Monolithic/Slab on Grade

[karimom]

I am working on a project where the geotechnical report specified that a monolithic slab is a required with thickened edge (see attached photo).

The line load will be on the exterior of the footing and will apply some eccentricity to it. I would assume from common sense that it would not overturn due to the shape of the footing (i.e. the whole slab is tied together). I just want to be able to back myself up with calculations on this one. I can't find a similar example in any text book.

The soils are good (3000 psf bearing capacity) and we're applying around 2kip/ft (factored). I think that with a 18" deep by 18" wide footing it should be good from rough bearing checks and experience but the traditional B/6 check for a strip footing doesnt seem to apply to this.

Can any one advise or point me in the direction of an example?

 

[Lomarandil]

You can think of it like a strap/combined footing -- where the monolithic slab and its reinforcing are able to provide some restoring moment that offsets the overturning moment caused by the eccentricity of load.

I don't have a favorite example for a strap footing calculation.. maybe somebody will be able to point you in that direction.

----
just call me Lo.

 

[Ron]

This is common and the minor eccentricity is ignored.

 

[karimom]

Ok - so even with eccentricity of ~6" I can just check the footing for bearing pressures assuming uniform distribution? How is it handled in the case of a point load? Same case over a 1m strip?

 

[StrucDesignPE]

I did a similar design for a IRC frost-protected shallow footing last year. I determined the resultant of the wall load and the footing self-weight and checked to see if it fell inside the kern of the footing. Mine did and then I felt okay with checking for a uniform bearing pressure. A similar procedure is described in Newman's book for designing metal building foundations.