Wind-induced vibration of variable cross-sections building with high-rise building machine: an aeroelastic wind tunnel study

High-rise building machines (HBMs) are temporary rooftop structures widely used in super-tall construction. During construction, the combined HBM–building features variable cross-sections and low damping. However, its wind-induced behavior remains insufficiently understood, posing safety concerns. In this study, a high-fidelity multi-degree-of-freedom aeroelastic model was developed based on a real project. Wind tunnel tests were carried out under city-center urban terrain conditions. The results show that intermittent vortex-induced vibration (VIV) in the variable cross-sections structure is driven by local frequency lock-in, which evolves across different structural parts with increasing wind speed. The RMS of VIV-dominated segments is significantly amplified compared with the full-time RMS, with the amplification factor remaining nearly constant across wind speeds. As wind speed increases, the cross-wind RMS first rises and then stabilizes, while the along-wind RMS continues to grow and may eventually dominate. Meanwhile, weaker intermittent VIV is also observed in the along-wind response when the local vortex shedding frequency approaches the along-wind dominant frequency. A peak response estimation method is proposed, and its accuracy in estimating intermittent VIV peak responses is validated through comparisons with multiple methods. The results indicate that local frequency lock-in leads to amplified peak responses at corresponding structural levels. Under the most unfavorable wind incident angle, the combined RMS increases approximately linearly with wind speed. Through qualitative and quantitative analyses, this study reveals the mechanisms and characteristics of intermittent VIV in variable cross-section structures, and the results also provide support for the wind-resistant design of HBMs.