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Kinematic pile bending during earthquakes: analysis and ®eld measurements S. NIKOLAOU Ã , G. MYLONAKIS { , G. GAZETAS{ a nd T. TAZOH} The passage of seismic waves through the soil surrounding a pile imposes lateral displacements and curvatures on the pile, thereby generating`kinematic' bending moments even in the absence of a superstructure. These moments are concentrated in the vicinity of interfaces of alternating soft and stiff soil layers and, in the case of restrained-head piles, at the pile head. The scope of this paper is threefold: (a) to critically review some existing design methods for kinematic pile loading; (b) to develop new analytical results for piles in homogeneous and layered soils; (c) to present a case study in which theoretical predictions are tested against ®eld measurements. To this end, an approximate beam-on-dynamic-Winkler-foundation (BDWF) model is implemented, speci®cally developed for the seismic response of piles in layered soil. Both ®xed-and free-head piles, and different boundary conditions at the pile toe, are considered. It is shown that the magnitude of kinematic moments depends mainly on the stiffness contrast between the soil layers, the pile±soil stiffness contrast, the excitation frequency, and the number of excitation cycles. A unique case history involving the instrumented pile foundation of a multistorey building in Japan is presented. Time histories of bending and axial strains recorded at six locations along two piles are successfully compared with results computed from simple formulae and methods presented in the paper.

This paper recognizes that soil layering may have a profound effect on the settlement of pile groups and that pile-to-pile interaction induces not only additional settlement at the head of each pile but also additional stresses along its shaft. A general analytical formulation is developed, based on the Winkler model of soil reaction, for determining the vertical interaction factors between two piles embedded in multilayered soil. It is shown that such interaction factors depend not only on the displacement ®eld arising from the settlement of a loaded (`source') pile but also on the interplay between the adjacent (`receiver') pile and the soil subjected to this displacement ®eld. Such interplay, which has not been considered (at least explicitly) in currently available simple methods, is quanti®ed here through an analytically determined factor ae, which lies between 0 and 1. The paper also develops closed-form expressions for pile stiffness and interaction factors in a two-layer stratum, and highlights crucial aspects of the problem. KEYWORDS: numerical modelling and analysis; piles; settlement; soilastructure interaction; stiffness. analyse, qui se situe entre 0 et 1. L'article pre Âsente e Âgalement des expressions de forme ferme Âe pour la rigidite  des pieux et les coef®cients d'interaction dans un sol a Á deux couches, et fait ressortir les principaux aspects du proble Áme.