Composite Slab Cracking under forklift load

[onsiteeng]

Good Day,
We have a client whose composite slab has been compromised by the wheel action of a forklift(8000lb loaded- approximate 3000lb on front small hard plastic wheels). The slab is 3" CFD with 1.5" cover over the deck. The deck spans 5ft onto I beams. There does not appear to be mesh in the slab but 1/2" bars appear to have been placed at 6" centres perpendicular to the flutes. The rebar was placed directly onto the top flute. A couple of things immediately come to mind 1) The thickness of the concrete cover does provide a I hour fire rating. 2) the concrete cover is insufficient around the reinforcing to make it effective. 3)The floor is very bouncy - vibration analysis required. 4)The forklift point load appears to be cracking the thin section of concrete and there appears to be a regular pattern of cracks running along the flutes. 5) It also appears to be cracking over the rebar where there is only around 1" cover. 6)We assume the only thing really supporting the slab is the 3" of concrete in the flutes which appears to be uncracked and the reinforcing bars which is spanning between.

Any suggestions on the best way to fix this problem. The obvious is remove the top layer of concrete and pour a 3.5" cover slab over the top. The issue I have would be the bond between old and new concrete. We would also place a mat of 3/8" rebar at 12" c/c in the new section of slab. of course we would have to check the steel framing for the increased dead load.

Thanks

 

[KootK]

I hate to say it but demo and replace might be a competitive alternative. Topping removal and composite dowel installation sounds like a ton of work.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Agree with KootK. That type slab is just not suitable for hard wheeled forklifts.

 

[JAE]

And with all that concentration of wheel loads, and probable overstress on the composite-deck slab system, you've probably got a lot of debonding between the deck and concrete (deck-concrete shear bond failure is the primary limit state for these decks). Therefore, the deck is starting to become a metal deck floor with a "loose" concrete topping doing very little structurally. At some point a forklift wheel load will punch through.

In addition - a heavy forklift will cause the supporting beams to deflect differentially which also adds to the bending and shear forces developed in the deck system.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[rlflower]

I agree with JAE and KootK. I would only add that industrial floors require a smooth finish with minimal cracking so that hard-wheeled apparatus such as forklifts and pallet jacks can function properly. Pallet jacks in particular cannot navigate well over even the slightest crack.

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

 

[onsiteeng]

Thanks All, They actually applied an epoxy coating to the traffic area to try and repair the floor which you can see in the photo(light grey). There was so much movement in this slab that it completely debonded and ripped up. I agree that possible complete slab replacement may be the only solution. There will be a very unhappy building owner.