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Kareem conducted an experimental study on across-wind aerodynamic forces on tall buildings with various section shapes in urban and suburban wind co research showed that for the buildings with , uncertainties of wind and structural parameters have small effects on PSD of the across-wind aerodynamic force, and the correlation between the along-wind aerodynamic force and the across-wind aerodynamic force or the torsion moment is negligible, but there is a strong correlation between the across-wind aerodynamic force and the torsion moment. This conclusion is important for the development of three-dimensional refined wind load model. Particularly, Gu and Quan and Quan et al. made detailed studies on the effects of the side ratio of a rectangular building, cross-section shape of a building, aspect ratio of a building, and wind field condition on the PSD of the across-wind aerodynamic force of tall buildings using a five-component balance. In fact, based on a large number of wind tunnel test results, formulas for across-wind aerodynamic force coefficients of the typically tall buildings have been derived by us and other researchers.
Across-wind aerodynamic damping
In 1978, Kareem performed an investigation on across-wind dynamic responses of tall buildings based on both of the aero elastic model technique and the wind pressure integration method. He found out that the across-wind dynamic responses calculated with the across-wind aerodynamic forces obtained from the wind pressure tests at a certain test wind velocity range were always smaller than those of the aero elastic model of the same building model. This important result made researchers realize the existence of across-wind negative aerodynamic damping.
Subsequently, researchers carried out numerous studies on the problem and developed effective methods for identifying aerodynamic damping. The first kind of method obtains aerodynamic damping by comparing the dynamic responses computed based on the aerodynamic forces from rigid building model tests and those from aero elastic model tests. The second one separates aerodynamic damping force from the total aerodynamic force measured from aero elastic building models or forced vibration building models. The third kind employs identification methods for extracting aerodynamic damping from random responses of aero elastic models. Moreover, researchers realized the effect law of factors, including structural shape, structural dynamic parameters, wind conditions, and so on, on aerodynamic damping, Isyumov et al. were the first researchers to propose a method for aerodynamic damping through comparing responses from a rigid building model test using HFFB technique with those of an aero elastic model of the same building. Cheng et al. adopted the method to study across-wind responses and aerodynamic damping of tall square buildings and proposed an aerodynamic damping formula.
Steckley initially developed a set of forced vibration devices for measuring total aerodynamic forces, including aerodynamic damping force and aerodynamic force. He measured the base bending moment of a tall building model, which was vibrated by a specially designed device. The aerodynamic force related to structure motion was separated from the total aerodynamic force, and then it was decomposed into aerodynamic stiff force and aerodynamic damping force to obtain aerodynamic damping. Vickery and Steckley proposed a negative aerodynamic damping model. Cooper et al. attempted to measure wind pressure on a harmonically vibrating building model to obtain total aerodynamic force. Aerodynamic damping was then computed using a method similar to Steckley’s. The advantage of this kind of method is that the characteristics of real buildings do not have to be taken into consideration in wind tunnel tests, which makes this kind of method more convenient to use, especially in popularizing the test results. The main shortcoming of this kind of method is that it requires complicated devices, especially because a multi-component coupling device was not available until now.