Composite deck reentrant corner bars 1

[haynewp]

For slabs on grade we always show reentrant corner bars where needed on the plan to control cracking (non-strucutural cracking). For elevated concrete floors on forms I have shown reentrant corner bars also.

On composite steel deck and concrete floors, I have never indicated additional bars for reentrant corners where elevators, ductwork, stairs, etc. penetrate the slab. We just have a detail with an edge angle (or pour stop) at the perimeter of the penetration with the typical welded wire reinforcing throughout the floor.

I got a question on why I did not show this recently on a project and I have never had a problem with cracking complaints on composite deck floor penetrations. I also have never shown control joints on these floors either. Does anyone else show these reentrant bars on steel form deck floor penetrations to control non-structural cracking at top of slab?

 

[JAE]

I would consider the corner bars if the concrete was going to be left exposed, or perhaps polished concrete. If covered with carpet, tile, etc. I don't know what good keeping the cracks closed does for you.

 

[hokie66]

I think the corner bars represent good practice regardless of the useage of the floor. The cracks may not be a serviceability issue to engineers, but the stress riser is there, so I like to try to minimise its effect.

 

[haynewp]

I have heard of shrinkage cracks reflecting up through ceramic tile floors, I haven't seen it myself. I guess someone could argue carpet could be removed in the future for a polished concrete floor.

 

[rowingengineer]

while i agree with Hokie, I wouldn't detail them as I would for a slab on ground, with the 180 deg to the corner detail. I would detail them with two sets of bars 90 deg to the corner in both directions, this way the bars are in layers of steel. I wish I was keen enough to do a sketch.

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[msquared48]

I hate to be the odd man out here, but if the steel deck is composite with the slab, why would you need them at all? Wouldn't the deck serve as the resteel here?

Mike McCann
MMC Engineering

 

[hokie66]

The deck stops at the corner as well as the concrete, and deck essentially provides reinforcement in one direction only. A crack can easily initiate from a reentrant corner, parallel to the ribs.

 

[msquared48]

OK. Thanks Hokie.

Mike McCann
MMC Engineering

 

[TXStructural]

I always detail corner bars on a 45 in all kinds of slabs. On composite deck, there is frequently quite a bit of restraint away from the corners due to the deck configuration, so any shrinkage will try to crack reentrant corners. Also, flexing of the slab as the steel beams deflect will tend to exacerbate these.

 

[dik]

I like to avoid them and when they occur, unless they are 'really small', I trim them with structural steel to 'eliminate' the re-entrant corner.

Dik

 

[TXStructural]

Dik, I find that framing with steel shapes doesn't adequately prevent crack propagation.

 

[dik]

didn't say it did... still put additional rfg at the corner, but to tighten up cracking... eliminate most of the problem by framing.

Dik