Abstract:
Earthquakes are among the most significant natural phenomena with highly negative social and economic consequences. The behavior of building structures during earthquake, the ensuing damage and other side effects are extremely important for all large cities. The dynamic characteristics of structures – predominant frequency and damping ratio used to assess the vulnerability of buildings, are most conveniently determined by analyzing ambient vibration data, as opposed to the more expensive and time-consuming traditional methods of Experimental Dynamics. In the present work, the damping ratio and the fundamental frequency are calculated by the RDM (Random Decrement Method). A bandpass filter with filter parameters chosen according to the predominant frequency obtained by the FSR (Floor Spectral Ratio) method is applied to the signal before the actual RDM processing. The results obtained by the RDM method are compared with those obtained by the FSR method. The investigated structure is the building of the National Institute of Geophysics, Geodesy and Geography (NIGGG), to the Bulgarian Academy of Sciences, which is a five-floor, cast-in situ RC building. Ambient noise measurements of 100 samples/second were made at ten locations on each floor using ETNA 2 mobile accelerometers.