STRENGTH OF HOOK

[allimuthug]

Hi ,

The shear from anchor bolt is transferred to stirrups and in some case the shear anchor bolt is transferred to the hook of stirrup,
It is either the strength of stirrup in tension or the hook embedded in concrete which ever is the minimum is the shear capacity of stirrup. But can any body explain how to calculate 135 degree and 90 degree hooLinkk capacity. please see the pic attached

 

[MacGruber22]

You have to develop the bars that are assisting in resisting the anchor blowout. So, that means you need hook development beyond the concrete failure plane. The requirements for developing hooks are in ACI 318-11 12.5. If you can't get the development you need, then you can't count on the stirrups to resist concrete blowout. I am not quite sure why you are counting on the stirrups to resist shear load.

 

[KootK]

This is still the state of the art I think OP: Link

My code allows 90 tie hooks but, in this situation, I'll usually detail 135 hooks for exactly the same reason that you're concerned about it. I've never seen an capacity evaluation method presented for hook capacity. Some folks will say that 90 degree hook capacity can be estimated by comparing the development lengths requires for straight bars and those required for hooked bars. I'm skeptical.

In general, 90 hooks seem to be considered sufficient if your cover concrete can be relied upon to remain in place. For application where the cover will be lost, such as plastic hinges in seismic applications, 135 hooks are the way to go.[tt][pre][/pre][/tt]

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.

 

[allimuthug]

HI i agree that cover has some role, But still if you consider in seismic the cover is lost , so how the 135 degree hook stays inside the concrete bonding , There should be a way to calculate the bond strength of 135 degree hook and the concrete .
Please everybody share there views

 

[KootK]

If your stirrups are #5 or smaller, the only requirement for full anchorage will be that the stirrups be hooked around vertical bars. In that case, your capacity will be the tension strength of the stirrups. In the unlikely event that you go with stirrups larger than #5, you would need to employ an anchorage method other than standard hooks.

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.

 

[CELinOttawa]

if you consider in seismic the cover is lost , so how the 135 degree hook stays inside the concrete bonding , There should be a way to calculate the bond strength of 135 degree hook and the concrete .

Actually in many cases the concrete inside the column remains in place through some number of cycles and is then itself lost... In the end you really only have the steel on steel. Japan and New Zealand now are developping special requirements for the tying of the rebar to ensure the stirrups remain in place and keep it all together. I'll try to dig up the relevant papers I have...

In the end this is not a hook capacity issue, but a stirrup remaining in place issue.

 

[CELinOttawa]

One more thing: Seismic hooks are not about developing the bar any more than you can develop laps in the main bars in seismic affected zones (plastic hinges, beam-column joints, etc.). Think about this when you next start thinking about the "strength" of a seismic hook...