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

A Simple Numerical Tool for Dynamic Soil-Structure Interaction Analyses Including Non-Linear Behaviour of Both Structure and Foundation

In this paper a simple model to take into account dynamic non-linear soil-structure interaction is presented: it consists of a 1 degree-of-freedom (dof) superstructure and a 3 dof macro-element foundation. Both the superstructure and the soil-foundation system exhibit a non-linear behaviour. In particular the superstructure is characterized by an elastic perfectly plastic behaviour, while the foundation macro-element encompasses the two sources of non-linearity that arise in the soil-foundation interface: a) the one due to the irreversible elastoplastic soil behaviour (material non-linearity) and b) the one due to possible foundation uplift (geometric non-linearity). The global model thus entails the following features: a) the coupling between the foundation and the superstructure when one or both of them enter into the non-linear range, b) the capability for the foundation and the superstructure to dissipate energy, c) a prediction of peak and residual displacements in both the superstructure and the foundation, d) the possibility to model the isolation effects for the structure due to the foundation non-linear behaviour and e) the possibility for the superstructure to reach a particular level of ductility demand. Therefore, the model can serve as a numerical tool for assessing performance-based design approaches that wish to take into account non-linear soil-structure interaction. This is illustrated through several case studies of bridge piers, in which a comparison between the results obtained by dynamic analyses performed with different base conditions (fixed base, elastic base, elastoplastic base with uplift) emphasizes the role of the non-linear soil-structure interaction in design

The effects of Soil-Structure Interaction on a reinforced concrete viaduct

International audienceThis paper presents a numerical strategy to model a three-pier viaduct made of prestressed concrete. The viaduct was tested pseudodynamically in ELSA laboratory (JRC Ispra, Italy). During the experimental campaign, only the three piers were tested, whereas the behaviour of the deck was simulated using the finite element method. The first part of the paper presents a numerical model of the viaduct based on the Timoshenko multifibre beam elements and non-linear constitutive laws. Comparisons with the experimental results show the good performance of the approach. In the second part, a parametric study is carried out showing the influence of Soil-Structure Interaction (SSI). Various types of soils are considered using a recently developed macro-element representing a rigid shallow foundation. The macro-element is suitable for dynamic (seismic) loadings and it takes into account the plasticity of the soil, the uplift of the foundation, P-theta effects and the radiative damping. Finally, the numerical results are compared with the ones coming from a classical engineering approach using linear elastic springs at the base of the piers. This comparison shows that SSI is a complex phenomenon inducing displacements and internal forces in the structure that are difficult to predict with the linear approach. Based on the results obtained in this paper, it seems now possible to use this approach to investigate numerically the behaviour of a wider variety of configurations

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

A simplified nonlinear sway-rocking model for evaluation of seismic response of structures on shallow foundations

This paper presents a simplified Nonlinear Sway-Rocking model as a preliminary design tool for seismic soil-structure interaction analysis. The proposed model is intended to capture the nonlinear load-displacement response of shallow foundations during strong earthquake events where foundation bearing capacity is fully mobilised. Emphasis is given to heavily-loaded structures resting on a saturated clay half-space. The variation of soil stiffness and strength with depth, referred to as soil non-homogeneity, is considered in the model. Although independent springs are utilised for each of the swaying and rocking motions, coupling between these motions is taken into account by expressing the load-displacement relations as functions of the factor of safety against vertical bearing capacity failure (FSv) and the moment-to-shear ratio (M/H). The simplified model has been calibrated and validated against results from a series of static push-over and dynamic analyses performed using a more rigorous finite-difference numerical model. Despite some limitations of the current implementation, the concept of this model gives engineers more degrees of freedom in defining their own model components, providing a good balance between simplicity, flexibility and accuracy