Improved expression for across-wind aerodynamic damping ratios of super high-rise buildings

To study across-wind aerodynamic damping ratios of super high-rise buildings, wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models with various aspect ratios and mass-damping parameters were carried out. The relationship between aero-damping ratio and reduced wind velocity (Vr), wind field roughness, aspect ratio, structural mass, structural damping as well as across-wind displacement was investigated systematically. It was found that the positive aerodynamic damping ratio is negatively correlated with the structural damping ratio and structural mass at Vr lower than critical reduced velocity of resonance (Vc). However, when Vr is close to or slightly bigger than Vc, the absolute value of negative aerodynamic damping ratio is positively correlated with structural damping but negatively correlated with structural mass. Therefore, the empirical function based on aerodynamic damping ratio alone cannot be reliably established, because the aerodynamic damping ratio alone is insufficient to assess aerodynamic effects. Thus, these considerations lead to a proposal of the concept of reduced damping ratio. This concept allows an improved empirical function of aerodynamic damping ratio to be established. Effects of the aspect ratio, reduced wind velocity, wind field terrain, structural damping and mass density were all considered in this empirical function.