pre-stressed concrete piles 3

[nader666]

Hi every one,

Does anyone know what the effect of cutting the pre-stressed strands to adjust the top pile elevation and weather the epoxy dowels to connect the pile to the pile cap is better than exposing the strands during the cut off procedure and tie them to the pile cap reinforcement, if this way is acceptable , how long is the exposed length should be? Does regularly reinforced piles when exposing top rebars provide better connection with the pile cap?

Thanks

 

[JedClampett]

Why do either? Most piles are just embedded in the cap 4 inches.
The guys doing this aren't exactly swiss watchmakers. Trying to get them to cut around the strands (or bars) is going to be tough. If you need additional uplift capacity, just embed some bars in epoxy.

 

[dik]

We generally embed the exposed strand into the cap by a distance of 1.5' to 2' or so...

Dik

 

[PEinc]

The pre-stressing strands are fully bonded. Therefore, the piles can be saw-cut at the desired elevation. I have never seen anyone try to expose the strands and then "tie" them to the rebars in the cap or try to expose the conventional rebars for their embedment into the cap. Use grouted dowels with their pre-set, cast-in-place sleeves.

http://www.PeirceEngineering.com

 

[PEinc]

Attached are common details of a prestressed concrete pile

www.PeirceEngineering.com

 

[jayrod12]

The guys here don't use a saw to cut the piles off they use a machine that pinches the whole pile and basically breaks the concrete leaving the strands generally intact. Our typical detailing calls for 18" of stands to be exposed and embedded into the pile cap. When the strands break off we require that they epoxy a bar into the top of pile

 

[hokie66]

PEinc,
Those details would work fine where the level is predetermined, but when the driven depth varies and you saw off the top, you remove at least some of the sleeve. How is that handled?

 

[nader666]

Does the pile loose any of it's capacity due to cutting the strands off, if that is an option?

 

[PEinc]

Hokie66, the notes on the plan indicate that the sleeves are 10' long but the embedded length of the dowels can be much less. It is assumed that the pile length determined by the test piles will help prevent having to cut off too much pile resulting in too little sleeve length.

nader666, the prestressing strands are fully bonded. Therefore, cutting off the top of a pile will not debond the strands.

http://www.PeirceEngineering.com

 

[PEinc]

hokie66, the plan notes also address drilling deeper dowel holes if too much pile needs to be cut off.

http://www.PeirceEngineering.com

 

[BUGGAR]

We design wharf/pile structures with moment connections at the top of the piles for seismic resistance. We dowel the top of the pile to the cap beams above, typically with high strength dwidag bars or equivalent. Usually the problem is getting enough embedment or hooks in the dowels in the caps to develop the bending moments at the pile tops. The dowels are typically embedded in corrugated plastic sleeves cast into the piles. We give the contractor cut-off and tip elevations and the contactor has to make the decision how deep to embed the sleeves; we leave room in the pile for extended length sleeves. When the sleeves are short, or we are retro fitting, we have cored the piles but the bond lengths can be high.

We have exposed prestress strand for embedment in the cap but the strand usually gets damaged - it's sensitive stuff to nicks, and we have to dowel anyway. And it's hard to find the bond values for strand - I've got the numbers in my notes somewhere.

Bob

Trouble with vertical hairline cracks when driving piles? You need additional tie reinforcement - See papers by Ben Gerwick.