Dynamic Instability Mechanisms of Unbalanced Traction Force During Swing Bridge Rotation

This paper investigates the overturning of swing bridges induced by sudden unbalanced traction forces during rotation. Through a combination of numerical simulations, scale model tests, and monitoring analyses, the study identifies the critical parameters controlling overturning and characterizes the anti-overturning behavior of support components. The results indicate that pin shafts significantly enhance the bridge's resistance to overturning under unbalanced traction, with a 47.4% improvement compared to configurations without pins. Specifically, for the studied bridge, the critical unbalanced traction force causing overturning is 12,700 KN with pin shafts, compared to 8617 KN without them. Additionally, a strong correlation is observed between the axial compressive stress in the spherical hinge slider and the superstructure deviation angle. Based on this relationship, a gray prediction model is developed, achieving high-precision forecasting of deviation angles with errors ranging from −7.4% to +8.0%. These findings provide a theoretical basis and quantitative guidance for identifying critical monitoring parameters and establishing quality control strategies in the construction of swing bridges.