Old Engineer Detailing Question: mild rebar in composite concrete slab on metal deck

[BecomingCurmudgeon]

I am trying to recall how things used to be detailed in the early 1990s.

I am looking at a current project where the design engineer spec'd a 4" concrete slab on 2" composite floor deck (6" overall depth). He used Fibermesh and no mild reinf. The slab cracked in tension down the backs of the girders and there are other cracks over the beams. It is going to be difficult to put a floor finish on now. The owner wants a second opinion.

I remember that in the 90s, my first boss always installed 6' long rebar spaced at 48" down the backs of the girders at the top of the slab. He also installed mild reinf over the beams at the top of the slab. We never had cracks. It was commonly done in upstate New York at that time. It was not so much an engineered solution but a conventional practice. I have since moved and the old firm is gone so there are no old colleagues to ask.

I have been looking for a source that discusses my old boss's detailing preference for this. Anyone remember?

 

[cliff234]

We still do that. We specify #4 top bars about 6' or 8' long spaced at about 18" oc, perpendicular to, and over top of the girders. And we specify those bars regardless of whether or not we have WWR or fiber reinforcing (macro fibers) in the slab. We've never had any significant cracks over the girders.

 

[BecomingCurmudgeon]

That sounds like what my first boss used to do. He also put bars over the floor beams as well. It might have been (2) #4 on either side of the beam center line. I'm going to go thru a few boxes this weekend to see if I can find an old print.

The project, that I saw without any mild reinf, used OWSJ floor beams on either side of a WF girder. The OWSJ deflection caused a crack down the back of the girder and had one side of the crack rise up 1/8" above the other side of the crack. Probably due to the different joist spans on either side.

I think using the mild reinf would have prevented this unfortunate outcome. For the want of a nail...