Research On Boundary Layer Wind Characteristics Over Urban Area And Dynamic Responses Of Tall Buildings

Due to the growing use of light-weight and high-strength materials, modern tall buildings have become more and more taller and flexible. As a result, these superstructures tend to be of more long-period and lightly damped and the sensitivity of these tall buildings to dynamic excitations by wind has increased. It is thus necessary to investigate wind effects on such dynamic-sensitive structures.The boundary layer wind profiles and atmospheric turbulence characteristics over a typical urban area were investigated based on the wind speed, direction and temperature data observed from numerous anemometers at heights between8m to320m in Beijing Meteorological Tower. The aerodynamic parameters of atmospheric boundary layer and the ground roughness exponents around the tower were determined from the measured wind speed profiles. Three empirical mean wind speed profiles (Power-law, Log-law and the D-H models) were compared with the measured profiles. Atmospheric turbulence information for all sectors were presented and a turbulence model over a typical urban area was also proposed.Statistics analysis of wind-induced response data measured from Taipei101Tower (508m,101floors) during typhoons and under earthquake excitations were conducted. The dynamic characteristics of the tall building were determined based on the field measurements and compared with those calculated from a finite element model of the building. The damping ratios of the building were evaluated by the frequency domain decomposition method and random decrement technique, which demonstrated amplitude-dependent characteristics. The characteristic of long-period waves of a distant earthquake excitations were investigated. The dynamic responses and dynamic amplification factors of the super-tall building under the long-distance earthquake were assessed based on the field measurements and numerical analysis results.To monitor wind effects on and movements of high-rise structures, two wind and movement monitoring systems were installed in the Two International Financial Centre (420m,88floors) in Hong Kong and CITIC Plaza (391m,80floors) in Guangdong, respectively. Significant field data have been acquired from the tall buildings by the wind and vibration monitoring systems during typhoon and tropical cyclone storms. The typhoon-generated wind characteristics over urban areas including mean wind speed, mean wind direction, turbulence intensity, gust factor, peak factor, turbulence integral length scale and power spectral density of fluctuating wind speed were presented and discussed.The variations of the turbulence intensities, gust factor and turbulence integral length scale measured during typhoons with mean wind speed were investiaged. The three-dimensional wind spectral models were proposed based on the field mesurements. A comparative study of the turbulence characteristics of typhoon winds and monsoon winds was conducted. Furethermore, the dynamic characteristics of the tall buildings were evaluated based on both the measured acceleration responses and displacement responses and used to evaluate the adequacy of existing theoretical and empirical models. The relationships of the wind-induced acceleration or displacement responses and the reduced wind speed were discussed. The field measured acceleration responses were compared with wind tunnel test results for verification of wind tunnel test techniques.Detailed wind tunnel tests for a supertall building were carried out and the variations of mean wind pressure coefficient with height were discussed. The differences of the shape coefficient from the wind tunnel tests and the building design codes of China were analyzed. The interference effects on the surface wind pressure and shape coefficient from adjacent buildings were assessed based on the wind tunnels results. The non-Gaussian characteristics of local pressure fluctuations were investigated. Horizontal and vertical correlation features between different pressure taps were studied and horizontal and vertical coherence fuctions between different pressure taps in windward and leewad faces of the building were presented.Based on the wind tunnel studies, the variations of longitudinal, lateral and torsional wind loads with wind attack direction were evaluated. The cross-correlations among various wind loading components were presented and discussed in detail. Furthermore, the effect of surrounding buildings on the cross-correlations was investigated. The spectral characteristics of of along-wind, across-wind and torsional components were studied and an empirical formula for estimation of the across-wind overturning moment spectrum for the super-tall building is presented. The wind-induced amplifier factors of the building were caculated based on the wind tunnel results and compared with those estimated from the building design codes of China. A parametric study on numerous variables was performed for the wind-induced vibration of the tall building (such as high mode, reduced wind speed, damping ratio and first-order frequency and so on).In this study, the boundary layer wind characteristics and dynamic responses of tall buildings were investigated in detail through field measurments, wind tunnel tests and theoretical analysis. The presented results are valuable for the design of super tall buildings.