Wind-induced high-order vibration of a twin-mast with large cross-section at top of Saige Plaza Building

The 5·18 vibration event of Saige Plaza Building indicates the importance of vortex-induced vibrations (VIV) of large cross-section pipes severing as the mast at the top of Saige Plaza Building. Based on the design documents and field measurements of the mast, two finite element models of the twin-mast were established for design conditions and actual stiffness degradation conditions, respectively. The wind-induced vibrations of these two models were analyzed and compared based on the aerodynamic loads derived from the computational fluid dynamics (CFD) simulation of wind flow around the twin-mast. A semi-analytical formula for predicting the maximum VIV amplitude of a cantilever steel pipe was proposed. The effects of load spatial distribution and load frequency on the vibration response properties of the twin-mast were investigated by applying the ideal VIV aerodynamic forces. The results show that the recent occurrence of high-order mode VIV of the twin-mast is closely related to the stiffness degradation of steel pipes due to the accumulated corrosion damage. The maximum VIV amplitude of 202 mm predicted by the semi-analytical formula agrees well with the result obtained from the finite element model considering stiffness degradation under the ideal vortex-induced force with a frequency of 2.12 Hz. The calculated maximum VIV amplitudes are also comparable to the observation during the 5·18 event. This work serves as a preliminary reproduction of VIV of the actual twin-mast at the top of Saige Plaza Building.