Optimisation of Tuned Mass Damper Devices Towards Structural Vibration Reduction: Theoretical Settings and Numerical Analyses

The present doctoral thesis concerns theoretical concepts and numerical studies on the optimisation of Tuned Mass Damper (TMD) devices towards the control and reduction of structural dynamic responses, with specific reference to the context of civil and seismic engineering. The fundamental background of the optimisation of the TMD parameters, also called tuning, is presented first in its main features, based on reference to the mainstream literature, and in the assessing the relevance of the structural properties and of the role of the characteristics of the external excitation. A comprehensive analysis on the tuning of passive TMDs as applied to a singledegree-of-freedom primary structure subjected to benchmark ideal excitations is carried out, focusing on a range of structural parameters typical of real engineering applications. Then, the outcomes have been interpolated through nonlinear least squares and optimum tuning formulas of the TMD parameters have been outlined for each excitation case, based on ad hoc polynomial fitting models. Comparisons with main references from the literature are provided. The optimisation of TMD devices has been also investigated for the mitigation of the transient response, with main focus on the impulse excitation. Initially, a throughout optimisation of the passive device is derived, with consideration of different excitation cases, objective functions and structural parameters. Then, the control device has been upgraded to a hybrid TMD by means of the addition of an active controller, with the main task of reducing as well the peak response. Different feedback control strategies have been evaluated, from the points of view of: stability, device performance and amount of supplied control force. An important part of this research deals with the concept of optimum seismic tuning of TMDs, with real earthquake input directly involved within the tuning process. This feature represents an innovative way of investigating the TMD performance, since the control device is theoretically optimised on each specific structure and seismic event. The proposed tuning procedure is presented in detail and applied to a significant selection of structures and earthquake input signals. The so obtained optimum TMD parameters are first depicted and compared to those obtainable from reference tuning formulas from the literature. A wide set of results concerning the performance of the TMD is presented, considering different kinematic and energy response indexes, in order to trace down general trends on the effectiveness of the TMD in reducing the seismic response. A further and important stage of this study deals with a crossed comparison involving the TMD performance and relevant indexes such as the modal parameters, the frequency amplitude of the seismic signal and the response spectra, so that to inspect possible connections between the efficiency of the control device and the characteristics of the structural and the dynamic context. The studies and related outcomes presented in this thesis shall represent a contribution to the development and improvement of Tuned Mass Damper devices in terms of optimum performance, towards the control of a wide range of structures. Therefore, the presented thesis work, though connoted by a main theoretical character, may display different crucial implications in practical engineering applications.