mildsteel reinforcement for temp and shrinkage in pt slab 1

[alvidz]

what is the ideal location for mild steel reinforcement for temperature and shrinkage in a one way posttension slabs.
Is it better in the middle of the slab or at the top in alignment the top rebar.

 

[tolchijb]

Many times PT does not necessarily require T&S reinforcing. I believe code says if the net compression on the PT section is greater than 100 psi, T&S reinforcing can be omitted. That being said, I would place the T&S steel closest to the face of which you want to control cracking. If this is an exterior slab in a parking garage, I would put it towards the top, but definitely note the T&S reinforcing shall not interfere with PT tendons. Obviously, the PT tendons take priority.

 

[csd72]

cracks tend to start at the surface, central reinforcement will not stop this.

 

[paddingtongreen]

"Mild steel reinforcement"? You do mean normal rebar, I hope.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ron9876]

If you mean a one way pt slab over beams/walls and if you chose reinforcing steel instead of pt for the opposite direction then they will probably want to use it to form profiles for cable placement.

 

[hokie66]

I don't think it makes much difference where the bars are placed, assuming the slab is not really thick. These bars are for control of direct tension cracks, which tend to extend completely through the slab. They are probably easier to place near the bottom, but need to make way for the cable profile.

 

[rapt]

alvidz,

For a roof slab I would put it at the top to improve waterproofing. Otherwise the surface on which you want to control cracks the most, so if you have marble tiles on it, then the top, if you have exposed soffits, probably the bottom.

Unless it is greater than about 250-300 thick, then both faces.

tolchijb
Beam PT cannot be assumed to provide s&T reinforcement in the slab. Thise who suggest an elastic distribution of the prestress from a beam into the parallel slab don't know what they are talkking about so do not listen to them.

 

[hokie66]

If you are trying to make a waterproof slab, you will need a lot of reinforcement, at least .6%Ag, probably more.

 

[larsacious]

Look at ACI 318-05, 18.9 for minimum bonded reinforcement required by code.

Also, I would recommend placing additonal steel at the bottom of the beams that frame into the exterior columns and lapping it with the column steel. There are restraint effects here caused by the footing that tend to put the bottom of the beam/frame into negative flexure.

Good luck.