Unbalanced Snow Load on monoslope roof

[BAGW]

Hi,

ASCE does not talk about unbalanced snow load for monoslope roofs. Does that mean unbalanced snow load need not be considered in the design? Unbalanced snow load is pretty much caused by wind and I can see this happening on Gabble roof structures. Does ASCE state that unbalanced snow load need not be considered for monoslope roofs?

Thanks

 

[JAE]

I don't recall them requiring unbalanced snow on monoslope.

But as an engineer, of course, you can certainly consider it in your design.

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[EngineeringEric]

ASCE does have criteria for when to consider vs not. it is in the tables. I believe less than a certain pitch it doesn't happen. And again this is for low-slope which sometimes is monoslope.

I believe a pitched mono-slope would have some unbalanced effects due to the wind going over the ridge and creating an extra amount of snow towards the ridge.

 

[JAE]

In looking through ASCE 7-05 and 7-10, section 7.6 outlines unbalanced snow and they do not refer to monoslope roofs - only roofs with ridges (gable/hip), Curved roofs, folded plate/sawtooth, barrel vault, and dome roofs.

They do have section 7.5 which talks about partial loading with continuous beam loads. So for a monoslope roof with continuous beams, you may have conditions where alternating spans are loaded vs. a full uniform load condition.

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[KootK]

Aerodynamically speaking, I just don't see the phenomenon occurring that normally initiates snow pick up and deposit. No eddy formation over structure. So, from a purely code perspective, my opinion is that unbalanced loading doesn't need consideration.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

If it is a high pitched roof, say 8:12 for argument. For wind perp ridge and hitting the taller face, i would see some eddy formation over the ridge and result in extra deposit at the ridge level. This unbalanced would be triangular in nature, up to a point where the wind responds and sheds the snow evenly.... But this is a hypothetical, and i am sometimes overly conservative.

I cannot argue with someone who was born in the Canadian snows. I only visit the snow

 

[ajh1]

Given that the current unbalanced provisions that you are referring to are based on an upwind fetch distance, i.e., the windward roof on the other side of a ridge, there is no basis for that particular provision to be used for a monoslope roof. ASCE 7 does have another section labeled "Partial Loading". It is primarily related to continuous beam systems although there is a little catch-all section, 7.5.2, that indicates "Areas sustaining only half the balanced snow load shall be chosen so as to produce the greatest effect on members being analyzed." There are probably some scenarios on a monoslope roof where this set of requirements might come into play.