Horizontal Reinforcement in CMU Retaining Wall Stem

[kmart30]

Im designing a cantilevered retaining wall and I am not sure if I should specify any horizontal reinforcement in the stem. Stem will be 8" CMU with No. 6 bars at 32" O.C. With standard masonry wall construction you have your horizontal wires usually at every other course with a tie-beam or bond beam at the top of the wall. I dont expect any lateral loads from the ends of the retaining wall; all the calcs check out for sliding, overturning, bearing, and stresses in the stem from the lateral soil loads. I didn't see anything in the ACI specifically for this either but I could be missing something. Any thoughts?

 

[KootK]

I'd include some horizontal reinforcing. You've got temperature and shrinkage stresses in the wall. Additionally, it's not realistic to expect your earth pressures to be uniform along the wall so some horizontal bending stresse ps will develop.

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.

 

[kmart30]

Ok that is what I figured. Do you think a bond beam with a bar in it at the top of the retaining wall is overkill? Their plans say they are going to put a chain link fence above this wall but I have a feeling they are going to at least put a wooden or nice vinyl fence on top because this is for a community with larger nicer homes. I added a surcharge on the retained side to account for this new load and any moments this fence may apply to the wall/footing. Do you think a bond beam at the top of the wall will help with the moments applied from the new fence?

 

[hokie66]

What is the purpose of a "bond beam", when as a retaining wall, I assume the wall will be fully grouted? I would use smaller vertical bars at closer spacing, maybe #5-16, and say #4-16 horizontal. Using knockout blocks or H-blocks will facilitate full grouting. And don't forget waterproofing on the earth face if you want to prevent staining of the face.

 

[msquared48]

2#4 @ 24 horiz

Mike McCann, PE, SE (WA)

 

[hokie66]

Mike,
Why would you use two in one course? That will just make fully grouting the wall more difficult.

 

[dik]

I'd just use 9 ga dur-o-wal each second course... like a normal exterior masonry wall. You can use type S mortar due to exterior condition...

Dik

 

[kmart30]

No I i didn't design it to be fully grouted. Its going to be about 250 feet long so I figured that would be some good cost savings. Like I said above everything checks out from a calculation perspective but I didn't know if there was something else I was missing like shinkage, temps, industry standards, ect. that would require additional horizontal reinforcement.

 

[hokie66]

I have never understood the concept of partial grouting. Where I am, contractors would charge you more, with all the fiddling around that is involved.

 

[XR250]

Don't forget control joints.....

 

[msquared48]

Hokie: Done all the time here for bond beams in 8 inch CMU walls. Still have a net of 5" or so to play with for the grout too. Never had a problem.

And regarding fully grouted, I thought that being fully grouted was a requirement for any CMU below grade.

Mike McCann, PE, SE (WA)

 

[kmart30]

Thanks for the heads up Mike! I looked up the building code and they require full grouting for CMU retaining walls.

 

[hokie66]

Mike,
So if it is fully grouted, would you still group the bars, or distribute them?

 

[msquared48]

I would either distribute them horizontally, or bundle the bars in a vertical stack. I also specify avpeavgravel concrete infil.

Mike McCann, PE, SE (WA)