Extreme Sliding Snow Load

[Gumpmaster]

I have a building that's under design right now with an upper roof that's 60 feet taller than the lower roof. The upper roof is sloped towards the lower roof. The distance from the gable to the eave is approximately 60ft.
My roof snow load is 50psf.

I'm trying to decide what snow impact load to design the lower roof for. It's going to be like a mack truck falling from the sky. I know F=ma, but my 'a' in this case is really large. Does anyone have any advice for such an unwise situation?

I'm planning on making the lower roof out of concrete deck over steel beams.

 

[JAE]

In your case I would investigate the use of snow guards (like the ones found here:

http://roofersedge.com/)

 

[cvg]

a is constant (at least generally on this planet) you need to design for momentum where your velocity is really large...

 

[JAE]

Well, the a (accelleration of gravity) is constant, but the force would be imparted due to the deceleration of the snow over a very short time - thus a very high deceleration and a resulting high force.

The trouble is that the force would not only depend on the total mass of the snow, but how each individual portion of that snow decelerated...some faster, some slower than others due to the density of the "blob" of snow, its size, length, orientation of that length, etc.

In short, extremely hard to calculate - thus - if you can't estimate the load, step back and try to avoid it altogether.

 

[frv]

cvg-

JAE is right. And momentum is essentially another way of looking at Newton's second law anyway.

 

[JKW05]

This is a long shot, but you may try asking the Cold Regions Research and Engineering Lab (CRREL)if they have looked at this. Wayne Tobiasson & Alan Greatorex did a lot of research on US snow loads with them.

USACE Cold Regions Research and Engineering Laboratory
72 Lyme Road
Hanover, New Hampshire
Telephone: 603-646-4100
E-Mail: info@crrel.usace.army.mil

Public Affairs for CRREL/ERDC Information: 603-646-4292

Technical Director's Office: 603-646-4200

I'd be curious to hear what you find.