Effects of time‐variant modal frequencies of high‐rise buildings on damping estimation

Summary This paper proposes a method to identify the time‐variant modal frequencies of high‐rise buildings and applies the method to the field measurements from a 68‐story high‐rise building during Super Typhoon Mangkhut (September 16, 2018). The analyzed results show that the fundamental natural frequencies of the monitored building first gradually decreased by about 9% and then returned to 94% of the original values over time. Moreover, the effects of time‐variant modal frequencies on damping estimation of high‐rise buildings are investigated by a comprehensive parametric study. The results indicate that the change rate of frequency has significant effects on the damping estimation by the conventional modal identification methods such as the random decrement technique and Bayesian spectral density approach. Accordingly, an error model for describing the relationship between the estimation error of damping ratio and main parameters of time‐variant modal frequencies is established. Then, an error model‐based correction method is proposed for the conventional damping identification methods to eliminate the estimation errors of damping ratios due to the time‐variant modal frequencies, which is proved to be effective through Monte Carlo simulation and is further applied to identify the time‐variant damping ratios of the monitored high‐rise building. This paper aims to further the understanding of structural dynamic properties of high‐rise buildings during typhoons and provide accurate estimation of structural modal parameters.