Macroelement modeling of shallow foundations

The paper presents a new macroelement model for shallow foundations. The model is defined through a non-linear constitutive law written in terms of some generalized force and displacement parameters. The linear part of this constitutive law comes from the dynamic impedances of the foundation. The non-linear part comprises two mechanisms. One is due to the irreversible elastoplastic soil behavior: it is described with a bounding surface hypoplastic model, adapted for the description of the cyclic soil response. An original feature of the formulation is that the bounding surface is considered independently of the surface of ultimate loads of the system. The second mechanism is the detachment that can take place at the soil-footing interface (foundation uplift). It is totally reversible and non-dissipative and can thus be described by a phenomenological non-linear elastic model. The macroelement is qualitatively validated by application to soil-structure interaction analyses of simple real structures

Rupture sismique des fondations par perte de capacité portante: Le cas des semelles circulaires

International audienceWithin the context of earthquake-resistant design of shallow foundations, the present study is concerned with the determination of the seismic bearing capacity of a circular footing resting on the surface of a heterogene-ous purely cohesive semi-infinite soil layer. In the first part of the paper, a database, containing case histories of civil engineering structures that sustained a foundation seismic bearing capacity failure, is briefly pre-sented, aiming at a better understanding of the studied phenomenon and offering a number of case studies useful for validation of theoretical computations. In the second part of the paper, the aforementioned problem is addressed using the kinematic approach of the Yield Design theory, thus establishing optimal upper bounds for the ultimate seismic loads supported by the soil-footing system. The results lead to the establishment of some very simple guidelines that extend the existing formulae for the seismic bearing capacity contained in the European norms (proposed for strip footings on homogeneous soils) to the case of circular footings and to that of heterogeneous cohesive soils

A Macro-Element for Dynamic Soil-Structure Interaction Analyses of Shallow Foundations

The scope of the paper is to present some aspects of the development of a "macro-element" for dynamic soil-structure interaction analyses of shallow foundations. Initially the concept of "macro-element" is introduced and is illustrated with the aid of a very simple example originating from structural engineering. Then the link is made with the modeling of the dynamic response of shallow foundations and the objectives and structure of such a tool are described with reference to the specific configuration of a circular footing resting on the surface of a heterogeneous purely cohesive soil. The principal features of the "macro-element" are then presented; the soil-structure interaction domain is reduced to a point that coincides with the center of the footing and all the (material and geometric) non-linearities are lumped at this point. A discussion on the most appropriate way to treat these non-linearities is undertaken based on experience gained with earlier works. It is suggested that the non-linearities be incorporated in the model within a unified formalism making use of the theory of multi-mechanism plasticity. Initial results concerning the definition of the ultimate surface for such a plasticity model, corresponding to the seismic bearing capacity of the foundation, are finally presented.Comment: 4th International Conference on Earthquake Geotechnical Engineering, Thessaloniki : Gr\`ece (2007

Effects of existing surface structures on settlements induced by tunneling

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (leaves 120-122).by Charisis-Sotirios Th. Chatzigogos.M.Eng

Comportement sismique des fondations superficielles: vers la prise en compte d'un critere de performance dans la conception

The objective of this thesis is to contribute to the study of shallow foundations under seismic excitation and to offer new tools for the treatment of related problems in engineering practice, with a particular focus on performance-based design. The undertaken research was organized following four axes of approach: a. Identification of the main characteristics of the problem by examining real foundation seismic failure. This effort led to the creation of a database of approximately 200 structures of all types that suffered a seismic failure at the foundation level.b. Theoretical approach for the determination of the seismic bearing capacity of shallow foundations. The problem of a circular footing on a heterogeneous purely cohesive soil was treated with the kinematic approach of the Yield Design theory. The established solutions suggest a significant extension of the design procedures incorporated in the European earthquake-resistant design norms by introducing three-dimensional footing geometry and soil heterogeneity.c. Experimental approach for the validation of the established theoretical results. A project with the French Central Laboratory of Bridges and Highways (Laboratoire Central des Ponts et Chaussées) was undertaken, focusing on the determination of the bearing capacity of the configuration treated in the theoretical approach through centrifuge tests. d. Development of a tool for efficient non-linear dynamic soil-structure interaction analyses. A new macroelement model has been developed comprising two coupled non-linear mechanisms: the irreversible soil behaviour via a bounding surface hypoplastic model and the uplift that may take place in the soil-foundation interface via a phenomenological non-linear elastic model. The perspective of these contributions is to enrich the existing design norms by orienting them towards the promising performance-based design philosophy.L'objectif de cette thèse est de contribuer à l'étude du comportement sismique des fondations superficielles et d'offrir de nouveaux outils pour le traitement de problèmes pertinents, orientés vers la nouvelle philosophie de conception parasismique des structures : la conception basée sur la performance (« performance-based design »). On a travaillé suivant quatre axes d'approche sur la problématique de la thèse :a. Reconnaissance des caractéristiques principales du problème par l'examen de ruptures sismiques de structures réelles. Cet effort a abouti à la création d'une base de données d'environ 200 structures qui ont subi une rupture par perte de capacité portante au niveau de la fondation.b. Approche théorique pour la détermination de la capacité portante sismique d'un système de fondation. On a traité le problème de la capacité portante sismique d'une semelle circulaire sur un sol purement cohérent hétérogène par l'approche cinématique du Calcul à la Rupture. Les solutions établies nous ont permis de proposer une modification/extension des procédures de conception existantes qui sont incorporées dans les normes de conception parasismique européennes (Eurocode 8). c. Approche expérimentale pour la validation de la solution théorique établie. Une collaboration avec le LCPC – Centre de Nantes a abouti à la planification des trois séances d'essais en centrifugeuse. Les deux premières séances sont incluses dans la thèse et portent sur la détermination de la capacité portante d'une semelle circulaire sur sol cohérent sous chargement quasi-statique. d. Développement d'un outil intégré permettant la mise en œuvre d'analyses dynamiques efficaces pour la prise en compte de l'interaction sol-structure non-linéaire au niveau de la fondation. On a développé un nouveau modèle de macroélément pour le système sol-fondation. Le macroélément est utilisé comme élément de liaison à la base de la superstructure et reproduit les effets non-linéaires qui ont lieu au niveau de la fondation lors d'une sollicitation sismique. Le modèle proposé comporte deux mécanismes en couplage : la plastification du sol et le décollement qui peut se produire sur l'interface sol-structure. L'objectif de cet outil est de permettre d'effectuer de manière efficace un grand nombre d'analyses de structures dynamiques non-linéaires.L'objectif ultérieur de nos développements est d'enrichir les normes de conception parasismique actuelles et de les orienter vers une philosophie de conception basée sur la performance des structures lors d'un séisme

Comportement sismique des fondations superficielles (vers la prise en compte d'un critère de performance dans la conception)

PALAISEAU-Polytechnique (914772301) / SudocMARNE-LA-VALLEE-ENPC-BIBL. (774682303) / SudocSudocFranceF

MODULATE: ANR project for the modeling of long period ground motions and the assessment of their effects on large-scale infrastructures

International audienceLarge-scale infrastructures are increasingly used in urban areas to meet the demands of continuously evolving societies. Recent seismic events showed remarkably that the construction of infrastructures with adequate seismic performance is the main factor in minimizing economic loss and long-term consequences to the communities. The modern design of large-scale structures, through the framework of performance-based earthquake engineering, requires consideration of the unique features of those structures, such as long natural period (> 2 seconds), interaction with the supporting soil, interaction with contained liquid, multi-support excitation, etc. In this project, we are concerned with the analysis, estimation and modeling of long period ground motions and their effects on the response of large-scale infrastructures such as high-rise buildings, liquid-storage tanks and long-span bridges. Intense long-period ground motions are usually generated at large distances from the source by large subduction-zone earthquakes and moderate-to-large crustal earthquakes. Such motions consist primarily of surface waves that arise when seismic waves encounter sedimentary deposits. One of the main objectives of the project is the development of a methodology based on the physics of surface waves, to describe the evolution of the spectral content of the ground motion for a site located in a sedimentary basin, and exposed to potential seismic sources, using relatively easily accessible input data. Furthermore, the stochastic description of ground motion will provide broadband realistic time histories that include basin-generated surface waves and which will be the means for practical assessment of the structural reliability and integrity of the considered large infrastructures. Realistic 3D numerical geological models will be implemented to study the physics of surface wave generation and propagation in sedimentary basins. The project is based on an inter-disciplinary effort with the synergy of Earthquake and Structural Engineers, together with Seismological and Numerical Modelling experts. The ultimate goal of the project is the development of novel, efficient and reliable tools and methods to be used by the earthquake engineering community for more robust and resilient designs of large-scale infrastructures