Dadoulis, George I.George I.DadoulisManolis, GeorgeGeorgeManolisDragos, KosmasKosmasDragosSmarsly, KayKaySmarsly2022-12-162022-12-162022-08-2413th HSTAM International Congress on Mechanics Paper 28: 63 (2022)http://hdl.handle.net/11420/14399System identification, either stand-alone or in the context of structural health monitoring (SHM), typically entails extracting information based on the dynamic response of monitored structures. Standard practice utilizes free vibration regimes, recorded during monitoring, to recover the structural key dynamic parameters, i.e., natural frequencies and mode shapes. In this work, we propose a methodology to transform the forced vibration regime, based on Gabor transform, to trace the time evolution of dominant eigenfrequencies of a reference pylon with an additional, time-variable mass attached at the top. The external forcing functions are harmonic ground motions. Two cases are considered, one where the mass decreases to a nearly zero value, starting from a reference value, plus the opposite case where the additional mass increases from zero to the same reference value, which can be substantial, i.e., reaching 20% of the pylon mass. The eigenfrequencies converge at the end of the monitoring time interval, when ground motion ceases, to the standard values computed when the additional mass has a fixed value on the pylon. The methodology presented herein is useful in extracting as much information as possible from dynamic responses and is also of interest in the SHM of typical civil engineering infrastructure ranging from pylons to bridges and buildings.enConference Paper not in Proceedingshttps://hstam2022.eap.gr/book-of-abstracts/Other