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RE: Foundation Min. reinforcement

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In some locations the moment can be zero, but here are ways to figure out a
moment to design for:

1) A load-bearing wall with a wide door opening:  For normal loads and
openings, the trench footing will have a theoretically uniform load along
the bottom of the trench footing and two point loads some distance apart on
the top with nothing in between.  This can be simply analyzed as an inverted
beam with fixed ends.  For higher loads and wide openings the load will vary
due to beam deformations, so you probably need to use an elastic support
analysis.

2) Most soil reports allow for differential settlements of up to 1/4 or 1/2
inch.  For bad soil, this number gets higher.  Convert the allowable loads
and settlements to two soil stiffness values.  Do an elastic support
analysis with sections of the wall supported by the different soil
stiffness.  The footing will try to resist the differential movement,
resulting in moments.

Except for higher than normal loads or really bad soil, our typical trench
footing reinforcing works almost all of the time.  It's well under the
200/Fy value.  You'll have to determine for your own conscience what
"normal" loads, "really bad" soil and "typical" reinforcing is.

Also as a minimum, you need to provide steel for shrinkage and temperature.

-----
Jason Kilgore
Leigh & O'Kane, L.L.C.
(816) 444-3144
jkilgore(--nospam--at)leok.com


-----Original Message-----
From: George Richards P.E. [mailto:george(--nospam--at)borm.com]
Sent: Thursday, March 14, 2002 5:44 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Foundation Min. reinforcement


Maybe but there is an exception.  If As is 1/3 greater than required by
analysis.  Hence: Moment = 0 As = 0.

Don't we just all love the code?

George Richards, P. E.

-----Original Message-----
From: syed faiz ahmad [mailto:syedfaiz23(--nospam--at)hotmail.com]
Sent: Thursday, March 14, 2002 3:35 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Foundation Min. reinforcement


Ed,

All foundation/grade beams are 'Beams on Elastic Foundtion'.

The minimum reinforcement for flexure apply, that is:

   - for beams, p = 200/Fy,

   - for slabs, P = 0.0018

Regards,

SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RYADH,SAUDI ARABIA.


>From: "Ed Najjarine" <enajjarine(--nospam--at)permasteelisausa.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: "SEAINT \(E-mail\)" <seaint(--nospam--at)seaint.org>
>Subject: Foundation Min. reinforcement
>Date: Thu, 14 Mar 2002 08:29:52 -0800
>
>Fellow Engineers,
>
>We normally design footings and grade beams with 1 or 2 # 5 T & B (or
>whatever is needed for the design moment) but we don't use the minimum
>reinforcement requirements for regular beams such as 200/Fy. Can you direct
>me to where the code makes the distinction between regular beam
>reinforcement and grade beams.
>
>T.I.A.
>
>Ed Najjarine, P.E.
>
>
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SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.


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