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Opee18 (Aerospace) (OP)
22 Jan 10 11:23
My company is looking at purchasing a forklift for our facility. I would like to find out the capabilities of our floor. We have approx 4 inch thick cement slab poured in 1961. What load can our floor handle? Ideally we would like to get a small profile stand up forklift capable of 3,500 lbf.  
dik (Structural)
22 Jan 10 12:47
Depends on frequency, channelisation, wheel size, spacing and hardness as well as subgrade... 4" thick slab does not appear to be any too thick for any industrial use...

cvg (Civil/Environmental)
22 Jan 10 14:08
don't forget steel reinforcement and concrete strength.
JAE (Structural)
22 Jan 10 18:07
Mostly subgrade.  That really affects the slabs performance.

And if you go ahead and buy the forklift, you probably won't know right away if there's a problem as the concrete will slowly fatigue and then cracks will suddently start appearing and propogating rather quickly.

dik (Structural)
23 Jan 10 8:17
and I think if we add 'wheel loading' we've just about covered everything... Dik
RonRoberts (Structural)
23 Jan 10 9:21
Here's a guide that will help. You really need soils, slab reinformcement, and wheel load information, but if you work through Chapter 5 it will get you a good idea of the size of forklift you can operate on the floor slab.

SirAl (Geotechnical)
23 Jan 10 20:32
The PCA (Portland Cement Association) has a good guideline for this kind of application.

For supplementary information, I commonly obtain the technical specs for the forklift being considered.  The specs will provide the vehicle wt, tipping load, wheel configuration, and tire specs.  You can then obtain the tire information from Michelin, Goodyear, etc. for the tire size/type specified to obtain pressure and contact radius. You should be able to find this data on line from the equipment and tire manufacturer's web sites.  You will need to know the type and condition of base and subgrade including modulus values
Ron (Structural)
23 Jan 10 22:21
JAE is right...subgrade has a great effect on the performance.

For a 3500 lb forklift, even a 4-inch thick slab should be can check by the references noted.  The two critical points will be the wheel closest to the forks.  Check the slab with these loads. It also makes a bit of a difference if your forklift has solid tires or pneumatic tires. The load radius on a solid tire is extremely small, whereas, the load radius on a pneumatic tire is reasonably large and helps the analysis.

In addition to the analytical approaches noted by others, you should consider an elastic layer analysis of the slab, checking the lateral tension at the bottom of the slab (you can do similar with a von Mises FEA stress analysis of a plate section, using concrete properties for the plate.  Don't forget that the subgrade mitigates the plate movement to a large degree so that should be figured into the model (you can use multiple point springs for the subgrade reaction).
concretemasonry (Structural)
23 Jan 10 23:15
The 3500# can be misleading as a forklift load since the fork lift has significant counterweights to the capacity. At times almost the entire load can be on the front axle when a load is lifted and the eccentric load can reduce the load on the rear.

If this apparently is in industrial application with frequent traffic and lifting is repeated patterns. Just a "seat of the pants" opinion is that 4" is not enough thickness.

What is the size of the current lift, if any?


Engineer and international traveler interested in construction techniques, problems and proper design.

hokie66 (Structural)
23 Jan 10 23:59
I agree with Dick.  These small forklifts have hard wheels, and typically tear up joints quite quickly.  If it is only a 4" slab, the joints are not likely capable of transferring substantial wheel loads.
dik (Structural)
24 Jan 10 9:30
ditto... but, I can offer an excellent repair detail for removing failed slab <G>.

jike (Structural)
9 Feb 10 10:39
When you say 3500#, is this the lift capacity of the truck, the empty weight of the truck or the loaded weight or the front axle weight?

We typically use 4" slabs for commercial grade buildings and 5" and greater for any industrial application with forktrucks.

I suspect that any 4" slab will fail miserably under any significant forktruck load. A pallet jack handtruck may work but needs to be checked.  

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