Amplitude dependence of natural frequency and damping ratio for 5 supertall buildings with moderate-to-strong typhoon-induced vibrations

Abstract

Modal parameters play a significant role in the wind-resistant design and vibration control of high-rise buildings. Results from previous studies demonstrate that the natural frequency and damping ratio of high-rise buildings usually exhibit nonlinear variation characteristics with the increase of structural amplitude. However, due to lacking relevant field measurements, the features of natural frequency and damping ratio for super-tall buildings under large wind-induced amplitudes have been less explored. This paper presents a field study on typhoon-induced structural responses of five supertall buildings whose structural heights all exceed 300 m. The peak acceleration responses at the measurement height of most buildings exceeded 10 cm/s2 (gal), with the maximum response reaching 20 gal. Two frequently used methods, i.e., the stochastic subspace identification (SSI) and random decrement technique (RDT) methods are utilized to compare and analyze the amplitude-dependent characteristics of target modal parameters. It is found that with the increase of wind-induced structural vibration amplitude, the fundamental natural frequency generally first decreased and then leveled off, while the damping ratio for the first-order mode of the buildings except the one equipped with a tuned mass damper (TMD) system first increased while then tended to decrease. More interestingly, the critical normalized structural vibration amplitude associated with the maximum damping ratio is found to be in the range of 10−4∼10−5, which agrees well with the theory of “critical tip drift ratio”. Potential explanations for the above phenomena are presented. Furthermore, the obtained results are further compared with existing statistical models, and associated discrepancies suggest the complexities of the dynamic features of supertall buildings.