Rotor platforms on pile-groups running through resonance: a comparison between unbounded soil and soil-layers resting on a rigid bedrock

Rotor platforms supported by pile-groups typically run through resonance during start up and shut down. End-bearing pile-groups resting on a rather stiff underground surface cause additional layer-resonances compared with pile-groups driven into a half-space. On the other hand, the system's eigenfrequencies are accompanied by energy dissipation due to radiation damping. Thus the question arises, and is treated in this paper, if this radiation damping for end-bearing pile groups is strong enough to significantly suppress the additional resonance-peaks. The analysis uses dynamical stiffness coefficients in the frequency-domain for unbounded media recently published by Padrón et al [1]. In order to treat transient excitations a transformation into the time-domain is necessary and is here realized through a rational representation which has been described and used in [2] but only for pile groups resting in an elastic half-space, which exhibit a much smoother behavior (with reference to frequency) than the case treated here.