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Re: Pile Interconnection (CBC & IBC)

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The purpose of the pile cap or caisson interconnection is to limit differential movement at the ground level.  A typical pile cap system usually consists of a hinge point, one column transferring to multiple piles.  The system you refer to is more like a cantilevered column system under 1807.5.  If the beams at the second level are to be considered as providing the necessary restraint, than the structure and slab above need to be capable of resisting the additional applied moments from a lateral displacement of the pile at the soil, as well as any companion forces from relative settlement during displacement.  Also, the piles need to be designed as free standing columns for the clear height plus point of fixity, vertical and lateral.  The construction you describe is more like a wharf than a typical pile system.
At a minimum, since it is single family, do they at least have a slab at grade level that captures all the pile bases?  If there isn't a slab, I would strongly recommend the potential for individual displacement be accounted for.  I do not believe the pile cap and caisson requirement of 1807.2 applies, but I also think a minimum amount of restraint is good practice.
The same is true for pad footings separate from the slab envelope.  I have seen severe slab distress where an outlying column was not tied back to the rest of the structure in more than one instance.  Soil migrates, and without tie beams or a restraining membrane like a slab, the movement induced moments can be considerable.  It may take 20 years, but it is the difference between good design and poor design.
----- Original Message -----
Sent: Friday, April 14, 2006 5:22 PM
Subject: Pile Interconnection (CBC & IBC)

I'm reviewing a single family project that piles do not have any interconnection grade beam at the "grade level".

The piles are 24" Dia. and continue to 2nd floor where they pick up suspended concrete slab and supporting concrete beams.
These concrete columns (or I should say piles) are above grade about 20 feet and embedded into the bedrock about 15 feet.


When I asked the designer about the "interconnection" of the piles (per CBC 1807.2) he commented that the concrete beams at 2 nd floor level (20 feet higher than grade level) would serve the same propose.

My question is: Does this condition fulfill the propose of the code?
Has anyone has direct experience in this regard?
I appreciate your comment.


Casey (Khashayar) Hemmatyar, PE