What You Should Know About Different Purlin Techniques

There are a few important factors to think about in formulating the optimum purlin reinforcement scheme for a steel structure that is precisely anchored and designed. To avoid sideways translation of the entire assembly of purlins and roofing, to arrest rotation as well as decrease turning or twisting (torsion), and to initiate horizontal flange reinforcement are your three primary objectives.

The two member flanges rely on horizontal stabilization for this design to function correctly. Which means, with the implementation of bracing, that they need to be put together so as to block sideways deflection of the two flanges at appropriate brace locations and at the ends. This corrects a familiar standing-seam pre-engineered roof custom of introducing a mere single line of sag angles alongside to the top of the purlin flange with sliding connections. In this course the lone line of bracing is too low to impede purlin rotation under load. To set purlin bracing as close as possible to the flange that needs to be constrained is crucial. Certain plans from manufacturers where the bracing is further away from the top flange is questionable when providing the two flanges with horizontal deflection protection and harmful rotation of members.

However, this grade of bracing process should only be applied once a through-fastened rooftop has been selected. Higher purlin integrity can be provided by correctly set up diagonal braces despite being positioned away from the flanges. Taking away a number of bracing worries is the well-deserved popularity of standing-seam roofing for pre-engineered steel structures employing sliding connections. This roof system permits the benefits of crosswise bracing to be easily accomplished by the addition of lines of bracing angles running next to each other by the highest flange.

Regardless, the selection of a through-fastened pre-engineered steel roof does not circumvent the need for proper purlin bracing. For its own part a steel roofing application can contribute lateral, but problematic torsional, buttressing for the steel purlin. The roofing diaphragm may not be engineered, unfortunately, to counter lateral translation under loading from being administered to the whole arrangement of roofing and purlins.

Close patterns of bolted channel blocking is the preferred arrangement for bracing of purlins. This is an outstanding approach to supporting of both purlin flanges negating rotation and translation with bolts that contain a bigger connection capacity than the inclusion of screws or tabs. On the other hand, a couplet of rows of angle braces joined to the top and lowermost flanges can be employed with smaller structures.

The correct purlin intervals designed for any necessary purlin bracing system are essential to calculate. A good pattern for configuration is to pick from defining the purlin sideways buttressing measurement at the minimum number of either the top non-reinforced purlin measurement of between 60 or 72 inches, or 25% of the purlin distance—whichever is least. Twisting as well as failure of the specific purlin location can occur as a result of miscalculations.

Consider all the points covered in this article when you are choosing the appropriate purlin reinforcing scheme for your pre-engineered steel building project. It is always a good idea to discuss your decision further with your manufacturer, and to ask the advice of several different key figures in your construction.