Corner reinforcement in slabs
Corner reinforcement in slabs
(OP)
Hi all,
I'm currently reading ACI 314-11 (GUIDE TO SIMPLIFIED DESIGN FOR REINFORCED CONCRETE BUILDINGS) and it appears that point 7.3.8 recommends the use of corner reinforcement at the exterior suported slab corners for a distance equal to one-fifth of the longer clear span of the slab. The area of the reinforcement should be sufficient to resist a moment equal to the required positive flexural strength, per unit of width, in the slab panel, in accordance with 7.3.8.1 and 7.3.8.2.
Does anyone know the reason of this?
Why do we need it in first place?
Why does the distance need to be 1/5 of the span?
Why does the area of reinforcement need to be equal to the positive flexural strength?
Best regards.
I'm currently reading ACI 314-11 (GUIDE TO SIMPLIFIED DESIGN FOR REINFORCED CONCRETE BUILDINGS) and it appears that point 7.3.8 recommends the use of corner reinforcement at the exterior suported slab corners for a distance equal to one-fifth of the longer clear span of the slab. The area of the reinforcement should be sufficient to resist a moment equal to the required positive flexural strength, per unit of width, in the slab panel, in accordance with 7.3.8.1 and 7.3.8.2.
Does anyone know the reason of this?
Why do we need it in first place?
Why does the distance need to be 1/5 of the span?
Why does the area of reinforcement need to be equal to the positive flexural strength?
Best regards.






RE: Corner reinforcement in slabs
"Unrestrained corners of two-way slabs tend to lift when loaded. If this lifting tendency is restrained by edge walls or beams, bending moments result in the slab. This section provides steel to resist these moments and control cracking...."
Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies
RE: Corner reinforcement in slabs
Like JAE mentioned, tying the corner down results in some oddball bending moments. See below for crack patterns etc.
Based on elastic structural analyses of slab systems, that's what was determined to be approximately required for adequate performance. It compares reasonably to rebar quantities and bar extensions that you might get from coefficient slab design methods and the like.
I see this detailing in the typical details for slab and beam systems but, to be frank, I almost never see the recommendations followed to the letter for two way flat slab and flat plate designs. Usually, designers seem to run nominal top bars (#5 x4' @12" for example) around the edges of wall supported slabs and, where those bars turn corners, you get a two way mat that looks a bit like the code recommendation. Usually that mat is short and insufficiently dense however. I've not seen any detrimental consequences of this practice to date.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Corner reinforcement in slabs
Dik
RE: Corner reinforcement in slabs
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Corner reinforcement in slabs
Dik
RE: Corner reinforcement in slabs
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Corner reinforcement in slabs
Dik