Steel Buildings in Europe

Part 8: Building Envelope 8 - 24 4 COLD ROLLED SECONDARY STEELWORK For steel portal framed industrial type buildings with low pitch roofs (5 to 10 degrees), the cladding panels or sheets are normally supported by a system of light steel purlins and side rails spanning between the rafters and columns respectively. See Figure 4.1 showing secondary steelwork in the roof where the purlins span between the rafters of the main frame. The primary function of these secondary members is to transfer load from the cladding to the primary steel frame, including cladding self-weight, wind loads and, for roofs, imposed loads due to snow and maintenance access. The purlins and side rails may also be used to provide restraint to the rafters and columns and to transfer horizontal loads into the bracing system. Figure 4.1 Purlins spanning between rafters in the roof This Section presents guidance on some of the key issues relating to the use of cold formed purlins and cladding rails. 4.1 Purlin and side rail options Purlins and side rails are generally cold formed light gauge galvanized steel members, supplied as part of a proprietary cladding support system, together with fittings, fasteners and other associated components. 4.1.1 Section options Purlins and side rails are available in a variety of shapes and a wide range of sizes. The depth of the section typically lies between 120 mm and 340 mm, with the profile thickness varying between 1,2 mm and 3,2 mm. Some of the more common section shapes are shown in Figure 4.2. Purlins and side rails, because of their high length/thickness values, are typically classed as Class 4