Structural Countermeasures Against Aerodynamic Torsional Divergence of a Suspension Bridge with a Main Span of 3000m.

Generalized structural and aerodynamic torsional stiffness of a suspension bridge with a main span length of 3 000 m are discussed first qualitatively in terms of analytical models. Two torsional divergence (TD) modes, symmetric and asymmetric, are compared in terms of the evolution of generalized torsional stiffness properties. It demonstrates that symmetric TD occurs prior to the asymmetric TD in a vast range of main span lengths. Numerical simulations of TD are then performed by the static finite element (FE) method. The results turn out a much lower critical wind speed of TD presented by the analytical model, due to stiffness degradation caused by main cable deformations. Finally, the effects of two types of countermeasures are examined. The replacement of the original deck section by a central slotted one can boost the critical wind speed of TD by 30%. Widening the main cable spacing enhances almost linearly the system's critical wind speed. A combined countermeasure of a slotted bridge deck and widened main cable spacing stabilizes substantially the system's aerodynamic static stability, resulting in a 45% increase in the critical wind speed of TD. [ABSTRACT FROM AUTHOR]