Seismic capacity-based design of narrow strap-braced cold-formed steel walls

• Testing and analysis of high aspect ratio cold-formed steel strap-braced shear walls
• High aspect ratio walls do not behave as pin connected truss systems.
• Frame action must be accounted for in the capacity design procedure.
• A simple analysis and design method is proposed for inclusion in relevant standards.

In North America, the seismic design of strap-braced cold-formed steel shear walls is carried out using the AISI S213 Standard, which is soon to be replaced by a new seismic specific standard AISI S400. Both standards require the use of a capacity-based design procedure in which the tension-only diagonal braces are assumed to act as the inelastic fuse elements in the pin connected seismic force resisting system, while all other elements remain essentially undamaged under loading. Experimental work has shown this assumption to be valid for walls with low aspect ratios; however, the testing of high aspect ratio walls has revealed that large moments develop in the frame members, which can result in their failure prior to yielding of the braces. This paper describes a simple method with which these frame moments can be determined and accounted for in the capacity-based design procedure.