ASCE 7 Ice Load Provisions for Netting

[KirkGH]

I need to figure out the ice load on some netting but am getting a nnumber that can't be correct. The equations are straight forward. ASCE 7-10 by the way.

t = 0.5"
Vc = 30 mph
temperature = 15 degrees Farenheit
Kzt = 1.0
Ii = 1.0
Dc = .0945 in.

Per 10.4-4
fz= 0.980

Per 10.4-5
td = .98 inches

This seems pretty consrevative to me since we only get a few freezing days per year.

Per 10.4-1
Ai = 3.3 in2

This seems way to high. After mutliplying 0.7 to get to ASD in corresponds to roughly .86 inch thickness of ice.

Anybody see something wrong with my calcs?

KGH

 

[msquared48]

"This seems pretty consrevative to me since we only get a few freezing days per year".

Remember that the code is not designing for your few freezing days, but a condition more drastic, based on local conditions. In the Pacific Northwest, I have seen ice storms on two occasions over the past 60 years where at least 1/2" of radial ice was deposited, and we rarely get long freezing stretches either, or ice storms for that matter. Those storms were within the last 20 years and are a real rarity, but they do happen.

7/8" of radial ice does not seem unreasonable to me.

Mike McCann
MMC Engineering

 

[EngineeringEric]

Without running your numbers i agree with M^2 and having done similar work for light strands and cables your values do not seem unreasonable... When i run them first they always seem far larger than i would think, i could never tell a contractor what they are designed for/to out of fear of being chastised relentlessly.

 

[JStephen]

I recall that in some previous posts where people were dealing with fabric-covered structures, it was pointed out that loads on the structure itself would be limited by the breaking strength of the fabric, and that idea might be helpful in your application.

 

[KirkGH]

That means for my net for one thread I have 1.28 lbs/ft. With 1 3/4" x 1 3/4" spacing I end up with roughly 17.6 psf LRFD, 12.3 psf ASD. Thats 1 1/2 gallons of water on each square foot of the net. Aye carumba. Thanks for the input.

KGH

 

[EngineeringEric]

I would think that the weight would almost be larger on a net than cables, since the corners would collect more water to increase the freeze. Not that i am saying you should increase your weight calculations