Aerodynamic performance and vortex-induced vibration of a completed triple-box girder: The role of gap ratio

This is the authors' abstract. We don't add key points for this paper.

Triple-box girders have recently emerged as an attractive cross-sectional form for long-span bridges, with their aerodynamic performance and vortex-induced vibration (VIV) strongly affected by slot gap spacing. However, for completed (as-built) triple-box configurations, a systematic understanding of how gap ratio governs aerodynamic performance, VIV, and the associated flow mechanisms remains limited. In this study, wind tunnel tests were performed to measure surface pressures and vibrations for five gap ratios, i.e., GW/H = 0.81, 1.62, 2.43, 3.24, and 4.05. Complementary computational fluid dynamics simulations were conducted to examine the vorticity evolution and clarify the underlying excitation mechanisms. The results indicate that gap ratio influences the mean pressure coefficient, force coefficients, fluctuating pressure coefficient, mean square amplitude spectra of fluctuating pressures, Strouhal number (St), VIV, and flow characteristics to different extents. In particular, the effects of gap ratio are more evident for the midstream and downstream girders than for the upstream girder. Further examination of St values derived from different dominant frequencies reveals a clear transition in the frequency domain response at GW/H = 2.43, whereas the maximum VIV amplitude is observed at GW/H = 3.24. Flow field visualization reveals that vortex shedding from the upstream girder interacting with slot gap recirculation amplifies unsteadiness around the midstream and downstream girders, while inter-girder interference weakens as the gap ratio increases. These findings improve understanding of how flow evolution governs aerodynamic interference and VIV in completed triple-box girders.