At the penultimate rafter, a longer sleeve is used at each joint in the same gauge material as the end bay purlins. Heavier-gauge purlins are used in the bays at either end. Lighter-gauge purlins are used on the inner bays, with sleeves of the same gauge material at every joint. This is a continuous system for a roof with a minimum of five bays and rafter spacings of up to 15m. The most economical purlin solution is the heavy end bay system. Single-span sleeved systems are preferable over double-span sleeved systems to avoid the transportation of long purlin lengths of 12-16m and to facilitate easier erection and stability of the primary steel frames during construction. Sleeves are short lengths of section placed over joints in the purlins, ensuring the system is continuous and therefore structurally more efficient than single-span, non-sleeved purlins. Sleeves are generally used in purlin and rail systems at the rafter positions to optimise the use of the steel. Key Features of Purlin and Side Rail Systems Z sections are usually installed with the top flange pointing up the roof slope so that the load is applied through the shear centre and serious twisting of the sections does not occur.Ĭold-rolled steel purlins are manufactured from hot-dipped galvanised steel to the European standard BS EN 10346:2009, generally with a yield strength of 450N/mm² and with a Z275 coating containing 275g/m² of zinc. Additional lips are included because unstiffened, wide, thin plates are unable to resist significant compression and the flanges become inefficient. In building uses, the most common and simplest of profiles are the lipped Z and C sections – both defined by a central vertical web joined to horizontal flanges at either end. Sections produced by cold roll-forming are essentially uniform in cross section and can be manufactured to very close dimensional tolerances. The principal advantage of cold roll-forming, compared with other methods of fabrication, is the high production capacity achieved. The strip is pre-pierced and cut to length in-line, prior to roll-forming. More complicated profiles will require 15 or more passes.
For example, five to eight “stages” or “passes” will be needed to form a lipped Z purlin, depending on the thickness of the material. Each pair of rolls progressively forms the strip until the finished profile is produced. The purlin is formed gradually by feeding the strip continuously through successive pairs of rolls, which act as male and female dies. Manufacture of Cold-formed Steel Roof PurlinsĬold-formed steel roof purlins and side rails are manufactured from pre-galvanised steel strip, in the form of coils, which have been slit to the desired width from the parent or “wide coil” supplied from the mills. This CPD will examine the benefits of cold-formed steel roof purlins, common applications and key design considerations. Light gauge cold-formed steel roof purlins are used on a wide range of building types including retail and leisure, industrial, warehouses and distribution, healthcare and education. Both purlins and side rails are used to provide restraint to the primary steel frame members. Similarly, a side rail is a secondary structural member that spans between the primary/main steel frame to support the wall cladding and transfer load from the wall cladding to the primary steel columns. The purlin transfers load from the roof cladding to the primary steel rafters. Light-gauge cold-formed steel roof purlins were first introduced to the UK construction industry in the fifties, to replace heavier hot-rolled steel angle and channel sections.Ī purlin is a secondary structural member that spans between the primary/main steel frame to support the roof cladding. To take this module read the technical article below and click through to a multiple-choice questionnaire, once taken you will receive your results and if you successfully pass you will be issued automatically with a certificate to print for your record.
#Cold formed steel framing members how to#
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