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Old April 16th, 2006, 11:52 AM   #1
jonsoon
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Is it advisable to cast concrete column at half?

to the construction pros,

i work as a quantity surveyor . last week my site is having a concrete column casting. due to excess volume of concrete.. my site personnel so called "senior site supervisor" ordered the workers to pour it into another empty concrete column mould (which was not scheduled for concreting on that day)..

to my agony, he cast the column (size of 1.2m x 0.6 m x 2.7 m high) which support the loads of 20 storeys half way..and he insist to continue the other half on the following day..even my site resident structure engineer oppose such action.

casting half of the column and continue a day later..will result a cold joint in the middle of the column..and will greatly affect the strength of the load bearing column...

to your surprise, the senior site supervisor shouted at us and said " i have been supervising concrete casting for 30 years, i say can means can!"...

so in your opinion, since we can cast the whole column to full height why not? is it advisable to do so?
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Old April 16th, 2006, 12:52 PM   #2
Kit
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I don't quite understand what you meant ny casting half way but columns are usually cast in sections. In fact, you don't usually structural members cast in full height at once.

Besides technical issues, there's the good o' "who's going to be responsible?" thingy to consider. If the structural engineer oppose to such a move, he/she has the authority to stop all works there and then. You site supervisor can have 2000 years of experience for all I care but is he going to put his name down on the paper?
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Old April 16th, 2006, 04:48 PM   #3
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I think you refer to the cast not being monolithic. In this case Kit is correct in that in a tall building you can't really cast the whole thing at once, assuming the correct ironworks are there, should be ok but of course this must be qualified depending on your situation.
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Old April 16th, 2006, 05:29 PM   #4
ch1le
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i think you both have misunderstood...

I think he is referring to casting moulds, where lets say some moulds were to be filled with conrete one day and the others a day later. Since they got leftover concrete, they poured half a mould full, so, the next day they would fill it fully, and the concrete would than set very unevenly...

Im no structural engineer, but its sounds fishy to me!
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Old April 16th, 2006, 05:33 PM   #5
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You're right Jonsoon, if possible to achieve maximum strength for the structure the base of the column should be poured monolithically with the beams, girders and floor slabs that it support but I have seen some contractors traditionally pour the column up to the base of the girder and beams as first stage and beams, girders and floor slabs as second stage.

Last edited by D'Transporter; April 16th, 2006 at 08:39 PM.
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Old April 17th, 2006, 12:56 PM   #6
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ch1le is right, exactly wat i am trying to said..the engineer advise us to cast it as a monolithic structure. usually we cast it this way, for example, the floor height is 3.2m and the beam size is 600mm..we usually cast it to the soffit of the beam (3.2m - 0.6m = 2.6m)..by the way, anyone have any technical informations regarding this issue? i wish to present it to my superior..
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Old April 17th, 2006, 04:19 PM   #7
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It depends. Just make sure that you don't cast it such that the cold joint is anywhere near the maximum bending moment.
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Old April 19th, 2006, 02:07 AM   #8
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Quote:
Originally Posted by Rachmaninov
It depends. Just make sure that you don't cast it such that the cold joint is anywhere near the maximum bending moment.
then pressumably, the middle of the column is where the maximum bending moment is gonna occur.. mmm... dangerous stuff!
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Old April 19th, 2006, 07:43 AM   #9
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When architects decided to have tilted and curved columns or twisted structures then it isn't necessariy so.
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Old April 20th, 2006, 04:57 AM   #10
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Are there chemicals you can apply to the unfinished, open section of the column before casting the second load, in a way that would eliminate the 'cold joint' ?

Let's say your guy decided to pour concrete into the mold, and then he realized he doesn'have enough to fill it up. It's 60% full. Then, he would spray paint the open surface with that chemical, which would then seal it for 24 hours or so.
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Old April 26th, 2006, 05:48 PM   #11
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This site contains a little bit about 'end of day' joints. The bit on 'construction joints' down the bottom is relevant.

http://www.pavingexpert.com/concjnt1.htm

Doesnt really answer the first question though.
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Old April 29th, 2006, 06:22 PM   #12
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No problem i work with reinforced concrete. Just scabble the the top of previous pour before the next. Problems only occur when a fair face finish on the concrete is required.
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Old August 31st, 2007, 09:19 PM   #13
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no problem

you can stop your concrete anywhere only you need to make rough surface and wet the surface before adding next day concrete
also make sure you have a clean surface no loose materials
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Old September 6th, 2007, 03:38 PM   #14
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If the column only gets pressure on it is not a problem, but if a momentum appears in the column you are in big problem nothing could solve this problem except from taking it down and redoing it. Since by a momentum it wants to twist at the weakest point since it will shift to there, and this will be at where the joint is, since concrete is reinforced to control that it will breakup there for sure (if the force is big enough).
Now another problem that might appear is the looks, if its a bare column in sight this will not look so pretty which might be a problem to the architect.
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Old September 7th, 2007, 11:11 PM   #15
Gordon Freeman
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hey, im a concrete formworker in vancouver, i dont see there being a problem as long as the reinforcing steel is still protruding out of the half cast column to connect the next half of the pour, 2.7m is not very tall so casting that in half a pour is not usual, as long as there are dowels sticking out of the column, and perhaps spray a bonding agent on the surface of the concrete it should be ok, however i would consult the engineer of the project
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Old September 8th, 2007, 05:31 PM   #16
glitz_boy
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wow ... its wrong thing to do ...
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Old September 15th, 2007, 11:27 PM   #17
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Seismic Considerations

I doubt if this would be allowed in California, and it doesn't seem to make sense in any region with seismic activity, because the joint must resist shear.
What jurisdiction is this in?
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Old September 17th, 2007, 08:42 PM   #18
Ted Ward
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What is the shear force in the middle of a column?

There are so many differing opinions on this thread, right now i tend to believe Gordon Freeman - he appears to be one of the more informed contributors to this thread.
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Old September 18th, 2007, 06:09 PM   #19
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shear force is definitely not zero.

frankly speaking, it can be done, yes but would need to ensure the cold joints/construction joints which happens on the column to be similar to monolithically casted column.
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Old September 19th, 2007, 02:43 PM   #20
n4m3l355
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Quote:
Originally Posted by glitz_boy View Post
shear force is definitely not zero.

frankly speaking, it can be done, yes but would need to ensure the cold joints/construction joints which happens on the column to be similar to monolithically casted column.
If the shear force is not zero depending on how big it actually is. But non the less a columnīs shear strength depends on the reinforcements since concrete canīt handle it. But the concrete itself has as well a margin in it though not to big. But I seriously doubt such situation would be safe. You dont have ESA or something to calc it through to compare the situations?
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