curb thickened slab

[delagina]

does thickened slab at curb serve other purpose like prevent erosion?
I was told about erosion but just want to confirm how it does it.

say the loads are very minimal do i need to thicken slab on the curb?

 

[Archie264]

In an exterior situation like that I think it strengthens the slab at what would otherwise be its most vulnerable point.

For an interior slab of a heated space in a cold environment it also serves to get bottom of the slab below frost depth in the location where the soil will freeze. (The soil under the middle of the heated space will also be heated and therefore not be susceptible to frost-heave.)

 

[msquared48]

Agreed on both points.

Mike McCann
MMC Engineering

 

[hokie66]

If it is a pavement slab rather than a building slab, no thickening would be required, as with the curb there, you obviously don't expect traffic transverse to the edge. But as the slab is shown as 4", and the grade is lower than the normal slab soffit, there will have to be some thickening to make it work. And as you indicated, erosion must be considered.

A thickened edge actually promotes shrinkage cracking of the slab, as the thickened part shrinks slower and less.

 

[racookpe1978]

Well, yes, but with the curb there, you would see a "row" of car front wheel lined up right at the 4" curb, and so see a greater concentration of load right at the edge of the slab than otherwise be "averaged" out over the whole driveway.

But if the rebar is actually installed per plan, the whole thing would respond as a aunit, right? Doesn't look like the 4 inch curb would break off under load - as would happen if it were poured separately or without the rebar loops going up into the curb.

 

[charliealphabravo]

This type of footing (at least for residential applications) has it origins in prescriptive codes such as SSTD-10 and older. Of course it works under certain conditions but I don't think it can be analyzed from rigorous engineering principles (sort of like conventionally framed hip roofs with no interior posts).

The problems are these: The load is applied at or near the edge, the load is outside the kern, and the point of rotation for determining soil pressures is not clear. You basically get an automatic soil pressure failure at the outside edge of the footing. Closely related is that the effect of the slab is unclear: is the monolithic slab part of the footing? If so how much, and how do you calculate the moment of inertia for rotational stability? do you assume the slab cracks at the edge of the footing? What is the effect of any slab reinforcement? is a hinge created or a complete force decouple? Also the embedment of the footing is inadequate to provide any calculated resistance to shear failure modes.

The whole exercise will put your brain in a fog. You can save yourself the grief by not looking too closely. Just stay within the prescriptive jimbob limitations or use a standard stemwall strip footing.