simple slab

[prmmel]

I have a simple slab about 40x70 that will be 6" thick for general walking traffic.

There is a 38'x 20' section of the slab that will have some heavy equipment. There will be a 3500 gallon vertical tank (6'D) that weighs about 32,000# full of water.

Can someone please advise on some quick calcs for slab design. I talked it over with an engineer who recommended 8" slab. Basically in the 38'x20' area, I just figured on adding 6" to make it 12" there and also added a grid of #4 rebar of 12" centers covering this area. Seemed pretty darn strong to me, however the powers that be want to see more detail.

 

[GoldDredger]

Have you got a geotech report on the area in question, what are your subsoils? Any clays, needing lime treatment? Proposing any base below the concrete? What PSI concrete?

This water tank, is it supposed to sit atop the slab with a spread load, or will it be sitting on columns with a point load. Something that heavy might need footers to support the load.

In my part of Texas, most light vehicle traffic applications work with 6" lime treatment, 5-6" of 3,600 psi concrete, #3 or #4 18" OC. Heavy duty increase conc to 8".

Sidewalks typically 4" with a sand cushion, #3 24" OC.

I always let the geotech report make that call.

12" thick with #4 12" OC is a pretty beefy slab, I would guess that would easily handle traffic applications. The water tank would be my concern.

 

[Ron]

What you did is isolate the heavily loaded area and guaranteed cracking to occur at the interface. Further, you have no benefit of the remainder of the slab for overturning or bending.

Assuming good soil conditions as Gold Dredger pointed out that you need to check, shear in the slab will control the design for the static vertical load. Your shear will be less than 50 psi for a 6-inch thick slab, which is low.

I'm not sure if you are in a high wind area, but you need to check the wind load on the tank that is about 16 feet tall and check for overturning moment. This might increase your slab thickness and reinforcement.

 

[DWHA]

I would recommend a compacted aggregate base. Doing so will reduce the amount of concrete required.

 

[bimr]

You need a geotechnical report, the climate conditions, and a structural engineer. The tank foundation is usually isolated from the slab.