Theoretical And Experimental Investigations On The Duplex Stainless Steel Axial Compression Members

With the economic development in China, people's demand for architecture appearances increases rapidly. The environmental-friendly stainless steel has become more and more popu-lar to the architect and engineer. As an important kind of stainless steel, the duplex stainless steel has been widely used in the structures due to its high strength, fine corrosion resistance and good welding performance. Given the current mainly production process about the duplex stainless steel pipe is cold forming, no domestic experts and scholars has carried on research on the characteristic of cold forming duplex stainless members until now. Based on the above background, this paper focuses on the study of the performance of duplex stainless steel axial compression columns.20 Material property tests,2 kinds of section form residual stress tests,12 stub column tests and 14 long columns subjected to axial compression tests were performed on the SHS, CHS on type of S22053 which was made in China. The two stage Ramberg-Osgood material model presents a close fit to the material proerty behavior of the duplex stainless steel over the full range of nonlinear stress-strain relationship on average. The proof stress is highly enhanced during the cold forming compared to the raw materials. The test results shows that the amplitude of longitudinal and transverse bending residual stress in cold forming members is big, while the amplitude of membrane residual stress is so small that it would be ignored in the next.The residual stress distribution model is put forward in this paper. The short axial compression col-umns both presents local buckling failure. With the increase of the length of axis compression members, the torque tube column presents the local and overall buckling failure and the overall buckling destruction respectively and the circle tube column only presents overall buckling failure. The long column test indicats that:based on the material property obtained from tests, there are some differences between the test values and the design value of the latest design codes four design codes ("Specification for the Design of Cold-Formed Stainless Steel Struc-tural Members" (SEI/ASCE 8-02), "Eurocode 3-Design of Steel Structures-Part 1-4:General Rules-Supplementary for Stainless Steel"(EN 1993-1-4:2006), "Australian/New Zealand Standard:Cold-Formed Stainless Steel Structures"(AS/NZS 4673:2001), "Technical specifica-tion for stainless steel structure"(CECS410:2015)) and the "North American Specification for the Design of Cold-Formed Steel Structural Members"(AISI S100-07)).Numerical modeling of the test specimens were developed using the commercial finite element soft-ware ABAQUS. Two sets of material groups and different imperfections were considered in the FEM modeling. FEM analysis can reflect the actual performance of compres-sion members, if reasonable material properties and correct model are adopted.Then the factors which affect the member carrying capacity were investigated The most effective factor is revealed-material property and the second is the section form. The residual stress has little influence on the bearing capacity of the member. Then the paper conducted a preliminary study on the carrying capacity of cold formed duplex stainless steel axial compres-sion members. Based on the strain hardening characteristics of stainless steel, an expression specific for the square and circular cross section of cold formed duplex stainless steel axial compression members has been presented according to the technical specification for stainless steel structure (CECS410:2015) and the FE results. The formula allows the use of plastic properties of stainless steel components. Based on the tangent modulus theory, a correction is made on the stability of axial compression members due to the different material mechanics performance. The revised overall stability curves are in good agreement with the results of finite element analysis. At last comparisons between the available test results and the proposed ap-proach were conducted. The comparisons indicats that the proposed approach can fit the test results well and has a good prediction ability for the cold formed duplex stainless steel axial compression members.The research results of this paper can provide test and theoretical basis for the revision of the technical specification for stainless steel structure (CECS410:2015).