Along-Wind Aero-Elasticity of High-Rise Buildings by Using Indirect Forced Actuation Technique

Abstract

The frequency-dependent aerodynamic damping and stiffness of high-rise buildings in along-wind motion have been systematically investigated and compared through wind tunnel tests under smooth wind flow. A novel identification scheme based on the indirect forced actuation technique was developed, involving only a simple curve-fitting technique on the frequency response function induced by the actuation. To ensure that global minimization in curve-fitting was achieved, a genetic algorithm and a conventional gradient search method were used in obtaining the final results. An alternative derivation of the frequency response function via the time-domain state space equation is also presented, which has the supporting advantage that the simulation of time history of the structural response becomes possible. To demonstrate the approach, various prism models representing different high-rise buildings with varied aspect ratios and height-width ratios were used in the experimental identification. A total of nine models with 15 different configurations were successfully tested and identified using the proposed identification scheme. The experimental results indicated that the wind flow suppresses the along-wind vibration and the effect becomes stronger as the wind velocity increases. The identified results showed that aerodynamic damping is always negative (and hence stabilizes the structure) and monotonically decreases with increasing reduced velocity. At the same reduced wind velocity, the aerodynamic damping becomes more significant as the height increases. The trend of the aerodynamic stiffness and its relation to the height is not clear and depends on each particular case. Considering approximation, the formulas of constant aerodynamic damping and stiffness ratios are also presented for comparison. Overall, the frequency-dependent aerodynamic damping and stiffness presented in this paper provide the database that can serve as a guideline for practical application.