Existing Precast Prestressed Pile Connection To New Pile Cap/Slab

[acwooten]

I have a situation where we want to reuse existing precast prestressed piles below our new structure. The thought is that we can just crunch off the concrete on the top x' of the pile, exposing the strands, and splay them out whatever their development length is in order to develop their full tensile capacity into the new slab above, which would be acting as the pile cap.

Does this sound like a reasonable approach? And if so, are there any factors to consider beyond just the full development length? i.e. transfer length, bond length, additional slippage, etc. I'm pretty new to the precast prestressed world and want to make sure I'm covering all of my bases.

Thanks in advance!

 

[dik]

That's what I would do... embed the P/C pile into the cap by 4" to 6".

Dik

 

[acwooten]

Thanks for the reply Dik.

Is there nothing else that should be considered when splaying out the prestressing strands beyond achieving their development length? Our concern is that when they crush the concrete to expose the strands, that some slippage might occur, causing the PCPS pile to lose some capacity and that for some reason, even with the development length into the new concrete, the full moment capacity wouldn't be able to be developed at the interface of the pile and the cap. Or is it really just that simple; get the development length into the cap (even if the strands have to be curved to achieve that length) then check the prestressing strands for the max moment at the interface through normal beam theory bending moment capacity?

As for the embed of the pile, I've read several posts on this site about suggested embed depths, all of which give a somewhat wide range of numbers. I've found where CRSI recommends 4" for concrete, but the only code-based minimum value to use (since CRSI is just a guide) is IBC which give a 3" minimum embed. Is there a reason why that wouldn't work?

 

[dik]

Spread them out as much as you can within the pile cap cage... other than compression there's not much force on the strand unless you have a huge eccentricity.

Dik

 

[acwooten]

It's a high seismic zone so there is a decent moment at the bottom of the slab that the pile-cap connection will see. That's why our main concern is whether or not it can develop the bar's full tensile capacity.