Tension Pile Detailing

[Baffled Engineer]

Hello,

I'm designing a reinforced concrete pile for pure tension that is anchoring a thick doubly-reinforced slab mat from uplift.

I'm just wondering, is it better to hook the vertical bars from the pile inwards or outwards?

It seems like hooking outwards would be better to spread the tension force and have vertical stirrups around the pile to resist the diagonal struts, versus concentrating all the compression struts inwards.

Any thoughts on this? Thank you.

 

[KootK]

For pure tension, I would stay that it's irrelevant. There's no diagonal strut being restrained and, therefore, no need for the hook to contain the strut. I would face the hooks outwards for constructability.

I agree with your assessment that outward facing hooks probably help to engage more of a punching shear frustum in the concrete. I don't see that as being significant enough to drive the decision however.

 

[Just Some Nerd]

Pointing outward also seems a bit more convenient, don't get those annoying clashes between them all...

 

[EZBuilding]

Outward facing hooks are likely structurally beneficial due to the lack of reinforcement conflicts.

In a number of different construction methodologies - outward facing hooks are a constructability challenge. In temporarily cased drilled shafts - outward facing hooks do not allow for the removal of the temporary casing. In auger-cast piles, the contractor will typically drill the piles from near grade elevation and chip out the top portion of the pile. We often find that straight bar development length is achievable in deep foundation pile caps, which are often thick and of higher grade concrete strength.

 

[Retrograde]

I agree with EZB. Make the cap deep enough that the bars do not need to be hooked at all - if possible.

 

[haynewp]

Came up on a project of mine, they need to face inwards if you are stripping casing. I don't mind having hooks into the cap otherwise.

 

[HTURKAK]

reinforced concrete pile for pure tension that is anchoring a thick doubly-reinforced slab mat from uplift.

In this case , the sketch showing the tension loads above the mat is not correct . The uplift load shall be applied as UDL under the mat surface . Variant 1 ( left one )is better for punching safety.