Researches On Full-scale Measurements And Modal Parameters Identification Of Tall Buildings Under Strong Wind

Many tall buildings have been or are being built with the development of world economic and construction technologies in the world. Modern tall buildings has manifested more flexible and lightly damped characteristics due to adopting high strength and lighter-weight materials with respect to those in the past. As a consequence, the sensitivity of these tall buildings to dynamic excitations, such as strong wind, has increasingly increased. On account of the increased sensitivity of tall buildings to wind, the design of wind loads as well as the estimation and control of wind-induced responses have become more important。The strong wind, such astyphoon, is a significant factor which gives rise to damage and vibration response of tall buildings or super tall buildings. The results of wind field full-scale measurements on tall buildings are the most direct information to afford insight into wind load effects, wind-induced dynamic responses, and wind-induced breakage on structures. Likewise, they are the most authoritative database used for revising both the present test methods and theoretical analysis models. The wind tunnel researches have showed that the assumption of Gaussian distribution and stationary process of the wind speed or wind pressure may not be consistent with the practicality in the civil engineering. The Gaussian model of wind pressure is unable to accurately describe wind pressure field of tall buildings. The wind velocity fluctuations may be not consistent with the typical velocity spectrum and the probability density functions also may be not accord with the Gaussian distribution under the special terrain conditions. On the other hand, accurate identification of structural dynamic parameters, especially for damping parameters, is becoming more and more importance for both serviceability design and safety design. However, there are serious scarcities of wind field full-scale measurement, especially wind pressure, and of damping data base for tall buildings. Naturally, modal parameters identification based on the excitation of environmental wind also requires an accurate identification method.The dissertation is supported by National Natural Science Foundation of China (Numerical simulation study on non-gaussian wind pressure of super high-rise building under the typhoon, Grant No. 50578092). Investigations on the wind field full-scale measurements of tall buildings in the special terrain conditions under the strong wind have been carried out. The analytic wavelet method applied to output-only model parameters identifications is explored by uese of the measured dynamic responses. Main works and results about the dissertation can be summarized as follows:1.Development in both the full-scale measurements of wind fields and modal parameters identification are firstly reviewed. Then, the dissertation elaborates the characteristics of the strong winds in the Earth's atmospheric boundary layer and analyzes the characteristics of the wind pressures on tall buildings.2.An approach has been proposed that the accurate levels of decomposing the time-varying mean wind speed are quantitatively determined by the saltation of simple scale wavelet energy. The accurate time-varying mean wind speed can then be gained by the inverse discrete orthogonal wavelet transforms of approximate coefficients in this level.3.Based on the basic principle of the wind pressure testing, a new type of wind pressure sensor has been invented in order to obtain the wind field characteristics of tall buildings under strong wind loads. An implementation scheme of wind field full-scale measurements on a super tall building is decvised. The wind velocity and pressure data measured synchronously are then analyzed in this dissertation to gain an insight into the characters of wind velocity, directions, and wind pressure.4.The coherence between wind pressures, with and without considerations of spurious coherence, respectively, has been analyzed by resorting to the wavelet transform. Likewise the coherence of wind-induced pressure fluctuations is compared with that of wind velocity fluctuations derived in accordance with an experiential formula.5.With resorting to matching mechanism between the wavelet function and complex-valued signal, both the amplitude and phase frequency information can be revealed by the analytic wavelet transformation (AWT) based on the Gabor wavelet function to achieve the modal damping ratios identification of structures. In accordance with the wavelet transform (WT) theory, the characters of Gabor wavelet function, the time-frequency resolutions, and end effects of the AWT are discussed. In order to effectively carry out the modal damping ratios identification of structures, the method selecting the parameters of Gabor wavelet function and the formula determining the usable lengths of signal are thus proposed.