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Lateral spreading has historically caused extensive pile failure in liquefaction‐prone areas during strong earthquakes. A critical design scenario involves piles embedded in lateral spreading ground composed of a nonliquefied soil crust overlying a liquefied layer; it is critical because both layers can exert loads on the piles. Different thicknesses of the liquefied soil and the upper nonliquefied crust may engender different pile response patterns. Accordingly, to investigate factors influencing the lateral responses of a single pile embedded in liquefied ground with a nonliquefied crust, we conduct parametric analyses. The effects of liquefied and nonliquefied soil thicknesses are analyzed first, followed by those of pile‐head rotational restraint, pile diameter, and lateral spreading displacement. We observe two main pile response patterns for various liquefied soil thicknesses. The ground can be categorized into thin or thick liquefied ground depending on whether its liquefied soil thickness is less or greater than a critical value, namely, critical liquefied soil thickness; this critical thickness is dependent on the pile‐head rotational restraint, pile diameter, and lateral spreading displacement. The difference in the patterns stems from the varying roles of the upper nonliquefied soil layer during lateral spreading. For the thin liquefied ground, the nonliquefied layer contributes to adding lateral spreading force; therefore, the displacement, moment, and shear force responses of the pile increase with the nonliquefied soil thickness. However, for the thick liquefied ground, the nonliquefied layer provides resistance to lateral spreading; therefore, the maximum displacement, moment, and shear force of the pile initially decreases and then gradually increases with the nonliquefied soil thickness. [ABSTRACT FROM AUTHOR]

Group piles with a cap under lateral loading behave like fixed-head piles because of the rotational restraint of the pile cap. They are susceptible to flexural yielding at the pile head due to high bending strains. In addition to soil nonlinearity, the pile-head flexural nonlinearity also significantly contributes to nonlinear responses of the piles, which is not covered in most existing analytical solutions. For a fixed-head pile buried in uniform elastoplastic soils, this study derives analytical solutions for the lateral responses to account for soil yielding, and flexural yielding and failure of the pile section at the pile head. The model assumes elastoplastic Winkler-type soil with constant subgrade stiffness and yield strength and a nonlinear moment-curvature curve for the pile section. Examples are provided to apply the solutions to determine the complete capacity curves (moment and horizontal load) of a fixed-head pile and the derived analytical capacity curves are in good agreement with those from numerical analyses that use nonlinear beam elements to reflect the nonlinear flexural behavior of the pile section. The solutions are also applied to evaluate the influences of the yield displacement of the soil and different forms of simplified nonlinear moment-curvature curves of the pile section on the lateral load-displacement curves. Key words: fixed-head piles, lateral loads, plastic hinges, soil nonlinearity, Winkler-beam model. Les pieux groupes avec une semelle sous charge laterale se comportent comme des pieux a tete fixe en raison de la retenue en rotation de la semelle des pieux. Ils sont sensibles a la flexion au niveau de la tete du pieu en raison des fortes deformations dues a la flexion. En plus de la non-linearite du sol, la non-linearite de flexion de la tete de pieu contribue egalement de maniere significative aux reponses non lineaires des pieux, ce qui n'est pas couvert dans la plupart des solutions analytiques existantes. Dans le cas d'un pieu a tete fixe enfoui dans un sol elastoplastique uniforme, cette etude propose des solutions analytiques pour les reponses laterales afin de tenir compte de l'ecoulement du sol, de la flexion au seuil d'ecoulement et de la rupture de la section du pieu a la tete du pieu. Le modele suppose un sol de type Winkler elastoplastique avec une rigidite et une limite d'elasticite constantes du sol de fondation et une courbe de moment de flexion non lineaire pour la section du pieu. Des exemples sont fournis pour appliquer les solutions afin de determiner les courbes de capacite completes (moment et charge horizontale) d'un pieu a tete fixe et les courbes de capacite analytique derivees sont en bon accord avec celles des analyses numeriques qui utilisent des elements de poutre non lineaires pour refleter le comportement en flexion non lineaire de la section du pieu. Les solutions sont egalement appliquees pour evaluer les influences du deplacement d'ecoulement du sol et les differentes formes de courbes non lineaires simplifiees de moment de courbure non lineaire de la section de pieu sur les courbes charge laterale-deplacement. [Traduit par la Redaction] Mots-cles: pieux a tete fixe, charges laterales, articulations en plastique, non-linearite du sol, modele de poutre Winkler., Introduction Group pile foundations with cap are common in foundations of bridge column structures. With the pile cap restraint, the piles under lateral loading behave like fixed-head piles. When the [...]

Scouring is one of the major causes of the failure of bridges and offshore wind turbines. Piles under extreme scouring and earthquake loads are vulnerable to failure and need to be investigated thoroughly. In this study, the seismic responses of an extended concrete pile with no scour and four scouring depths conditions are investigated under an input motion based on a Kobe earthquake record. The effect of water during an earthquake has a significant impact on the structure as hydrodynamic pressure; however, it is generally ignored in the seismic analysis of piles. The present study uses the concept of added mass to consider the effects of water. The combined soilstructure-interaction and shear beam model is used to simulate pile and soil using the beam-on-nonlinear-Winkler foundation (BNWF) method. Soil is divided into multiple layers with increasing shear modulus and the mass of each soil layer is lumped into two nodes of the layer. Modal analysis and nonlinear time history analysis are performed on different models. Results of the modal analysis show the decrease in fundamental frequencies of the pile with increasing scouring depths. The time history analysis results are reported in the form of Arias and Housner intensities, envelopes of acceleration, velocity, displacement of pile top, and envelopes of shear force and bending moment of the pile. Results show significant changes with scouring depth and the effect of water.

Pseudostatic analysis can be an efficient approach to evaluating the dynamic response of structures for a preliminary design. In this paper, we present a pseudostatic method based on a pushover analysis to assess the seismic performance of bridge piers supported by rocking‐governed shallow foundations. The method has two stages. In the first stage, the capacity spectrum method (CSM) is applied to evaluate the maximum acceleration and displacement response of the bridge system. To have an appropriate system damping ratio in the CSM, we propose a method to consider various earthquake energy dissipation mechanisms for the pier and foundation. In the second stage, the footing settlement is evaluated based on the maximum footing rotation; an incrementally cyclic pushover analysis with a fixed footing rotation increment is performed to estimate the footing settlement. Examples are presented to demonstrate the applicability of the proposed method and the results of the proposed method are compared with the dynamic analysis results. Compared with the conventional CSM, the proposed method improves the estimation of system damping and can estimate the settlement after earthquakes. [ABSTRACT FROM AUTHOR]

Displacement ductility capacity of a pile is an important concern when its ductile behavior is taken as a mechanism of energy absorption in seismic design. Existing methods to assess the ductility capacity of a pile have not considered all major influencing factors, such as the overstrength ratio of the pile section. This study uses a simple ideal model to link the displacement ductility capacity with parameters in the pile-soil system for a fixed-head pile in cohesive soils. Based on the simple model, an expression about the displacement ductility capacity is firstly derived for a pile in linear soils and then modified to consider the possible softening of subgrade stiffness for a pile in nonlinear soils. Through reduction of the expressions derived, a set of simple equations are proposed to estimate the ductility capacity of a pile in linear and nonlinear soils. For a pile in linear soils, its ductility capacity can be computed only from the sectional property of the pile; for a pile in nonlinear soils, an increase in the displacement ductility capacity due to the soil nonlinearity can be considered. Finally, a series of numerical nonlinear static pushover analyses of full pile-soil models are conducted to examine the performance of the proposed equations. Key words: cohesive soil, ductility capacity, pile, plastic hinge, seismic design. La capacite de displacement ductile d'un pieu est un aspect important a tenir compte lorsque son mecanisme ductile est considere comme un mecanisme d'absorption d'energie en conception sismique. Les methodes existantes servant a evaluer la capacite en ductilite d' un pieu ne tiennent pas compte de tous les principaux facteurs qui ont une influence, comme le ratio de sur-resistance de la section du pieu. Cette etude utilise un modele idealise simple pour relier la capacite de deplacement ductile avec les parametres du systeme pieu-sol pour un pieu a tete fixe dans des sols cohesifs. A partir de ce modele simple, une expression decrivant la capacite de deplacement ductile est premierement derivee pour un pieu dans des sols lineaires, et est ensuite modifiee afin de considerer un possible adoucissement de la rigidite pour un pieu dans des sols non lineaires. Grace a la reduction des expressions derivees, une serie d'equations simples sont proposees afin d'estimer la capacite en ductilite d' un pieu dans des sols lineaires et non lineaires. Dans le cas d' un pieu dans des sols lineaires, sa capacite en ductilite peut etre calculee a partir de la propriete sectionnaire du pieu seulement; dans le cas d'un pieu dans des sols non lineaires, une [Δ.sub.u]gmentation de la capacite de deplacement ductile causee par la non linearite du sol peut etre consideree. Enfin, une serie d' analyses numeriques statiques non lineaires de renversement avec des modeles complets pieu-sol sont realisees afin d' evaluer la performance des equations proposees. Mots-cles : sol cohesif, capacite en ductilite, articulation de plastique, conception sismique. [Traduit par la Redaction], Introduction In pile engineering, a fixed-head pile requires a large flexural curvature demand at the pile head when the pile cap undergoes a horizontal displacement, such as under a seismic [...]

The capacity of a pile-soil system can be obtained by pushover analysis using the beam-on-nonlinear-Winkler foundation model. When the pile section enters the plastic state, the plastic hinge method is usually adopted to model its postyielding flexural behavior. The propagation of the plastic zone in a pile can be traced using a series of plastic hinges distributed along the pile that is embedded in the soil. This study proposes a proper model for arranging the distributed plastic hinges along the depths of the pile that are prone to yielding. A modified definition of plastic curvature is proposed herein in order to correctly simulate the nonlinear flexural behavior of a pile. Examples are presented to show the effectiveness of the proposed model. DOI: 10.1061/(ASCE)GT.1943-5606.0000015 CE Database subject headings: Nonlinear analysis; Plastic hinges; Soil-pile interaction; Models; Piles.

In this study, three in situ laterally loaded tests on bridge columns with caisson foundations in gravels were numerically explored. The three tests differed in the application position of lateral loads and the exposed length of the foundations. The analysis model used beam–column elements with distributed plastic hinges to simulate the column and a six-component Winkler beam model to simulate the foundation. The lateral stiffness of the foundation with combined moment and horizontal loading and a large exposed length was the smallest. Although the foundations were situated in a gravel stratum, the caisson with a large exposed length underwent significant foundation flexibility and nonlinearity; however, with increasing lateral loading, the influences of foundation flexibility and nonlinearity on the lateral displacement of the columns were reduced because column yielding limited the load transfer to the foundation. The horizontal soil reactions in front of the foundation and the side horizontal shear soil reactions along the caisson shaft provided major resistances to lateral loading (horizontal load and overturning moment). With increasing foundation exposure, the contribution of the base soil reactions increased, but the contribution of the side horizontal soil reactions decreased accordingly. The side vertical shear soil reactions and base normal soil reactions contributed moment resistance to reduce the foundation displacement and rotation and thus promoted the overall lateral capacity of the caisson foundations although they did not provide direct counterbalances to horizontal loads. [ABSTRACT FROM AUTHOR]

Lateral cyclic load tests were performed on an aluminum model pile in dry sand. Two levels of loading were adopted to represent different service load conditions. The maximum number of loading cycles was 1,000. From the test results, it was found that the even though in the service load condition, the pile response was still affected by cyclic effects and a larger load level would produce more significant influence. In a global point of view, the lateral displacement and maximum moment increased with loading cycles, while the secant stiffness within a cycle decreased with cycles. The cyclic effect was more significant on the lateral displacement than on the moment. In a local point of view, cyclic loading would degrade the equivalent subgrade stiffness for the soil shallower than about seven times diameter. In addition, the secant subgrade stiffness within a cycle increased with loading cycles. Some experimental relationships of lateral pile response and loading cycles were built and compared with those in the literature. [ABSTRACT FROM AUTHOR]