As novel cross sections, aerodynamic behaviors and vortex-induced vibration (VIV) inducement of split box girders, especially split three-box girders, are not fully understood. Analysis of vortex-excited force (VEF) evolutionary characteristics in the VIV process may reveal valuable information. Based on displacement and pressure measurement wind tunnel tests on a large-scale section model, the evolutionary characteristics of typical VEF indexes were expounded. VIV was divided into four stages: pre-VIV, ascent, extreme point, and descent. At the extreme point, high-order harmonics were found, which indicates that VEF has obvious nonlinearities. Mean and RMS values of global VEF appear to be controlled by upstream and downstream boxes. An increase in RMS values is the main cause of VIV. VEF spanwise correlation is mainly dominated by structural vibration at the extreme point, while spanwise distance is dominant in other stages. Local aerodynamic forces on the surfaces include upstream box surface (excluding partial lower surfaces of the wind fairing), upstream and downstream curved surfaces in upstream gap, upper surface of downstream box, and the wake are the main contributors to global VEF and the main cause of VIV. This work provides a comprehensive understanding of aerodynamic behaviors and VIV inducement of split three-box girder bridges.
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