Advantages & Disadvantages of Pouring Concrete Beam-Slabs Monolithic with Concrete Column

[ditapark]

Seriously, I hope I'm in a wrong thread, and I really need a quick answers here, hopefully you guys can help me on here. So what are the advantages & disadvantages if we pouring the concrete beam-slabs monolithic with concrete colomn? Like we pour the concrete beam-slab right after we done poured the concrete colomn?

 

[KootK]

I can’t think of any significant advantages of going with a monolithic pour. I guess you would eliminate a non-critical shear friction joint and perhaps improve water tightness? I would think that constructability would suffer with a monolithic pour.

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.

 

[manstrom]

It would be pretty tough to pour a column with all the beam rebar in place. You need a good 4" to 6" opening to fit in the chute.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[BAretired]

The main disadvantage is that the column will shrink, causing cracks under the beam-slabs. It is definitely not recommended.

BA

 

[hokie66]

BA is correct, but I think it is more accurate to say that the plastic concrete in the column will settle, while the beam concrete will be held up by the reinforcing. A crack at the junction develops, which is obviously not good. This subject has been discussed here before, and the answer is always the same.

 

[ditapark]

Thank you guys for the comments. I was thinking the same as well, but the construction project that I was internship-ed did all the job in one day even without waiting the column to be harden. When I asked the 'higher' people there, they said because they got a very short time schedule, so that why they did that. And as the result there are some columns that shrink at the end.

 

[RHTPE]

As one who has designed a substantial amount of shoring/falsework/formwork, I feel compelled to comment on this.

BAretired hits on one disadvantage, the column concrete will shrink. If the shoring supporting the beam/slab is stiff enough, there will be some concern regarding cracking. ACI does address this issue and recommends a delay in the placement of the slab/beam concrete after completing the column concrete placement.

My main concern is lateral stability of the entire formwork & falsework system. The entire system must be designed for the potential and required lateral loads (2% of the dead load or 100 lb/lineal ft). When the columns are placed a couple days before the slab/beam is placed, one gains some stiffness to resist lateral loads (by edge bearing of the deck plywood against the sides of the columns).

This is a common situation in NYC mid-rise projects. The column & wall concrete is often placed after the deck formwork has been installed. Generally there is a delay in the deck concrete placement.

I do know that because of the column concrete shrinkage, the forms used for the columns can become 'locked' into place. This can result in having to destroy (or damage) the forms in order to remove them.


Ralph
Structures Consulting
Northeast USA

 

[doka1]

I'll admit, as a concrete contractor I have done both. I will reinforce that even in a 2 day cycle, the concrete columns are poured the day before. Not only does it benefit the structure (in terms of shrinkage as BA mentioned) to place the columns the day before, it also makes the process more efficient as the concrete deck placement starts right in the morning, opposed to waiting until the columns and shear wall to be filled.

 

[CELinOttawa]

To the best of my knowledge, there are no advantages beyond "time", which I think can be shown to be a false savings, when pouring monolithically.

It is always a mistake, and principally poor pour practice, pal.