Novel smart variable stiffness tuned mass damper and its real time identification and control using time frequency techniques
Doctor of Philosophy thesis
The semi-active variable stiffness tuned mass damper (SAIVS-TMD), developed in this thesis, is capable of continuously varying its stiffness and retuning its frequency due to real time control, and is robust to changes in building stiffness and damping. In comparison, the passive tuned mass damper (TMD) can only be tuned to a fixed frequency, which is the first mode frequency of the building. The building fundamental frequency can change due to damage or other reasons. The developed SAIVS-TMD overcomes the limitations of the TMD by retuning the frequency in real time. Real time instantaneous frequency identification and control algorithms are developed in this thesis based on time-frequency techniques. Real time tuning algorithms that identify and tune the instantaneous frequency of the SAIVS-TMD are developed based on Hilbert Transform (HT), Short Time Fourier Transform (STFT) and Empirical Mode Decomposition (EMD). A new method for smoothing the end effects of EMD algorithm is proposed and verified through numerical examples. The mathematical formulation of the linear time varying (LTV) system is developed. A new predictor-corrector algorithm is proposed for the LTV system. The LTV analytical model is developed to study the response of SAIVS-TMD under harmonic, sinesweep, random, wind and earthquake excitation. The effectiveness of the SAIVS-TMD and new identification and control algorithms is verified by means of shake table tests of a three-story 1:10 scale steel model. The confirmation of the performance of the SAIVS-TMD and the real time controller is studied analytically in a 76-story benchmark tall building. The results confirm the robust performance of the SAIVS-TMD, even in cases with +/-15% building stiffness uncertainty. The effectiveness of the SAIVS-TMD in reducing the responses of the structures excited by much stronger seismic ground motion is also presented. The effectiveness of the instantaneous frequency identification algorithm, based on EMD/HT method, in offshore structures is also presented.