Unrestarined Cold Form Design for Monoslope Roof

[Arun4567777]

"Hello everyone,

I'm reviewing a design featuring purlins supporting a standing seam roof. Since the purlins are unrestrained the top as well as bottom flange, I need to design for both gravity and wind uplift loads. To prevent lateral-torsional buckling (LTB), I want to implement a bridging system to restrain both the top and bottom flanges.


The roof has a monoslope configuration with a slope of 5 degrees.

Would a rigid fixed strut system with diagonals at the ends be an effective solution?

What about Sag rods top to purlin bottom with diagnols at end on ridge.

 

[jayrod12]

The standing seam roof doesn't provide top flange restraint?

 

[XR250]

Can you provide a sketch of the size and the proposed materials used?

The standing seam roof doesn't provide top flange restraint?

I don't count on standing seam roofs to provide any diaphragm action. They are typically supported with clips that can slide in the seams.

 

[Arun4567777]

The AISI requires Base test method to be done to arrive at R value for Stsnding Seam.
Plus the client wants it to be designed as unrestrained.

 

[Arun4567777]

We are using Z Purlins with 200mm Depth spanning 7.5m

 

[jayrod12]

Your client is pretty knowledgeable if they know what that means. Are they aware that it will result in increased sizing?

I don't necessarily count on the standing seam for diaphragm action, but for compression flange bracing I feel it's more than adequate. Especially for light-gauge purlins. I know that's how the PEMB suppliers get them to work out. That plus some dodgy moment splices.

 

[Arun4567777]

Since we cannot take any advantage of the Standing Seam. Can anyone suggest some discrete bracing arrangement that we can give for the purlins.