Rebar Detailing

[4wilmar]

We are currently constructing several low rise (2, 3 & 4 story) office buildings. All cast in place with concrete shear walls. The column spacings and beam spans are quite uniform so we are looking for ways to pre-fab the beam cages & slab steel and drop them into place. I recon this could be done by pre-fabricating a beam cage with all full lenght bottom bars and 2 small top bars just to tie all the stirrups in place. The main top bars could be loosely placed inside the beam cage and easily slide thru the column cage once the beam cage is set in place. If necessary we could also slide a few short bottom bars thru the column cage as well. However ACI requires that bottom bars extend 6" into the supports (unless otherwise specified by the Arch./ Eng.) which makes it difficult if not impossible to place a prefabicated beam cage between the column cages or a prefabricated mat of slab steel (bottom bars) between the beam cages. Has anyone found a way around this, surely someone has done this before.

 

[JAE]

Not only 6" into the supports, but check out the end of Chapter 7 - Structural Integrity requirements requires additional bottom and top continuity bars that must be satisfied.

What you are proposing can be done. It would save time, but would probably add additional labor and materials in that you'd have to have more spliced bars to accommodate the insertion of the cages.

 

[SperlingPE]

I am with JAE on this. The reinforcing sub-contractor asked to do the exact thing you are asking. It did indeed to additional bars to accomplish. Did it save time? Probably debatable. Did it make it easier for the guys tying the steel? Yes. If you intend to do this, be sure and note it as such on your drawings. If a sub asks to do this, be sure that he asks before you get a price, to truly see if there is a cost savings. I suspect that it could be either way.

 

[4wilmar]

Thanks for your help, I will discuss the issue with our Eng. & detailer.