Stepped footings / Stemwall Design
Stepped footings / Stemwall Design
(OP)
When it comes to footings combined with stemwalls for most of my residential projects I am usually concerned with bearing loads (ie. sizing the footing for 1,500 psf or less) or if there is unbalanced fill I sometimes have to look at retaining wall designs. Up until now I have not given much thought to how the designer/contractor is actually building steps into their footings and stemwalls. Most of my homes, until recent, have been on level ground but as I've seen more jobs with sometimes very complex stepped footing configurations I've begun to give this some more thought.
Are there any specific details or resources which delve into this subject further, both from a construction standpoint and engineering?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
Are there any specific details or resources which delve into this subject further, both from a construction standpoint and engineering?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com





RE: Stepped footings / Stemwall Design
I've noticed I don't usually see a step more than 24" in height, that seems to be a good rule of thumb...
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
I will allow steps up to 4 feet, although 2 feet is common.
Mike McCann, PE, SE (WA)
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
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.
RE: Stepped footings / Stemwall Design
Alternative 2 probably does not comply with the IBC. It prohibits slopes on the bottom of footings exceeding 1V:10H.
RE: Stepped footings / Stemwall Design
I do have quite a few designers on their plans that will draw something like this (the dimensions and notes are for clarity and questions below):
The step is 24", they usually don't even show the footing at the haunch, I'm am wondering how this actually gets constructed in the field and what the appropriate detailing should be.
Per KootK's detail above, overlapping the footing would result in an large quantity of concrete at the haunch, or at least to my untrained eye.
I'm also wondering about the overlap of the stemwall above the footing.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
Would you mind sharing the clause so that I can check it out for myself? I'm not beholden to the IBC these days. The practical distinction strikes me as a bit wishful. It's not like you're getting the hard 90 degree angles shown in detail one unless you're dealing with a very stiff clay and an unusually talented excavator. Most stepped footing end up being sloped footings to some degree.
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.
RE: Stepped footings / Stemwall Design
Don't sweat this. Remember, most of the cost is in the formwork. A localized blob like we're talking about here is economically irrelevant.
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.
RE: Stepped footings / Stemwall Design
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
Explain the diagonal crack control reinforcing in the wall. Typically what I see for most residential stemwalls is 24" in height with one #4 bar in the top and some vertical #4 bars at 24" or 48" o/c. I only specify something above and beyond that when there is significant shear loads on the wall (ie. high aspect shear walls or portal frames that induce large bending moments into the stemwall/footing below).
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
1) Bring the thing up on screen.
2) Use the windows snipping tool to capture the image and save it someplace.
3) Use the button circled below to select the file for inclusion in your post.
#2 can be skipped but can lead to weird results with respect to display size etc.
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.
RE: Stepped footings / Stemwall Design
Thanks for that wannabeSE. I can empathize with your interpretation but, alas, I've been interpreting it differently.
Is my interpretation valid? Dunno. I've been able to get it past code reviewers for good long time. I cling fervently to my previously expressed opinion that it's not realistic to expect those hard 90's in detail one. Neither is it realistic to accomplish a footing "step" by way of incremental slopes not exceeding 10H:1V
I found the blurb below at the journal of light construction website which takes yet another tack. They don't count the portion of the soil in the "wedge" as bearing. I've not accounted for that but I can certainly see the logic in it.
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.
RE: Stepped footings / Stemwall Design
Our typical stepped footing detail is similar to your alternative 1. I did a quick search of the internet to find the reasoning behind IBC §1809.3 without much luck. The only thing I found is in FEMA 232 Homebuilders' Guide to Earthquake-Resistant Design and Construction (2006) where it states "To aid in providing sliding resistance, the bottom of the footing should be level." See oage 60 (pdf page 12) in https://c.ymcdn.com/sites/www.nibs.org/resource/re...
I think most engineers wouldn't upsize the footing to compensate for the little wedge of excavation at a steep angle. While I have nothing against JLC, the cranked bars at the wedge don't make much sense to me unless they are more fully developed to prevent cracking at the reentrant corner.
RE: Stepped footings / Stemwall Design
RE: Stepped footings / Stemwall Design
Thanks KootK
RE: Stepped footings / Stemwall Design
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Stepped footings / Stemwall Design
dik's detail gives the max. step rise to run as 0.70
JLC gives it as 0.75
I would probably opt for a more conservative 0.50 ratio. That way a double step in the stemwall would have a min. 48" overlap as shown above.
It is very interesting to me how the building practices tend to be very geographical. In certain areas (ie. Portland) for example they like to set the floor joists inside the stemwall rather than on top with a rim board, I find this very strange but I guess it works. This tends to make the crawl space rather tight with a standard 24" stemwall height and not easy to work in but I guess it is done for the overall cost savings on the structure.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com