How do you treat snow drift corners?

[Serhiy2]

Good evening,

I'm working on evaluation of existing OWSJ roof structure impacted by the rooftop unit addition. I'm trying to do detailed load take off and wondering how most of you deal with snow drifts in the corner of the obstacle. I have seen some people ignoring it but I don't think it's right as snow drift also forms around the corner of obstacle (in this case is box shaped rooftop unit). I did evaluate it as 1/4 of the cone volume and the total snow drift weight in one corner is about 900lbs in my case which makes difference so I can't really ignore it. The way I was going to approach it is to take slices in orthogonal directions (directions aligned with unit sides) but it is somewhat time consuming.

Appreciate your input.

 

[JAE]

We typically just extend the triangular drifts and intersect them similar to how two planes of a hip roof intersect at a hip ridge line.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[JLNJ]

Rightly or wrongly, ASCE allows you to omit or ignore the drift on any side which is less than 15' long.

If your unit is less than 15' on the short side, the drift doesn't wrap around.

 

[JAE]

Yes - agree with JLNJ on that for sure.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Serhiy2]

I've done it the way JAE described but I was wondering if there is a quicker way of doing it.

Regarding the 15' cut-off limit, I'm using NBCC and this cutoff dimension depends on design snow load and in my situation it produces 6' cut-off limit.

 

[RPMG]

Taking slices does sound difficult. It's more common to use averages and trib widths, with uniform loads, and linear drift slopes collapsing to zero.

When in doubt, draw it to isometric scale and solve the averages graphically.

 

[Serhiy2]

RPMG, could you please elaborate on the approach you described?