Ultimate bond stress and direction of concreting relative to the reinforcing bar 1

I think you misinterpret the figure.

My understanding is that As in US and Canadian code, figure c) indicate that when there is a lot of concrete below, above rebar (top rebar) have reduce bonding

It is the same thing for angled rebar, as shown in figure a. I am not sure if it apply to vertical bar...

Hi Pico, thanks

I may be misinterpreting the code, but how would you interpret fig a)? The angle alpha actually cover upto 90d which is the case for vertical rebar.

As you noted fig b,c & d are all covered in one sentence on ACI318 as below, but what fig. a shows is confusing me. Does this mean good bond condition is achieved for retaining wall vertical bar?

where's Kootk?

ACI

Where horizontal reinforcement is placed such
that more than 300 mm of fresh concrete is cast
below the development length or splice, ψ t= 1.3. For other situations,
ψ t= 1.0.

I think those illustrations are just for flatwork, not vertical elements. Figure a) just says that good bond is achieved where bars are bent.

Thanks Hokie, but can we not assume good bond for vertical bars below the top 300mm (12in) concrete? one example could be column starters from deep mat foundation. Why do you think fig a) is not addressing vertical bars?

Reading the quote below i think we could assume good bond condition for any bar vertical or horizontal below the top 300mm of the concrete.

PD said:

During the placing and vibration of the concrete, some air and excess water tend to rise toward the top of the concrete, and some portion may be caught under the higher bars. In addition, there may be some settlement of the concrete below. As a result, the reinforcement does not bond as well to the concrete underneath, and increased development lengths will be needed

Click to expand...

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In what follows, keep in mind that my knowledge of European codes is cursory at best. I'll say, however, that the sections that you've posted here seem quite difficult to interpret. Perhaps there is other information in the commentary that makes this section more easily decipherable.

I agree with PicoStruc that this looks much like the "top bar" provisions in North America. And the quote that you've provided in your last post matches my understanding of the mechanisms involved. It has always been my undestanding that the top bar provisions do indeed apply to vertical concrete. The code section that you provided specifically mentioned slip formed pours which, in my experience, are associated with vetical concreting.

Here's how the top bar requirements are applied in my jurisdiction:

1) Flatwork: self explanatory.
2) Vertical steel in vertical elements: "good" condition.
3) Horizontal steel in vertical elements: "bad" condition.

The part that confuses me is detail "a" in your original post. Does it mean that any bar that is steeper than 45 degrees is effectively a vertical bar and is "good"? Or like Hokie speculates, are they alluding to anchorage hooks?

And if detail "a" is about hooks, does that mean that only the non-horizontal portion of the hook has favourable bond? This is further complicated by the fact that, unlike North American codes, European codes seem to allow development lengths to extend around corners.

Hopefully this thread catches the eyes of a few more Europeans.


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.

Hi Kootk... great post, as usual.

Thanks for the summary of top bar requirement as applied in your jurisdiction. For my part, i have never used this leeway for vertical bars. But now i think you are right in considering good condition for vertical bars. And i also think that fig a) above is an extension of the same idea effectively saying good bond condition can be achieved for bars steeper than 45d.

The Eurocode doesn't have a side commentary like ACI with detailed explanation of each clause, i think that makes it difficult to interpenetrate.