About Reinforced Concrete Column Casting 3

[dr. rifat]

Hello,

In rcc column casting how many times we can casting each column?

Say can we casting a 12' column or 10' column in 3-4 times?Which precaution we may follow in this situation?

if f'c=3 ksi ,fy=60 ksi

Sorry for my bad english.

RIFAT

 

[Ron]

I'm sorry, but I don't understand your question.

Are you asking how many times a column form can be re-used?

 

[jayrod12]

I think he's asking how many cold joints could you put in a column. Theoretically lots, but it's bad practice, it should be one pour

 

[dr. rifat]

My question is practically we casted a concrete column in 2 steps,1st step casing 2' then the rest portion are done.

Yes,in concrete column how many joints we use.

RIFAT

 

[KootK]

As jayrod mentioned, you can technically break the column up into numerous pours so long as the mating concrete surfaces are appropriate, any rebar splicing is tended to, and any shear across the cold joint has been considered. In my experience, most two story column will be multiple pour. And, certainly, there are tall bridge piers out there that have been cast in numerous pours successfully.

All that said, I would expect the contractor to have a valid reason for using multiple pours. You know, a reason other than lousy quality control. In my opinion, multiple pours does impact the quality of the finished product to a degree. Consider:

1) There will often be slight angular change in the column and/or rebar at the joint that was probably not accounted for in design.

2) At every joint, you develop some local restraint stresses where the shrinkage of the new concrete is retrained by the presence of the old.





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dr. rifat]

Very helpful.After some days I have to face this problem.Because,we have to construct a basement with 9 storied building,here floor height of basement is 9',there still ground floor beam,then some of my basement floor are 2' down from that floor so that we have to connect downward beam,which is 7' height from basement floor.Here my beam are in two vertical position in one column,because of different direction.So, one column is connected with 7' vertically high beam as well as 9' vertically high beam.Thats my condition.So that we think that we casted that column by multiple pour.

RIFAT

 

[KootK]

Certainly I would consider that a good reason for the multiple pours. Really, it'll be four pours anyhow including the portions of the column that are encompassed within the beam.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SlideRuleEra]

A (reputable) Contractor has to put much thought into the height of column placement. The overriding factor is internal pressure on forms from fresh concrete. Concrete volume of a single column is very small, compared to it's height - pour the concrete quickly and (together with concrete vibration) you get full hydrostatic pressure of fluid concrete. Need really stout forms for that.

Pour the concrete "slowly", to keep pressure low, and it takes "forever" to place a small concrete volume.

Have many columns ready for "slow" placement in each one, and Contractor needs lots of forms. Also, the placement crew has to move placement operations between forms on a planned, uninterrupted, regular schedule.

As a bridge Contractor, we opted for fast placement of cylindrical columns (36" diameter) using steel forms. Of course circular forms are the optimum shape for high internal pressure. If columns are any other shape (say square or rectangular) then form design detail become even more important to effectively resist the concrete pressure (both for strength and without excessive form deflection).

Even with all factor being favorable (steel circular forms) the practical limit for fast placement of a single lift is essentially 20 feet height (hydrostatic pressure of 3000 lb/ft[sup]2[/sup] at the bottom of the quickly filled forms).

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