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The lateral resistance of pile foundations to combined horizontal and moment loading was examined by means of numerical analyses and experimental tests. Initially, Broms' theory for the lateral capacity of a horizontally loaded pile was revisited and extended to the derivation of closed-form analytical expressions for the failure envelope in moment–horizontal force (M–Q) space for various soil conditions. It is shown that within a limit equilibrium framework the normality of plastic flow is an inherent property of pile response at failure. The developed failure envelope and associated plastic flow rule expressions were numerically verified by way of: (a) a beam-on-Winkler-foundation analysis, in which the lateral soil reaction against a yielding pile was represented by an array of uncoupled non-linear springs, and (b) a continuum mechanics analysis in which both the pile and the soil were discretised with three-dimensional elasto-plastic finite elements. The effect of key model parameters – such as (a) mesh density, (b) soil type and associated strength properties, (c) interface non-linearities and (d) soil constitutive models – on the post-failure response of the pile–soil system were parametrically investigated. Finally, an experimental validation of the problem is also provided through a series of 1g small pile load tests, conducted at the National Technical University, Athens.

Abstract. The main purpose of this study is to investigate the influence of soil p-y nonlinearity in soil-pile-structure kinematic and inertia interaction. Within this context, a beam on nonlinear Winkler foundation model is adopted based on the Boundary Element INTRODUCTIONThe seismic response of column-pile systems under transient earthquake excitation is an area of extensive active research, since pile foundation is widely used to support superstructures such as bridges, wind-turbines and offshore platforms. As the seismic shear wave propagates through the soil deposit, the embedded foundation tends to modify the transmitted excitation due to the soil-foundation stiffness contrast, the boundary constrains of the head and tip of the pile as well as the dynamic response of the system (frequency correlation). This interaction develops even in the absence of a superstructure and is referred to as the kinematic interaction. At the same time, the dynamic response of the superstructure itself induces additional deformations to the pile and the near-field soil. This effect is known as inertial interaction. Kinematic and inertial interaction constitute a complex and unique phenomenon referred to as Soil-Pile-Structure Interaction (SPSI) which includes a number of parameters, such as the soil stratigraphy and properties, the non-linear stress-strain behavior of the soil and pile (material nonlinearity) and the geometrical nonlinearities (p-δ effects, separation and slippage).The main purpose of this study is to investigate the influence of soil p-y nonlinearity in soil-pile-structure kinematic and inertia interaction. Within this context, a beam on nonlinear Winkler foundation model is adopted based on the Boundary Element Method (BEM), accounting for the effects induced by geometrical nonlinearity, rotary inertia and shear deformation, employing the concept of shear deformation coefficients. The soil nonlinearity is taken into consideration by means of a hybrid spring configuration consisting of a nonlinear (p-y) spring connected in series to an elastic spring-damper model. The nonlinear spring captures the near-field plastification of the soil while the spring-damper system (KelvinVoigt element) represents the far-field viscoelastic character of the soil. An extensive case study is carried out on a pile-column-deck system of a bridge, founded in two cohesive layers of sharply different stiffness and subjected in various earthquake excitations, providing insight to several phenomena. The results of the proposed model are compared with those obtained from the Beam-FE model employing OpenSees code [1] as well as from a rigorous fully three-dimensional (3-D) continuum FE scheme materialized in the ABAQUS code [2]. The essential features and novel aspects of the present contribution compared with previous ones are summarized as follows. i. Soil nonlinearity is taken under consideration by means of a hybrid spring configuration consisting of a nonlinear (p-y) spring for the near-field plastification, connected in series to...