ABSTRACT
Variation in dynamic characteristics of a SFSI system for about ten years is investigated based on 67 earthquake records observed in and around a densely instrumented structure. The results show about 30% reduction of the base-fixed and sway-fixed frequencies in ten years. On the other hand, the extracted rigid-body rocking mode frequency is unchanged over the years. It is shown that the change of the structural frequency is attributed to the deterioration of stiffness of the superstructure. The variation in frequency during some specific earthquakes is also studied, whose result exhibits strong amplitude dependence during the shaking and the frequency recovers almost to the initial state as the shaking is terminated.
