Pre-Engineered Steel Buildings: A Specific Purlin Support Technique
There are some important factors to contemplate when planning the correct purlin support scheme for a pre-fabricated, pre-engineered steel structure. These factors involve preventing lateral translation of the complete unit of steel roofing and purlins; warding off rotation and alleviating any turning or twisting (torsion); and to initiate lateral flange support.
If this plan is to work it is key to have sideways stabilization of the two member flanges. With the use of bracing, they should be adhered so as to stop lateral deflection of both flanges at appropriate brace spots and at the ends. A common standing-seam roofing practice of establishing a single line of sag angles, parallel to the topmost purlin flange with sliding connections, is remedied with this approach. The sole line of bracing in this technique is too low to alleviate purlin rotation under load. It is crucial to install purlin bracing as proximate as feasible to the flange that needs to be constrained. A manufacturer’s plan specification where the bracing is further away from the top flange is suspect for supplying the two flanges with horizontal deflection protection and destructive rotation of members.
A high degree of purlin stability can be yielded by correctly installed crosswise braces, despite being put some distance away from the flanges. Provided a through-fastened pre-engineered steel roof is used, then this type of bracing technique can be employed. As the well-deserved acceptance of standing-seam steel roofing for pre-engineered and pre-fabricated steel buildings employing sliding connections negates a lot of bracing concerns, this is ordinarily not a complication. By affixing lines of bracing angles running next to each other near the highest flange, this roofing assembly allows the benefits of diagonal bracing to be achieved easily.
The need for appropriate purlin bracing, however, is encouraged by choosing a through-fastened rooftop. On its own, a steel roofing application can deliver lateral, but questionable, torsional reinforcing of the steel purlin. The steel rooftop diaphragm may not be engineered, unfortunately, to stop lateral translation under loading from being introduced to the whole arrangement of purlins and roofing.
Fixed intervals of bolted channel blocking are the best arrangement for supporting purlins. This is a superior course to bracing of the two purlin flanges against translation and rotation, with the inclusion of bolts with a greater connection capacity than tabs or screws. Two rows of angle braces, alternatively, secured to the highest and lowest flanges, can be applied to smaller buildings.
It is critical to have the suitable purlin spacings generated for any selected purlin support approach. A purlin section can contort and/or fall apart owing to a deficiency in important computations. The minimum numbers of either the highest unbraced purlin measurement of either 50 or 72 inches, or 25 percent of the purlin span are two ways for establishing the purlin horizontal buttressing expanse as well as a good guide for spacing. Consider the points addressed in this article when selecting the best purlin support technique for your pre-engineered steel structure project. You may find it useful to contact a steel building manufacturer if you have any specific questions.