Maximum capacity of 5" Slab on Grade in "Warehouse"

[structuralengr89]

I have a client who wants to change the use of an existing 5" slab on grade to be used as the floor for a "warehouse" that was previous office space.
I've asked for what type of forklift he intended on using and if there were racks to be used in the warehouse.

The plans state the SOG=
5" concrete sog with #4 @ 48 ew and 6x6-W1.4x1.4 wwf on a granular 4" fill
f'c = 3000 psi

Using ACI 360-06 COE curve A3.1
flexural strength = 411psi
I assumed a modulus of subgrade reaction of 100, but even if I say its 200 then the charts say Design Index I...4000# capacity...design axle load of 10000#
Does that sound right? Do you think I should have them core the slab to make sure it's 5" thick and then check the subsurface as well?

How do you know what the weight/reactions on a rack system will be?

Thanks!

 

[Ron]

First, I would definitely core the slab for thickness and run compressive strength tests on the cores.
Check the aggregate size...if smaller than No. 57 stone, you likely do not have a 400+ psi flexural strength.

Check the stress in the bottom of the slab. If greater than 50% of your flexural strength, you will need to consider fatique loading.

A 5" slab should handle a 4000 lb wheel load. Forklift wheels are relatively close together, so check for overlapping stresses. I would use elastic layer analysis to check these items.

As for the rack loads....shear at the rack baseplate footprint will usually control. Check the rack post loadings and see if the shear is critical. If so, you can typically increase the bearing plate size to accommodate.

 

[racookpe1978]

But won't his forklift wheel (tires) be running very close to the support points (frame supports) of his rack loads? Or are you assuming that the rack loads will be a simple 45 degree cone down into the concrete, and so only spread out 5 inches from the rack poles?

Still, if a forklift is running between two racks, then its left hand wheels will add into the rack loads on the left, and the right hand wheels will add into the rack loads on the right. If so, then will the 5" thick concrete spread out the total of rack + wheel (right side) and rack + wheel (left side) so the theoretical soil underneath the concrete on each side won't be overloaded?

 

[hokie66]

The joints are likely to be the weak link for fork lift loading.

 

[structuralengr89]

thanks for the input guys