Moment in masonry stem at concrete shearwall footing 1

[Rev17]

Hey guys,

So basically I have a situation where I have 2 CMU shear walls, separated by a few feet(door in between) in the same line of action. I am checking their footing in a combined footing analysis(By Hand). So, since there is the separation in between the walls, there will be flexural stress at the stem/footing location there. Typically, when I have a concrete stem on top of a concrete footing I treat it as a monolithic T-beam and only have the footing(the flange of the t-beam)take the moment. My question is this: Does anyone have any ideas how I can justify this monolithic action for a CMU stem on top of a concrete footing so I don't have to heavily reinforce the stem to take the moment?(I am already reinforcing the bottom and top of the stem with 2 bars for load transfer). If anyone has a good reference they could point me to, that would be helpful.

Thanks in advance

 

[BAretired]

If you treat the stem wall and footing as a monolithic T-beam, how did you conclude that only the footing resists moment? In that case, the entire T-beam resists moment. That would be true whether the stem wall is concrete or CMU. If you want the footing to carry all of the moment, omit the stem wall under the door opening.

BA

 

[bowlingdanish]

I'm not sure of the load of wall, depth of footing, height of stem, or any of that guff, but I have never used a stem as monolithic with a footing for design purposes.

Either way if you have some restrained horizontal bars in the stem, unless the loads are enormous, I doubt you could prove on paper that the stem compression block will burst under service loads. In which case reinforce the footing for the full load and in my book she'll be right!

My book is pretty lenient though

 

[KootK]

1) if the footing works on it's own, I feel that you could tolerate some stem wall damage during an extreme event.

2) My experience had been that it's tough to make the footing work. Punching shear on one side of the opening and anchorage issues in the other.

3) Because of number two, I typically go the other way and do my best to get a stocky grade beam in there as the stem wall and let it deal with the local moment and shear concentration.

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.