Slab on grade-no reinforcing
Slab on grade-no reinforcing
(OP)
How many of you have used a slab on grade without any reinforcing at all? We did this on one project and I am not aware of any problems resulting from it. I have discussed doing this before with a concrete professor/engineer who thinks this is the best way to go (referring to slabs with warehouse type loads or less on decent soil). His thought is that the wwf that normally ends up on the bottom of the slab due to the highly ineffective pull-up method does more harm than good.
That is, use a better mix and tighter control joint spacing and leave out the reinforcing completely.
That is, use a better mix and tighter control joint spacing and leave out the reinforcing completely.





RE: Slab on grade-no reinforcing
Let us say the warehouse is later sold to another buyer that has more forklifts or stores heavier loads, with rebar you have better quality.
As engineers, we have to be cautious of designing the same way just because failure has not occured and also explain to clients that it is cheaper to do it better now than later have to pay investigation and fixing costs.
Nearly one third of our firms forensic studies involve problems with unreinorced slabs, 20 to 30 years after they constructed.
RE: Slab on grade-no reinforcing
WWF is normally specified to be placed in the top 1/3 (for crack control at surface from shrinkage) so even if it ended up where it is supposed to be, it would not help a whole lot for the case of loss of soil support.
Have the forensic investigations been with slabs with no reinforcing or were they slabs with fibers only? I understand fibers are supposed to be good for shrinkage crack control but are not to be relied on for structural means (though the manufacturers are likely to tell you differently).
RE: Slab on grade-no reinforcing
You bring good point about cost. Most developers of large warehouses insist on no reinforcement. For those clients, if the site is on sandy soils, obviously no frost and very deep Ground water, then I accept 7.5" slab without rebar vs 6" reinforced. However if they are on clayey soils then we give them thicker aggregate base plus 15 mil plus minimal reinforcemnt(#4 @ 24" o.c.) for example.
RE: Slab on grade-no reinforcing
I don't use WWF... too many instances of it being on the bottom and spacing too close to allow workmen from easily walking between the bars <G>.
Dik
RE: Slab on grade-no reinforcing
thread507-126594
thread507-144777
RE: Slab on grade-no reinforcing
I used to work for a major US industry and we always poured warehouse slabs "unreinforced" for forktruck traffic.
I prefer "polypropylene fibers" for commercial grade structures.
RE: Slab on grade-no reinforcing
In general, there is not a good reason to reinforce a soil-supported slab unless the loads are tremendous, which they usually are not. As an example for pavement loads, including fork lifts, they are typically analyzed as plain concrete slabs. The primary design parameter is the tensile stress at the bottom of the slab induced by loads on the top....(extreme fiber stress for the beam jockeys)
WWF vs. fiber has long been an argument, with both sides raising good points and lieing about the bad ones!
Proper control joint design, proper mix design for the application, proper placement, proper finishing, and proper curing will do more to achieve good performance from the slab than either the WWF or fiber, without regard to fiber type such as polypropylene or steel.
Fluctuating groundwater typically does not cause underslab erosion. That's typically a surface runoff issue and lack of slab edge protection.
RE: Slab on grade-no reinforcing
Dik
RE: Slab on grade-no reinforcing
RE: Slab on grade-no reinforcing
RE: Slab on grade-no reinforcing
Dik
RE: Slab on grade-no reinforcing
I have started a new thread since I am asking more questions:
"slab on grade for tile floor"
thread592-155870 (how do you link)
Thanks.
RE: Slab on grade-no reinforcing
Dik