| Super-tall building is a kind of typical wind-sensitive structure, and wind load is one of the horizontal controlling loads for this type of structures. This paper involves field measurement and wind tunnel test studies on several key issues of the wind effects on super-tall buildings. The major work and inovations include:(1) The scale effects of wind tunnel test on tall buildings are studied. Wind tunnel tests were conducted for three scale ratios models, 1:300, 1:400 and 1:500, of the CAARC standard tall bulding. The scale effects on some important parameters, including the mean wind pressure coefficient and shape coefficient, the root mean squre(RMS) wind pressure coefficient, the power spectral density(PSD) of fluctuating wind pressure and it spatial correlation, and the PSD and spatial correlation of wind loads corresponding to different pressure tap layers, are studied. It was found that the measured positive wind pressure coefficients on the windward elevation of different scaled models match well, and comparatively, the relative error of the negative pressure coefficients on the side and rear elevation is larger. For the models with larger size, the spatial correlation of the measured surface pressure and the wind loads are weaker than those of the models with smaller size. The PSD of the wind pressure and the wind load of the pressure tap layer obtained from different model tests can match well.(2) The damping characteristics of super tall buildings under typhoon exitaions are studied. Some researchers involved in wind enginnering proposed a point of view: the daming raio of a super-tall building under wind excitation varies nonlinearly with its vibration amplitude, and these results were mostly obtained by two modified random decrement technique(RDT). In this paper, the simulated ideal signals that include constant damping ratios and signals with specified signal-to-noise ratio(SNR) were used to observe the validation of these two modified RDT methods. It was found that in some cases, the identified damping ratios correspond nonlinearly to the vibration amplitudes, while the real damping ratios were originally specified as constants for these cases. Therefore, the validation of these two modified RDT methods and the consequent results are questionable. A super tall building, the Zhuoyue Centuray Center with the height of 280 m, was taken as an example to study the damping characteristics of super-tall buildings under typhoon excitations. Based on the measured data during the passage of four typhoons, and some data measured under the weak wind and the ambient vibration conditions, the dynamic parameters of the building were identified. It was found that the damping raito has no obvious relationship with the vibration amplitude.(3) A new method was proposed for determination of the dynamic parameters of the model-balance system for high-frequency force balance(HFFB) wind tunnel test. The data measured by HFFB must be pre-processed to remove the amplification effect of the model-balance system to the aerodynamic wind forces or moments. The dynamic parameters of a model-balance system are traditionally determined by the knocking test. In this study, a new method was proposed to identify the dynamic parameters of the model-balance system. Unlike the traditional knocking method, the new method does not need knocking tests, but adopts the measured loads at the base of the building model in wind tunnel test directly to identify the natural frequency and damping ratio of the model-balance system. Using this method, one can obtain different natural frequency or damping ratio for different wind angle cases, and of course, the identified damping ratios include the aerodynamic damping. Apparently, the knocking method only gives the structural damping and cannot consider the aerodynamic damping, therefore, the priority of the new method to the traditional method lies not only in requiring no extra knocking tests but also in capable of giving more accurate results. Three examples, including a hypothetical tall building with rectangular cross-section, an actual tall building with approximately rectangular cross-section and an actural tall building with nonrectangular cross-section, were employed to show the validation of the proposed method.(4) A new method was proposed for computing the equivalent static wind load(ESWL) based on the HFFB wind tunnel test. Compared to the traditional method, the proposed method uses an additional item for consideration of the correlation between the background and resonant response. Results given by the new method are more accurate than those given by the traditional method. Two examples, the Guangzhou East Tower and Guangzhou West Tower, were used to show the effectiveness of the proposed method.(5) Four reference wind pressures corresponding to four different wind climate models were used to compute the wind-induced response of the Guangzhou East Tower. It was found that there is considerable variation in the results based on different reference wind pressure values. The Guangzhou West Tower was taken as the example and the computed acceleration responses atop the building by adopting the four wind pressure values were compared to the field measured data recorded in the past 7 years. It was found that the field measured maximum instantaneous acceleration is obviously smaller than the wind tunnel test, indicating that the four wind climate models might overestimate the reference wind pressure. The wind-induced response of Guangzhou East Tower was compared to that of the Guangzhou West Tower, the results show that the peak acceleration response at the top of the building and peak bending base moment response coefficients of the East Tower are smaller than those of the West tower, indicating that the ‘setback’ design scheme adopted by the East Tower makes its wind-resistant performance better than that of the West Tower.(6) With the wireless accelerometers of model LAC-I, developed by the authors especially for full-scale measurements of wind-induced response of tall buildings, the acceleration of a super-tall building of 441.8 m, Shenzhen Kingkey 100(KK 100), was monitored continuously for over 5 years. The recorded data during four major typhoons from 2011 to 2015, including Nesat, Doksuri, Vicente and Usagi, combined with other data measured under normal weak wind and ambient excitation, were used to identify the dynamic parameter of KK100. Then the field measured data was compared to the results of wind tunnel test to verify the reliability of the wind tunnel test. It was found that the identified natural frequencies of the structure are almost the same for all cases, and the identified result is about 21% larger than the computational result based on the finite element modeling analysis provided by the structural design consultant at the design stage, whereas the identified damping ratios are relatively discrete, distributing at the range of 0.6% ~ 0.9% in x-direction and 0.33% ~ 0.71% in y-direction. Moreover, the identified damping ratios have no obvious relationship with the vibration amplitudes. It was also found that under nearly the same wind circumstance, the results of full-scale measurements and wind tunnel test can match well. In the dominant lateral-wind direction, the peak acceleration response of wind tunnel test is 4.2% larger than that of full-scale measurements, which shows the reliability of wind tunnel test. Meanwhile, maximum wind speed that nears to the 10-year return period wind speed in Shenzhen, has been observed in the past 5 years, however, the recorded maximum instantaneous acceleration of KK100 was just 0.123 m/s2. The field measurement results show that the serviceability requirement of the building can be well satisfied. |
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