From: "Rich Lewis" <sea(--nospam--at)lewisengineering.com>
Subject: RE: Nashville, TN area foundation help
Date: Fri, 1 Apr 2005 12:31:03 -0600
I guess I look like an old guy. I went into Wendy's early in the week and
got a discount on my meal. When I asked why she said "senior citizen". I
asked if I looked that old and she wouldn't give me a straight answer.
is my first senior discount.
Can you clarify your third paragraph? You gave two conditions for a
tie. Did you mean for the first to be hairpin?
When I use a tension tie I detail a 'U' shaped bar to wrap the anchor
Is that what most people use as a tension tie. I should also say that for
hairpin I detail a 'V' with a flat bottom to wrap the anchor bolts.
Also, can you give the ISBN for the text "Foundation Design and
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
Sent: Thursday, March 31, 2005 1:56 PM
Subject: Re: Nashville, TN area foundation help
OK... I am an old guy.
For smaller (30 to 40' span) PEMB's with just spread footings, hairpins are
very efficient in transferring the lateral thrust from the anchor bolts
the slab and the slab WWR forms a tension tie. For longer spans you need
put in a tension tie in the form of a rod or rebar in a tie beam. If you
have drilled piers, you are correct, they can take a lot of lateral thrust
depending on the soil.
The best resource for PEMB foundations is Foundation Design and
Manual by Buettner, Fisher, and Manske (Computerized Structural Design,
Inc.). It was written for Butler Manufacturing.
My own practice is to use a tension tie until you get beyond a 15.2 k
service thrust load. Beyond that I use a tension tie. Again, if the soil
requires them for gravity loads, I may use a drilled pier. The only
potential problem is that you have to calculate the long term lateral
movement of the top of the drilled pier. It is not a huge problem, but it
has to be considered.
If you use a turned down edge of a slab in bearing, you generally have to
discount the top 18" (no overburden to facilitate passive) which puts
moment into the slab, and again, the passive pressure is allowed, but there
is the potential for sideways settlement in some soil types. It is doable,
but it adds some considerations.
The Foundation Design and Construction Manual also has some good
on using horizontal soil resistance.
>From: Bill Polhemus <bill(--nospam--at)polhemus.cc>
>Subject: Re: Nashville, TN area foundation help
>Date: Thu, 31 Mar 2005 11:40:44 -0600
>Harold Sprague wrote:
>>In a former engineering life, I designed foundations for several PEMB
>>The first attempt was always to use the turned down slab with the
>>to take the thrust out of the 3 hinged arch. If the thrust was too
>>or you had a feature that precluded you from using the slab as a tension
>>tie, you went to a tie beam and spread footings. In that case it did
>>much matter what the edge of the slab was like.
>>The US Army Corps of Engineers lists the frost depth at 22" for
>>but you should call the local building official if applicable.
>Stepping right in it...
>I never got the "hairpin" thing. It always seemed to me to be in the
>category of "stuff the old guys did because they always did it that way."
>Because My PEMB foundation designs are typically on drilled piers, with
>edge beams typically on the order of 30" depth or so, I figure there's
>plenty of "oomph" there to resist the thrust without worrying about