ANALYSIS AND DESIGN OF LIGHT GAUGE STEEL ROOF SYSTEMS

The lack of a useful and efficient analysis and design method is a hindrance to the widespread acceptance of cold-formed structural steel members as roof purlins in conventionally engineered buildings. This paper outlines a practical method for the analysis and design of roof Z-purlins. The details used in formulation of the design method are described and a practical design example is included. The roofing system is idealized to behave in a manner analogous to a stiffened plate in evaluating the section properties and allowable bending stresses. This idealization is considered appropriate as the roof system is composed of Z-purlins which are supported at intervals by structural framing and has roof decking attached continously to the outer flange. The roof decking is corrugated and serves as diaphragm bracing for the condition of flexural bending of the Z-purlin. The section properties are considered based upon a composite section, the Z-purlin and deck. In evaluating the allowable bending stress, Fb, the top flange of the Z-purlin is considered to be fully braced by the roof deck whereas the bottom flange is considered to be unbraced except at supporting frames and interior inflection points. © 1990.