SUPER FLAT FLOOR REINFORCING

[rlewistx]

I'm looking for recommendations for minimum longitudinal reinforcement for a super-flat floor. I have a requirement of Fmin=65 and am designing the strips for the floor. I have the strip joints located in the middle of the storage racks. The strips are 200 feet long. What is the recommendation for longitudinal reinforcement in the strips to distribute the cracks?

ACI 360.1 section 8.3 states to use p=0.005 for the steel reinforcing. It does not state if this is top reinforcing or total. And it does not state this is for super flat strip pours. I have an 8" slab with a requirement of top & bottom reinforcing by the client. Would the pmin=0.005 be for top bars of #5 at 11" o.c. or T&B #4 @ 10" o.c.? Or should I be looking at another recommendation?

Thanks.

 

[bones206]

I frequently try to use 0.5% reinforcement in slabs that will not have control joints, based on ACI recommendations. The 0.5% is total reinforcement allocated for T&S, so you can do half on top and half on the bottom if you want. I don't have experience with super flat slabs, but if you want the random cracking kept tight, you are on the right track.

 

[rlewistx]

Thanks for the info. I would appreciate any other's input as well that may have designed superflat slabs.

Another question, for a super flat slab, is it okay to put a sand cushion base below the slab, or will that cause potential problems for settlement movement in the future?

Thanks.

 

[SlideRuleEra]

rlewistx - I have not designed superflat slabs, but have designed/constructed/used continuously reinforced ones and was an early adopter of the f-number system (c. 1991). IMHO, nothing special about a superflat slab other than high F_F and (usually) correspondingly high F_L.

For continuous reinforcement, the rebar (0.7 to 0.8%) needs to be relatively high. I see you have a two rebar mat requirement in an 8" slab. If "force" two mats into the slab (distributing rebar between them) there will not be enough near the surface for effective continuous reinforcement. Perhaps you can "cheat"... put 0.7% in the upper mat plus a "token" bottom mat, say, #3 bars @ 18". I would do it... but that would be for inhouse use, not a client.

Continuous reinforcement has been mostly used for concrete pavement, see Federal Highway Administration, "Continuously Reinforced Concrete Pavement Manual", particularly Chapter 4.

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