Slab on Grade - Reinforcement Design and Placement

[Skay999]

Currently looking at designing a slab on grade for a small transformer (40 kips). The slab is currently 18 inches thick (controlled by frost depth) and I am trying to figure out the reinforcement design.

I looked into ACI 360R and they require a minimum of 0.5% to eliminate the need for sawcut joints. However, if my slab's longest dimension is less than the required joint spacing (8ft by 14ft slab), would I need to follow this 0.5% rule to limit crack widths? In this case, would the minimum temperature and shrinkage reinforcement refer back to ACI 318 (the 0.0018Ag)?

Also, if I have an overturning moment on the transformer due to wind/seismic, should the slab be designed for this concentrated moment? Would I just go back to ACI 318 to determine the flexural reinforcement needed?

Thinking of going with #6's at 12 inches c/c both ways, top and bottom.

 

[DaveAtkins]

You do not need to provide 0.5% reinforcement for such a small pad. That reinforcement ratio is for an infinitely large slab with no control joints.

You should design the pad for any loads imposed upon it. I typically create a 3D finite element model supported on springs.

 

[XR250]

40K ain't much for a slab of that size. I would think your proposed rebar would be fine.

 

[EngDM]

Also, if I have an overturning moment on the transformer due to wind/seismic, should the slab be designed for this concentrated moment? Would I just go back to ACI 318 to determine the flexural reinforcement needed?

I think I would rather add a line load of uplift and downward force (your moment but as a force couple) based on the feet of the transformer to get a more accurate representation of the load behaviour. But I agree with others, an 18" slab reinforced for shrinkage alone is probably enough steel.