Modal Parameter Identification Under Ambient Excitation And Their Effects On Wind-induced Response Of Tall Buildings

With the development of science and construction technology, several super high-rise buildings emerges in the modern urban city, such as Guangzhou West Tower (432m), Taibei 101 Tower (508m) and Shanghai Center (632 m) etc. In this paper, typhoon characteristics and wind-induced responses of Guangzhou West Tower has been studied based on the field measurement data during typhoon Megi, and modal parameter identification of Taibei 101 Tower has been also studied by the measured wind-induced response data . The main content of this research work are shown as the following:(1) First modal parameters (including natural frequencies , vibration modes and damping ratios) identification of Taibei 101 Tower was conducted by the SSI method and EFFD method. For the SSI method, the effects of different factors on the estimation accuracy of modal parameters, including excitation types,projection channel technique,the maximum state space dimension of stabilization diagram,the intensity of ambient excitation and selection of weighting projection matrix (SSI-UPC, SSI-PC and SSI-CVA), were analyzed and discussed in this study. Meanwhile the effect of selected frequency resolution on the actuary of modal identification was also studied in this study by EFDD method.(2) The wind characteristics and wind-induced response of this tall building were simultaneously measured when Typhoon Megi affected this tall building. Some results for wind characteristics at about 440m height were obtained from the statistical analysis on the measured wind data: 1) The turbulence intensity decrease with the increasing mean wind speed, while gust factor increases with the increased turbulence intensity, 2) The measured power spectral density of fluctuation wind speed in longitudinal and transversal direction could be fitted very well by Von Karman spectrum. The statistical analyses on the measured wind-induced acceleration response atop the building have shown that the measured natural frequencies are very close to the numerical FEM analyzed results. Finally the relationship between the wind-induced acceleration response atop the building and mean wind speed were obtained from the measured data. 3) Based on the measured acceleration data, amplitude-dependent damping ratios of the building were also obtained by the random decrement method. The typhoon-generated wind characteristics and wind-induced structural vibrations were investigated in detail on the basis of the full-scale measurements.(3) A simplified and reduced model was established based on the 3D finite element model of Guangzhou West Tower. By adopting the time history record of aerodynamic wind load acting on the center of mass at each floor, a modified Newmark-βmethod was developed in this study to evaluate the effect of different amplitude-dependent structural damping and aerodynamic damping models on the wind–induced response of this tall building. Comparing results showed that results obtained from amplitude-dependent structural damping models were some different from those obtained from constant damping assumption. Results from time-domain method were also compared with those from wind tunnel tests, and good agreement between them was found in this study.