Assessment of the dynamic characteristics of a multi-storey parking structure using ambient vibration measurements

The assessment of the dynamic characteristics of a reinforced concrete (RC) 13-storey parking structure was carried out using passive ambient vibration measurements. Three independent stations consisting of a high sensitive digital velocity sensor with 3 components (2horizontal and 1 vertical) were deployed in four different arrays at the target structure. These sensors were synchronised through an internal GPS antenna. The modal vibration characteristics were initially identified in the predominant frequencies of the two horizontal (NS and EW components) Fourier amplitude spectra, after applying the Fourier transforms to selected 16 seconds time frames of steady stationary microtremors in each array. A new technique for the interpretation of these predominant frequencies was introduced using the comparison of waveforms and the instantaneous particle positions obtained in horizontal or vertical orbits for the three stations of each array. Based on these comparisons, the EW and NS fundamental translational modes, as well as, the NS first higher translational and the torsional modes were identified. The values of these predominant frequencies would be useful to find appropriate values for the unknown equivalent elastic parameters, such as the equivalent Young's modules and Poisson's ratio, which are required in the FEM model of the target structure.