150 mm Mat Foundation With Top & Bottom Steel Bars ??

[TekEngr]

i am designing the mat foundation for light gauge steel structure as per my calculation 150 mm slab is enough with top and bottom layer (both direction) of steel bars according to the SAFE software, so my question is that can i provide top and bottom layer of steel in 150 mm mat foundation in accordance to the concrete cover recommendations??
but my boss is forcing me to provide the single layer of steel top or bottom , what will happened in practical if i provide single layer (but both direction) however my all loads are UDL (Uniform Distributed Loads) and steel load bearing walls will be connect to foundation through anchor bolts???
thanks in advance!!

 

[Teguci]

A 6" slab being used as a Mat Foundation? - Not allowed by ACI 318 - a minimum of 6" above reinforcement is required - no code commentary provided. As for 2-layers of rebar in a 6" slab, no way. The bottom layer is already 3" up (ie not bottom).

 

[tempeng]

As noted above, there isn't enough concrete to have T&B reinforcement. You'll just end up with a lot of steel in or around the middle. Lose the re-bar make it a thicker mass concrete slab, although you may still need some mesh in there for cracking.

 

[MotorCity]

I agree with the posts above, you need a thicker slab to hold 2 layers of rebar. Secondly, if you only provide a single layer in the top OR bottom, that will leave one face unreinforced when resisting stresses from the negative or positive moments in the slab.

 

[TekEngr]

thanks for your reply.
what is the minimum thickness of mat foundation code recommends for using 2 layers of steel (top and bottom)??

 

[SemiPE]

Hi Shang, min thickness of Foundation depends on code.

However in practice, I would assume a concrete cover of 75 for bottom bar and 50 for top bar, that adds into about 125 but since you must have a lever arm for the rebars to "work" you must say add another 100mm to cater for the bar diameter and lever arm. total thickness of say 225 or 250mm.

From what you are saying that 150 thick foundation will work for the loads that you have. I don't know the number but then may be you will no longer require tension bars for a 250 foundation (add one layer of shrinkage bar or design the mat as plain concrete)