Early loading of RCC slab
Early loading of RCC slab
(OP)
Can someone share with me the criteria or requirement for early loading of concrete slab while it is still under curing period. The early loading is primarily due to movement of crafts, formwork table for next level of slab, temporary storage of rebar, wooden planks etc. Appreciate your help. Thank you. Regards






RE: Early loading of RCC slab
It is also important to clarify what is your visualized scenario ... "moving of formwork" might mean entire inmediate removal or underlying formwork, and of course if the slabs get unsupported at an early age the scenario needs be carefully considered. The actual procedures need be ported to the necessary analyses to ensure that nor danger nor lack of serviceability will result from them.
RE: Early loading of RCC slab
RE: Early loading of RCC slab
In any case, mantaining "some" shoring is always good to the longterm defelection performance, and attainable through (only) some shoring systems (and not always compatible with what to be made in the to be by then initilly unshored floors.
Effect of progress of construction is analyzable, and I think to have seen some articles on it mainly in the context of composite columns and beams construction, since through the advance of the steel parts more floors can be loading in a number of shored or partially shored slabs. From the technical standpoint for RC it is not much a challenge (more of patience), it is a matter of making the model for each of the stages of the construction, be it by themselves or in the context of one program able to deal with staged construction. When as you have the design strength as early you might even use final concrete properties (if met by the schedule) to make such "construction time" analyses.
RE: Early loading of RCC slab
Dik
RE: Early loading of RCC slab
RE: Early loading of RCC slab
http://www.transportation.njit.edu/nctip/final_report/IMPLEMENTATION_OF_CONCRETE_MATURITY_METERS.htm#_Toc42508288
RE: Early loading of RCC slab
RE: Early loading of RCC slab
Dik
RE: Early loading of RCC slab
Dik
RE: Early loading of RCC slab
Deflection & shear strength is proportional to sqrt(f'c).
Formwork is typically removed at a compressive strength of 75% f'c.
For form removal and reshoring purposes, the key is determining the strength of concrete in the actual structure. ACI 318 & ACI 301 allow various test methods like field-cured cylinders, cast-in-place cylinders, penetration resistance, pullout strength, maturity factor etc. Although field-cured cylinders typically under estimate strength of in-place concrete, it is suggested for simplicity and reliability.
RE: Early loading of RCC slab
Dik
RE: Early loading of RCC slab
If you are achieving full concrete strength in 3 days, you obviously are not using a standard concrete mix. You would need to do tests on that mix to determine all concrete properties (creep, shrinkage, modulus etc) and do the deflection calculations based on those properties. You cannot assume that you have 28day properties just because strength is achieved.
RE: Early loading of RCC slab
RE: Early loading of RCC slab
RE: Early loading of RCC slab
Dik
RE: Early loading of RCC slab
I know this is a different topic, but how did early high temperature increase the deflections by that much? Yes, it will introduce restraint stresses when the temperature reduces, and can cause some ugly effects in columns due to excessive shortening of long lengths of slab/beams, but I would not expect its effect on deflection to be any where near 4 times (then 4 times acceptable does not mean 4 times expected I suppose, depending on the calculation method used to calculate the expected)!