ACI 318-05 6.4.6 1

[TomWaggoner]

Beams, girders, or slabs supported by columns or walls shall not be cast or erected until concrete in the vertical support members is no longer plastic.


I have a condition where a contractor wishes to pour two separate decks with an connecting column in the same sequence. I am looking for a ACI manual reference which defines plastic. This may or may not determine if they accomplish this.

 

[TomWaggoner]

I found ACI 301-22 5.3.2.4,., any other takes on the definition of plastic?

 

[hokie66]

The reason for the provision is to assure that plastic settlement in the column has finished before the deck above is placed. So the concrete needs to be hard enough to finish.

 

[TomWaggoner]

I get it,. the ACI 301 reference says when column is no longer plastic or at least 1 hour. I'm just looking for a more defined definition of plastic. The post tensioned decks are to remained shored for 3 days.

 

[hokie66]

With a deck that large, surely the contractor can cast the columns soon after the lower deck starts, then while the rest of the lower deck is cast, the column goes off. You would have to be careful that the columns are not cast above the soffit of the beams in the upper deck. As to the definition of plastic, on my job it would be whatever I say it is. A code won't help, but engineering judgment will.

How will they adequately place and consolidate the concrete in the columns with the next level column cages already in place? Looks like to me this contractor is getting ahead of himself.

 

[TomWaggoner]

Agree on the lower deck and column to bottom of upper beam. Also agree to the difficulty in vibrating down through post tension cables and rebar. My concern is the possibility of cracking at the assumed cold joint at the upper deck. I've had jobs with 1'-6" beam offsets, but not 8'+. It's design build so ultimately it falls back on them. I'm just looking for a past experience or something that would definitively say yes or no to the proposed pour sequence.

 

[hokie66]

Those short columns will definitely crack, regardless of the casting sequence. The shortest ones near where the ramps meet will be the worst, as they are the stiffest. When you say it is design build and their problem, what do you mean? Aren't you the engineer?

 

[TomWaggoner]

Wasn't really suggesting that it isn't my problem,. only that I was hired to design the structure and by means and methods it is up to the contractor to construct. The only reason the issue was brought to my attention was by means of the city inspector whom is questioning the sequence. There are mixed emotions in my office as to how the structure will perform if the decks are poured just a few hours apart. I do appreciate your willingness to comment on my post. I will definetly let you know what happens after Tuesdays pour!

 

[BAretired]

I would advise the contractor (in writing) to pour the lower deck and short columns on Tuesday, then to pour the upper deck on Wednesday.

BA

 

[TomWaggoner]

They poured it all in one day. They said it went smoothly. We shall see when they pull the forms