Identification of Dynamic Characteristics of High-Rise Buildings Considering the Influence of Modal Direction

The structural dynamic characteristics of super high-rise buildings are key to understanding how they respond to wind-induced vibration. Currently, one widely adopted method involves using vibration sensors to capture structural vibration responses through on-site measurements, followed by identifying structural dynamic characteristics using output-only methods. However, when measuring and analyzing the dynamic characteristics of super high-rise buildings, the modal directions associated with the vibration modes of the structure are often ignored, which can lead to identification errors. This is particularly true for super high-rise buildings with irregular cross-sections, for which research into the impact of actual structural vibration modes is notably lacking. Therefore, this study uses a normal mode decomposition method to examine the determination of structural vibration mode directions in detail. This method identifies the angular deviation between the viewing and normal coordinates by analysing the spectral energy distribution. It then decomposes the measured signal in the viewing coordinate system based on this deflection angle. This achieves decoupling of modes that are coupled in both directions. Specifically, the study analyses the phenomenon of modal aliasing in structural modal parameters from both time-domain and frequency-domain perspectives based on the measured acceleration response signals of a super high-rise building with a non-circular cross-section during Super Typhoon Saola, and employs the structural modal orthogonal decomposition method to determine the modal directions. The fundamental sway modes of the structure exhibit aliasing between the two adjacent modes at 0.1748 Hz and 0.1825 Hz due to a 46° angle of deviation between the viewing and normal coordinates. Based on the clarification of modal directions, the study further refines the identification of structural modal parameters. Following decoupling, the dispersion of the damping ratio and frequency identification results in the normal coordinate system decreased significantly (concentrating at 1.0-2.0% and 0.175-0.185 Hz, respectively). The damping ratio increased by 1.0% with increasing amplitude, while the frequency decreased by 0.005 Hz with increasing amplitude. The research findings help to improve the accuracy with which the dynamic characteristics of super high-rise buildings can be identified, thereby enabling the structure's wind-induced response to be assessed more rationally.