minimum reinforcement

[fyaure]

I have a slab which is 6 feet thick. Using 50 ksi bars, i need to put minimum steel percent = 0.2% for shrinkage crack control. This is extremely high (because slab is so thick)and my design for moment does not require even 1/10th reinforcemnt of that.
1. Do I still have to give 0.2% steel even if I use expansive concrete?
2. Does the minimum steel criteria still hold true for slabs of such depths?
3. Does the minimum steel also include negative reinforcement too?
4. Is there a specific way to place the shrinkage crack control reinforcement? evenly distirbuted/at bottom/at top???

 

[JAE]

Please describe more about your slab, its function, shape, purpose, support, etc.

 

[dbuzz]

It's more a monolithic foundation than a slab at 6' thick!

 

[DaveFlax]

You mention .2% steel for crack control. I think you mean .02% steel. If you want to use steel, expansive (Type-K) concrete requires only .0015% steel per ACI 223. The steel in Type-K concrete is not there to prevent shrinkage. It is there to prevent to concrete from expanding too much. There is even a system available called System-K that uses little synthetic fibers to restrain the expansion and no steel at all is required.

 

[DaveFlax]

I apologize for my previous message. Your .2% is correct. ACI requires .0015 which is .15%. That's what I get for trying to type faster than I can think. Sorry. At least I got the information about Type-K and System-K correct.

 

[flamby]

Is it the same mine cap/plug thing you discussed in the other thread?

If so, I do not think provisions of shinkage reinforcement will be binding on you. You can design the slab for actual thickness, say 2', and provide minimum reinforcement on that. The additional thickness of 4' of concrete can then be treated as sacrificial dead load and an increased margin of safety. However you can also add some surface reinforcement on top.

Ciao.

 

[fyaure]

thank you everyone, with all the help and brain storming i did finally design it as a regular slab.
flamby, my present design is almost like what you have suggested. thanks again.