There are a lot of purlin alternatives to choose from for pre-engineered steel buildings. Let’s discuss a few favorite options.

Hot-rolled steel beams are one type of purlin used in many buildings. Several years after the introduction of hot rolled steel purlins, pre-fabricated steel buildings came into widespread use. In the early 1900s building roof frameworks were spanned with hot-rolled channel and I-beam purlins ““ an approach that is still used today, for instance, in fabrication factories needing substantial internal reinforcement. As compared with lighter gauged designs, the growing popularity of hot-rolled steel beams is due to their large load-carrying abilities. This type of structural beam can be implemented even if traverses exceed 30 feet. Hot-rolled purlins can also support substantial overhead loads within the interior. This design, although “beefy,”� can be very expensive. Braced or unbraced hot-rolled steel purlins are easily modifiable for uplift, but “Z”� and “C”� cold-formed framing are not as readily adaptable to this force.

A specific wide flanges and channels design produces the hot-rolled steel structure roof purlins. Employing hot-rolled purlins in combination with steel decking results in optimum reinforcement and can span extensive distances. They are an economical option when installed above the primary frame rafters. The desired load carrying ability of the steel deck determines the appropriate purlin spacing. Stresses involving the purlins can be addressed by including a roof-deck diaphragm or sag rod bracing. Installation of sag rods can be placed up to three inches below the topmost part of the steel, which will reduce torsional concerns.

Another purlin design uses open-web steel joists. Steel building systems that are greater than 30 feet wide or buildings that need wider bays will benefit from the prudence of using open web joists. They can reach larger areas than cold-formed or hot-rolled purlins. They are sometimes called bar joists.

Pre-engineered steel buildings utilizing open-web joists can achieve diaphragm proficiency with a standing-seam roof that is braced by cable or horizontal rods. Bar joists, unfortunately, have an inability to withstand substantial torsion burdens, as there are no solid webs to aid in transfer of this stress.

There are a couple of efficient engineering techniques that use bar joists to sustain standing-seam steel roofing. One approach is to include a steel deck and add thin gauge above the deck and upright to its flutes. Another option is to use closely spaced cross bridging instead of a steel deck. The cross bridging enables stability along the compact intervals and allows the complete assembly withstand any prevalent energy forces.