Experimental study on the coupling effects of wind-induced vibration of square-sectioned high-rise buildings with different stiffness ratios

In the wind-resistant design of high-rise buildings, the wind-induced response, excited by incident turbulence and vortex shedding of the wake flow, is an important design component. Larger self-excited across-wind responses occur when the wind speed closes to the vortex lock-in wind speed during which the vortex shedding frequency is basically equal to the natural frequency of the structure in the across-wind direction. Because of the similar natural frequency and damping in two sway directions in actual construction applications, the alongwind response will be significantly affected by the across-wind response. This phenomenon is called the coupling effect. In this paper, the coupling effect of wind-induced responses of high-rise buildings with square section is investigated using a stick aeroelastic model in wind tunnel tests. The effects of the sectional stiffnesses ratio on the along-wind and across-wind directions are clarified. Experimental results show that responses are significantly coupled when the wind speed approximates to the 'lock-in' region with a stiffness ratio close to 1:1. Compared with the wind-induced response measured in a single-degree-of-freedom system, the across-wind response of a two-degrees-of-freedom model decreases significantly and the along-wind response increases within the lock-in wind speed region. Furthermore, the characteristics of the along-wind response are observed to be shifted from buffeting to vortex-induced vibration with increasing responses and hardening Gaussian probability density function of the response within the lock-in region. The coupling effect can be identified from changes in the magnitude of dynamic response and probability density function of the along-wind response beyond the lock-in region. At a Scruton number of about 10.5, the coupling effect is strong with the stiffness ratios approximate 0.85:1, 1:1, and 1.15:1. However, at a Scruton number of about 20, the coupling effect only emerges when the stiffness ratio approaches 1:1.