Performance Research On Buckling Of Cold-formed Thin-walled G-section Steel Flexural Members

As a new type of building material with uniform mechanical properties,high utilization rate,energy saving and environmental protection,cold-formed thin-walled steel has been recognized by the industry and developed rapidly in production and application.At present,the research mainly focuses on the steel with non edge or primary edge,but there are few studies on the complex edge steel.Because of G–section has more than one edge compared with channel section,its section characteristic is more superior,and the bearing capacity and the steel utilization rate of the member are improved.Therefore,it is very important to systematically study the stability of members of this section.Judging from the current research status,the existing research results are not very rich for the G-section,and the research object is mainly non-complex edge channel steel.Therefore,it is necessary to systematically study the influence of the change of section characteristics of G-section steel on the performance of flexural members.As for the design method,the relevant specification in most countries in the world are based on the effective width method when calculating the stable bearing capacity of members.It does not consider the distortional buckling performance of the member,which becomes its biggest shortcoming.In addition,the direct strength method,which has been gradually applied,can calculate the overall buckling,local buckling and distortional buckling capacity of the member.However,its calculation method is mainly based on the research of non-complex edge channel steel.It remains to be verified and evaluated whether it conforms to the complex edge G-section steel.Therefore,it has become one of the most urgent tasks to study the stability of the complex edge G-section bending members and to establish an effective bearing capacity calculation method in cold-formed thin-walled steels.In this paper,the distortional buckling performance and overall buckling performance of the members are studied by experiment and the finite element parameter analysis,and the application of direct strength method in such members is also studied.At the same time,the methods for calculating the bearing capacity of the flexural member with G-section is presented.The main contents and conclusions are as follows:(1)In this paper,the distortional buckling and global buckling performance of cold-formed G-section steel flexural members are studied experimentally.The tests were divided into two categories,in which the distortional buckling completed 18 members in 9 groups and the global buckling completed 16 members in 8 groups.The distortional buckling and overall buckling performance of the flexural members were investigated by changing the geometrical parameters of the specimen section,and the strain and deformation data of the specimen of the whole process were tested in detail,which provided the experimental basis and comparison basis for the subsequent finite element numerical simulation analysis.Under the experimental conditions,the designed specimens all suffered from the distortional buckling or the overall buckling of the pure bending section,which verified the distortional and the overall test device,the specimen design and section selection were scientific and reasonable in this paper.(2)In this paper,the accuracy of the finite element model is verified by experimental data,and the influence of different section parameters on distortional buckling and global buckling is analyzed by using the finite element model.In order to show that the boundary condition of the global test reaches the fixed connection,this paper established two overall buckling finite element models-test model and ideal model,through the results comparison of two kinds of model analysis,It found that the test boundary condition basic close to the fixed boundary conditions,and it can be considered that this paper studies the overall stability of G-section beam under fixed conditions.(3)In this paper,the distortional buckling and global buckling behavior of cold-formed G-section steel flexural members are analyzed by finite element simulation.The effects of different web height,flange width,edge width and section thickness on the bending behavior and ultimate bearing capacity of cold-formed G-section steel members were investigated.The results show that there are correlative effects among the influencing factors,which have important effects on the buckling mode and ultimate bearing capacity.Within a certain range,the increase of section will increase the ultimate bearing capacity of components.However,the increase of flange size will reduce the distortional buckling bearing efficiency and improve the overall buckling bearing efficiency.The section thickening will improve the section bearing capacity and bearing efficiency.And the thickness of the plate and the size of the edge are the important factors that affect the buckling mode of the members.(4)This paper compared direct strength method curve of the current north American specification S136-16 with experimental and finite element results of distortional buckling of G-section beam.It found that the distortional buckling bearing capacity formula of direct strength method in north American specification S136 is conservative.So on the basis of this formula,through the regression analysis,a modified direct strength method curve is fitted out,and the bearing capacity of the parametric analytic specimen is calculated by the revised curve of direct strength method,it found that the difference compared with the results of the finite element parametric analysis is very small.(5)This paper compared global buckling curve of the Chinese code GB50018-2002,European code EN1993-1-3-2006 and North American code S136-16 with experimental and finite element results of global buckling of G-section beam.It found that the global buckling bearing capacity formula of Chinese code and north American code direct strength method is unsafe and European code is conservative,So on the basis of experiment and finite element data,According to the different calculation methods of elastic critical moment,modified direct strength curves are fitted.And the bearing capacity of the parametric analytic specimen is calculated by the revised curve,it found that the results agree well with the finite element parameter analytic results.