You must consider several important factors when formulating the optimum purlin reinforcement scheme for your steel structure. Firstly, you must avoid sideways translation of the entire assembly of purlins and roofing; secondly, you must prevent rotation and minimize turning or twisting (torsion); and thirdly, you must initiate horizontal flange reinforcement.
The two member flanges rely on horizontal stabilization for this design to function correctly. Therefore, with the implementation of bracing, they must be put together so as to block sideways deflection of the two flanges at appropriate brace locations as well as at the ends. This corrects a well-known standing-seam pre-engineered roof custom of introducing just one line of sag angles adjacent to the top of the purlin flange with sliding connections. In this technique the lone line of bracing is too low to prevent purlin rotation under load. To set purlin bracing as close as possible to the flange that needs to be constrained is absolutely crucial. Some manufacturers specify that the bracing is further away from the top flange, but this is questionable in terms of providing the two flanges with horizontal deflection protection and harmful rotation of members.
Note, however, that this bracing process should only be applied once a through-fastened rooftop has been selected. Higher purlin integrity can be provided by properly installed diagonal braces despite being positioned somewhat far from the flanges. Those standing-seam roofs for pre-engineered steel structures employing sliding connections are very popular because they remove a number of bracing worries. This roof system allows the benefits of crosswise bracing to be easily accomplished by the addition of lines of bracing angles running next to each other next to 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, adversely, to counter lateral translation under loading from being administered to the whole unit of roofing and purlins.
Close patterns of bolted channel blocking is the better 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. However, a pair 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 implement. A good method for arrangement is to choose 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. Miscalculations can result in twisting or even complete failure of the specific purlin location so it is absolutely vital that care is taken in figuring the correct arrangements.
Therefore, in conclusion, when choosing the most appropriate purlin reinforcing technique for your steel building project, you should refer to the information discussed. The importance of the correct purlin method should not be overlooked and is integral to your building.