step footings

[rittz]

In the case where the grade slopes I spec step footings to create a situation where the footings are always the required min distace below grade at all points. The steps by code are a max 2' rise and a min 2'run. A contractor wants to set the footings on a slope to match the slope of the grade outside so that the footings are founded the required distance below grade at all points . Does anyone have a problem with that.

 

[MiketheEngineer]

Footing are supposed to be flat..IMHO

 

[msquared48]

Unless the footings are flat, there is a downward component of sliding that has to be resisted... somehow.

This is not a good scenario and I would never do it. Flat footings are good.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

I meant lateral component. Sorry.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

I hope you meant that the bottom of the step wanted a steeper slope and you're not providing a sloped footing.

 

[BAretired]

I would normally detail stepped footings, but see nothing wrong with sloped footings provided there is enough resistance to sliding.

Unless the top of wall is sloped parallel to the grade, sloped footings result in variable length of bars which is a bit of a nuisance but doable.

BA

 

[concretemasonry]

There is a big difference between "level" and "flat".

Strip footings with proper limits on the rise and run of the components to meet the slope requirements have been sucessfully used for centuries.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[msquared48]

Never seen a flat roof that was not "supposed" to be level Dick. (ponding tends to get in the way here)

Nevertheless, sorry for any confusion.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[rscassar]

The maximum I allow for sloped footings is 10H:1V. Anything steeper than this needs to be stepped.

 

[csd72]

otherwise hoe do you lay the first course of bricks on a sloping footing without using a very deep mortar bed.

 

[concretemasonry]

Flatness is determined by the allowable deviation from the desired plane of the surface. A flat surface can be sloped.

Level (usually assumes flatness) is a surface that does not slope, or in common terns, does not drain.

Either flat or level footings can be acceptable, depending in what the materials above it are. A flat footing is not very good for setting precast or long masonry walls on because of the variations in elevation depending on the location and can require large amounts of leveling materials to maintain truly vertical elements above. You have no idea of the elevation at a point unless you either have an elevation shot or want to rely in a measurement from a known point to use in a calculation based on the slope.

Some types of construction may require a specified distance below grade (as in frost protection) and the footings can be built cheaply, but the walls or elements above the footing can be costly to build and may not perform as expected.

Step footings with level tops and even reasonable flatness are proven and can be the best approach for most structures.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.