Development length of 90-deg bend hooked bar in tension

[LearnerN]

For a 90-deg bend hooked bar in tension, what is the actual development length being measured? I think I've seen conflicting illustrations. Is it: (1) a distance along the bar from the critical section to the furthest distance parallel to the bar that the hook reaches, OR (2) the distance along the bar from the critical section, and then including the distance of the bar 90-deg up after it bends? So if you envision it as an "L"-shape: is the development length just the long leg of the "L", or is it the entire length of the "L" (assuming the critical section starts at the top of the capital "L")?

 

[TehMightyEngineer]

Figure R12.5 in ACI 318 has you covered.

It's (1) in your post.

Maine Professional and Structural Engineer.

http://www.fepc.us

 

[DaveAtkins]

Agreed.

It does not matter how long the bar is after the 90 degree bend--a longer extension does not gain you anything compared to just using a standard hook.

DaveAtkins

 

[rapt]

It is important that questions and responses specify the Design Code they are referring to.

While this may not matter in the ACI code, it does in the Australian, British and Eurocodes, none of which automatically assume that a standard hook provides 100% development. They require increased radius in the bend and a longer length pasty the bend to develop full strength.

 

[KootK]

For a routine, north american design, I agree, the extension of the hook beyond the minimum gets you nothing worth having. What follows is primarily just for theoretical interest.

In most cases, I suspect that hook extension beyond minimum will actually get you some extra capacity. Some of the non-US/CAN codes have provisions for bar development around bends. The trick to it is to pay attention the bend radii to ensure that the concrete within doesn't crush. The curved bar node STM model (Link)is one way to do this in compliance with North American codes.

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.