drifting snow on exterior decks
drifting snow on exterior decks
(OP)
ok folks. this has been asked on here before but I haven't seen a concise answer.
For a commercially-loaded exterior deck at a restaurant, does one consider drifting snow as well as flat snow? We're still using ASCE 7-05, and the snow section is all about drifting onto lower roofs. This is definitely not a roof, and honestly, no one would be using the deck at a restaurant when it's cold enough to have drifting snow on it. Thoughts?
For a commercially-loaded exterior deck at a restaurant, does one consider drifting snow as well as flat snow? We're still using ASCE 7-05, and the snow section is all about drifting onto lower roofs. This is definitely not a roof, and honestly, no one would be using the deck at a restaurant when it's cold enough to have drifting snow on it. Thoughts?






RE: drifting snow on exterior decks
Mike McCann, PE, SE (WA)
RE: drifting snow on exterior decks
Mike McCann, PE, SE (WA)
RE: drifting snow on exterior decks
If you are asking whether drifts/snow should be added to live load - per ASCE 7 I believe that Chapter 1 includes load combinations with both live load and snow.
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RE: drifting snow on exterior decks
As you move away from the vertical projection, the snow load decreases, eventually to a level less than the design roof snow load... In other words, where the design flat snow may be 40 psf at the foor as an example, the drift load may vary from 80 to 20 or 30 psf over several feet, then level off at the 20 or 30 psf value, below the design level for the roof.
Mike McCann, PE, SE (WA)
RE: drifting snow on exterior decks
Mike McCann, PE, SE (WA)
RE: drifting snow on exterior decks
With wind you could get the base snow on the lower roof with the additive drifting on the lower roof from higher roof snow blow-off.
Additive.
I don't have ASCE 7-05 with me but I believe it actually states that you add drifting to the base snow.
What you don't do is use the minimum Pf base snow with the drift. You always add the drift to the actual calculated Pf independent of the minimum snow.
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RE: drifting snow on exterior decks
Correct for a higher roof next to a lower one. Different for a parapet condition I was thinking of.
Mike McCann, PE, SE (WA)
RE: drifting snow on exterior decks
slta....yes, drift should be considered. Even though the deck might be "wind permeable" with spaces between deck boards, snow will bridge those easily and once the base snow is there, drifts will occur against building. My former partner and I did a failure investigation of a snow load collapse of a low roof adjacent to wall below high roof. Drifting was significant culprit of progressive collapse.
RE: drifting snow on exterior decks
cheers. Now go enjoy Saturday night.
RE: drifting snow on exterior decks
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RE: drifting snow on exterior decks
RE: drifting snow on exterior decks
But ASCE Load combinations DO include both snow and live load together. Note combination 4 below:
1. D + F
2. D + H + F + L + T
3. D + H + F + (Lr or S or R)
4. D + H + F + 0.75(L + T ) + 0.75(Lr or S or R)
5. D + H + F + (W or 0.7E)
6. D + H + F + 0.75(W or 0.7E) + 0.75L
+ 0.75(Lr or S or R)
Similar case for the LRFD combinations.
And I'd just like to point out that the definition of "S" in ASCE 7 is "snow"....NOT "roof snow".
So if the snow falls on an exposed floor you still have to treat it the same as a roof.
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RE: drifting snow on exterior decks
cheers everyone for the good debate!
RE: drifting snow on exterior decks
RE: drifting snow on exterior decks