Study Of Ultimate Axial Compressive Capacity Of Cold-formed Medium Wall Square And Rectanglar Hollow Steel Columns With Initial Imperfections

Because of convenience of process and economical efficiency, cold -formed steel members are being applied more and more widely in recent years. The section thickness is becoming larger and larger with the advancement of technology.The cold-formed steel columns with medium wall square and rectangular hollow sections, whose thickness are larger than 6mm, have favorable application prospect in building steel structure for the great inertia and highly axial loading-bearing capacity.There are two current technical specifications in China for calculating the ultimate load carrying capacity of the axial compressive steel members, which are respectively named Code for Design of Steel Structures (GB50017-2003) and Technical Code of Cold-formed Thin-wall Steel Structures (GB50018-2002). The former code is mainly aim at hot rolled steel and welded members of composite sections, while the latter is just suitable for cold-formed thin wall steel which thickness is less than 6mm. It is still an unknown problem whether the two current codes are suitable for the overall stability calculation of cold-formed medium wall steel members. There will be some academic meanings and engineering value for the research of the axial compressive loading capacity of cold formed medium thickness wall steel members whose thickness is larger than 6mm.The residual stress will lead some local area in the section into plastic state in advance, resulting in the reducing of the buckling bearing capacity. The initial geometry imperfection and cold-forming harden also has great influence on the failure mode and ultimate bearing capacity of the axial compressive members.The three affecting factors above are called initial imperfections. For the axial compressive cold-formed medium-wall steel members, whose thickness is larger than 6mm, there are few research literatures considering the imperfections' influence on their ultimate bearing capacity.Base on the research at home and abroad, this paper summarizes the calculation method about the ultimate bearing capacity of the axial compressive members considering the influence of the initial imperfections. The cold-formed steel medium thickness wall columns with four different square and rectangular hollow sections, produced by Hankou Roll-forming Steel Plant, are taken as research object. The residual stresses' distribution and magnitude are proposed. The initial geometry imperfection's distribution and the material harden considering cold-formed effect are provided base on the measurement. Considering the effect of three kinds of imperfection, the finite element analysis software ABAQUS is used to analyze the ultimate bearing capacity of the cold-formed medium thick-wall hollow rectangle and square section columns, whose thickness is range from 8 to 9 mm. The finite element analysis model is proven to be effective by comparing the analysis result with the test data. A series of finite element analysis are carried on for cold-formed medium thickness wall hollow rectangle and square section columns of different length. Relative column curve are obtained and compared with the Chinese Design Code for of Steel Structures (GB50017-2003) and Technical Code of Cold-formed Thin-wall Steel Structures (GB50018-2002) . Some beneficial conclusions are presented to provide reference for the similar members's research and the revision of relative codes.