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Re: Elevated Structural Floor Slab Joint

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I have to come in with Roger on this one.  If there must be a joint, I
prefer the joint at the theoretical inflection point rather than mid-span.
(Mild steel slabs).  I agree with what you are saying regarding moment
transfer, however placing the joint at the point of maximum moment places
the joint at the location of maximum stress. A properly detailed joint will
still have the ability to transfer shear across the joint through shear
friction and dowel action or interlock from keyways.  I do not agree that
only the monolithic concrete can transfer shear.  The concept of zero shear
at mid-span is only in a perfect world, and for a continuous structure this
point will vary with the envelope.


Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message ----- 
From: "Structures Online" <3.sol(--nospam--at)spectranet.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, July 10, 2003 10:07 AM
Subject: Re: Elevated Structural Floor Slab Joint


> Dear Roger,
>
> Construction joints are points of possible weakness.
>
> Consider  2 scenarios
>
> 1. In case of weakness at a section where there is moment, the steel will
> still take the tension, while concrete being in compression will still be
> able to transfer the compressive forces from one side of the joint to the
> other, so effectively the joint is still capable of transferring the
moment.
> Secondly the moments have a tendency to redistribute too.
>
> 2. In case of weakness at a section where there is shear, the joint is in
> the plane of shear failure, and in a RCC slab, there are no mechanisms
> present for transfer of shear from one side of the joint to the other
except
> through the monolithicity of concrete. Also shear does not redistribute.
>
> What do others think?
>
> Regards
>
> Pankaj Gupta
> Structures Online
> India
>
>
>
>
> ----- Original Message -----
> From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Thursday, July 10, 2003 9:02 PM
> Subject: Re: Elevated Structural Floor Slab Joint
>
>
> > I agree and disagree with Pankaj Gupta's post.
> >
> > I agree that construction joints should be avoided when possible.
> >
> > I disagree with the location of construction joints.  When construction
> > joints are necessary, I try to locate them at or near service load
points
> of
> > inflection, where both moment and shear are not maximum or close to
> maximum.
> >
> > A. Roger Turk, P.E.(Structural)
> > Tucson, Aridzona
> >
> > Pankaj Gupta wrote:
> >
> > . > Construction joint should be avoided if possible.
> >
> > . > If not possible to avoid, then the joint should be at mid span,
where
> > . > shear is zero.
> >
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