Uplift Capacity of Z-Purlins

Roof systems constructed using cold-formed steel components, i.e., Z-shaped purlins and interconnected roof panels, have become a very popular form of construction. This roof system is used extensively for single-story commercial and industrial buildings in the United States. The popularity of cold-formed steel members is due in part to their superior gravity load strength-to-weight ratio; however, because of their relatively light weight, a cold-formed member is very susceptible to wind uplift loading. 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. A general analytical approach, based on the concept of biaxial bending, is presented for evaluating the load capacity of a cold-formed steel roof system having a Z-shaped purlin. The analytical 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.