Modal Characteristics of Two Kinds of 5,000 m Mixed-Cable Suspension Bridges with Ruled Curved Surface Cable Net

This paper aims at the needs of 5000 m super-long-span strait suspension bridge. According to the equation of quadric ruled surface, two new bridge types of univalent hyperboloid mixed spatial cable suspension bridge and hyperbolic paraboloid mixed spatial cable suspension bridge are proposed. The steel wire cables and the carbon fiber spatial cables in spatial mixed cable suspension bridges work together well, so the torsional mode appears much later than the parallel suspension bridge's. The torsion frequency, the torsion-bending ratio and the flutter critical wind speed are all greatly improved. The first-order positive symmetric torsion frequencies of the parallel suspension bridge, the univalent hyperboloid spatial cable suspension bridge and the hyperbolic paraboloid spatial cable suspension bridge are: 0.079 88 Hz, 0.198 40 Hz and 0.155 78 Hz respectively. The torsion-bending ratios of the three are: 1.22, 2.88 and 2.35 respectively, and the critical flutter wind speeds are: V_cr^p=20.83 m/s, V_cr^d=91.21 m/s and V_cr^s=71.18 m/s respectively. The two kinds of spatial mixed cable structure systems have good wind resistance and stability, which opens up the new train of thought for the future construction of 5000 m super-long-span suspension bridges.