Standard Hook Development

[dcarr82775]

ACI318 allows for a reduction in the 'ldh' with a standard hook for the ratio "As req'd/As provided". I have a situation where I have a standard hooked bar, but the length of the hook is only about 11 bar diameters instead of 12 bar diameters. It would take too long to explain how this happened but the concrete is already cast.

ACI doesn't address this condition, but I wanted to see if others thought a similar reduction ratio (91%=11/12) on the bar strength is a reasonable approach? If the hook was drastically shorter I don't think I would look at this approach but for something this close I do not think it is too far out in left field.

 

[ishvaaag]

Since nobody is going to be wanting to hear of anything outside the code, to salvage huge amounts of such short anchors you may resource to test a number of them in pullout.

You can also resource to the literature of the test, and evaluation of every kind of meaningful parameters to see if in their light your faulty set is exected to work well. I think someone gave a reference about such numbers for this kind of bond-pullout test this same year in this forum, from eurocode or something so.

11/12 is truly a small difference in structural terms so as soon as one gets any positive appraisal of the salvage, most would be tempted to accept the construction; the meaningful for the case are those with authority to decide on the project and its acceptance for actual use, since no others will be warranting the safety of people and goods.

 

[DWHA]

I think that it can be justified. Is the location of the hook bars the location of max stress? And what is the actual stress vs allowable stress at this location?

Also realize that the hooks lengths laid out in the code are for a condition that there is no reinforcing within or adjacent to the hook. If there is reinforcing within or adjacent to the hook, addition development capacity exists. How much?? that is probably not known, but can help you justify an existing condition.

 

[TXStructural]

It sounds like you are not talking about ldh, but rather the extension of the end of the hook (which is generally described as 12 db beyond the center of the radius of the hook bend.)

The measured dimension is from the cut end of the hook extension to the outside of the main length of bar. This is 12 db extension + bend radius + 1 db, or roughly 16 db. ACI 117-06, section 2.1, shows an allowable tolerance of one inch (1") on this dimension (as well as overall bar length.) I do not have my copy of 117-10 handy right now, but do not expect that this has changed.

For most bar sizes, the condition you are describing is not a deviation from code provisions, since ACI 117 tolerances are considered in the ACI 318 requirements.

It does concern me a little that the bars will not be developed where they are needed, based on the misunderstanding about ldh.

 

[dcarr82775]

TX,

I may not have been clear enough, but there is not a problem with the length of ldh, that is fine. It was only with the 12d value on the hook itself.

 

[TXStructural]

The 1" tolerance makes hook extension of 11 db (plus bend radius) acceptable for bar sizes up to #8. Hope that helps.

 

[ztengguy]

how close on development length are you if you ignore the hook, and just calculate the Ld?