Pier Cap Embedment Into Pier Cap?

[Medina.]

Hello all,

IBC2018 section 1810.3.11 requires that a pile extend 3” into the bottom of a pile cap and the pile cap extend 4” beyond the edge of the pile. (this requirement has been in place since the original IBC2000). Is this meant for piers that have reinforcing steel connecting the pier and pier cap?

Any resource or help would be greatly appreciated, thanks.

 

[MotorCity]

No, I think you are confusing terms. The section you quoted is for piles with a pile cap on top. Piers are not the same as piles, they are basically short, stubby columns. If I remember correctly, they typically have dimensions that do not exceed 3:1 (height:width). Piers would be found on top of a pile cap and are not embedded in a pile cap.

 

[slickdeals]

While I don't disagree that the embedment requirement shouldn't apply to reinforced piles/drilled shafts/caissons etc, I want to point out what the language in the code seems to imply. Please correct me, if I am mistaken.

An older geotechnical engineer once told me that the requirement for embedment was primarily for timber piles, H-Piles or precast piles with strand extending into it and not for reinforced concrete piles. The capacity from a 3" embedment is an extremely small percentage of capacity that is derived from the reinforcement crossing the joint.

Even though the language says "pile cap", don't think the code intends to separate a pile cap from a pier cap.

..all elements to which vertical deep foundation elements are connected.

1810.3.11 Pile caps. Pile caps shall be of reinforced concrete,
and shall include all elements to which vertical deep
foundation elements are connected, including grade beams
and mats

 

[BridgeSmith]

AASHTO has a similar provision drilled shafts (AKA concrete piles or caissons). It's for shear resistance at the interface with the footing/cap on top of the shafts. The provisions do not apply to the connections at the bottom of piers or columns, nor the top. There are other provisions for embedment of steel piles into pile caps or pier caps.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[Medina.]

Thanks for the reply guys, yeah I was mainly asking for drilled piers. It seemed like it would be enough to have bars going into the pier cap without embedding the pier itself.

 

[BridgeSmith]

By drilled pier, you mean a drilled shaft or caisson? If that's the case, I don't know what the IBC says, but the AASHTO bridge design spec would definitely require the shaft to be embedded into the cap. Now, if it's column on a drilled shaft that goes up to a cap above ground, then no, it wouldn't have o be embedded.

Pile caps are on the ground or below ground, anyway, so I don't understand why there would be reluctance to embed the shaft. It's no more difficult than not embedding the shaft.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[KootK]

In the case of drilled CIP piers, I think the requirements are really just good rules of thumb that acknowledge how these thing are built. Cast the piles a little high, place the rebar on the piles, carry on. If you do something different but you still have the right covers where you need them, sufficient anchorage of your bottom steel, and sufficient capacity in the joint via shear friction / breakout or whatever... you're off to the races.

 

[Medina.]

I meant to say CIP drilled shafts with the pier caps on grade or below grade. Anyways, thanks again guys big help.