Critical Structural Support: Calhoun’s Proprietary J-Purlin Design

The importance of purlins in any fabric structure design is that they provide additional roof support. By creating a horizontal ‘diaphragm’ that supports the weight of the structure’s roof, purlins assist in making the entire roof structure more rigid and stable.

 

Calhoun takes its roof support one step further in its larger structures through our proprietary J-purlin design. Calhoun’s proprietary J-purlin fabric structure design is unique to Calhoun and found in our Versatile Profile (VP) line of buildings. Our J-purlin is so-named because the shape of the section profile resembles the letter J. This proprietary profile was created in an effort to design a purlin with unmatched stiffness and strength that allows Calhoun to increase bay spacings while simultaneously reducing the quantity of purlin runs in the building. All of this combines for a more cost-effective structure, both in materials and erection cost.

 

The J-purlin profile was also designed with material shedding in mind, as our VP series is commonly used for commodity storage which is an environment conducive to dust build-up. The J-purlins are mounted in the building such that the bottom of the J is positioned upwards. This allows for dust and debris to shed off, mitigating potentially harmful build-up on the purlins.

 

In comparison to the previous generation of VP’s, the purlin runs have been moved from the inner truss chords, to approximately mid-way between outer and inner chords. This change, in conjunction with the new purlin profile, eliminates supplemental purlin-to-truss bracing, which reduces cost and installation time significantly.

 

Another big plus of the new generation design is the revamped process for installing roof panels. The new fabric structure design allows the installer to temporarily remove some purlin-to-truss connection bolts, which allows them to tilt adjacent truss frames towards one another to pull the fabric panels with relative ease. Once each fabric panel is pulled, the truss frame is reset to plumb, and the bolts that had been removed are re-installed. This differs from the previous generation wherein it was necessary to pull the adjacent truss frames together using ratchet straps, deflecting the frames, and putting significant strain on the purlins and their connections to the trusses. The new method avoids this entirely so less potentially damaging strain is put on the structure during this process.

 

The new generation VP buildings exclusively use structural grade ASTM A325 hot-dip galvanized hardware. This ensures a reliable and high-strength connection in every location of the building.

 

Additionally, with the new generation fabric structure design, Calhoun has been able to design out all eccentricities at the web to chord (branch) connections. This has been accomplished with the use of new, proprietary bracketry at these connection points. Eliminating the eccentricities eliminates secondary bending in the chord of the truss, and effectively results in a “perfect” truss structure. This allows Calhoun to make full use of the chord capacity for an efficient, reliable, and more cost-effective structure.