Estimating Uplift Capacity of Light Steel Roof System

Roof systems constructed using cold-formed steel components, i.e., C- or Z-shaped purlins and interconnected roof panels, have become a very popular form of construction in the United States. This type of roof system is used extensively for single-story commercial and industrial buildings. The popularity of cold-formed steel purlins and panels is due in part to their superior gravity load strength-to-weight ratio. However, because of their relatively light weight, a cold-formed steel member is very susceptible to the loading resulting from wind uplift. The behavior of roof systems of this type, when subjected to wind uplift, is very complex to define analytically. The design specification in the United States for cold-formed steel construction does not provide a comprehensive analytical solution to the problem of wind uplift strength of a cold-formed steel purlin. Therefore, an easily applied, empirically based design procedure has been developed for evaluating the moment capacity of a cold-formed steel C- or Z-section. The approach is applicable only for a through-fastened roof system, i.e., a roof system for which the roof panel is attached to the purlin by a self-drilling or self-tapping screw.