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prestressed piles

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Acie,

The prestressing in concrete piles is simply to facilitate handling them 
during transport.  Prestressed piles are typically precast and must be 
transported from the plant to the site, then moved from a horizontal position 
to a vertical position and driven.  Any driving force simply reduces the 
tension in the prestress strand.

A side benefit of prestressed piles is that you *know* that the pile can take 
a load equal to the prestress force.  Therefor, if your final prestress 
force  is 240 kips plus a factor, then you know that the pile will take 240 
kips.  An old rule of thumb was that a vertical pile could resist a 
horizontal load equal to 2% of the pile capacity.  Battered piles were used 
to resist horizontal loads greater than 2%.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Acie Chance wrote:

<<     I could use the help of anyone who has experience designing 
prestressed concrete piles. I need to design a 100 foot long pile to take 240 
kips of vertical load and 45 kips of horizontal load. The top 25 feet will be 
a composite pile,  30" diameter drilled pier with conventional reinforcing 
and the prestressed pile extending up through the composite length to the pile
cap. The idea is to predrill the 30" section then drill a smaller hole for 
the remaining 75 feet. The prestressed pile will then be driven and a rebar 
cage lower around it for the first 25 feet. The soils engineer has given the 
240 kip load for a 14" diameter pile. The top 25 feet will take the 45 kip 
horizontal load.
     I have been reading about prestressed piles but the information I have is

not  specific and none have any thing about a composite pile. As this project 
is to go for a review of the 100% package in three weeks time is important to 
me. Any help on references which include design examples of prestressed piles 
would be appreciative. Additionally any pitfalls on using pile splices would 
also be appreciated.<<

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