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Monolithic/Slab on Grade

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karimom

Structural
May 21, 2019
20
CA
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?
 
 https://files.engineering.com/getfile.aspx?folder=654bbf58-8663-4cac-b00f-e71e440f4c60&file=Frost-protected_shallow_foundation_detail.jpg
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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.
 
This is common and the minor eccentricity is ignored.
 
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?
 
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.
 
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