Aerodynamic damping in certain conditions appears to have a negative value, which increases the dynamic response of a tall building. Six single-degree-of-freedom (SDOF) aeroelastic models of tall buildings with typical cross sections (square, square with concave or bevel corners, and rectangular) are tested in a wind tunnel with a suburban terrain flow field condition. The along-wind and across-wind aerodynamic damping ratios of the tall buildings are identified by using the eigensystem realization algorithm (ERA) method in conjunction with the random decrement technique (RDT). The effects of wind speed, corner modifications (concave or bevel corner), side ratio, and wind direction on the aerodynamic damping are studied. The results indicate that in most cases the along-wind aerodynamic damping is positive and gradually increases with the increase of reduced wind speed (Ur). The across-wind aerodynamic damping is likewise a positive value at lowUrin most cases, but suddenly becomes negative whenUrbecomes greater than 10.5 for the square cross-section building.
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