Bending Retaining Wall Rebar Stubs
Bending Retaining Wall Rebar Stubs
(OP)
I am working on a job where they have to drive a some equipment over retaining wall footings. As such, the contractor wants to epoxy in the rebar later. I am not a big fan of epoxying in rebar for an 8 ft. retaining wall due to the likelihood that it won't get installed properly. Is it OK if he casts in the vertical rebar stubs (#5 sticking up 30") and then bends them down until the equipment passes and then bend them back up? He is going to pack 6" of dirt over the footing for the travel lane. Any other ideas?
Thanks
Thanks






RE: Bending Retaining Wall Rebar Stubs
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
thanks
RE: Bending Retaining Wall Rebar Stubs
If you still don't want to do that, I'd use bar couplers rather then bending them. I've specified Leton's and the Halfen ones linked above.
RE: Bending Retaining Wall Rebar Stubs
ACI allows field bending with restrictions.
RE: Bending Retaining Wall Rebar Stubs
If it was a retaining wall that would be ultimately supported at the top, I would ignore the creep since they were only in tension during construction.
RE: Bending Retaining Wall Rebar Stubs
1) Small-ish bars.
2) One time rebend.
3) Rebend done to suitable radius using suitable equipment.
4) Rebend done at a suitably warm temperature.
Here's some info from a source that tends to be quite contractor friendly: Link
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: Bending Retaining Wall Rebar Stubs
I imagine all the bending will occur with a long pipe.
@Kootk - what would be suitable equipment? - a conduit bender?
I would also be concerned about how they will get the bar straight on the rebend. Seems it will be tough to control where it bends.
I might go the Hilti certified installer route as a compromise.
Thanks
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
For cracked / seismic reductions, more than 24" of vertical embedment req'd just for #5 dowel. That's not to say that a shorter embed wouldn't pass a pull test.
RE: Bending Retaining Wall Rebar Stubs
I don't know much beyond what's contained in that link that I posted previously. Basically, not a pipe.
See the attached pages. It's a pretty tricky connection really.
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: Bending Retaining Wall Rebar Stubs
They use a special drill bit that does most of the hole cleanout that used to be conveniently "forgotten" by the installer. Gives me some peace of mind that I'm not relying on some random laborer (nothing against them) to remember a convoluted brush-blow-brush-whatever procedure to get full capacity on the anchor.
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
They say a bar can be bent and straightened with the approval of the EOR (wonderful...). There are some stipulations on bend diameter and what to do in the event of cracking (heating the bars). They also refer to a document, "Bending and Straightening of Grade 60 Reinforcing Bars" which I don't have. Maybe that text will have information on what type of tools are required and other industry practices, though it's 30 years old.
RE: Bending Retaining Wall Rebar Stubs
I thought I would just have to embed it deep enough to develop the design tension in the bar?
He is going to have equipment moving all over this thing as they are suspending a house 10 ft. above the footing so I don't think I can give him a path.
I might end up going the bar splice route as they seem to be readily available here and only require a 4" stub.
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
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: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
I find all of the eurocode stuff in that document pretty hard to follow myself. Ever since I found it, I've been dreading having to convert it to Canadian. Essentially, it says pretty much what you said previously: what is required is not just bar development but, rather, a true moment connection with the footing. Hilti's said it with strut and tie logic; you said it with common sense and a fundamental understanding of concrete detailing.
I think that they're just taking the development length from the end of the bar so as to produce the most advantageous strut and tie model (the one in which the effective lever arm is reduced the least). There's a blurb about flexural concrete cracking near the embed surface in there as well.
Yeah, there is. The reduced lever arm business is the most significant aspect in my estimation.
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: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
That is pretty complicated. Seems they could make some simple tables out of all those equations. Since I am not about to go thru all of those calculations at this time, the bar splice seems to be the best solution.
Thanks everyone!
RE: Bending Retaining Wall Rebar Stubs
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: Bending Retaining Wall Rebar Stubs
I guess I don't really understand that document. If I use hilti's tables to embed the rebar enough to develop the strength of the bar, does that not take into account the cone failure of the concrete? If so, then I have the tension side of my force couple.
RE: Bending Retaining Wall Rebar Stubs
The crux of the document is that the T/C lever arm is likely less than that associated with your stem flexural design. As such, you don't really know what tension to anchor for without considering the reduced lever arm. While the tension demand may be higher than expected, the individual bar anchorage is probably better than indicated in the tables. Part of the tension will react against the wall compression block.
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: Bending Retaining Wall Rebar Stubs
I take from it that the main difference between this and the standard pullout situation is that flexure cracks will form around the anchored bar from having tension/compression fields in such close proximity - this then reduces the length of bonded epoxy to bar (worse than hiltis tables). However, they then proceed with a strut/tie analysis (i.e. using the reinforcement in the footing to help with confinement, which I don't think the standard hiltis tables do), which would help significantly. But THEN, using the footing reinforcement to help with pullout results in higher tension forces in the footing top reo mat than there would be if you resolved the tension by taking the standard footing lever arm. I think.
Christ if you worked for Hilti you really would know absolutely everything about absolutely nothing.
RE: Bending Retaining Wall Rebar Stubs
1) a post-installed rebar connection that is carefully engineered and;
2) a CIP rebar connection that generally goes un-engineered.
Terminating the dowels with a bend makes for a better joint but not necessarily an adequate one. If we were checking the wall to footing connection rigorously for the cast in place dowel condition, I suspect that a lot of the same issues would crop up.
Just to be clear, I'm not doing this any better than anyone else at the moment. I'm not running strut and tie models on my wall to footing connections. However, I do:
1) Install the diagonal bars per the CRSI manual and;
2) Have the decency to feel guilty in the morning.
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: Bending Retaining Wall Rebar Stubs
If you do not have the confidence that the contractor can properly install epoxy-set rebar extensions, why would you have any confidence that he could properly straighten out a bent bar, given that is a trickier proposition than the other, and fraught with all sorts of mistakes (assuming it was properly bent to start with)? I think that the suggested option of using mechanical rebar couplers on short stubs makes more sense to me that any of the other, trickier suggestions. As for puncturing the tires: cover the travel lane with 8" of gravel, then put down a 1/2"-thick steel, temporary cover plate over that. That should allow for traffic flow, without sacrificing any expensive tires.
Hoping you come up with a good, workable scheme,
Dave
Thaidavid
RE: Bending Retaining Wall Rebar Stubs
I def. don't have much confidence in him.
I think i will go with the splice route.
He is also the mason, so hopefully he gets his bars in the right place.
They are also in a hurry, so waiting 7 days to drill in some anchors and then a few days for the RE500 to cure is not likely going to be acceptable for them.
RE: Bending Retaining Wall Rebar Stubs
Apparently, you need over 14" of embedment for a #5 bar in 4000 psi concrete.
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
Fortunately, I think the owner is going to go back to me to get a proper detail which will likely involve designing a buttressed wall.
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
I love having to compete with the incompetent in a space where there are rarely consequences. Last month I looked at a big RTU add on OWSJ. The contractor wanted to just put a post right under the RTU so as not to have to reinforce the joists. I explained that solution would do nothing to shelter all the neighbouring jousts from code mandated drift loads. We got the joist supplier to detail the reinforcing and everything. I was on site last week and, low and behold, there's the damn post, with no joist reinforcement. And stamped sketches for it from an alternate engineer. Now I've got an ethics problem to boot as the contractor is a good client in many respects.
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: Bending Retaining Wall Rebar Stubs
I think the owner wants me to stay so he told them to hold-off.
What are you going to do about your ethics problem?
@Buggar - never heard of doing that. I want to stay reasonably conventional on this job as there is alot of question on the competancy of the contractor. I already have my liability limitation in my contract and will over-design everything by about 100% to allow for his impending mistakes.
RE: Bending Retaining Wall Rebar Stubs
If your top diaphragm can take it, I would assume a bottom pin for calculation and keep your footing small and simple.
If you want a cantilever type wall then the connection at the top will need to be detailed for slip.
RE: Bending Retaining Wall Rebar Stubs
RE: Bending Retaining Wall Rebar Stubs
Oh well.