Fork truck on mezzanine slab
Fork truck on mezzanine slab
(OP)
I'm researching the new construction of a mezzanine slab (100,000 sf) that will carry a fork truck in the range of 5-6K pounds total weight. Pallet weight is about 2000#.
The structure is steel with composite metal deck. There is a real concern to prevent slab cracking since fork truck wheels tend to eat at the cracks causing more spalling etc.
Another concern is that wheels can "crack" a rib so slab thickness is critical also.
My thought is to limit overall span deflection to L/540, use fibermesh concrete, and saw cut joints.
Does anyone have any guidance on this?
The structure is steel with composite metal deck. There is a real concern to prevent slab cracking since fork truck wheels tend to eat at the cracks causing more spalling etc.
Another concern is that wheels can "crack" a rib so slab thickness is critical also.
My thought is to limit overall span deflection to L/540, use fibermesh concrete, and saw cut joints.
Does anyone have any guidance on this?






RE: Fork truck on mezzanine slab
RE: Fork truck on mezzanine slab
The floor in the vicinity of the truck dock was a mess. Lots of cracks and spalling, very bouncy due to the loss of stiffness in the slab. The owners were fearful because directly below the dock was a movie theater.
What we discovered in our study was that the wheel loads, positioned on a single floor joist (I think they were 22" bar joists) would deflect the joist to a degree that would cause bending in the slab relative to the adjacent joists and the stress was higher than the cracking stress.
Once the cracks started, others propogated out from there and the constant loading and unloading began to totally deteriorate the concrete to the point that it was individual chunks of concrete sitting on the metal deck.
The joists only had horizontal bridging and were fairly low-Ix for the spans.
I would definitely study your floor framing and ensure that cracking is minimzed as much as possible. Look especially at joist-to-joist relative deflections with specific wheel load placements.
We've used fiber (steel plus poly) reinforcing in slabs to help but these won't prohibit stress cracking, just tend to keep them smaller.
RE: Fork truck on mezzanine slab
Second of all, fibermesh is used for shrinkage but not to carry structural bending moments created by the wheel loads.
You will have to calculate both positive and negative bending moments created by the wheel loads and reinforce the slab with sufficient reinforcing steel. Make sure that you have not only the proper main steel (both positive and negative) but also adequate distribution steel (bottom at right angles to the main steel) to allow the concentrated loads to spread out over an effective slab width. Make sure you calculate the overlapping bending moment created by the adjacent wheel loads. Since you will have two layers of steel, you might want to consider a 6" minimum slab thickness.
Since the size of the mezzanine is sufficient to have two or more trucks operating at the same time, you might want to consider two loaded trucks passing in an aisle.
If you design the reinforcing properly for all the various stress conditions created by the wheel loads, you should minimize any cracking. The size of the mezzanine might require some expansion joints.
Good Luck!
RE: Fork truck on mezzanine slab
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Fork truck on mezzanine slab
2) In the publication "Designing with Vulcraft Steel Joists, Joist Girders, and Steel Deck" by James Fisher et al., they say "The use of composite deck is not recommended where forklifts are used unless the use is an infrequent occurrence".
RE: Fork truck on mezzanine slab
Why would you use fibers to limit "stress" cracking instead of whatever rebar size may be required?
GregLocock's suggestion is a good one. I would also use an impact factor.
Often owners will want to increase the capacity of trucks over the years. This might be something that you may want to discuss with the owner.
RE: Fork truck on mezzanine slab
RE: Fork truck on mezzanine slab
The problem with this job is that the steel design is being controlled by a pre-engineered building manufacturer, I get the concrete design. The adjacent warehouse mezzanine had joists 3 foot on center ( I didn't design this one) and the slab cracked over virtually every joist with a great deal of spalling. Trucks were only hand trucks and limited to one pallet or 125 psf.
So this thread will help my confrontation with the steel fab. Can you image that they ever limited deflection to L/1000.
RE: Fork truck on mezzanine slab
The theory being to force cracks to the location of a uniform joint you can fill with epoxy.
I have never done this since the reinforcing (and deck) ties everything together.
RE: Fork truck on mezzanine slab
Regards,
-Mike
RE: Fork truck on mezzanine slab
When you hear on crack that sounds like a cannon going off, that could be a sign that perhaps some rebar was overlooked, either in design or construction.
I don't like the idea of using joists for these floors. I prefer rolled beams.
RE: Fork truck on mezzanine slab
Dik
RE: Fork truck on mezzanine slab
So, as Greg says, assume "the entire weight of the truck plus the full lift capacity exerted on just the front wheels."
Thanks,
-Mike
RE: Fork truck on mezzanine slab
RE: Fork truck on mezzanine slab
You must design the slab for two actions....the macrostructural to hold the forklift and its load in a concentrated fashion and as GregLocock stated to consider the load distribution, AND, the stresses imparted to the concrete from the wheel loads. They present different problems and you can't pick one or the other....you have to design for both. For instance, the wheel loads might initially dictate the concrete thickness, while the structural loading will dictate the overall deflection and bending resistance.......however, the overall deflection under the macroloading must be considered with the lateral strains and lateral stress at the bottom of the slab caused by the wheel loads. Compound all that by the formed deck interaction and you actually have an engineering problem!
RE: Fork truck on mezzanine slab
RE: Fork truck on mezzanine slab
Dik
RE: Fork truck on mezzanine slab
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No cracking in that slab.
rmw
PS: Sorry, I just couldn't resist. The thread was quite well developed by now.