SIMPLIFIED MODEL FOR SEISMIC PILE BENDING AT SOIL LAYER INTERFACES

 GEORGE MYLONAKIS

ABSTRACT: The curvatures and subsequent bending imposed to piles by the surrounding soil during the passage of seismic waves is studied. This type of bending develops even in the absence of a superstructure and is referred to as "kinematic" bending, to distinguish it from pile bending generated from inertia forces in the superstructure (termed "inertial" bending). Although kinematic bending may be severe in the presence of sharp stiffness discontinuities in the profile and may lead to damage, it has received little attention by engineers. The scope of this paper is threefold: (1) to review some existing design methods; (2) to present an improved analytical model for estimating kinematic pile bending moments at an interface between two thick soil layers under dynamic SH-wave excitation; and (3) to propose a simplified analysis procedure to be used for designing piles against kinematic loading. To this end, a dimensionless bending strain parameter (instead of the commonly-used bending moment) and a strain transmissibility function relating pile bending strain and corresponding soil shear strain are introduced. The two indices provide insight into the physics of the problem which is often obscured by the use of bending moments. Results from the model are in good agreement with more rigorous solutions. Numerical examples are presented.

Key words: analysis, bending moment, earthquake, interface, kinematic loading, pile, wave (IGC: E8/E13)