Rebar dowels driven into concrete

[charliealphabravo]

Hi all,

Has anyone ever heard of rebar dowels being installed by pounding them into a pre-drilled hole? Apparently this happens in precast tilt-up construction for the dowels at the base of the wall panels.

 

[TehMightyEngineer]

In non-structural cases (alignment, to hold formwork, etc.); yes. For anything structural or long-term; no, or at least not without grout or something similar.

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

https://www.facebook.com/AmericanConcrete/

 

[JAE]

There is no real structural load resisting effect of rebar pounded into pre-drilled holes. No pullout capacity and very little shear capacity.



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[KootK]

This is a common structural connection in precast hollowcore construction: Link. I don't know where/if research exists for the wall panel case.

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.

 

[JAE]

Basically it appears that the shear capacity is even less than pure shear on a 60 ksi - 1/2" diameter rod.
Not sure I'd depend on this for any seismic loading...just my view.



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[KootK]

Basically it appears that the shear capacity is even less than pure shear on a 60 ksi - 1/2" diameter rod.

That's as expected though isn't it? It's a rare anchorage situation where one is able to shear yield the steel anchor before all of the terrible app D stuff happens.

Not sure I'd depend on this for any seismic loading...just my view.

And I sympathize with that view. I wouldn't use the detail myself if I wasn't forced to my the behavior of my competitors. It gets worse too. I'm a precaster's engineer a day or two each week now so I see a lot of this detail by other EOR's. The spancrete testing was based on a very specific geometry with respect to edge distances etc. Most everybody applies the detail with much worse geometry. 2" edge distances, 0" edge distances... And my friends on the erection crews tell me that the driven dowels just end up spalling the plank apart in many cases and, thus, are even more worthless than they seem on paper. The next time that the New Madrid fault acts up, one of the first things that will happens is that 1/2 the basements in the Midwest will collapse inwards.

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.

 

[TehMightyEngineer]

Jeez, I didn't know you guys used anything like that for hollowcore slabs. I was about to comment that I expect they're cracking the panels or deforming the holes a bunch when I saw you confirmed that was what was happened. I wouldn't care what the competition is doing, I'd tell them to stop it. If they've drilled the hole then they've done 90% of the work anyway; put some cheap epoxy or non-shrink grout in the hole and make a proper anchor. This makes me glad that even the most fly-by-night operation I've seen up here has no problem with properly drilled and epoxied dowels.

I'm a precaster's engineer a day or two each week now so I see a lot of this detail by other EOR's.

Hah, you've been absorbed as well. [Precast engineers fist-bump]

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

https://www.facebook.com/AmericanConcrete/

 

[KootK]

Fist-bump indeed. That reminds me, I still owe you a sketch in my thread regarding zero tolerance pilasters supporting precast columns.

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.

 

[charliealphabravo]

Thanks all,

This doesn't happen to be in a seismic/high wind area so I can see how the practice persists for precast wall panels. Unfortunately, in the circumstance I am looking at the detail was adapted for the footing dowels in a landscape retaining wall.

 

[hokie66]

In pure shear, I think they would work fine, as the controlling factor is dowel bearing on the concrete. But I still think it sends the wrong message to site workers. They don't know the difference between shear and tension.

charliealphabravo, if they bars in flexure, they would be no good.

 

[Ron]

Agree with hokie66...true shear can be mobilized without regard to its bond with the concrete. Anything else...no.

 

[wallisathome]

Smooth dowels driven through predrilled holes in precast construction is a form of diaphragm attachment (i.e. to masonry or other precast or cast-in-place elements) that has been in use for decades. There is no grouting, no epoxy; just a friction-fit dowel hammered into a very snug hole. In my time in the field, I've seen very few instances of problems arising from use of this detail.

It's long been a standard detail in PCI's literature, and can still be found in precast supplier details, as well. Some (e.g. Spancrete, for instance) even publish test values for the shear than can be developed using this approach for lateral design.

It's not exactly the same as pounding in rebar, as the original query asks; but it is bars pounded into predrilled holes...

 

[msquared48]

Greased dowels in slabs keep the slabs aligned vertically as would rebar pounded into predrilled holes.

Mike McCann, PE, SE (WA)