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RE: pointed stem wall under a PEMB?

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Frost will push on a grade beam whether it square or pointed.  Your
contractor needs to lay off the wacky tobacky. Anchorage Alaska has a local
amendment to the IBC that allows connecting grade beams to be shallower than
the standard frost depth if they are protected from frost heave.  One way I
have seen is to put a void under the grade beam.  This would be good if there
is not high ground water that could fill the void. 

Frost heave would be independent of the footing shape.  The problem is when
you get ice lenses forming in silt, the silt wicks more water to the ice
lense and the lense keeps growing.  The lenses do not form uniformly under
the foundation and it can cause the foundation to have differential movement.

If you had a triangular grade beam and only the exterior froze then the grade
beam would be pushed up and inwards. If the interior and exterior froze it
would be pushed upward.

Scott Haan

-----Original Message-----
From: Brian K. Smith [mailto:smithegr(--nospam--at)bellsouth.net] 
Sent: Wednesday, April 27, 2005 7:36 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: pointed stem wall under a PEMB?

If you have piers under the columns/main frames, why not build the grade 
beam with a void below it.  If the bottom of the footing is below the frost 
line, the soil should theoretically never freeze, and the void is just an 
extra precaution.

bks




----- Original Message ----- 
From: "Jim Wilson" <wilsonengineers(--nospam--at)yahoo.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, April 26, 2005 9:15 PM
Subject: pointed stem wall under a PEMB?


>A contractor explained a detail to me today where the
> perimeter stemwall of a PEMB building was shaped with
> a pointed bottom at about 18" below grade in an area
> with 36" frost depth.  There is no footing under the
> stem.  The concept is that the frost heave will not
> push on the pointed bottom.
>
> The steel frame still sits on concrete piers with
> footings, hairpins, etc.  The stem won't be figured in
> the structural load resisting system.
>
> This sounds a little bit clever, but I'm not
> convinced.  He claims that he has used it before and
> it has been accepted (by the building inspector, the
> structural engineer, etc.)
>
> Is there such a detail and does it actually work?  I'm
> suspicious, but who knows, maybe I learned something
> today...
>
> Jim Wilson, PE
> Stroudsburg, PA
>
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