Improved equivalent bracing model for seismic analysis of mid-rise CFS structures

An improved equivalent bracing model of cold-formed steel shear wall with concrete-filled rectangular steel tube column as reinforced end studs was proposed, for seismic analysis of mid-rise cold-formed steel structures. The model can consider end stud's compression buckling and beam-column joint's behavior. Elements and parameters of the model were described, comparisons between the model and pinned equivalent bracing model were performed. The results show that: (1) compression buckling can be simulated by setting an axial spring at the bottom of end stud; the reinforced end stud can be defined as a composite section, and the sectional properties can be determined according to the principle of equivalent flexural rigidity; the spring's axial stiffness can be determined by the shear capacity F-p of the wall and its corresponding deformation Delta(a); (2) beam-column joint's behavior can be simulated by rotational spring, which can be defined by pinching4 model after its constitutive relationship has been determined by experiments or the moment-rotation prediction model proposed in this study; (3) the shear behavior of the wall can be represented by equivalent diagonal braces with nonlinear springs whose restoring force properties can be defined by pinching4 model according to the load-displacement hysteretic curve obtained from full-scale cyclic loading test or numerical simulation etc.; (4) the model can predict actual seismic performance of mid-rise cold-formed steel structure more accurately than pinned equivalent bracing model; moreover, a wall's yield limit directly affects the response modification factor R, the model can thereby provide more reliable design objectives for the structure.