Hooks at drilled pier shaft reinforcement ends

[AValdes]

Hello,

Is there any good reason to use 90° hooks at longitudinal reinforcement ends for drilled pier shafts (inwards) either at the bottom or top?

Thanks!

 

[RPMG]

They can be used at the top to reinforce for anchor tearout. Otherwise, no.

 

[jayrod12]

That depends on what loads you are transferring. And what is sitting on the pier. If it's a structural slab, then I would hook them just because a straight embedment is not enough to do anything. If it's a tall beam or pilaster or column, then straight embedment may be enough.

 

[r13]

Similar to jayrod12 noted above, the requirement exists only if the bars need to be developed into structure above that does not have adequate depth for such development. Otherwise, no.

 

[STrctPono]

Hooks at bottom - Not necessary at all
Hooks/Heads at top - Useful if embedded into relatively short cap and need to develop strength for uplift loads.

 

[RPMG]

Is that the question, whether or not to hook dowels? I think the question is asking whether the verts should be bent in at the top and bottom of the drilled pier, itself.

 

[jdonville]

Don't (shouldn't) need it for strength at the bottom. I prefer 180 hooks at the top (if there is a need to transfer loads there) so that the installation rig can drive over them if need be.

 

[AValdes]

The pile works as a foundation for a metal column (the building is a warehouse). As you can see, 90° hooks are required on top and bottom. I am sure that on the bottom are just pointless.
My understanding of Chapter 17 of 318 suggests me that those hooks on top will not help reinforcing a breakout cone. (Of course I might be wrong).

As you guys are watching this thread, any comments on the ties @ 4” for the anchor length?

Thank you very much everyone!

 

[KootK]

1) There is no code requirement to hook the bars at the top that I know of.

2) Whether or not hooking the bars is necessary for anchorage depends on the anchorage design approach that you choose to use. There are several possible methods including ACI anchorage, AISC Design Guide on Base Plates and Anchor Bolts, and Widianto (below).

3) Where possible, I prefer to get the anchorage done without the use of hooks. I feel that they add congesting in a situation where it is unwelcome.

4) Your ties at 4" oc are also a function of your anchorage design and design methodology. If you need 'em you need 'em. It's not a bad practice at all.

 

[EZBuilding]

Providing adequate development of the reinforcement in relationship to the loads you are transferring could lead to hooks at top or bottom.

If you have are utilizing skin friction for tension resistance and have narrowed your capacity down to the last feet or so, I would recommend that you have enough developed reinforcement at the bottom sections to transfer those loads.

 

[STrctPono]

Yes, the details appear correct. The hooks at the bottom though are not needed for engineering reasons but may prove useful for tying their spacer blocks off on when they are setting their rebar cage. You definitely want the hooks at the top. Since the steel structure has force continuity into the foundation you will need to develop your vertical reinforcing steel in a short distance (i.e. from top of shaft to bottom of anchor bolts) and the hooks reduce this distance. The tighter spiral/tie spacing at the top is because some codes allow you to take a further reduction on your rebar development lengths if you surround them with closed ties at no greater than 4" spacing. I know AASHTO does. Not sure about ACI or Eurocode. The tighter spiral/tie spacing at the top will also theoretically increase the anchor bolt breakout, however, I don't think ACI recognizes it per that configuration.

 

[slickdeals]

Contractors would prefer it turned in for easier shipping. Sometimes, they like to lap loose dowels in the field. A lot of contractors we're working with these days prefer to use buttonhead terminators.

 

[r13]

Unless subjected to direct tension as pointed out by KootK, I wouldn't bend the bars at the top, nor bottom. The hook tails create congestion that may impede vibration, and may give chance to air voids below the bars.

 

[KootK]

Contractors would prefer it turned in for easier shipping.

How do you mean? Do they pick the cages up by the hooks? Or do you just mean that hooks in are better than hooks out for stacking on truck beds etc?

 

[EZBuilding]

Hooks turned in also allows for the removal of temporary casings.

 

[slickdeals]

@Kootk - yes, from stacking on truck beds view point. Again, applicable not to 24" and 18" diameter piles but to larger piles where turned in hooks don't conflict with each other unless you start to stagger hooks.

 

[JLNJ]

There is no pile cap and from the looks of the detail there is intent that the base plate be a moment connection. This seems to indicate hooks turned in.

What sometimes gets missed is that the detail is in 2D, drawn without regard to bar sizes. If you have a lot of flexure, the bars can get quite big. Big bars require big hooks - they don't form a nice 90 degree angles like those cartooned on the detail, and they have long tails.

It's best to lay out the hooks to scale in plan to see if they fit without a lot of overlapping. I specified some big hooked bars in the top of a drilled pier once (#10s, I think) and I grossly underestimated the real hook radius and tail length. Not pretty.

Sometimes 180 degree hooks lay out better. Sometimes proprietary terminators are better.

And the hooks at the bottom seem totally unnecessary to me.

 

[hokie66]

In all my time, I've never seen hooks (or cogs) on vertical bars in a bored pile. They would be useless at the bottom, and could cause problems of congestion and plastic settlement cracking at the top. Much better to provide supplementary reinforcement if needed for development at the top.

 

[RPMG]

AValdes, you asked for any reason, and that's what you got. Should you hook them? No.

See Figures R17.4.2.9 & R17.5.2.9 for reinforcing for anchor tearout. The detail above doesn't qualify.

 

[AValdes]

Thank you very much, everyone! I appreciate a lot every single reply.

At the end, the guy who designed the piles argued that those hooks “help confine the concrete” …whatever that means. He didn’t argue about tearout, development length, etc. The thing is that those hooks are just long enough to require spliced bars, when without them, single bars would have worked for the whole pile length.

Thanks again everyone for your help, I really appreciate it. I have been reading this website for a couple of years now, but this is my first question. I am amazed by the amount of specialized knowledge and the cooperative spirit of everyone here.

Thanks!