Does CSA A23.3 apply to SOG? 1

[Joe Eng]

Curious on this, I've got 3rd party review telling me my slab-on-grade design is under-reinforced. It's a simple SOG for a shop, no racking or special loading considerations. Basically just pickup trucks and materials. I've applied subgrade drag method for crack control only, and IMO the reinforcement is already over-designed (partially because the client is very cautious). However, they've got other engineering involvement for other portions of the work, and happened to comment that the slab does not meet minimums required by A23.3 7.8.1.

IMO it is unnecessary, and additional cost isn't worth it, but they're paying for it, so ultimately I don't care if it's over designed. But the standard is a bit ambiguous in this regard, and I do like certainty, so curious if anyone else has better information or an explicit definition or guidance based on CSA A23 that I could reference.

Thanks!
joe

 

[atrizzy]

I think they're right... I'd never reinforce a SOG with less than 0.2% steel for temperature and shrinkage alone.

 

[canwesteng]

Is it designed as plain concrete? If not I'd expect 0.2%.

 

[Joe Eng]

I suppose if less than 0.2% it is plain concrete by definition? I used principles from ACI 360 R92 with respect to relief cuts and reinforcement for crack control.

 

[KootK]

You are correct in that the structural concrete provisions do not strictly apply to slabs on grade. Obviously, slabs on grade are structural in a different sort of way.

In my experience, most of the "non-structural" slabs on grade in the wild have less than the temperature and shrinkage reinforcement. This blurb is from ACI 314 and recommends half that amount.

 

[dik]

What is the slab thickness and the amount of reinforcing in it? What is your control joint spacing?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[skeletron]

Agree that SOG are different beasts. But I do apply 0.2% like CSA A23.3 requires for slabs. There are plenty of ways to skin the cat, though. Given that ACI and other standards use 0.18% and 0.15%, I think there is potential that these ratios be considered acceptable depending on the load, thickness of slab, subgrade preparation, etc.

What is your slab thickness, rebar spec, and subgrade prep?

EDIT: I have been the reviewer that flags the "less than minimum" at one point in time. I think it was something like 10M @ 24" o/c for a 4" or 5" slab. It wasn't a sticking point for me to pass/reject the design, but I did talk with the EOR. Their comment was that they've had many successful projects using that spec, clients don't want to spend the extra money on rebar, and they monitor joints and subgrade in the field.

 

[dik]

I seem to recall there is a lot of literature on the effects of small amounts of reinforcing is SOG construction. I also seem to recall that the effect is negligible. Kicker is a good concrete mix, a good compacted base material and sawcutting it at the right time.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ajk1]

I remember this question being around from time immemorial, such as from before I retired.

I believe that the general thought was that the minimmum area of welded wire steel mesh was not only unhelpful in slab-on-grade; it was counterproductive, and it was better not to put it in, because it reduced the effectiveness of the sawcut control joints, unless you sawcut through the mesh.
Also, the mesh generally ends up near the bottom of the slab, unless special measures are taken.

So we did our non-industrial and non-warehouse slabs just as plain concrete with no reinforcement in them, but with:
- properly designed mix with minimum water (it is the absolute water content that determines shrinkge (not the w/cm that causes the shrinkage)
- no welded wire mesh or other reinforcement unless there are substantial subgrade weakness issues
- 125 mm (5") minimum thickness
- start wet curing as soon as possible; can do by covering with polyethylene sheet, but ensure that no one lifts the sheets off in any area until the proper length of wet cure has occurred, and then reduce the wet curing gardually
- erect wind breaks as necessary on windy day
- do not place concrete on very hot day or very windy day
- sawcut control joints made as soon as possible without causing the sawcut edges to ravel when cutting
- sawcut into limited length and widths (see pca publications, etc.)


There are publcations by such as PCA, books,etc. dealing exclusively with this topic.

For rack storage floors, reinforced with steel fibres, see publications. Should be done by specialized contractor experienced in this.

 

[dik]

@ajk: You, I think, are right on.

Any SOGs I've designed, have usually assumed 0.2% reinforcing, but not included this in the design at all. They have been designed as plain concrete. I've often used the Airport slab design program for design of racking loads, point loads, etc. This is based on Packard's stuff. There have been no issues. Only for a couple of heavy industrial slabs have I used steel fibre, and considered it in the design... and also a few with hardened surfaces. I've never done a SOG using reinforcing bars for flexural strength... Reinforcing used for dowels occasionally, but prefer keyways.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Joe Eng]

Thank you all for your responses and providing your knowledge and experience! Gives me a bit more to look into, I really appreciate the feedback.