Sloped Footings

[nicholi]

I am in the process of designing a foundation for a carwash with strip footing for a client. The carwash pit is approximately 3.0m deep and the footing is 1.6 to be below frost. They have a standard detail that shows a sloped footing going from 1.6 m down to the footing of the pit. This is load bearing wall. Given the footing is on slope, how does the load get transferred to the soil since it is at an angle? Am I missing something?? It is late Friday afternoon and the clients standard says it works, but my logic says no. Thanks in advance for your support.

 

[Sean2]

If the base of your footing is sloping, then some load will still be transferred to the soil, but there will be a horizontal component also. The question is whether that horizontal component is properly transferred and is provided with sufficient resistance. However the horizontal resistance is provided, allowance must be made in the design for the vertical movement (settlement and rotation) of the foundation.

It is difficult to be sure I have understood the problem without a drawing, and difficult to explain my concerns without another drawing.

Is it possible that ALL of the load is transferred to the pit structure itself? In that case, design your sloping "footing" as a structural member, as though there is no support from the soil underneath that footing.

 

[jheidt2543]

Sloped footings look nice on a drawing, but they are difficult to construct in the field. An easier to justify design and one that is much easier to build is to use footing steps. What I usually see are vertical steps of the same thickness as the footing width. So, if the continuous footing is 2' wide the steps are in 2' verical increments, twice as long as the width. That is, starting at the higer elevation, drop 2', run 4', drop 2', run 4' etc.

Regarding the sloped footing, yes it has a horizontal component, but it is the vertical component I would worry about. Wouldn't the verical load accumulate "downhill" and possibley over load the soil at the bottom??