Performance-based assessment of CFS strap-braced stud walls under seismic loading

Abstract

The use of cold-formed steel (CFS) systems has significantly increased in the past few decades, especially in the construction of low to mid-rise buildings. Compared to hot-rolled sections, CFS members are often more economical and efficient due to their low weight, ease and speed of construction and greater flexibility in manufacture. In most conventional CFS buildings, diagonally strap-braced stud walls provide the primary lateral force-resisting system. This study aimed to develop a better understanding of the structural behaviour of CFS strap-braced stud wall systems under seismic loading. To achieve this, a detailed numerical model was developed, accounting for material nonlinearity, initial geometric imperfections, nonlinear behaviour of the connections and secondary moments due to P-Δ effects. This model was validated against previous experimental results on full-scale wall systems. A comprehensive parametric study was then conducted using the validated model to investigate the effect of key design parameters, namely the number of studs, the presence and intensity of vertical loading, the thickness of the structural elements and the steel grade of the straps, on the seismic performance of the system. The lateral load-resisting capacity, deformation capacity, ductility and energy dissipation under lateral loading were investigated and are here discussed. An efficiency index was proposed for each of these variables, allowing design solutions to be rated in terms of their ability to improve the material efficiency of the system, and design recommendations were derived for performance-based design.