Slab on grade for mechanical equipment

[ajc2014]

I have ACI360, but this seems to only address wheel and concentrated loading. Am I overlooking or not understanding how this can be applied to an unit that is bearing over a large area, like a air handling unit or large compressor? I'd like to be able to design slabs with reinforcement for crack width control, but the thickness design is based on an un-reinforced slab, per ACI360.

I would assume I would need to check punching shear, and bearing on the concrete and soil. Additionally investigate cracking due to negative bending of the slab around the unit, this could be fixed by reducing the "cover" around the unit. Anything else?

Thanks for any help.

 

[ajc2014]

I guess saying "negative bending" isn't correct, let's just say bending.

 

[jayrod12]

If you know what your bending is going to be why don't you just design the slab so thick that the concrete in tension never reaches fr?

 

[ajc2014]

That is definitely an option. I guess I was more looking for if I was overlooking this in ACI, and if not, then how have people adopted it to apply to this scenario. Or what checks to assure a good design.

 

[Splitrings]

The older PCA document, "Concrete Floors on Ground" has guidance on allowable uniform floor loads. You could have both positive and negative moments. The negative moments would be some distance away from the edge of the load.

 

[ajc2014]

Thanks, I think I figured out a way to do it. Altho I wish It was covered in ACI somewhere.

 

[Denial]

On my website (

http://rmniall.com)

there is a spreadsheet for calculating the bending moment at any location in an infinite slab supported on an elastic foundation.[ ] The loading applied can be of any size and shape.[ ] The spreadsheet only calculates the bending moments (not shearing forces).[ ] And it is purely an analysis, ie it knows nothing about any design rules.[ ] However at the very least it can be used for comparison purposes, to compare your unknown case with a known case.

This spreadsheet requires that the loading be well away from any slab edge, hence the word "infinite".[ ] The website also has a companion spreadsheet for the situation where the loading is close to the single straight edge of a "semi-infinite" slab.