Study Of Ultimate Axial Compressure Of Cold-formed Medium Wall Hollow Sections With Initial Imperfections

The thickness of cold-formed thin wall steel in tradition is less than 6mm thick. With the expanding of the field using cold-formed steel, the progess of production technology and the improving of steelproperties and anticorrosive coating, the cold-formed steel whose wall is over 6mm thick can be produced in out country at present. The cold-formed medium wall steel has the advantages of cold-formed thin wall steel, but also its axial loading-bearing capacity is highly increased. And the cold-formed medium wall steel will be extensively applied in light-steel structures.But a quantity of theory research and few tests on axial compressure of cold-formed medium wall steel have been done, and there is no special code at all. The current Chinese Thechnical Code of Cold-formed Thin Wall Steel Structures is just suitable for cold-formed thin wall steel. And the stability factor of axial compression member presented by the code are determined according to PerryJ. empirical formula based on edge yield criteria as well as considering the results from the 164 columns of all kinds of sections tests. However, the code does not consider synthetically the initial imperfections such as initial geometrical, residual stresses, cold-formed effect and so on. The Chinese currant Code for Design of Steel Structures is generally suitable for hot rolled steel and welded members of composite sections. It is still a unknown problem whether the code is suitable for design of cold-formed medium wall steel. Therefore it is necessary to study the utimate axial compressure of cold-formed medium wall steel in order to provide a pilot theory gist of steel design.In the thesis, cold-dormed square hollow sections and rectangular hollow sections whose thickenss is from 8mm to 12mm were taken as study object. Using the universal FEM program Ansys as well as taking account of the initial imperfections such as initial geometrical imperfections, residual stresses,cold-formed effect, the ultimate carrying capacity of cold-formed hollow sections was analysed, and the column curves were presented. By comparing the results obtained from finite element method with those of current Chinese Code for design of steel structures and Technical code of cold formed thin wall steel structures, pilot method to determine stability factor of cold-formed medium wall steel is given.Meanwhile, the ultimate carrying capacity and the local buckling of cold-formed medium wall hollow sections and hot-rolled H section whose cross section area is equal or close are anlysed contrastively. Then the corresponding conclusions are drawn and the references to design columns are provided.