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Re: footings a beam or a slab?

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Alex:

Good call.  I don't know what I was thinking (obviously mixing up shear and
flexure).  Thanks for the correction.

Mike

-----Original Message-----
From: Alex C. Nacionales <anacio(--nospam--at)skyinet.net>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Wednesday, September 30, 1998 6:25 PM
Subject: RE: footings a beam or a slab?


>Mike,
>
>It is the shear that is maximum at  distance d from the face of a wall or
>column. Flexure is theoretically maximum at the face of the support however
>in this case it is so small that  the min. requirements for temp. steel
will
>govern.  The  footing is more like a one-way slab and that placing minimum
>temp. bars  for transverse reinforcement  is a good practice.
>
>
>Alex C. Nacionales, C.E.
>
>-----Original Message-----
>From: Mike Brown [mailto:mike.brown(--nospam--at)cshqa.com]
>Sent: Thursday, October 01, 1998 6:57 AM
>To: seaint(--nospam--at)seaint.org
>Subject: Re: footings a beam or a slab?
>
>Marlou:
>
>Several things can be argued about this situation.  To begin with the
>footing will act like a beam across any weak soils in the longitudinal
>direction (I think this issued is resolved for you).
>
>As for the reinforcing in the transverse direction, an argument can be made
>stating that there is no flexure in this direction (assuming the wall is
>centered on the footing).  To back this argument up, the maximum flexural
>stress occurs at a distance 'd' from the face of the wall ('d' is the depth
>of the footing to the tensile reinforcing).  With a 16 inch deep footing,
>d=16-3-0.25(#4bar)=12.75 inches.  Assuming an 8 inch wall thickness and the
>wall is centered on the footing, you have 8 inches from the face of the
wall
>to the edge of footing which is less than the 12.75 inches, therefore no
>flexure.  The vertical forces from the wall are transferred directly to the
>soil without putting the footing in flexure in the transverse direction.
In
>other words, there is no tension zone in the transverse direction.
>
>However, we do use transverse reinforcing in our footings.
>
>If anyone does not agree with the above, please respond.  I would like to
>hear other opinions, especially if I'm not seeing the whole picture.
>
>Mike Brown, P.E.
>
>-----Original Message-----
>From: MRodrig273(--nospam--at)aol.com <MRodrig273(--nospam--at)aol.com>
>To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
>Date: Wednesday, September 30, 1998 4:14 PM
>Subject: footings a beam or a slab?
>
>
>>I have a case where I have a footing that is 24 inches wide and 16 inches
>>deep.  I found that the footing only requred minimum steel reinforcement.
>In
>>the longitudinal direction I used 3 #5 bars and in the transverse
direction
>I
>>used #4 @ 6".  I was told that my #4 bars were not needed and that I can
>just
>>space them at 18 inches.  This was argued that the footing acts like a
>beam,
>>which I understood, and in a beam you don't need to satisfy the 0.0018bt
>>critiria.  But as I was reading the ACi.  In the flexural reinforcement
>>section 10.5.4 it states that "For Structural slabs and footings of
uniform
>>thickness the minimum area of tensile reinforcement in the direction of
the
>>span shall be the same as that requred by 7.12.  Maximum spacing of this
>>reinforcment shall not exceed the lesser of three times the thickness and
>18".
>>If my footing acts like a beam, does it span the length of the footing or
>does
>>it only span the 24 inches in the transverse direction.
>>
>>What does everyone else use as the minimum reinforcement for the
transverse
>>direction for a 24 inche wide beam.
>>
>>Thanks in Advance
>>
>>Marlou B. Rodriguez, EIT
>>Robert Englekirk Inc.
>>Honolulu, HI
>>
>>
>>
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