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RE: Control joints in Elevated slabs (Re: Harold)

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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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