Snow Load Reduction due to Grating

[JohnnnyBoy]

All,

I've recently read this thread

http://www.eng-tips.com/viewthread.cfm?qid=291105

about snow loading and grating and there does seem to be a mixed opinion on it.

I'm currently desiging a frame system to support a MUA unit for a soccer field. The platform is to be 16'-6" x 27'6" x 8'-0" high and placed against a much higher structure. Through some very quick snow drift calculations the inside edge would accumulate a snow load of approximately 80psf and the outside edge to be quick significant as well as it would drift against the MUA unit.

My question is weather I should account for this or not or have a reduction factor at least for the snow load.

My factored weight of the unit is 55psf assuming 10psf dead load for the structure.
Now I'm questioning for my live/snow load if I should calculate 1.5 * 20 psf Live + 0.5 * Snow Drift Loading or can eliminate altogether.

Any opinions would help.

 

[JohnnnyBoy]

Assuming there is a certain amount of bridging that would occur on the grating i've never personally seen grating with the amound of snow of a normal structure/support system. Also It seems like quite the over design if I were to design for full drift loading, 0.5 Live loading and Dead loading.

 

[msquared48]

Where are you, and do you ever get ice storms with snow over the ice?

Is there any heat coming up from the grated area, like a transformer vault?




Mike McCann, PE, SE (WA)

 

[JohnnnyBoy]

In Alberta so yes we do get ice storms with the possibility of the grating freezing over but again I have not seen it practice that much. In saying this although I don't see it in practice although this does not mean it shouldn't be design for.

The only heat that may occur is heat loss from the Make Up Air Unit.

 

[canwesteng]

You don't consider snow and live load on roofs. I don't see how this is any different. Your load cases 1.25D + 1.5L or 1.25D + 1.5S + 0.5(live load on platforms without snow). In my mind there is enough bridging it sees full snow load though, I have some grating at my place and snow piles on it sometimes. Of course if you shovel it or something it falls right through.

 

[JohnnnyBoy]

Okay thanks, that's what Ill go with. I wasn't sure if a platform would be considered the same as a roof. But your right if a worker was to be working up there during winter, it would be shoveled before he works therefore should not consider both.

Thanks for the Help!

 

[racookpe1978]

Well, the worker shoveling is certainly a live load = his own weight, plus the snow and ice weight (maximum thickness) + the dynamic lifting and throwing forces of each shovel/snowblower action. Fingles Law says the snow and ice will occur at the worst possible combination too of loading: equipment and lights and "temporary cables" for example, left up on the scaffolding before the storm.

But maximum wind will probably not occur at the same time as shoveling.

 

[ColinPearson]

For what it's worth, I've definitely seen grating (bar spacing typically 1.25" O/C) accumulate a lot of snow, even to the point of drifting several feet deep. If the weather is right (wrong?), it is a possibilty that you could accumulate a bunch.

 

[CTW]

According to "Snow Loads on Non-Building Structures" (

http://ascelibrary.org/doi/abs/10.1061/9780784412367.129),

the authors state in reference to snow on grating that "balanced snow will accumulate on this surface just as it would on a checkered plate or any other continuous flooring material". They further state that snow drift should be considered.

I've also seen snow accumulate on grating as if it were a solid surface.

 

[msquared48]

Me three.

Mike McCann, PE, SE (WA)