Cyclic testing and numerical modelling of carbon steel and stainless steel tubular bracing members

In order to study the cyclic response of tubular bracing members of three structural materials–hot-rolled carbon steel, cold-formed carbon steel and cold-formed stainless steel–a total of 16 square and rectangular hollow section members were tested under cyclic axial loading. The load–displacement hysteretic response, compressive resistance, lateral deflection, energy dissipation and fracture life of the specimens of these three materials were investigated. In addition, finite element models, verified against the experimental results from the current study and two other research programmes, were used in conjunction with a strain-based damage prediction method to conduct parametric studies. It is shown that existing empirical expressions for predicting the buckling resistance, post-buckling compressive strength and mid-length lateral deflections can be applied to both carbon steel and stainless steel specimens. However, the relationships between member ductility and slenderness are not representative over the full slenderness range, and are not applicable to cold-formed stainless steel members. New relationships, one for each material, are proposed to take into account the inter-relationship between global slenderness and local slenderness. The tangent stiffness throughout the loading cycle, which differed between the three materials, is found to be a crucial factor in determining the resistance to local buckling and number of cycles to failure of the braces.