Precast topping reinforcement
Precast topping reinforcement
(OP)
Have had lots of complaints lately about specifying a minimal welded wire fabric for a 2" hollow core slab topping with contractors preferring no reinf. or fiber mesh. The hollow core manufacturers catalog states that the topping reinforcement is to comply with ACI318 as determined by the EOR.
The topping is primarily for the composite slab action and a decent finished floor surface. It’s not really needed for the diaphragm and is in a non-seismic region so it could be considered plain (unreinforced) concrete. Anyone else putting reinforcment in toppings?
The topping is primarily for the composite slab action and a decent finished floor surface. It’s not really needed for the diaphragm and is in a non-seismic region so it could be considered plain (unreinforced) concrete. Anyone else putting reinforcment in toppings?






RE: Precast topping reinforcement
RE: Precast topping reinforcement
RE: Precast topping reinforcement
RE: Precast topping reinforcement
RE: Precast topping reinforcement
I don't like the WWF due to the high degree of difficulty for placement. Maybe fibers would help reduce the plastic shrinkage but I'm not sure they're worth the effort either.
RE: Precast topping reinforcement
The same way that S-O-G's crack is the same way the topping could crack. A SOG is just as bonded to the stone beneath it, but because of the drag on that stone, it cracks. If it wasn't bonded at all, then it wouldn't crack (like pre-cast).
The restraining forces not allowing it to shrink is what causes the cracking
RE: Precast topping reinforcement
RE: Precast topping reinforcement
RE: Precast topping reinforcement
As far as it being for composite action, when you consider the camber in the slab how much topping do you really have? Personally I feel that composite topping is a bad idea, there are too many variables - the biggest one being the topping thickness.
I highly recommend using at least a 3" topping. I used to get complaints constantly about "too much camber in the plank". I have not had one complaint since going to 3" topping.
RE: Precast topping reinforcement
RE: Precast topping reinforcement
RE: Precast topping reinforcement
RE: Precast topping reinforcement
Read the PDF pages 33-39 sections 2.4 & 2.5
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I understand the theory with composite topping but when you factor in the tolerance for levelness of the bearing surface, camber in the plank and differential camber in the plank, which all effect the thickness of the topping, I'm quite sure you don't get what you think. You can spec 2" uniform thickness but the floor may not end up level.
Also, proper surface preparation is extremely important. The precast mfr. in my area (Kerkstra) no longer has load tables for plank with composite topping for theses reasons.
RE: Precast topping reinforcement
One thing I learned the hard way is not to expect the camber listed in the PCI Manual. I have 12'-5" clear-spanning 6" planks with a 1" camber!
I consider the planks without the topping slab as a diaphragm as long as the key way between planks is not cracked.
Eric McDonald, PE
McDonald Structural Engineering, PLLC
RE: Precast topping reinforcement
The only way to endure it acts as a diaphragm is to put in some WWF.
CTSeng,
builders are always complaining, just do what you think is right. What is the point of saving $10/sqft on a $100+/sqft floor if it is only half as good?
It will be you that is sued if they dont like the cracks, not the builder.
RE: Precast topping reinforcement
RE: Precast topping reinforcement
I would question the effectiveness of those keys ways if the topping concrete cracks due to shrinkage.
RE: Precast topping reinforcement
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