Continuous monitoring of dynamic parameters of the DGFSM building (Zagreb, Croatia)

Continuous broad-band measurements of vibrations on the 3rd floor of the building of the Department of Geophysics, Faculty of Sciences and Mathematics (DGFSM) in Zagreb provided high quality data that enabled monitoring of fluctuations of the building's basic dynamic parameters (fundamental frequencies and the corresponding damping). It was found that nonlinear behaviour is present even for the small strains induced by ambient vibrations, which was manifested in measurable reduction of fundamental frequency and increase of damping for larger excitation levels. Notable correspondence of the long-term wander of the fundamental frequency with the relative air humidity and the annual precipitation cycle indicate that variation of soil saturation may have caused variability in the soil-structure interaction. The damping was found to vary synchronously with the air temperature. The results point to the importance of considering all aspects of nonlinearity of building response even for small strains.