Drifting Snow from Multi-level roofs

[EngDM]

Hey all,

I'm curious what the typical approach would be for calculating snow loads where you have multiple different levels of source areas, some of which already have drifts.

The situation I've got is a building with balconies/terraces at every floor, but the balconies increase in overhang as you go down. So I'd imagine my 10ft balcony up top could accumulate a snow load, and then this could blow to the 15ft balcony below, so on so fourth. The balconies could re-fill with snow between wind events and just keep blowing down the balconies.

I considered back calculating my Ss value to find what "base snow" of the top balcony drift is, and then using that amplified Ss in the drifting equation as I go down the building for subsequent drifts, but I get an insanely high drift, which if I divide the kPa by my snow density of 3 kN/m3 gives me a height thats larger than my floor-floor height.

Another problem I'm having is that the accumulation factor equation for Ca doesn't account for having source areas from both sides. By this I mean that the component lcs is based on length of longest side to shortest, not based on area. So I'm concerned that the Ca isn't accounting for both source areas for my drift if I calculate two seperate drifts for each of the source areas. I considered taking the overall plan dimension, but you end up taking into account a lot of dead space and get a very high load.

Here is a little sketch to illustrate:



This is a weird situation that I'm not really sure how to approach, but my floor type is hollowcore and I don't think 8" or 10" hollowcore can span 25ft with a 15kPa drift load.

 

[DanKile]

If ASCE 7 is applicable in Canada, this might fall into the open air provisions and allow the balanced (and fetch distance) snow load case to be reduced.

Outside of the drift requirements, I would check a load case of snow being shoveled from a higher balcony to a lower balcony.

 

[EngDM]

If ASCE 7 is applicable in Canada, this might fall into the open air provisions and allow the balanced (and fetch distance) snow load case to be reduced.

Outside of the drift requirements, I would check a load case of snow being shoveled from a higher balcony to a lower balcony.

I'll look into ASCE 7, but I don't think we have something similar.

As far as snow being shoveled, would you take the sum of the snow from balcony 1, and attribute it to balcony 2 but only in the area not covered in overlap? Like if balcony 1 has a 100psf drift, calculate the total lbs of that and spread it over the non-covered portion of balcony 2?

There is talks of having a heated floor and drain snow removal system but I'm not sure if I can rely on that as per the code, in the event that it becomes not operational during service life.