Floor slab loading and building columns

[fne]

We are beginning to get into buildings with large floor loads 500-1000 psf. When looking at this as a surcharge above footings when designing the foundations, what are people using as a reduction to the allowable soil bearing at a building column? The large surcharge loads may reduce our soil capacity by half. Are you using the full slab load or some portion thereof?

 

[fne]

No one has an opinion or was the question unclear?

 

[ahypek]

Not sure I follow.

If you're designing the footings and you have a slab on grade above then you would include the full service load pressures and the soil in between. I've never heard of any reductions in these cases.

 

[fne]

As a young engineer we never concerned ourselves with the floor load and ite affect on the foundations, but I must admit most of that work was commercial with lightly loaded floors. As noted in original post, we are now getting into heavily loaded floor slabs that might constitute half of the bearing capacity thus making footings larger. Wondered how others were dealing with this. Thanks for the response.

 

[jayrod12]

If it were me, I'd be accounting for a reduction in bearing capacity equal to the design loads. Unless the areas around the columns cannot see the expected floor design loading for whatever reason.

 

[Once20036]

If you have a geotechnical engineer who provided the allowable bearing value, I`d raise the question to him.
Intuitively, I think that the pressure on your floor slab would need to be accounted for in the design of the footing, possible by reducing the allowable bearing value by the expected surcharge.

 

[KootK]

I can't see any basis for using less than the full load applied to the SOG as reducing the available soil bearing capacity. It need not affect the footing bending and shear design but that's a separate matter.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.