Pile Head Fixity for 12" Pile Embedment

[aleks25]

I am currently analyzing a pile cap with 12.75" diameter bored-in piles. The embedment of the pile into the cap is 12". Since no dowels are provided except a central core rebar, is it a valid assumption to assume that the pile is pinned? The foundation is subject to very high lateral loads and there is a substantial difference between pinned and fixed condition. Are there any references which might shed some light on the fixity criteria? Any help will be appreciated.

 

[civilperson]

A model of the top of pipe pile in the concrete has greater fixity than the maximum bending moment of the pipe. I would model it as fixed against rotation and translation in all axes.

 

[jdonville]

civilperson,

aleks25 did not say they were pipe piles, but rather bored piles (I'm thinking ACIP piles or small drilled shafts).

Aleks25,

Since there is no designed moment transfer, I would assume the pinned condition. However, you may want to look at a fixed condition if the deflections under the pinned condition are small.

Jeff

 

[civilperson]

The maximum bending moment of drilled and cast-in-place piles is less than concrete filled pipe piles, therfore the the relative fixity is even greater for the bored piles. The moment is transfered by a couple with the top few inches of the pile being pushed one direction and the few inches above the bottom face of the cap being pushed in the other direction. The amount of moment that can be resisted with 12" embedment is greater than the moment strength of the pile.

 

[aleks25]

"civilperson", "jdonville", thank you for your replies. I guess there is a little confusion in nomenclature. It is really a mini-pile with its top portion encased in steel to provide moment resistance. I will probably model it as fixed since that gives me the most conservative pile loads (the pile group acts as the moment frame inducing tension and compression in the piles due to the lateral force alone). And the deflection for the pinned condition is not greater than allowable

 

[jdonville]

civilperson,

I think we're driving at the same point from opposite directions.

Cheers,

Jeff