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

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

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

Conception parasismique du pont de Rion-Antirion

Le pont de Rion-Antirion, qui franchit le golfe de Corinthe, se situe dans une zone sismique aux caractéristiques très défavorables: grande profondeur d’eau, sols de mauvaise qualité, mouvements tectoniques. Sa conception, basée sur le principe de dimensionnement en capacité, fait appel à des concepts nouveaux, tant pour ses fondations que pour sa structure. Ce grand ouvrage, mis en service en 2004, a passé avec succès en 2008 son premier test sismique, lors d’un séisme de magnitude 6,5

Rapport sur la contribution des nouvelles technologies à la modernisation du système éducatif

Dans le cadre des audits de modernisation de l\u27Etat, les inspections générales de l\u27éducation nationale, des finances et le conseil général des technologies de l\u27information étudient le rôle que les TIC pourraient jouer dans la modernisation du système éducatif, au niveau de la gestion, de la pédagogie, de l\u27apprentissage et du marché des ressources

Eurocode 8: Seismic Design of Buildings - Worked examples

This document is a Technical Report with worked examples for seismic design of buildings following the Eurocodes. It summarizes important points of the Eurocode 8 for the seismic design of concrete and steel buildings including foundations utilizing a common generic building as a basis. An overview of EN 1998 with focus on the performance requirements and compliance criteria for structures, ground conditions and seismic actions is presented at the first section. An introduction to the example reinforced concrete building with its geometrical and material properties as well as the main assumptions for analysis and the detailed structural analysis calculations are presented in the second chapter of the report. Specific rules for design of the building for ductility and the design of concrete foundation elements are presented in the following chapters. For the sake of completeness, the details of design and detailing of the same example as a steel building with three different configurations, namely; with (i) steel moment resisting frames, (ii) composite steel concrete moment resisting frames, and (iii) composite steel concrete frames with eccentric and concentric bracings is also presented afterwards. Key concepts of base isolation is summarized by utilizing the example building. Seismic performance assessment and retrofitting according to EN 1998-Part 3 is explained as the last past of the report. The reinforced concrete/steel building as worked example analyzed in this report was prepared and presented at the workshop “Eurocode 8: Seismic Design of Buildings” that was held on 10-11 February 2011 in Lisbon, Portugal. The workshop was organized by JRC with the support of DG ENTR and CEN and in collaboration with CEN/TC250/Sub-Committee 8 and the National Laboratory for Structural Design (Laboratorio Nacional de Engenharia Civil - LNEC, Lisbon). The document is part of the Report Series ‘Support to the implementation, harmonization and further development of the Eurocodes’ prepared by JRC in collaboration with DG ENTR and CEN/TC250 “Structural Eurocodes”.JRC.G.5-European laboratory for structural assessmen

The challenge of defining upper bounds on earthquake ground motions

Recent studies to assess very long-term seismic hazard in the United States and in Europe have brought the issue of upper limits on earthquake ground motions into the arena of problems requiring attention from the engineering seismological community. Few engineering projects are considered sufficiently critical to warrant the use of annual frequencies of exceedance so low that ground-motion estimates may become unphysical if limiting factors are not considered, but for nuclear waste repositories, for example, the issue is of great importance. The definition of upper bounds on earthquake ground motions also presents an exciting challenge for researchers in the area of seismic hazard assessment. This paper looks briefly at historical work on maximum values of ground-motion amplitudes before illustrating why this is an important issue for hazard assessments at very long return periods. The paper then discusses the factors that control the extreme values of motion, both in terms of generating higher amplitude bedrock motions and of limiting the values of motion at the ground surface. Possible channels of research that could be explored in the quest to define maximum possible ground motions are also discussed

Estimation du mouvement sismique maximal à la surface du sol pour une celerite d'ondes non nulle en surface

The increasing need for probability seismic hazard assessment (PSHA) of critical facilities sometimes leads to unrealistic earthquake scenarios with very high induced ground motions. From a physical standpoint these high motions cannot exist because of the limiting resistance capacity of the soil strata through which the seismic waves travel. A simple analytical model is proposed to bound the maximum ground surface acceleration that any soil deposit can transfer. This model is an extension to non zero ground surface velocity of a previously presented model.La demande croissante d'études probabilistes de l'aléa sismique pour les installations essentielles pour la sûreté conduit parfois à des scénarios sismiques irréalistes donnant naissance à des mouvements très élevés. D'un point de vue physique ces mouvements ne peuvent exister en raison de la capacité de résistance limitée des couches de sol que traversent les ondes sismiques. Un modèle analytique simple est proposé pour estimer l'accélération maximale en surface que tout profil de sol est susceptible de transmettre. Ce modèle représente une extension au cas d'une célérité d'ondes non nulle en surface d'un modèle présenté précédemment