Slab thickness for PEMB

[NFExp]

What is the minimum slab on grade thickness I should use for a PEMB. The architect said the building is going to be used for manufacturing.. The building dimensions are 150' x 80'. I was going to go with a 6" slab but I am looking for code guidance. Please let me know your thoughts.

 

[structSU10]

Depends on the loading and if it is going to be reinforced or unreinforced. If they have equipment to mount to the floor and not its own foundation, if they have fork trucks / other equipment that drives around, if they have storage racks, etc. will all affect the end design.

 

[phamENG]

Your foundation design will also factor into it. Will you have independent spread footings or will they be poured with the slab? If independent, how are you handling lateral forces and forces at the base of the rigid frames? If your slab is acting as a tie, you'll need to make sure you have room for the necessary reinforcing.

 

[AskTooMuch]

Depends on geotech report. I'm curious what you guya will prefer to us if this is on expansive clay or fill material.
I've seen PEMB on piles because geotech states bad fill material for several feet.

 

[WARose]

Depends on a lot of factors (as the others have said)......but in a manufacturing environment, I don't think I've used anything less than 6".

 

[NFExp]

Thanks for your responses. The Tennant of the building is unknown at this time. The slab will be formed on fill and the soil is mostly sand. I will be using a stem wall foundation with slab to take the lateral forces.

 

[chicopee]

Your statement about Manufacturing operations leaves a lot of questions answered. What type of manufacturing operations do you know about. In manufacturing, you'll have forktrucks, heavy equipment perhaps causing tremendous impact forces, overhead cranes lifting and lowering heavy loads on the manufacturing facility floors, storage tanks, obviously air compressors. So 6" thick concrete floors could be adequate or marginal.

 

[dik]

If the tenant (and they may change) is unknown, then I'd use an 8" slab and make it clear, to the owner, that this is for light/medium industrial usage and that use should be investigated by an engineer prior to occupancy. Let the owner know that there are caveats to the design. Use proper placing, curing and sawcutting and that forklift use should be 'soft wheeled' else joints may fail.

Dik

 

[Prof. Circuit]

It depends on many factors, such as the loading, the material, the tenant, and so on.

Member of IPC
Champion of PCBWay 2nd Design Contest
Enthusiastic of finding and clearing the failures on PCBs

 

[phamENG]

Use caution when tying it with the slab in a "vanilla box" type building. In one case I've seen, the EOR had the same intention but the contractor/owner got together during construction and decided to omit the slab. They got lucky - it was up north and the depth to the frost line gave the stem wall and footings enough "accidental" fixity to hold the building in place (fortunately it didn't see any storms or major snow falls in the interim). Your profile says you're in Florida - if this is project is near home, you won't have any such "accidental" help.

 

[JLNJ]

There is no cookbook to tell you what thickness slab to put in a building, but the procedure is simple:

You hire an engineer who knows what they are doing, they look at the different design inputs, and they make a decision on the slab thickness, strength, and everything else which needs to be specified.

 

[r13]

First to discuss with the architect on what type of manufacture he had in mind, light assembly, heavy warehouse...etc. The former usually do not possess big problem, design use a reasonably determined uniform load shall suffice; the latter will likely to see equipment load, storage racks, and moving load, that will produces concentrate load on the floor. For manufacturing environment, I prefer to use at least 8" thick slab (10"-12" for known operations are not rare) with two layers of reinforcement. Quite conservative, but provides some flexibility in attracting potential tenants. For your building size, I doubt the latter case will occur. Concentrate on selecting the design load, and provide good joint design. For foot traffic only, 6" slab might just work.

 

[Gerber_EIT]

Seems like the architect needs to get a better idea of what is going on in the building. My approach would be to discuss with them what types of equipment (if any) will be used in the building, and then calculate reinforcing and thickness based on equipment wheel loads. Maybe get the architect to pick a standard mid-size forklift and use that as basis of design. I typically use two different references for slab on grade design for uniform and equipment loads: PCA's Slab Thickness Design for Industrial Concrete Floors on Grade and ACI 360-Design of Slabs-on-Ground. There is also a pretty handy spreadsheet on AISC's steelTools website called GRDSLAB (located in the Floor/Diaphragm Systems category), which I use quite often to double check things. Hope that helps.

 

[phamENG]

OP indicated that the tenant isn't known at this time. I've run across this several times - and is why I referred to the "vanilla box" above. Owner knows they want to invest in the building, but can't secure a tenant until they have a building to offer. Usually, the slab is left out of the design in those cases so the tenant (when they find one) can determine layout for plumbing, etc. and the slab becomes part of their build out, rather than tearing up a brand new slab to do the build out.

It may be worthwhile to look at lowering your ties below slab level and putting your columns on pedestals. That way the new tenant can determine the floor requirements. Otherwise, you run the risk of limiting the owner's potential tenants to those who can operate on a thin slab. Conversely, you could end up making the owner pay for a thick, heavy industrial slab and the tenant ends up being a light commercial business that could have gotten by with a 4" slab.