Aerodynamic Damping in the Along-Wind Response of Tall Buildings

We present a novel methodology for the estimation of the aerodynamic damping that affects the along-wind response offal] buildings. The estimation uses (1) measurements of the external pressures on the windward and leeward faces under wind normal to a building face; (2) a simplified model of the relation between those pressures and the longitudinal fluctuating velocities with respect to the building; and (3) time-domain estimates of the along-wind building response that preserve the phase relationships between pressures and response. The methodology accounts explicitly for the shapes of the building's modes of vibration, the natural frequencies of vibration, and the mechanical damping ratios, and takes advantage of the recent development of efficient time-domain algorithms for calculating dynamic structural response to wind. The methodology is applied to an isolated tall building in suburban terrain. The results of the calculations show that, for the example being considered, the aerodynamic damping (1) is positive, that is, it has a favorable effect; (2) is small relative to the mechanical damping; (3) is for practical purposes independent of the shape of the fundamental mode of vibration: and (4) is unaffected by higher vibration modes.