Additional reinforcment in PT flat plate 1

When providing additional reinforcement over the column in post tensioned flat plate, what is the good practice for spacing of the bars? Would it depend on the number of bars required as well or do I just spread the bars over the width of the column strip?

 

[RiBeneke]

It is not just a case of following a rule for detailing the bars.
You have to check the shear stresses and follow your code of practice for the shear reinforcement required.

 

[Taro]

Because of the reference to column strip width, I believe Verada is inquiring about the spacing of flexural reinforcing, not shear. In the U.S., ACI code requires a minimum quantity of reinforcing to be placed close to the column, the rest can be spaced farther apart.

 

[rapt]

It depends on the design approach being used. If the tendons are detailed as "banded" in one direction, then the reinforcement should be concentrated over the top of the column as close to the column as possible.

If the slab is being detailed as a true two-way slab with column and middle strips in each direction, then I would still tend to place more of the reinforcement concentrated over the colum especially if it was only a small amount of reinforcement because the highest moment concentration is over the column but, if the area of reinforcement was fairly large then I would distribute it over the column strip width with a few extra bars over the column.

This is all assuming that the reinforcement is for ultimate strength.

If the reinforcement is for crack control, then for the banded 2-way solution, the logic is too complicated to detail here. The whole design approach needs to be looked at in detail as a banded solution cannot inherently provide crack control, hence the (grossly unconservative) limit in ACI limiting the maximum stress in these slabs.