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Re: soils pressure

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Joe,

I have been lurking  this thread, but when you asked about the I joists, I
decided to chime in.

In the Denver metro area, we have many problems with expansive soils and its
not uncommon to see 80 pcf equivalent soil pressure required by the soils
engineer. Many engineers doing residential foundations/framing have pondered
the possibility of using the floor joists to brace the top of the wall. Most
single family residential construction in the Denver area is constructed
with basements. (Weight of the concrete walls helps to increase the dead
load on the footings/piers to counter the lifting of the expansive clay
soils.)

Not to long ago, I spoke with one of the I joist manufacturers locally -- an
engineer that I have a great deal of respect for -- and he told me that
their company hasn't researched this. He also told me that trying to develop
the load path is very difficult and expensive. And, the bottom line, the
manufacturer would not back their warranty if the I joists were used to
directly brace the walls.

Several engineers in this area have been thinking "outside the box" and have
used steel beams diagonally from corners to mid-span of the walls, with
large, thick plates at each end connected to the walls to distributed the
forces. This also is expensive and I am not sure how it worked out. I have
seen drawings showing 2x12's butted against the concrete walls and
"sistered" on to the side of the floor joists, using multiple fasteners.
Also, not sure if this has been successful.

I think the most common solution has been to use counterforts centered on
walls over 16 feet in length. For really long straight walls, they are
typically at 12 feet on center.

HTH

Bruce Pooley


----- Original Message ----- 
From: "Joe Grill" <jgrill(--nospam--at)swiaz.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, April 23, 2004 12:17 PM
Subject: RE: soils pressure


We did.  They were so certain that the geotech. would prove me wrong.  He
came back with the same criteria that I used.  Score 1 I guess.

While we are on the subject (or at least related) how do some of you feel
about using wood "I" joists (TJI's, BCI's etc.) in resisting the forces at
the top of a restrained basement wall?  I'm not real crazy about it, but I
have talked to one of the manufacturers.  They were on the fence, at least
from what they would say to me.  I have another basement with opposing soil
loads from opposite walls that will put these joists into compression.  I
used the maximum allowed moment for the joists, calculated the compression
web force from that and deducted the compression web force from the actual
loading and looked at the net capacity that is left as the available
restraining force that the joist would take.  It calcs out that way, but I'm
still a bit nervous.  Any thoughts on this one?

-----Original Message-----
From: Neil Moore [mailto:nmoore(--nospam--at)innercite.com]
Sent: Thursday, April 22, 2004 12:45 PM
To: seaint(--nospam--at)seaint.org; seaint(--nospam--at)seaint.org
Subject: RE: soils pressure

Go tell your contractor and architect to talk to the geotech and let them
argue to him!

Neil Moore, S.E.



At 11:27 AM 4/22/2004 -0700, Joe Grill wrote:
>O.K. guys, one more time, I did design the wall for full soil pressures,
and
>once again (in one of my posts) what I used was confirmed by a geotech.
The
>contractor and architect were trying to tell me there wouldn't be any soil
>pressure due to the vertical cut in close proximity to the wall.  The
>vertical cut is not soil, rock rubble, rock with soil or even large
>boulders, it is a vertical rock face... solid rock.
>J. Grill
>
>-----Original Message-----
>From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
>Sent: Thursday, April 22, 2004 10:58 AM
>To: seaint(--nospam--at)seaint.org
>Subject: RE: soils pressure
>
>Thanks, Paul.
>
>I was hoping someone would say out loud what I was thinking.
>
>T. William (Bill) Allen, S.E. (CA #2607)
>ALLEN DESIGNS (http://www.AllenDesigns.com)
>San Juan Capistrano, CA
>
>:-----Original Message-----
>:From: Paul Feather [mailto:pfeather(--nospam--at)SE-Solutions.net]
>:Sent: Thursday, April 22, 2004 10:08 AM
>:To: seaint(--nospam--at)seaint.org
>:Subject: Re: soils pressure
>:
>:Joe,
>:
>:I would not design a 12 foot retaining wall without a soils report. I do
>:not
>:see how you can assume anything less than full soil pressure occurring at
>:some point in the life of the structure.  Anything less is opening
yourself
>:up to all kinds of potential problems and liability.  Soil moves and
shifts
>:with time and changes in moisture content, the cut will not stand
>:indefinitely.  Also, who is liable when the near vertical cut does not
hold
>:and kills one of the construction workers?
>:
>:
>:Paul Feather PE, SE
>:pfeather(--nospam--at)SE-Solutions.net
>:www.SE-Solutions.net
>:----- Original Message -----
>:From: "Joe Grill" <jgrill(--nospam--at)swiaz.com>
>:To: <seaint(--nospam--at)seaint.org>
>:Sent: Wednesday, April 21, 2004 3:00 PM
>:Subject: soils pressure
>:
>:
>:> I have been asked to design a basement wall with a 12' retained height
of
>:> soil.  There has been no geotechnical review of the residence, but the
>:> architect, who has done other work in the area, tells me the cut will
>:> probably stand almost vertical.  If this near vertical face is just a
>:couple
>:> of feet away from the wall and the backfill is a free draining fill,
will
>:> the fill be able to achieve full lateral soil pressure against the wall.
>:> The architect/contractor/owner wants to use the floor diaphragm to
>:restrain
>:> the top of the wall.  If the full lateral soil pressure is achieved then
>:the
>:> diaphragm doesn't have the capacity to restrain the wall.  I have
>:suggested
>:> a geotech be brought in to look at the excavation and make
>:recommendations
>:> at that point, but of course that hasn't been received very well.  If
the
>:> full soil pressure is not activated will there be any pressure at all
and
>:> how is it calculated.
>:>
>:> Any ideas?
>:>
>:> Joseph R. Grill
>:>
>:>
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