experiments and finite element variable parameter analysis.Firstly,30 cold-formed thin-wall G-shaped steel composite columns were studied under axial compression test.The test results showed that the failure mode was mainly local buckling and the overall buckling around the weak axis.With the increase of the length of the test specimen,the failure mode changed to the overall buckling around the weak axis.With the increase of the width of the web,the failure mode of the specimen changed to the overall buckling around the weak axis along with the local buckling;for the specimen with a long column length,the failure mode was the overall buckling around the weak axis.As the length of the test specimen increased,the ultimate bearing capacity of the same cross-section test specimen decreased.Secondly,on the basis of the test,the finite element model was adopted to carry out the numerical simulation analysis according to the measured dimensions of the test.By comparing the numerical simulation results and the test results(including the instability mode,the ultimate bearing capacity of the test specimen and the axial displacement curve of the load),verified the reliability and feasibility of the finite element model.The same finite element model was used to analyze the axial compression performance of the coldformed thin-walled G-shaped steel double-limb columns.The length-to-thin ratio of the members,the ratio of the thickness of the web,the thickness of the members,the longitudinal intermediate spacing of the self-tapping screws and the secondary lip width on the ultimate bearing capacity of the members were discussed.The results showed that with the increase of slenderness ratio,the ultimate bearing capacity of the same section was decreasing.And as a whole,the stability reduction factor of the member decreases with the increase of the slenderness ratio.When the component was long,as the heightthickness ratio of the web increasing,the ultimate bearing capacity of the component did not change much.When the component was short,if thickness of the component was large enough,the ultimate bearing capacity of the component increased with the thickness ratio of the web.The bearing efficiency of the member cross-section decreased as the web height-thickness ratio increased.The width of the secondary lip reduced from 15 mm to5mm,the ratio of the mean value of the ultimate bearing capacity reduction to the mean value of the reduction of the cross-sectional area was greater than 1,indicating that the increase in the width of secondary lip can increase the constraint on the flange and thereby increase the ultimate bearing capacity of the component.;The longitudinal intermediate spacing of the self-tapping screws was between 100 mm and 400 mm,and the ultimate bearing capacity of the components did not change much.Therefore,it was reasonable to take a longitudinal intermediate spacing of the self-tapping screws of 350 mm.Finally,according to the effective width method of GB50018-2002 and the related design methods of AISI S100-16,the axial bearing ultimate bearing capacity of the finite element variable parameter component were calculated,and the calculation results were compared with the finite element analysis results.It was concluded that the calculation results of GB50018-2002 according to the superimposed bearing capacity of single limb members were conservative;the calculation results of GB50018-2002 according to the overall section of the component were unsafe;the calculation result of the AISI S100-16 according to the component correction slenderness ratio was conservative.Combined with the results of a large number of finite element simulation analysis,the applicability of the calculation method of the bearing capacity of the built-up columns in the current specifications JGJ227-2011 and JGJ/T421-2018 was evaluated for the complex lipped Gshaped steel.The analysis results showed that the existing specifications are conservative for the prediction of the axial bearing capacity of the G-shaped steel open built-up columns.In this paper,based on the superimposed bearing capacity of single limb and the bearing capacity of the whole section,a formula for calculating the axial bearing capacity of the cold-formed thin-walled G-shaped steel double-limb opening section was proposed.The calculation results of the proposed formula agree well with the results of the finite element analysis and the experimental results.