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# RE: ASCE 7 Snow Drifts

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: ASCE 7 Snow Drifts
• From: "Brian S Bossley" <BSBossley(--nospam--at)venturaengineering.com>
• Date: Sat, 29 Jan 2005 08:18:38 -0500

```I think the correct way is to look at the drift from both directions and
find where the greater of the two intersects the lesser.  The loads
aren't additive, but they aren't independent, either.  So draw a
diagonal slope line from that intersection point to the point where both
drifts taper down to the minimum.  I think the equations for finding the
drift loads from either direction is the same in UBC, IBC, NBC, and ASCE
7.

That's the way I've always done it in the past because I'm in NBC
country, but also it seems the safest.

Brian S. Bossley, PE
Ventura Engineering
7610 Olentangy River Rd.
Columbus, OH 43235
(614) 847-1110 x121

-----Original Message-----
From: Will H [mailto:haynewp(--nospam--at)hotmail.com]
Sent: Saturday, January 29, 2005 12:09 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: ASCE 7 Snow Drifts

Then how should interacting snow realistically be considered? I have
always used ASCE7 but I have thought the same thing before, they were
not independent.

Will Haynes, P.E.

>From: "Brian S Bossley" <BSBossley(--nospam--at)venturaengineering.com>
>To: <seaint(--nospam--at)seaint.org>
>Subject: RE: ASCE 7 Snow Drifts
>Date: Fri, 28 Jan 2005 22:35:11 -0500
>
>But also, an additional lesson is that the snow loads from two
>different directions should not be considered independently (unlike
>ASCE 7-98 wind load).  That was what I was really trying to figure out.

>I remember looking at a diagram showing the two drifts interacting, and

>remembered how they were supposed to be considered, but I didn't know
where I got it from.
>
>Now I know that it was from the NBC or UBC.
>
>________________________________
>
>From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
>Sent: Fri 1/28/2005 6:32 PM
>To: seaint(--nospam--at)seaint.org
>Subject: Re: ASCE 7 Snow Drifts
>
>
>
>Even in the intersecting snow drift model contained in the UBC, it
>still used the model predicated on the upper roof that would be
>responsible for the snow drift on the lower roof.
>
>Basically it was the greater of the snow drifts.  Perhaps a figure like

>UBC Figure A-16-8 would be helpful, but the requirements are pretty
>much the same as ASCE 7-02.  The lesson here is that the drifts from 2
>roofs that intersect are not considered to be additive.
>
>Regards,
>Harold Sprague
>
>
>
>
> >From: Drew Morris <dmorris(--nospam--at)bbfm.com>
> >To: seaint(--nospam--at)seaint.org
> >Subject: Re: ASCE 7 Snow Drifts
> >Date: Fri, 28 Jan 2005 09:51:35 -0900
> >
> >Brian S Bossley wrote:
> >
> >>Does anyone know where in ASCE 7 it addresses intersecting snow
drifts?
> >>
> >
> >I don't believe ASCE 7 deals with intersecting snow drifts. It treats
>snow
> >drift as essentially a one dimensional problem.
> >I have to go back and use Appendix  Chapter 16 in the 1997 UBC to
>calculate
> >intersecting drifts.  I have found ASCE 7 to be a step backwards when

> >it comes to snow.  The design procedure seems to be more cumbersome,
> >more limited, and generates significantly greater unbalanced snow
> >loads compared to the UBC.
> >Hopefully, in the next release of ASCE 7, they can come up with
> >something more along the lines of the UBC.
> >
> >
> >
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