Time-frequency evolutionary characteristics of aerodynamic forces around a streamlined closed-box girder during vortex-induced vibration. Issue 182 (November 2018) - Hu, Chuanxin
Abstract: The mechanism of vortex-induced vibration (VIV) of long-span bridges is a key issue in bridge wind engineering. It's necessary to have an understanding about aerodynamic loads and then take corresponding countermeasures to mitigate VIV. Vortex-excited forces (VEFs) and the structural behaviors of a spring-suspended sectional model (SSSM) were synchronously measured in multi-scale levels in terms of distributed aerodynamic forces around a streamlined closed-box girder, general integral loadings, and structural wind-induced displacements in the VIV-development process, involving the pre-VIV stage, the ascent stage, extreme amplitude point, descent stage, and post-VIV stage. Based on the synchronized measurement technologies above, time-frequency evolutionary characteristics in those stages were analyzed considering numerous correlations between local and general aerodynamics around a bridge deck. The spatial distribution of mean, RMS values of pressure coefficients, predominant frequencies of the distributed aerodynamic forces, phase lags and correlation coefficients between the distributed aerodynamic forces at each tap and the general VEFs, pressure coefficients at predominant frequencies, etc., have close evolutionary relationships with displacements in the VIV-development process, especially near the downstream region of the upper surface and the corner region of the lower surface and tail wind fairing, showing dependency on the development stage of the VIV process. Aerodynamic forces near the downstream region of the upper surface make major contributions to VEFs, which are predominant and mainly responsible for the VIV phenomena. Highlights: To reveal the VIV mechanism of streamlined bridge decks, evolutionary characteristics of aerodynamics during the VIV-developing process were analyzed using synchronous measurement. The VIV of a bridge deck have obviously evolutionary regularity in time- and frequency- domains. Spatial distribution of pressure coefficients have obviously evolutionary regularity in the VIV process. Correlation of distributed pressure are highly related to the VIV stage, and pressure in partial areas make major contributions to VIV.