Two way slab - reinforcement requirement at middle strip

[RHT2020]

Hi, I am new here and hope to get some suggestions on the two way slab design.

I am designing a single story car dealership here in Canada (CSA codes). We decided to use structural slab for this building due to expansive soil on site. We layout concrete pile at 4.8x4.8m and slab is 150 mm thick with 50mm topping for in-floor heating pipes, C/W 1.2x1.2x0.15m drop panel at the column.

I propose to provide 15M bottom rebar 300C/C over the whole area and only provide 2.4x2.4m mat rebar at column strip to take 100% nagetive moment. I don’t think I need top rebat at M-M trip. Anybody please comment. Looks like CSA required at least 10% negative moment distributed to middle strip.

Thanks.

 

[MIStructE_IRE]

In theory, if there’s no bending stress then you don’t strictly need steel. I do however put it in as anti-crack and to provide a robust/safe rebar cage for the guys to walk on.

 

[BAretired]

The easiest way to accommodate negative reinforcement in the middle strips is to enlarge the top mats over the supports so that they encroach slightly into the middle strip.

BA

 

[hokie66]

I would reinforce it as a typical flat slab, with C-C and C-M top reinforcement. You can leave out top bars in the M-M area.

Will your slab be cast on void former to prevent uplift from the expansive soil?

 

[rapt]

Assuming that the topping will reflect any cracking that happens in the top of the slab, I would have top reinforcement in the middle strips to control it. Strength will be ok with 100% in the column strip, but that does not guarantee crack control.

 

[RHT2020]

Void form will be placed under the slab. What kind of anti-crack reinforcemen I should specify? Welded wire mesh are good option?

 

[hokie66]

No, stick with bars. If you have enough flexural reinforcement, you will have enough crack control.