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RE: Control joints in Elevated slabs

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My philosophy is to use draped WWF over joists and composite beams. I 
require a cont. slab bolster over each bar joist to support the WWF. I also 
require a cont. #3 support bar wired to the studs of composite beams to 
support the WWF. This locates the WWF in the top over the beams or joists.

I also add top rebar over the girders. On longer deck spans where the 
negative moment over the beams cannot be handled by one layer of draped 
WWF, you can add another small piece of WWF or provide supplemental bars 
over the beams.

It maybe possible to sawcut elevated slabs to control cracking, as long as 
it is done over non-composite beams or joists. I do not recommend sawcuts 
for slabs with composite beams as it may affect the composite action (if 
placed over the beam). Of course an unwanted crack over a beam may also 
affect the composite action.

On slabs where it is critical not to have cracking, I will use top rebar 
thruout.

Jim K.

-----Original Message-----
From:	Daryl Richardson [SMTP:h.d.richardson(--nospam--at)shaw.ca]
Sent:	Thursday, November 29, 2001 9:42 AM
To:	seaint(--nospam--at)seaint.org
Subject:	Re: Control joints in Elevated slabs (Re: Harold)

Keith,

	Please post them on the server.  I'm sure we would all like to see
them.

				Best regards,

				H. Daryl Richardson

Hyndman, Keith wrote:
>
> Thanks all for your responses, I spoke with Rick Smith of Structural
> Services Inc. of Dallas, Texas how works for Eldon Tipping (ACI 
Committees
> Member).  He was very helpful on this issue and also emailed me 2 
articles
> (pdf format) on the subject.  If any are interested let me know, I'll
> forward them.
>
> In any case, there are some cases where control joints are used in 
elevated
> slabs, I learned something there.
>
> Harold, could you direct me to resource or formulas for calculating the
> shrinkage crack widths?
>
> Keith
>
> -----Original Message-----
> From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
> Sent: Wednesday, November 28, 2001 7:44 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Control joints in Elevated slabs
>
> Hyndman,
>
> No.  But cracking in concrete slabs on metal deck is an issue.
>
> Number one, never use polypropylene fibers.  Use mesh or rebar.  This is
> another topic.
>
> If the slab is covered by carpet, use the minimum SDI recommended steel 
and
> forget about it.
>
> If the slab is going to be exposed or covered with a material that could
> reflect cracks, CONTROL the cracks and consider the following.
> *       Add TOP rebars about 5' long perpendicular to beams and girders.
> This is not required for strength.  It is just to CONTROL the cracks that
> WILL form due to negative bending along the center line of steel girders,
> beams, and joists.  The only exception is if the joists or beams are 
spaced
> at about 6 ft. or less or if you drape the mesh.  You will still need the
> rebars at the girders.  The crack widths can be calculated, and when they
> reach the point of ugly (architectural term), add rebar.
> *       Use the ACI minimum reinforcing steel (as opposed to SDI).
>
> It is important to note that the tables that we all use for composite 
steel
> deck design were derived with no consideration for negative bending at 
the
> supports, and the SDI recommended WWF for crack control was developed
> empirically (SWAG method).  You will not find this information published. 
 I
> just called the guy who developed the tables one day.
>
> Regards,
> Harold O. Sprague
>
> > >From: "Hyndman, Keith" <KHyndman(--nospam--at)engineeringsi.com>
> > >Reply-To: seaint(--nospam--at)seaint.org
> > >To: "Seaint@Seaint. Org (E-mail)" <seaint(--nospam--at)seaint.org>
> > >Subject: Control joints in Elevated slabs
> > >Date: Wed, 28 Nov 2001 14:04:01 -0500
> > >
> > >Anyone ever heard of putting control joints in elevated concrete slabs 
on
> > >deck?
> > >
> > >Keith Hyndman, P.E.
> > >khyndman(--nospam--at)engineeringsi.com
> > >Engineering Solutions Inc.
> > >436 Creamery Way, Suite 100
> > >Exton, PA 19341
> > >Phone: 610-524-1357
> > >Fax: 610-524-1317
> > >
>
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