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Equivalent Fluid Pressure for Snow
4

Equivalent Fluid Pressure for Snow

Equivalent Fluid Pressure for Snow

(OP)
I have a tall metal stud roof parapet that was designed to resist the applicable components and cladding wind forces.  Behind this parapet is the potential for up to 7 feet of snow drifting.  The roof system has been designed to accomodate this drifting load.

Now, a peer reviewer brought up the subject of wether or not the parapet had been designed for horizontal thrust or bending due to snow "pileup".  The analogy I come up with is equivalent to soil pressure on a basement or retaining wall.  If soil density is approx 110 pcf and EFP roughly 35 psf, then if snow denisty is 18 pcf, would EFP snow equal 6 psf?

Any thoughts, comments, ideas?  Overall, I think the wind pressure will govern the parapet stud design, but I now need to justify that.

RE: Equivalent Fluid Pressure for Snow

I don't think the snow would ever control over the wind for perimeter parapets.  In addition, the UBC and ASCE 7 have NO provision for lateral loads from snow - all is vertical gravity.

RE: Equivalent Fluid Pressure for Snow

Pylco,

I agree with JAE.   The lateral load of snow should be  minimal, and the wind load will control.    

If you want to compare the lateral pressure of snow with those of the soil, snow has a larger angle of internal friction, a larger cohesion, and a smaller unit weight.   These properties will reduce the lateral pressure considerably.

RE: Equivalent Fluid Pressure for Snow

One special case I am thinking. If the roof system is sloping towards the wall, ice may form a solid wedge and exert pressure on wall by sliding towards it depending upon the slope of the roof.

RE: Equivalent Fluid Pressure for Snow

Another thought for buildings with parapets, what happens if a roof drain becomes clogged?  You should always provide an "overflow scupper" just in case the roof drain is clogged by leaves or ice.  Water on the roof gets pretty heavy pretty fast!

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