Successfully implemented in pre-engineered steel building systems are an assortment of purlin styles that you may wish to familiarize yourself with before embarking on a steel building project. Two of the most popular methods may be ones you wish to consider in the first instance.
A specific purlin technique used in many systems is that of hot-rolled steel beams. For production use in the early 1900s, roof framework assembly consisted of the roof trusses being spanned by hot-rolled channel and I-beam purlins. Only after many years after the origination of hot rolled steel purlins did steel structure systems come into prevalent use. Today, this technique is still used for all-steel structures, especially in manufacturing facilities that need a great deal of interior support. In comparison to lesser gauged designs, the growing approval of hot-rolled steel beams is in large part due to their elevated load sustaining features. The beams themselves can be used with traverses above 30 feet. They are also supportive of hefty overhead building loads throughout the internal building but this approach can be more costly, although it is also very rugged.
The configuration of hot-rolled steel structure roof purlins are determined by the channels and wide flanges design. Hot-rolled purlins can be used with steel decking which allows for excellent support and can traverse protracted intervals. Installing the primary frame rafters lower than the purlins is usually quite economical and a specific deck’s load bearing capacity determines the purlins’ intervals. Incorporating a roof-deck diaphragm or sag rod bracing can adapt the strains acting on the purlins. There can be installation of sag rods up to three inches below the top of the steel. This aids in lowering torsional features.
Braced or unbraced hot-rolled steel purlins are readily adaptable for uplift but “Z” and “C” cold-formed framework are not so easily customizable. An additional purlin set-up to analyze is the use of open-web steel joists, also known as bar joists. These can reach greater expanses than hot-rolled or cold-formed purlins. Open web joists are very inexpensive to use in pre-engineered steel systems that exceed 30 ft. in span, and also in structures needing wider bays.
The inability to withstand torsion, as they don’t have solid webs to assist in easing of this pressure, is a hindrance when using bar joists. A standing-seam roof can be readily assembled and the diaphragm capability is supplied by horizontal rod or cable bracing with pre-engineered steel systems with open-web joists.
In sound design arrangements using bar joists to support standing-seam roofing, there are a couple of authoritative approaches. To select a steel deck and to use thin gauge hat channels which run above the steel deck, vertical to its flutes, is one method. An additional technique is to avoid use of the steel deck in the formation but establish closely spaced cross bridging instead. The immobility at the compact spacing is given by the cross bridging, with the whole unit resistant to any force functions that are present.
You should investigate all purlin options prior to settling on any one design. Discuss these with your manufacturer and ensure that you comprehend all aspects before embarking on the fabrication process. The selection of any purlin scheme is hugely important to the structure of your building as a whole and should not be rushed.