Exterior Column Loads on Thickened Edge Slab Foundation 1

[MrEngineerUS]

My company frequently designs structures with a thickened edge slab supporting the exterior walls of the structure. Recently I was asked to size this thickened edge for a structure that had posts spaced 8-ft on center. I have yet to find a reference for this type of situation. Typically, the load is assumed to be a line load from a wall not a point load from a column or post. There are some references that give guidance for interior columns on slabs; however, they all explicitly state the procedure is for interior columns only.

Anyone out there have some guidance for concentrated loads on a thickened edge slab foundation?

Thanks!

 

[Ron]

At 8 feet on center, I would expect that the loads are not high. Check the thickened edge for shear.

 

[KootK]

I would tend to treat the thickened slab edge as a discrete strip footing which, I think, is similar to Ron's suggestion.

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.

 

[jayrod12]

Agreed with the two above. As an addition to KootK's comment I also treat it as a discrete footing that is only the two square dimensions (side and base of thickened edge), if the number comes back close then I look at accounting for a bit of the sloping portion.

 

[MrEngineerUS]

Figured I would update those who commented on my question. I did end up designing the footing as a discrete strip footing using the two "square" (i.e. straight, not sloped) dimensions. The building reviewer was not convinced so we ended up having to defend our design. After doing some more research I am convinced this is an adequate procedure for the simple design of thickened edge foundations with light (less than 30 kip) column or post loads. In addition to checking the shear the footing is treated as a continuous beam and designed to resist moment resulting from the bearing pressure reaction. From my research, when dealing with loads above 30kips (or even near 30kips for architecturally sensitive structures) it probably would be advisable to use a spring model for the soil in lieu of the typical rigid method of calculating the bearing pressure reaction. Cheers!