Impact loads due to sliding snow
Impact loads due to sliding snow
(OP)
Does anyone have a good reference for calculating or estimating the design load due to snow sliding off an upper roof onto a structure below?
The ASCE 7-05 reference, 7.9, for loads due to sliding snow, severely underestimates the load in my case. This was for snow falling 28 feet from an upper roof (10 feet from eave to ridge) onto a lower deck. Design flat roof snow load was 100 psf. The 5"x24" glulam beams of the deck structure were smashed by the impact, though there was ample structural capacity according to ASCE guidelines.
Thanks.
The ASCE 7-05 reference, 7.9, for loads due to sliding snow, severely underestimates the load in my case. This was for snow falling 28 feet from an upper roof (10 feet from eave to ridge) onto a lower deck. Design flat roof snow load was 100 psf. The 5"x24" glulam beams of the deck structure were smashed by the impact, though there was ample structural capacity according to ASCE guidelines.
Thanks.






RE: Impact loads due to sliding snow
RE: Impact loads due to sliding snow
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"...does NOT give guidance on specialist aspects of snow loading, for example:
– impact snow loads resulting from snow sliding off or falling from a higher roof"
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RE: Impact loads due to sliding snow
I had a similar situation in Alaska. There's some research and literature out there, but nothing definative that I found. Best way is maybe to run an engergy balance to find the impact load. It's really a dynamic analysis rather than static.
I don't quite remember how I analyzed it, but I came up with around 1500-2000psf (my eave to gable was on the order of 50 ft).
We changed the building orientation so that the snow was shed into an empty area. We added snow blocks so the snow couldn't slide off unimpeded, and we added heating to the roof to minimize the amount of snow accumulation.
You also have to think about someone standing on the deck when the snow slides off. It doesn't matter if the deck holds together but the person gets pulvarized.
cvg, it's not just ice that does the damage. A big chunk of snow will do some some serious damage after falling 28 ft.
Good luck.
RE: Impact loads due to sliding snow
RE: Impact loads due to sliding snow
The codes obviously recognize that impact analysis is difficult and do not include it. The dissipation of the kinetic energy is so sensitive to the amount of deflection and the time taken to bring it to a halt that the possible range of loads is very wide.
Fortunately this facility is closed during the winter, except for occasional inspection, so there was no life safety issue to be concerned with.
I am on the track of a program to use Roark's Formulas for Stress and Strain which I'm told has an impact analysis.