curing in high rise building

Kier,
From my experience, curing time does not affect the floor cycle time as long as the frame contractor has enough decking & back propping material available for the subsequent areas/floors. You cannot strike the back propping until the slab has gained sufficient strength. Also, on a tight programme, the backpropping timing is likely to dictate when the following trade can start.
You can start working on the slab the day after it has been poured.

Regards,
Larry

Kier,

u can start columns & walls activities after pouring the RC slab directly (eg. without having to wait for curing time), but u can’t start the next RC slab until the RC reaches its designed strength.

Regards.

Hi Karim,

How long does the concrete used in high rise usually attained strength 2? 3? days. Floor cycle can be done in 5 to 6 days right? You mean the floor cycle is dependent on the early attainment of concrete strenght?

Best Regard,
kier

kier,

Concrete gets its compressive strength in 28 days, u should refer the specs. of the project.

Hi Karim,

You mentioned "but u can’t start the next RC slab until the RC reaches its designed strength.


If the the floor cycle of a building is 6 days and it takes 3 days to complete the next slab form/steel concrete.
then concrete should reached its designed strength in 3 days in order to complete next slab.

Regds

eduardo

What i meant is that u can start the erection of steel rft. of the Rc columns of the 2nd slab directly after pouring the 1st slab, u can’t put shoring/decking (of the 2nd slab) directly over the 1st slab until the concrete (of the 1st slab) reaches its designed compressive strength.

Regards.

Hi Clive,

Thanks, you enlighten me.

Can you give a sample sequence of work of typical floor say 5 or 6 day cycle for the structural works(corewall,col, wall,slab).

Say day 1 casting of slab
day2 col/ wall steel works
day 3......
day 4....

Thanks,
kier

Hi Larry,

How much formwork/backpropping should be used for say 60 storey?

Regards,

Clive,

Your explanation and share of techniques based on your wide range of experiences are very well appreciated.I’m sure that such would help us a lot not only in the improvements of our technical know how, but also helps to open up the door for everybody to openly participate in the discussion without hesitation in fear of outright rejection of thoughts and ideas...Thank you and keep it up...

Kier,

I think you have enough information already with regards to the effect of curing period for your programme. 6-7 days cycle time period is very logical I think. Such that if you are looking at the 28 days curing period, you might need at least 3 sets of system table formworks for slabs and 2 sets for your vertical structures like columns, elevator shafts, shear walls, etc...However, I would like you to look at the availability of your tower crane and man lifts for your programme. A 60 storey building is a tall and huge one. You might need to conduct a detailed tower crane analysis in order to make sure that you have enough tower crane hours available to support your 6 day cycle time period in consideration to other activities like the MEPF and architectural works that are of equally important as far as tower crane and man lifts utilizations are concerned.

Hope it helps...

Regards,

Arman

kier

You can strike vertical shutters the day after is has been poured. Hence, 2 sets might be a little excessive.

Generally, 2/3 Design Strength will suffice to strike the decking. 2/3 Design Strength is usually reached within a week. Note that some systems allow you to strike decking panels earlier without disturbing the back-propping.

The amount of back-propping is not as straight forward and will required an engineers input. However, from my experience, 2-3 floors will be necessary.

If you are doing a costing exercise, please remember that decking panels need to be replaced as they wear.

Regards,
Larry