Retaining Wall - Flexural Reinforcement from Stem Into Footing 21

[CWEngineer]

I am trying to get some clarification regarding the flexural reinforcement of the stem of a retaining wall into the footing.

Does the flexural reinforcement in the stem of a wall, need to be developed into the toe, such as show in Figure 1 of the attached document. Or is providing a standard hook (12db), sufficient, such as that show on Figure 2 of the attached document? If providing a standard hook is sufficient, can the hook be turned towards the heel?

Thanks in advance

 

[KootK]

So the anchorage of B stops working once you add the A bars?

Nope. Rather, once the B bars are extended all the way, the A bars are no longer required. At that point, all that matters is the proper anchorage -- not lapping -- of the B bars.

Very much like this:

The intent seems to pretty clearly be extending the corner bars to the end of the toe. With that being the case, the additional bottom bars in the toe become extraneous and lapping requirements would be moot. The prime requirement would be successful anchorage beyond the face of the stem.

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.

 

[KootK]

Show me test results that show a standard hook going into the toe tears up the concrete and I'll happily concede it's an abominable detail.

Well golly then, let me just go fire up the retaining wall yielder that I keep in the back yard for just such happiness emergencies.

Some details don`t get much research attention because the engineering community deems them so unworthy as to not justify the effort. Some other conditions that you won`t find much testing data for:

1) Effectiveness of rebar installed in the project down the street.
2) Effectiveness of rebar installed via teleportation fifty years in the future.
3) Effectiveness of rebar that`s been replaced with black licorice.

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.

 

[KootK]

That last batch was for opening joints. As in the connection between the heel and the wall. It would be helped some by the presence of the toe of course.

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.

 

[Tomfh]

Well golly then, let me just go fire up the retaining wall yielder that I keep in the back yard for just such happiness emergencies.

I was not asking you to go test retaining walls. You said there is "all the research". I was simply asking for you to show the research that shows a hook turning into the toe is no damned good.

That last batch was for opening joints.

We are talking about cog going into the toe of a retaining wall, not opening joints with cogs turning outwards.

 

[KootK]

We are talking about cog going into the toe of a retaining wall, not opening joints with cogs turning outwards.

I would argue that detail A in my last batch comes pretty close to proving my point about the abominable detail. Based on what you`ve told me of your understanding, it goes like this:

If the bars coming into a moment joint are developed with standard hooks, then the joint should be adequate.

By that logic, detail A should work. After all, the only reason to care about the direction of the hook is if you`re like me and you mistakenly think that you need to transfer rebar tension around the corner and into the to bottom of the toe.

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.

 

[CELinOttawa]

Seriously Kootk? People can disagree with you without it being an all or nothing...

1. I think the orientation of the hook matters.
2. I believe it should be developed outside the stem.
3. I do not believe the joint behaviour is analogous to a beam column joint as the loading conditions are significantly different and the state of stress within the joint differ significantly.
4. I think the number of crappily detailed walls which never fail, nor even exceed SLS for thst matter, not to mention the CMU walls for which you disaprove of the detailling prove that the joint in question cannot be as easy to fail as you think. I believe it prooves that we do not need to get the load around the corner, but instead just need to ensure thst the area stressed by the bar development can handle the stress required.

Overall I suspect we're just going to have to agree to disagree, but I am hoping we can all still do that respectfully.

 

[Tomfh]

I would argue that detail A in my last batch comes pretty close to proving my point about the abominable detail.

It's a completely different situation. It's an opening joint with the cog going outwards. We are talking about retaining wall with the cog going into the toe.

Attacking the easy target that is detail (a) and declaring yourself victorious is pure strawman arguing.


You correct though that it shows we shouldnt automatically assume all embedded hooks can develop the bar. Some clearly cannot.

 

[KootK]

Seriously Kootk? People can disagree with you without it being an all or nothing...

What exactly are you objecting to here CEL? I wouldn't continue to debate with you if you weren't continuing to debate with me. It's kind of of a two way thing. And you'd led me to believe that you were enjoying the debate. That said, if you can't take the heat...

I believe that you are harboring an egregiously erroneous misunderstanding about the nature of these joints and I've very respectfully suggested that you reconsider you position. That's all. It's hypocrisy to jump into a nine month old thread, suggest that all my work is incorrect, and then complain when I defend my position.

Attacking the easy target that is detail (a) and declaring yourself victorious is pure strawman arguing.

I didn't attack anything. I presented an argument that I believe in as an attempt to persuade. And no where -- not one damn place -- did I claim to be victorious.

You correct though that it shows we shouldnt automatically assume all embedded hooks can develop the bar. Some clearly cannot.

All of the details can develop the bar. They fail because modes other than development kick in. That's the whole point. There's more to a joint than just development.




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.

 

[Ingenuity]

Turning into a mass-debate without a happy ending...

...wow, I got a lot of reading to catch up on this thread.

 

[KootK]

I've ponied up for the Linda Hall Docserve request on the Nilsson stuff. I'm going to hang back on my maniacal quest for world domination until I can report back with those results. Probably late next week. Rarrr!!!

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.

 

[Tomfh]

I didn't attack anything. I presented an argument that I believe in as an attempt to persuade. And no where -- not one damn place -- did I claim to be victorious.

You referred to those details as "crap" and you said it "proving your point"

All of the details can develop the bar.

No, they can't. The concrete ruptures first.

 

[Tomfh]

I've ponied up for the Linda Hall Docserve request on the Nilsson stuff.

Good job. Please post the article when you get it.

 

[CELinOttawa]

What do I object to? Posts like 30 Sep 16 00:18. It is exactly that type of non-collegial and argumentative post that had me so sick of Eng-Tips I didn’t log in for the better part of a year.

 

[TehMightyEngineer]

No, they can't. The concrete ruptures first.

Just because the concrete failed doesn't mean it wasn't developed. By my understanding you can "develop" a bar in a concrete cylinder barely large than the bar. Assuming tension only; at the location this bar terminates the concrete will fail well below the strength of the bar. Developed bar does not equal concrete sufficient to avoid failure; it's simply a bond strength check. Otherwise why would appendix D even exist?

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[Tomfh]

Just because the concrete failed doesn't mean it wasn't developed.

We're clearly all at cross purposes now as it makes no sense to me to say a bar is being developed despite the concrete failing well before the bar breaks. Concrete breaking at 50% of bar break load = bar not developed.

Concrete failing and the bar pulling out at 50% of the load at which the bar breaks is about as clear a case of a bar not being developed as I can imagine.

Developed bar does not equal concrete sufficient to avoid failure

that precisely what I understand bar development to be - sufficient enough concrete that the bar breaks first. Sufficient enough concrete that the ring tension stresses around the bar are sufficiently diluted to avoid concrete rupture. It's better in the toe as the clamping force fights against this. When it goes the other way, into the heel, there's already tension and cracking to start with and so the hooked bar pullout stresses overwhelm the concrete a lot easier. Hence the opening joint with outward hooks being so "crap".

By my understanding you can "develop" a bar in a concrete cylinder barely large than the bar.

you need sufficient hoop-stress/ring-tensile capacity in the concrete around the bar to resolve the outwards strutting-forces/shear from the bar. A very thin concrete sleeve around the bar has very limited ring tensile stress. This is why concrete cover is so critical to bar development. It governs the thickness of concrete in ring tension around the bar.

 

[TehMightyEngineer]

Concrete failing and the bar pulling out at 50% of the load at which the bar breaks is about as clear a case of a bar not being developed as I can imagine.

Yes, this is a lack of development if the bar is "pulling out". I'm talking about a failure of the concrete section:

Here I've provided the full development length of the bar and thus "developed" the strength of the bar; yet the concrete still failed. Perhaps I'm just using a different definition of "development length" as I think I get what you're saying? I just think "development length" is the wrong term for it.

Per ACI 318: "Development Length - length of embedded reinforcement...required to develop the design strength of reinforcement at a critical section."

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[CELinOttawa]

Wow - What exactly constituted a "Development Length" seems to vary by more than what non-contact means in reinforced concrete.

So fsr I have found (paraphrasing):

1. Sufficient length of embedded bar to transfer all stress to the surrounding concrete without failure.
2. Sufficient length of embedment to prevent pull out.
3. Sufficient length to ensure the bar yields rather than causing a concrete breakout cone.
4. The length of the bar required after a hook. (NOT kidding - uck!)
5. A length dependant on bar size and concrete strength required for continuity of concrete construction.
6. Sufficient lenght to ensure the bar does not pull out more than X under Y percent of ultimate strength loading.

That was a couple of minutes with google. I think the issue is between two fundamental schools of thought:

A. Ld means the bar transfers all stress to the surrounding concrete without a failure.
B. Ld means the bar performs to some lesser standard where concrete is allowed to fail, something more akin to a Capacity Design approach.

Could it be that most codes mean 'B', while most engineers think 'A'? If so, then I am about to learn something very fundamental about concrete detailling that I have misunderstood as not being the case for non-seismic regions...

 

[TehMightyEngineer]

So fsr I have found (paraphrasing):

1. Sufficient length of embedded bar to transfer all stress to the surrounding concrete without failure.
2. Sufficient length....

Yeah, this is what I think I going on here. To be clear I'm not disagreeing or agreeing with Tomfh regarding the wall details; I just wanted to make sure either I or he wasn't misunderstanding the term development length. From your search it does appear that some variations in what people mean with "development length" do indeed exist.

Could it be that most codes mean 'B', while most engineers think 'A'?

I believe so; as I said above, why else would ACI 318 appendix D even exist?

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[TehMightyEngineer]

Ok, 1+1, can we agree it equals 2?

Well, I think 1+1 = 3 for sufficiently large enough values of 1.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[Tomfh]

Wow - What exactly constituted a "Development Length" seems to vary by more than what non-contact means in reinforced concrete.

I understand it as the length of bar embedment beyond a cross-section required to yield the bar. If instead of yielding the bar is instead tearing out of the concrete (and resulting in joint efficiencies of 30-50%) then by definition it's not developed.