Experimental investigation on the longitudinal residual stress of cold-formed thick-walled SHS and RHS steel tubes

This paper is mainly focused on the longitudinal residual stress of cold-formed thick-walled square hollow section (SHS) and rectangular hollow section (RHS) annealed and non-annealed steel tubes. The sectioning method was used to study the longitudinal residual stress. It was found that the longitudinal residual stress consisted of bending and membrane components and the magnitude of residual stress was mainly influenced by factors such as thickness (t), depth to thickness ratio (D/t), depth to outer radius ratio (D/R), yield strength of flat plate (f(yp)) and tensile strength to yield strength ratio of flat plate (f(up)/f(yp)). On this basis, the distribution models were proposed separately for annealed and non-annealed specimens and it was proved to have a high accuracy. Finally, a comparison was made between the annealed and non-annealed specimens and it was found that the bending and membrane residual stress of annealed specimens could be reduced by about 80% and 50% respectively which means that the annealing process could significantly reduce the longitudinal residual stress.