impact loads due to sliding snow

huangyhg

impact loads due to sliding snow
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.
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i think the issue is a severe point impact load and for ice, not snow. i have observed this personally when a large ice slab fell off the roof, hit the 2x12 redwood deck below and snapped the 2x12. there was little snow involved, all ice and it hit vertically, on the edge of the slab. so you had nearly the full weight of the slab (200 - 300 lbs at least) impacting an area of maybe 20 square inches. this works out to a lot more than 100 psf. maybe 10 times that or more.