Across-wind response characteristics of tall-square towers in urban flow: An experimental study focused on the aeroelastic effects

To fully use the land resource in the urban regions of metropolises, high-rise buildings of large aspect ratio maybe preferred for the new constructions. To systematically investigate the across-wind responses of these quite slender structures, the urban boundary layer flow of high turbulence intensity was simulated in the wind tunnel, and aeroelastic tests realized by the pivot model setup were carried out for the square cross section towers of various heights resulting in large aspect ratios (λ = 12, 16, 20). No appreciable aeroelastic behaviors have been observed for the λ = 12 tower even for a very low damping ratio (0.57%). This is in line with the many previous studies for the tall-square tower with an aspect ratio not higher than 10, likely due to the very high turbulence intensity in the urban terrain, mitigating the occurrence of possible aeroelastic behaviors. In contrast, the λ = 16 and (especially) the λ = 20 towers exhibit strong oscillations known as the across-wind galloping, evidenced by the monotonic increase in the amplitude–velocity curve and the clear characteristics of simple-harmonic oscillations. Moreover, it is observed that for a certain range of low damping ratios, these large oscillations were initiated at the same wind speed very close to the vortex-resonance wind speed. The interaction mechanism between vortex induced vibration and galloping is thus supposed responsible for this observation (even in urban flow). Finally, peak across-wind responses at various damping ratios were provided as well, serving as a useful reference for the future design of similar tall-square towers.