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In this study, the vortex-induced vibration (VIV) performance, mechanism, and control of a self-anchored suspension bridge with the central-slotted box girder (CSBG) under the operating wind velocity of the bridge were investigated via numerical simulations and experimental methods. First, the VIV responses and mechanism of the original CSBG at a wind angle of attack (AOA) of α = 0° were investigated by fluid–structure interaction (FSI) calculations. Then, based on the VIV responses and mechanism, the corresponding aerodynamic countermeasures were proposed to suppress the VIV of the original CSBG. Finally, the small-scale (1:50) sectional model wind tunnel tests were conducted to verify the vibration suppression effect of the aerodynamic countermeasures. Moreover, the large-scale (1:30) sectional model wind tunnel tests were conducted to further verify the vibration suppression effect of the modified CSBG with the final aerodynamic countermeasure. The results showed that the vertical VIV occurs in the original CSBG at an AOA of α = 0°, owing to the strong flow field connection between upstream and downstream box girders and vortices shedding off alternately at the tail of box girders. Moreover, for six types of closed grid plates with different BGP/BCS ratios (where BGP is the width of the closed grid plate and BCS is the width of the central slot), the flow field around the stationary CSBG showed that as BGP/BCS increases, less flow passes through the central slot, the tail vortex intensity weakens, and the fluctuating pressure coefficients become more stable. The 3.5-m-wide closed grid plate (BGP/BCS = 63.6%) at the central slot 0.5 m away from one side of the box girder was selected as the aerodynamic countermeasure, and the results of the FSI calculation showed that the vertical VIV of the original CSBG can be suppressed after taking the aerodynamic countermeasure. The results of the small-scale and large-scale sectional model wind tunnel tests verified the vibration suppression effect of the 3.5-m-wide closed grid plate. However, there were discrepancies in VIV responses between the small- and large-scale tests, especially for torsional VIV at an AOA of α = −5° to +3°. This study verified the potential of the computational fluid dynamics method to advance the VIV suppression of the bridge girder before conducting the wind tunnel tests. [ABSTRACT FROM AUTHOR]

This study employed an enhanced social force model to investigate the impact of bidirectional crowd load on the vertical vibration characteristics of pedestrian bridges. The research incorporated a two-step prejudgment approach to optimize agents' transcendental behavior and introduced a fan-shaped pedestrian perception area for bidirectional crowd movement simulation based on the social force model. The structural vibration response resulting from the evolution of these behaviors was numerically simulated and analyzed. Vertical crowd–structure coupling models were established using a pedestrian moving dynamics model with spring, mass, and damping. A real-time solution method for the structural acceleration response, varying with the moving pedestrian load entering the footbridge deck, was implemented in a numerical environment. Subsequently, the structural response under crowd load, considering multiple behavioral factors, was investigated on an interior steel footbridge. The results demonstrated that bidirectional crowd load generates a higher vertical acceleration response than unidirectional crowd load under the same pedestrian density conditions. The vertical peak acceleration reached its maximum when the number of left- and right-oriented pedestrians was the same, while the peak acceleration of the structure decreased as the difference between the left- and right-oriented pedestrian numbers increased, both in steady-state and transient-state conditions. Bidirectional crowd load poses a higher risk of inducing severe potential vertical resonance of the structure due to synchronization issues, highlighting its significance in the operation of the footbridge. [ABSTRACT FROM AUTHOR]