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Re: combined seismic load with creep load

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Dave-

Yes, we usually combine the seismic loads with the creep loads on the piles.
 However, 3 things to consider.  First, when combining the loads, you get a
1.33 increase on your passive pressure and a .75 reduction in your ultimate
load combination so the seismic+creep combination does not always govern.
 Second, when the piles are tied with grade beams (as they should be), the
beams will often transfer the seismic load back to the stiffest element, i.e.
the shortest pile, which conversely has the smallest creep load.  Typically,
we reinforce all of our piles the same because of this concern, unless there
is a gross difference in fill heights.  Third, be aware when combining loads
that the creep is downhill but the seismic is up or down.  For small fill
depths and large seismic loads, don't forget the uphill case if you are
providing more reinforcing on one side of the cage than the other.  Our
office standard is to use a circular rebar pattern in our piles so this is
not a problem for us.

Good luck.

Bruce Resnick