Deterministic and stochastic responses of smart variable stiffness and damping systems and smart tuned mass dampers
Doctor of Philosophy
Semi-active control algorithms are developed and examined for a variety of civil engineering applications subjected to a wide range of excitations. Except two control algorithms based on continuous variable structure control and Lyapunov control, the semi- active controllers developed in this study are based on real-time estimation of instantaneous (dominant) frequency and the evolutionary power spectral density by time-frequency analysis of either the excitation or the response of the structure. Time-frequency analyses are performed by either short-time Fourier transform or wavelet transform. The semi-active strategies are applied to three categories of structures: (1) smart single- and multi- degree-of-freedom (sSDOF/sMDOF) systems subjected to pulse-type and random ground excitations, (2) single/multiple smart tuned mass dampers (sTMD/sMTMD) subjected to random wind and ground excitations, and (3) smart tuned liquid column dampers (sTLCD) subjected to random wind and ground excitations. For sMDOF/sMDOF systems, nonlinear control algorithms developed to independently vary stiffness (continuous variable structure control) and damping (Lyapunov control) are examined against near-fault earthquakes and pulse type of excitations fitted to them. Another semi-active (time-frequency) controller is developed based on minimizing the instantaneous H2 norm of the response of the structure. Two time-frequency controllers (feedforward and feedback) are developed for single/multiple smart tuned mass dampers (sTMD/sMTMD) subjected to either force or base excitation. In the feedforward control, the smart tuned mass damper stiffness and damping are varied based on the instantaneous (dominant) frequency of the excitation, whereas in the feedback control the smart tuned mass damper stiffness is varied based on the instantaneous (dominant) frequency of the response. The developed algorithms are also extended to semi-active smart tuned liquid column dampers (sTLCD) subjected to either force or base excitation. The performance of the control algorithms are evaluated by studying the deterministic and stochastic responses of the examined semi-active structures. Stochastic responses are computed from Monte Carlo simulations of various target evolutionary spectra. It is shown that smart variable stiffness and variable damping systems and smart tuned mass/liquid column dampers lead to significant response reduction over a broad frequency range and under a wide set of excitations.