Influence of Type of Wave and Angle of Incidence on the Seismic Response of Pile Foundations and Pile Supported Structures

Abstract eng:
The dynamic response of pile foundations and pile supported structures has been extensively studied during the last four decades. Even though, there exists yet the need of achieving a better understanding on different aspects of the problem, such as the response of inclined piles, the influence of the presence of nearby structures, the importance of various kinds of non-linearities, or the influence of the different parameters of the soil-foundation-structure system on the seismic response of the superstructure and on the internal efforts arising along the piles. The type of seismic waves impinging on the site, and the angle of incidence of the waves, are important parameters of the seismic excitation. However, vertical incidence of waves is usually assumed in the analysis of the seismic response of piles, and only a small percentage of the large amount of works related to this topic take the angle of incidence into account. In this work, the influence of the type of wave and its angle of incidence on the seismic response of pile foundations and pile supported structures is investigated using a direct approach. To this end, a frequency-domain boundary element - finite element formulation is used, being the Boundary Element Method used to model the soil as a homogeneous, isotropic, viscoelastic, semi-infinite region; and the Finite Element Method used to model both piles (as EulerBernoulli beams) and superstructure (formed by horizontal rigid slabs and extensible vertical elastic piers). The code is able to model the incidence of Rayleigh waves, and also P, SH and SV body waves with a general angle of incidence. The formulation is briefly presented at the beginning of the paper. Some validation results, in terms of kinematic interaction factors of pile foundations, are presented. Then, different results in terms of internal efforts in piles and inter-storey drift in the superstructure are presented for different types of waves. It is shown that the angle of incidence has a great influence on the structural response, especially in the case of the SV wave, where the critical angle (at which there is a change in the nature of the reflected waves, and whose value depends exclusively on the Poisson’s ratio) plays a very important role, as the seismic response of the structure increases greatly around such angle. It is also shown that, in general, the vertical incidence is not the most unfavourable situation. 1

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