Help with Retaining wall rebar detailing

[bsh117]

I need some help evaluating this retaining wall. I know that there is "extra" reinforcement shown in the detail, but I was hoping for some input on the detail.

Essentially, the only rebar that doing work is the left vertical bar in the wall and the bottom right horiz and upper left horiz in the footing.

My question is whether the left vertical bar is adequate as detailed. The embedment into the footing is greater than what is required by ACI 12.5 (development of standard hooks in tension). I'm also wondering what people think about the direction of the standard hook. My thoughts are that it doesn't matter which direction the bar is hooked as long as it's developed.

Thanks!

 

[a2mfk]

The soil side vertical bars in the wall are the tensile reinforcement. Depending on the thickness of the wall, sometimes you may show vertical bars on the front at a large spacing to hold the horizontal shrinkage reinforcement.

Traditionally, I would show the bar hooking away from the wall as shown in the footing detail. However, on this message board about a week ago someone sent in a reference indicating in tension situations you should do the opposite. See page 15 of the attached CRSI document. I forgot who posted this to thank them for it...

HTH,
Andrew Kester, PE
Florida

 

[bsh117]

Thanks a2mfk.

If I turn the reinforcement in, as shown in the CRSI sketch, then is the rebar detailing acceptable? I know other CRSI details showing the vertical, tensile wall rebar lapping with the foundation rebar. I feel that I don't need to lap the rebar since the vertical rebar has the required standard hook development. I would like to know what other engineers think.

Thanks again!!

 

[msquared48]

A few comments:

Being a 12" wall, you need two layers of steel, but the vertical steel on the face away from the soil only needs to be 50% of the other face. The horizontal steel is fine, but you could get away with #4@18 each face.

Also, the top steel of the toe can be deleted, allowing for the proper development length of the top heel steel, and the bottom steel of the heel can be deleted.

The 90 degree bend of the stem wall soil face steel dowel should be in the other direction to align with the toe bottom steel.

The thickness of the toe and heel only need to be 1" greater than the stem wall thickness for soil cover considerations. The heel and toe steel "d" should be based on this thickness.

Regarding clearances, for the soil face of the stem wall, 2" is required, but for the other face, only 1.5" is required.

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

 

[bsh117]

Mike,

Thanks for the input!

Do you feel that the detail would still be acceptable if the only thing that I changed is turning the soil face steel hook? Does it need to lap with the bottom reinforcement or is the standard hook acceptable.

Thanks!

 

[msquared48]

As you are tying the tension leg of the stem to the tension leg of the toe, I would use the full development length. In fact, if you wanted to, and I frequently do myself, just have the toe steel align with, and be the same size as, the stem wall tension steel. It's conservative, but simpler for the contractor to place.

It is OK otherwise - just could use less material and still work.

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

 

[chrislaope]

bsh117:

Just curious, why heel length is shorter than toe length in your design? should that usually heel length be longer than toe length in retaining wall design?

Thanks.

 

[bsh117]

The surcharge load over the soil was so large that I had to reduce the heel length.

 

[msquared48]

Gets into not overstressing the toe soil.

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

 

[miecz]

This wall looks like it will have problem resisting sliding, particularly if there is a surcharge load. Soil weight over the toe is commonly ignored in sliding resistance calculations.

 

[bsh117]

Good catch miecz,

I actually took out the key when I posted since it didn't directly effect my question.

Thanks for the comments guys!

 

[bsh117]

Mike,

I understand that the typical CRSI detail will show the vertical tensile wall steel hook and continue to become the foundation bottom tensile steel.

However, why can't a standard ACI hook as it was detailed work? If we break down the analysis into two parts, the wall and the foundation.

The wall portion; The vertical wall reinforcement has been sized to resist the required tensile stresses. It also has the required embedment into the foundation associated with a standard hook so that it can transfer the required stresses.

The foundation portion; If we use our free body diagram and place a moment on the foundation, we can design both the top and bottom steel in the heel and the toe.

I can't see why the vertical wall steel needs to be lapped with the foundation steel.

Again, thanks for all the comments!

 

[rscassar]

bsh117

I would provide U-bars closers to both the wall and slab reinforcement.

I think the left vertical bar is detailed adequately because the cog will be located in a compressive zone so it will be more beneficial for the anchorage of the vertical reinforcement.

The post that a2mfk is referring to (page 15 CRSI manual) is for seismic applications. Or that is what I gathered from reading through the post thread507-284040.

For your situation, as long as the reinforcement is tied to the footing reinforcement I don't think it would be a big issue. That's my opinion, but for the sake of arguing the theory and legality of things I would just provide a detail as per the CRSI manual.