AWC-NDS Connection Yield modes for Metal Roofing Drag Loads

[Mike L]

Hello. Trying to evaluate drag load capacities of metal roofing over plywood roof deck. This would primarily due to high snow loads wanting to slide metal roofing off the roof deck. Up near ridge we would run a particular number of fasteners to resist these drag loads. It appears we need to evaluate fastener drag load capacities based off of the connection failure/yield modes in the AWC-NDS (Im, Is, II, IIIm, IIIs, IV). Is this the correct approach? Are there any of these yield modes we can discount? This seems a bit confusing to us, especially since cold formed steel roofing is governed by AISI S100, but connection capacities fall under AWC-NDS since it is a wood attachment. Any help or direction would be appreciated. Thanks, Mike.

 

[jayrod12]

Do you find you have drag loads between metal roofing and snow? I'd of thought that the adhesion between snow and metal roof to be low.

I'd also expect that the capacity of those connections is more likely governed by yielding of the thin metal roofing as opposed to the capacity of the fastener into wood.

 

[Mike L]

Thank you for the response. Yes, there are many applications in snow country that utilize snow guards on the roof to prevent liability issues with snow sliding off and doing personal or property damage. In the California Tahoe area, we see snow loads of upwards of 300lbs psf which creates a very significant drag forces wanting to pull the metal panels off the roofs. It's not uncommon to utilize 20-30 drag load fasteners for each metal roof panel to keep it stationary on the roof.