No abstract

The dynamic through-soil interaction between nearby pile supported structures in a viscoelastic half-space, under incident S and Rayleigh waves, is numerically studied. To this end, a three-dimensional viscoelastic BEM-FEM formulation for the dynamic analysis of piles and pile groups in the frequency domain is used, where soil is modelled by BEM and piles are simulated by one-dimensional finite elements as Bernoulli beams. This formulation has been enhanced to include the presence of linear superstructures founded on pile groups, so that structure-soilstructure interaction (SSSI) can be investigated making use of a direct methodology with an affordable number of degrees of freedom. The influence of SSSI on lateral spectral deformation, vertical and rotational response, and shear forces at pile heads, for several configurations of shear one-storey buildings, is addressed. Maximum response spectra are also presented. SSSI effects on groups of structures with similar dynamic characteristics have been found to be important. The system response can be either amplified or attenuated according to the distance between adjacent buildings, which has been related to dynamic properties of the overall system.

In this paper, a 3D BEM-FEM coupling model is used to study the dynamic behavior of piled foundations in elastic layered soils in presence of a rigid bedrock. Piles are modelled by FEM as beams according to the Bernoulli hypothesis, and every layer of the soil is modelled by BEM as a continuum, semi-infinite, isotropic, homogeneous, linear, viscoelastic medium. First, the main points of the model are set out. Then, several results of vertical, horizontal and rocking impedances for single piles and 2 × 2 pile groups embedded in a stratum resting on a rigid bedrock, are presented. The influence on the dynamic response of stratum depth, soil stiffness and piled foundation configuration is discussed. Finally, the influence of the stratigraphy on the seismic response of a 3 × 3 pile group is analyzed, together with the pile-to-pile kinematic interaction and the wave-scattering phenomena.

S U M M A R YThe collective excitation of city structures by a seismic wavefield and the subsequent multiple Structure-Soil-Structure Interactions (SSSIs) between the buildings are usually disregarded in conventional seismology and earthquake engineering practice. The objective here is to qualify and quantify these complex multiple SSSIs through the design of an elementary study case, which serves as a benchmark for theoretical, numerical and experimental crossed-analysis. The experimental specimen consists of an idealized site-city setup with up to 37 anisotropic resonant structures arranged at the top surface of an elastic layer and in co-resonance with it. The experimental data from shaking table measurements is compared with the theoretical and numerical results provided respectively by an equivalent city-impedance model derived analytically from homogenization in the long-wavelength approximation and a model based on boundary elements. The signatures of the site-city interactions are identified in the frequency, time and space domain, and in particular consist of a frequency-dependent free/rigid switch in the surface condition at the city resonance, beatings in the records and the depolarization of the wavefield. A parametric study on the city density shows that multiple SSSIs among the city structures (five are sufficient) can have significant effects on both the seismic response of its implantation site and that of the buildings. Key parameters are provided to assess site-city interactions in the low seismic frequency range: They involve the mass and rigidity of the city compared to those of the soil and the damping of the building.Key words: Earthquake dynamics; Earthquake ground motions; Body waves; Seismic anisotropy; Site effects; Wave propagation. I N T RO D U C T I O NUrban and industrial areas require a particular attention in seismic analysis due to the concentrations of population, real estates, strategic public services and human activities having a large socioeconomical impact. However, the presence of the city is usually disregarded in conventional methods applied in seismology and earthquake engineering: The ground motion is supposed to result from the seismic source and substratum properties only, for example, Bonnefoy-Claudet et al. (2008), while the response of a structure to the ground motion is studied independently from the surrounding buildings, for example, Jennings & Bielak (1973). These standard approaches omit the effects of multiple soil-structures dynamic interactions on the seismic field and the buildings' response.While these approximations are reasonable in most cases, they are questionable in urban areas, where high-rise buildings, similar in height and design, are built closely from one another. Neighbouring buildings can exchange significant amounts of energy with each other, and form, with the soil, a fully coupled dynamic system that should be treated as a whole. The problem of mutual interactions between two buildings have been formulated initially by Luco & Contesse (19...

The influence of inclined piles on the dynamic response of deep foundations and superstructures is still not well understood and needs further research. For this reason, impedance functions of deep foundations with inclined piles, obtained numerically from a boundary element -finite element coupling model, are provided in this paper. More precisely, vertical, horizontal, rocking and horizontal-rocking crossed dynamic stiffness and damping functions of single inclined piles and 2 2 and 3 3 pile groups with battered elements are presented in a set of plots. The soil is assumed to be a homogeneous viscoelastic isotropic half-space and the piles are modeled as elastic compressible Euler-Bernoulli beams. Results for different pile group configurations, pile-soil stiffness ratios and rake angles are presented.