Headed reinforement bars in compression
Headed reinforement bars in compression
(OP)
Hello,
I am considering using headed reinforcement bars to anchor bars which are subject to compression. ACI 318, Clause 12.6.3 explicitly rules out use of headed bars in compression, with an explanation that there are no data available to confirm their effectiveness. I am curious to understand what are the reasons for the headed bars not benefiting from the heads, what mechanism would prevent the heads from reducing the required anchorage length.
I am considering using headed reinforcement bars to anchor bars which are subject to compression. ACI 318, Clause 12.6.3 explicitly rules out use of headed bars in compression, with an explanation that there are no data available to confirm their effectiveness. I am curious to understand what are the reasons for the headed bars not benefiting from the heads, what mechanism would prevent the heads from reducing the required anchorage length.






RE: Headed reinforement bars in compression
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: Headed reinforement bars in compression
RE: Headed reinforement bars in compression
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: Headed reinforement bars in compression
If you have a column subject to creep and you want to justify a head using appendix D, I'd say to at least design the cone against the full compression (max) yield strength of the bar.
RE: Headed reinforement bars in compression
It's not that you can't put a head on bars being developed in compression, it's just that you can't count on it. Similar to a standard hook in compression, you'd just need to embed the standard compression development length as if the head/hook wasn't there. If you're not concerned with ductility then would think that even if you did break out the end you'd still have the bond over the compression development length to transfer the force from the bar.
RE: Headed reinforement bars in compression
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: Headed reinforement bars in compression
Would need your compression development anyways, would tend to argue that even if you don't work for breakout at the end that you still have that bond from the compression development length to transfer the load. You'd pop the end and then immediately grab hold in bond.
RE: Headed reinforement bars in compression
Originally, I thought the concept recursive. You start with a big bar that can't be developed in compression, add a headed anchor to compensate, then tie it all back with some smaller bars that need to be developed in tension. All tolled, it would just be the compression development of the whole assembly so you'd be back to square one. I still think that but, having sketched it, my impression is now that it amounts to an effective increase of the bond stress perimeter. My sketch below is a hypothetical case where not enough footing depth was available to compression develop some column bars.
Practically speaking, I wouldn't expect there to be many cases where you'd have enough space to exercise this concept to any real advantage.
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: Headed reinforement bars in compression
If the bars are developed before it gets to the headed part why is there a problem? .... Like I said maybe I'm missing the point here?
RE: Headed reinforement bars in compression
RE: Headed reinforement bars in compression
I bet if we saw the exact constraints you might get a more focused answer (one that might help you instead of theoretical this and thats). We also might highlight other issues.
Weld a plate to the bar at the face if you are sure it's always in compression (reverse the head). Use this plate in bearing at the face of the joint, if there is joint...
RE: Headed reinforement bars in compression
1) I love the theoretical this and thats and believe that they are often the source of genuine understanding.
2) In my experience, development issues are usually just one symptom of a poorly proportioned joint. Exotic development solutions rarely resolve the underlying deficiency.
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.