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Re: Construction/Isolation Joints for Composite Slab on Steel Beams

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For joints parallel to secondary members, ACI 302 has locating the
construction joint in the middle of the slab between beams (middle 1/3rd is
probably sufficient) and close to a support where the joint crosses the

When parallel to a girder, it has to locate the joint off of the girder
enough to develop the girder slab flange in bending, which it states that
about 4'-0" is usually enough for this. The joint should be on the side of
the girder that will split the pour up so that the girder flange will be
part of the second pour allowing the secondary beam to deflect in the
initial pour and the girder to deflect completely before the second pour

I don't know your slab thickness but a dowel basket plus lapping the WWF
through the joint should work, added rebar fully developed on either side
of the joint I think would work better if shear is a concern.

Will Haynes

On Sat, Dec 21, 2013 at 1:42 PM, Polhemus, William

> Having a bit of trouble deciphering what I'm reading in various sources
> including ACI 302.
> If I have a composite slab on steel beams (steel form deck plus stud 
> shear connectors), what is the proper way to "isolate" each adjacent 
> floor slab panel? For instance, I really don't want the negative moments 
> over the girder between panels in the slab. I THINK ACI 302 is 
> recommending an isolation joint "offset" from the centerline of the 
> girder about four feet or so (rule of thumb I guess).
> Is this correct? How should it look? Use the "dowel basket" detail shown 
> in ACI 302?
> William L. Polhemus, Jr. P.E.
> Lead Civil/Structural Engineer
> CRA Engineering Group, Inc.
> 6320 Rothway
> Suite 100
> Houston, TX 77040

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