Bending Retaining Wall Rebar Stubs 4

[XR250]

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

 

[SlideRuleEra]

IMHO, mechanical rebar splices on short rebar stubs (a few inches) would be better than bending, then rebending long rebar. Could be expensive. Here is one product, of many: Link

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Archie264]

Be careful bending rebar. I remember hearing that a highway department approved such based on tests they had conducted. However, on the project it caused problems because in practice it was done using a pipe “cheater” bar for leverage, which proved to cause a shorter bending radius than the laboratory conditions. The point is that the method it’s bent could affect performance even if it would be acceptable otherwise.

 

[XR250]

I imagine a cheater would end up being used. Maybe if he lays a 4x4 wood block down near the base, it would keep the radius big and also keep it from getting folded down flat by the vehicles?

thanks

 

[DETstru]

I would just use epoxied bars. You can (and really should) require them to be installed by manufacturer certified installers (Hilti certifies installers) and get them inspected during install.

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.

 

[BUGGAR]

Interesting - would retaining wall dowel bars to be epoxied in place be subject to the same permanent, creep-inducing load that overhead concrete panels induce in their epoxied anchors?
ACI allows field bending with restrictions.

 

[DETstru]

I almost always design for long term load in situations like this unless the anchors are 'just there' for the sake of attaching things. There is a standardized test for creep (along with temperature), which results in capacity reductions.

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.

 

[KootK]

I'd be fine with the bending given:

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.

 

[XR250]

This is a pretty small time operation. Probably have never heard of couplers and the stubs that get coupled to may still pop some tires.
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

 

[hokie66]

Using splicers such as the ones SRE referenced would work. Bending will also work, provided it is done correctly with the proper radius. Your rebar supplier should be able to provide you with a field bender. I would in no circumstance allow glued in starters for a cantilevered retaining wall.

 

[XR250]

Hilti has not certified installers in my area - aparently only in NY and PA

 

[ATSE]

I like the epoxy idea in principal, but in design practice, getting the embedment required per ACI 318 Appendix D and ESRs is very difficult.
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.

 

[KootK]

@Kootk - what would be suitable equipment? - a conduit bender?

I don't know much beyond what's contained in that link that I posted previously. Basically, not a pipe.

I might go the Hilti certified installer route as a compromise.

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.

 

[DETstru]

Not trying to advertise for Hilti but their latest adhesive product (Hilti HIT-HY 200) removes a lot of the issues that used to plague post installed anchor installation. I've been specifying it exclusively for most applications. The contractors like it as well because it's faster and easier than the old stuff.

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.

 

[Archie264]

I think the issue with adhesive anchors is not so much whether they function as advertised but, rather, that this is the wrong application for them. In a cantilever retaining wall the tension steel needs continuity with the tension steel in the base. An adhesive anchor will not achieve that.

 

[BUGGAR]

Or you could just backfill with soil cement and make the wall redundant.

 

[bookowski]

can you sidestep the entire problem and give him a width (6', 8', etc.) of no vertical bars that he can use and then design the wall to span horizontally with add'l vertical at each side of this zone. In that corridor you can drill/epoxy later or bend/rebend etc. but you'd have suspenders for the operation.

 

[DETstru]

Check out ACI 318-08, section 7.3 and commentary. They have some good notes on field bending.

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.

 

[XR250]

I think the issue with adhesive anchors is not so much whether they function as advertised but, rather, that this is the wrong application for them. In a cantilever retaining wall the tension steel needs continuity with the tension steel in the base. An adhesive anchor will not achieve that.

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.

 

[Archie264]

Well I'm no expert on anchors or anchorage. However, it was pointed out on these forums a while back (sorry, I can't find a link to it) that to achieve continuity the doweled-in bar has to be in close enough proximity to the bar it's to interact with that the forces transfer to each other through the concrete. And that's in just a straight-forward lapped bar situation, not relying on epoxy. To drill the holes for the epoxied-in bars close enough to the cast-in-place bars for the forces to transfer...well, it would make me nervous. There would be a lot of concrete disturbed, cracked, fractured, whatever, by that drill bit. It's a lot to hope to get right.