Title: Notional Piles for Generalized Foundation Modeling Based on the Novak Procedure
Author(s): Tim Hogue, David Kerins, and Matthew Brightman
Publication: Symposium Paper
Appears on pages(s): 125-144
Keywords: ACI 351.3R, dynamic analysis, foundation modeling, notional piles, Novak procedure, pile cap flexibility, pile/cap interaction, pile group modeling, model validation.
The “Notional Pile” formulation is developed for modeling a group of piles in a foundation. It is a new
procedure for foundation modeling for dynamic analysis in conformance with ACI 351.3R. It is an augmentation of
the well-known Novak procedure. Foundation stiffness is represented as a set of notional pile elements. This differs
from conventional procedures in which the pile group stiffness is represented by a set of springs lumped at one point.
With notional piles and finite element modeling of the cap, flexible-cap modes of vibration can be extracted. With
conventional procedures, only lower-frequency rigid body modes can be extracted. Notional piles distribute stiffness
more realistically and enable cap-pile interaction. A specific case is used to illustrate the new procedure. For that
case, the cap did not have a regular distribution of mass or stiffness. Dynamic loads were applied with considerable
eccentricity, at multiple locations and with multiple frequencies. Notional piles accommodated these irregularities.
The notional pile formulation was validated by comparing measured to computed foundation responses. The
comparison was good but not great. The foundation was to be reconfigured for new machinery. The retrofit design
was modeled using notional piles. Responses were computed and compared to applicable limits.