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Development length of nonstandard hooks

Development length of nonstandard hooks

Development length of nonstandard hooks

I need to develop a #5 epoxy coated rebar from a bridge parapet into an 8" slab. The bottom clearance is 1". Therefore, the hook is only embedded 7" into the slab. Can I achieve full development by extending the tail of the #5 bar?

RE: Development length of nonstandard hooks

How far are you willing to extend? I am not sure any code will allow you to combine hook and straight lengths, even though it is clear to me this would work... Maybe I'll learn something here as well.

I cannot see how anyone could argue you're wrong to develop the bar with a full development length after the hook.

RE: Development length of nonstandard hooks

You may end up crushing the concrete on the inside corner of the bend before the tail of the bar becomes effective.

RE: Development length of nonstandard hooks

CANPPRO is correct, but so long as this doesn't happen until ULS, in absense of pull out it is not a failure.

RE: Development length of nonstandard hooks

Good points. I am concerned about splitting failure in the plane of the hook inside the bend. If that occurs, the failure could progress along the hook extension (tail) and reduce any additional straight development length I have provided.

I would expect to see some research on this topic but cannot find any research mixing hooked and straight development length.


RE: Development length of nonstandard hooks

Your "Ultimate Limite State", ie: Where the only thing that matters is that no unsuspecting member of the public is harmed...

Sorry, it is a tenant of most engineering outside the USA. I take it you are in an American ASD or LRFD jurisdiction?

RE: Development length of nonstandard hooks

ULS = Ultimate limit state.

There are code provisions for calculating the capacity of hooked anchor bolts in tension...I would go that route and see if you can get the capacity you need with that. I'm not sure how effective the straight tail part of the rebar would be beyond a certain distance from the bend...my gut feeling is that the concrete would crush inside the bend before the straight section became effective. If you post a cross-section of the slab and parapet you may get more responses/suggestions.

RE: Development length of nonstandard hooks

ACI has consistently held that extending the tail does you no good.

RE: Development length of nonstandard hooks

AASHTO LRFD Bridge Design Spec.

JAE, does ACI spell that out explicitly in the code or commentary? Would you send me the reference please? I have looked through ACI 318-08 12.5 but have not seen that stated explicitly.

I am questioning the P502E bar in the Attachment.

RE: Development length of nonstandard hooks

JAE is correct, it was aq finding of 1960s research and presented in ACI's Committee 408 report in 1979. I'll try to lay my hand on a copy...

BUT, I would think that even if not developped as a hooked bar, having a full extension past this would enable you to fully develop the bar. Doesn't matter if the concrete crushes, if the result is that the bar continues to withdraw slowly without failing.

RE: Development length of nonstandard hooks

Normally, the straight length past the bend can be used if the bend radius is increased sufficiently to reduce the crushing stresses in the curve. BS8110 gives a method and I think Eurocode does also.

RE: Development length of nonstandard hooks

cwipf, do you need the full bar capacity?
It looks like a traffic barrier. You're looking for it to reach it's design limit once. After that, it probably needs to be repaired or replaced.

RE: Development length of nonstandard hooks

JedClampett, yes, full capacity. It is a traffic barrier that will need to be repaired or replaced after the design collision. We use a "yield line" analysis per AASHTO LRFD BDS A13.3.1.

RE: Development length of nonstandard hooks

I can't find an ACI direct reference (Committee 408 is the development group).

However, it was taught to me in school and I found a reference in my Wang & Salmon text book that stated:
"With 90 degree hooks particularly, designers have often assumed that satisfactory anchorage is obtained by adding length to the end of the bar in excess of 12 bar diameters required as part of the hook. This is an unsatisfactory practice."

RE: Development length of nonstandard hooks

JAE, thanks for looking.

RE: Development length of nonstandard hooks

If it's a #5 bar, provide a perpendicular nosing bar at the bend in the hook and the bar is developed automatically.

RE: Development length of nonstandard hooks

Lion6: Code clause? The bar within the hook has some added valaue, in the range of 20% if memory serves, but I have never heard of an "automatic full development" effect in any research or code.

RE: Development length of nonstandard hooks

It's a stirrup hook. It applies only to #3, #4, and #5 bars. Check out ACI 318-05

RE: Development length of nonstandard hooks

Ah,I see what you're doing there.... Only for a vehicular barrier this is a great principal longitudinal tension bar. I don't know if you can really apply a stirrup clause to this because of the action on the section.

RE: Development length of nonstandard hooks

Don't you do something similar in corbels, although it's typically a welded reinforcement of the same size.

RE: Development length of nonstandard hooks

I, and many other engineers I know, use this clause all the time. It's especially helpful for a PT where you need to develop a top bar within the thickness of a wall that can be 8" less cover.

A stirrup is a bar in tension so I see no difference from a mechanics perspective.

RE: Development length of nonstandard hooks

Lion06, I'm still not sure 12.13 would apply here. If it does, then why did ACI publish 12.10 & 12.12 dealing with development length? I would assume the continuous slab and longitudinal rebar within the bend would provide some resistance to splitting, but I do not know how to quantify that. Right now, we are assuming a partially developed hat bar. We assume the partial development is linearly proportional to the (actual Ldh)/(required Ldh) ratio.

rapt, I am not familiar with your code references. Do you have a minimum required radius to consider the additional extension for #5 bar?

slickdeals, I don't think I can design it as a corbel since the height of the parapet is large compared to the base of the parapet.

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