Seismic ground motions associated to basin-induced surface waves can be particularly damaging for long-period large-scale infrastructures such as bridge pylons. In the present work, we perform a parametric study within an Incremental Dynamic Analysis (IDA) framework with a twofold aim: a) to quantify the additional distress induced by Rayleigh waves on bridge pylons and identify potential correlations with the frequency content of these waves and b) to examine whether the acceptance of nonlinearity at foundation level can render the overall design more vulnerable to the incidence of surface waves. The effects of Rayleigh waves are studied by extracting the Rayleigh wave component from signals recorded in sedimentary basins and by performing structural analyses with and without this component. The effect of the rotational seismic component, often neglected in engineering practice, is also considered. Two types of foundation design are studied: a) "conventional" design (large foundation dimension) with the aim of developing limited nonlinearity at foundation level and b) "innovative" design (reduced foundation dimension) inviting for development of high foundation nonlinearity but offering an isolation effect for the superstructure. In this context, we develop a simplified model using a nonlinear soil-foundation macroelement and a multifiber model for the bridge pylon. We show that Rayleigh waves can increase up to approximately an order of magnitude the severity of relevant engineering demand parameters according to the studied configuration. Amplification factors due to Rayleigh waves are quantitatively similar for both types of foundation design (conventional - innovative) but they need to refer to the most relevant engineering demand parameters for each case.

Soil-structure interaction (SSI) can potentially compromise structures that are subjected to seismic excitation. In recent years, real-time hybrid testing (RTHT) has been used to study soil-structure interaction. However, a very simple soil model has been adopted in existing hybrid testing, which cannot simulate nonlinear effects in a soil-foundation system under vigorous seismic shaking. To study the stability and accuracy of RTHT for nonlinear SSI and to evaluate the dynamic impact of soil nonlinearity on an SSI system, real-time hybrid shaking table testing was performed based on full-state control via simulation (FSCS), in which the soil-foundation system was simulated using a macroelement model. The results demonstrate that FSCS-controlled RTHT is an effective approach for investigating nonlinear SSI. The nonlinear characteristics of the numerical substructure had little influence on the stability and accuracy of RTHT for nonlinear SSI systems, but the nonlinear characteristics of the soil had a positive effect on the structural seismic response. An effective dynamic testing method was proposed for the SSI studies.

This article aims to propose new criteria for dynamic decoupling between primary and secondary systems, supplementing existing criteria in the French nuclear industry. The criteria developed are based on frequency and response decoupling of both systems and can be directly used by engineers to complement existing criteria. They provide information on the types of interactions between the systems (inertial or kinematic interactions) and on the types of modeling to be adopted (lumped masses or complete model).

Modeling of soil-structure interaction for shallow foundations entails three sources of nonlinearities: foundation uplifting, sliding along the soil-footing interface and irreversible displacement due to soil plasticity.Foundation macroelements allow reducing computational efforts in the resolution of seismic response including nonlinear soil-structure interaction.This is achieved by replacing the soil domain and the foundation by a 2-noded element with a sophisticated nonlinear constitutive law reproducing the aforementioned nonlinearities.Definition of uplift and soil plasticity models and of the coupling between the two require a set of parameters that depend on the soil characteristics and the foundation geometry.For practical applications, calibration of these parameters is required.In this paper, calibration tables have been produced for the parameters describing the foundation uplift behavior.In the case of a rectangular foundation (that has been calibrated for the first time), two extra parameters are introduced with respect to the strip and circular footing: the footing aspect ratio and the direction angle of the resultant overturning moment.In addition, a standardized methodology has been proposed to calibrate the parameters describing soil plastic behavior.The macroelement validation procedure has been carried out in the case of a bridge pier founded on a strip footing.The discrepancy between macroelement calculations and detailed finite element modeling has been evaluated for twenty earthquake records.Prediction of the superstructure maximum displacements (mean error < 10 %, standardized deviation < 20%) and efforts (mean error < 20 %, standardized deviation < 10%) is validated.Macroelement limitations concern the evaluation of foundation residual displacements, suggesting that further development should be focused on the improvement of plasticity model for soil irreversible behavior.

Overhead travelling cranes are common equipment in industrial facilities and are usually designed to resist dead and live loads. Seismic motion produces noteworthy horizontal loads that can cause damage and jeopardize the stability of the crane or its components. Moreover, effects of seismic loads on the crane depend strongly on the mechanical char a teristics of the carrying structure. In some cases, travelling cranes may represent an important m ss with respect to the carrying structure and their support arrangement may constitute a real con strai t for the dynamic response of the carrying structure. For steel frame carrying structures, due to their flexibility and light mass, dynamic interaction with massive travelling cranes (especia lly for crane multi-support configurations) can significantly influence seismic response. Adopting a proper seismic analysis technique is in such case s an essential step for the seismic design of overhea d cr nes since it should describe accurately the dynamic response of the crane on carrying structure . Three numerical analysis techniques are examined in the present study: (a) uncoupled response spectrum method; (b) inertial coupled response spec trum method; (c) dynamic coupled response spectrum method. The aim of the study is to evaluat e conservatisms and inadequacies associated to each technique. The study concerns the seismic resp onse of an overhead crane supported by a steel frame building exhibiting linear elastic material b ehaviour and modelled using a three-dimensional finite element mesh. In order to cover a wide range of configurations, different crane and trolley locations and crane loading states are taken into a cc unt in the study. Since structural integrity and stability assessment of travelling crane under seismic loads is the final objective of the study, conservatisms and/or inadequacies of each analysis technique are accounted for with respect to structural failure an d standard collapse criteria. The implementation of a suitable analysis technique may lead to a radical redefinition of seismic capacity and stability margins of travelling cranes . The present paper outlines the key features of cr ane and carrying structure that must be accounted for i n der to carry out a concise seismic analysis. 1 Project engineer, Géodynamique et Structure, Bagne ux, andrea.godoy@geodynamique.com 2 Project engineer, Géodynamique et Structure, Bagne ux, frederic.barbier@geodynamique.com 3 Project engineer, Géodynamique et Structure, Bagne ux, charisis.chatzigogos@geodynamique.com 4 Project engineer, EDF/SEPTEN, Lyon, nicolas.besson @edf.fr 5 Project engineer, EDF/CIDEN, Lyon, alfred.thibon@e df.fr 6 Team Manager engineer, EDF/CIDEN, Lyon, martin.ray @edf.fr

In this paper we provide an overview of recent research work that contributes to clarify the effects of non-linear dynamic interaction on the seismic response of soil-foundation-superstructure systems. Such work includes experimental results of seismically loaded structures on shallow foundations, theoretical advancements based on improved macro-element modeling of the soil-foundation system, examples of seismic design of bridge piers considering non-linear soil-foundation interaction effects, and numerical results of incremental non-linear dynamic analyses. The objective of this paper is to support the concept of a controlled share of ductility demand between the superstructure and the foundation as a key ingredient for a rational and integrated approach to seismic design of foundations and structures.

The work is concerned with the development of an original macro-element model for shallow foundations within the context of performance-based design of structures. The macroelement can be viewed as a link element placed at the base of the structure that reproduces in a simplified, yet coherent way the non-linear interaction phenomena arising at the soil-footing interface during dynamic excitation. As such, it offers an efficient prediction of the maximum and permanent displacements at the foundation level by identifying the non-linear mechanisms that produce them. These are: (a) the sliding mechanism along the soil-footing interface, (b) the irreversible soil behaviour mechanism and (c) the foundation uplift mechanism. These non-linear mechanisms are introduced within the macro-element model in a fully coupled way. In its present state of development the model can be used for strip and circular footings in purely cohesive or purely frictional soils.

The paper presents results of incremental dynamic analyses (IDA) of a simple structural system with consideration of non linear soil structure interaction. The analyses are facilitated using a non linear dynamic macroelement for the soil-foundation system. Three base conditions are examined, namely fixed base, linear foundation and non-linear foundation including uplift and soil plasticity. IDA curves are produced for a variety of intensity and damage parameters describing both the maximum and the residual response of the system. The results highlight the beneficial role of foundation non linearities in decreasing the ductility demand in the superstructure but point out the need to carefully assess the variability of the response when non linearity is allowed at the foundation design.

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 “macroelement” 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 nonlinearities is undertaken based on experience gained with earlier works. It is suggested that the nonlinearities be incorporated in the model within a unified formalism making use of the theory of multimechanism 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.

Within 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.

L'objectif de cette these est de contribuer a l'etude du comportement sismique des fondations superficielles et d'offrir de nouveaux outils pour le traitement de problemes pertinents, orientes vers la nouvelle philosophie de conception parasismique des structures : la conception basee sur la performance (« performance-based design »). On a travaille suivant quatre axes d'approche sur la problematique de la these : a. Reconnaissance des caracteristiques principales du probleme par l'examen de ruptures sismiques de structures reelles. Cet effort a abouti a la creation d'une base de donnees d'environ 200 structures qui ont subi une rupture par perte de capacite portante au niveau de la fondation. b. Approche theorique pour la determination de la capacite portante sismique d'un systeme de fondation. On a traite le probleme de la capacite portante sismique d'une semelle circulaire sur un sol purement coherent heterogene par l'approche cinematique du Calcul a la Rupture. Les solutions etablies nous ont permis de proposer une modification/extension des procedures de conception existantes qui sont incorporees dans les normes de conception parasismique europeennes (Eurocode 8). c. Approche experimentale pour la validation de la solution theorique etablie. Une collaboration avec le LCPC – Centre de Nantes a abouti a la planification des trois seances d'essais en centrifugeuse. Les deux premieres seances sont incluses dans la these et portent sur la determination de la capacite portante d'une semelle circulaire sur sol coherent sous chargement quasi-statique. d. Developpement d'un outil integre permettant la mise en œuvre d'analyses dynamiques efficaces pour la prise en compte de l'interaction sol-structure non-lineaire au niveau de la fondation. On a developpe un nouveau modele de macroelement pour le systeme sol-fondation. Le macroelement est utilise comme element de liaison a la base de la superstructure et reproduit les effets non-lineaires qui ont lieu au niveau de la fondation lors d'une sollicitation sismique. Le modele propose comporte deux mecanismes en couplage : la plastification du sol et le decollement qui peut se produire sur l'interface sol-structure. L'objectif de cet outil est de permettre d'effectuer de maniere efficace un grand nombre d'analyses de structures dynamiques non-lineaires. L'objectif ulterieur de nos developpements est d'enrichir les normes de conception parasismique actuelles et de les orienter vers une philosophie de conception basee sur la performance des structures lors d'un seisme.

This study concerns the determination of the seismic bearing capacity of a circular footing resting on a purely cohesive heterogeneous soil layer. The problem is treated using the kinematic approach of the Yield Design theory. The soil strength is modelled by the Tresca criterion with C0 the cohesion at the soil surface and G the vertical cohesion gradient. The loading process of the system is described by four loading parameters: an inclined force (N: vertical component, V: horizontal component), a moment (M) acting at the center of the footing and horizontal uniform inertial forces (Fh) acting in the soil volume during the seismic excitation. Two cases are considered for the soil: a soil with an infinite tensile strength and a soil with zero tensile strength. The soil-footing interface is considered purely cohesive with zero tensile strength. The study presents optimal upper bounds for the ultimate combinations of the dimensionless loading parameters (N, V, M, Fh) by the examination of a series of three-dimensional virtual kinematic mechanisms of failure. The results are presented in the form of surfaces in the space of the parameters (N, V, M) for a range of values of Fh.

Within 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 heterogeneous 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 presented, 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.