Structural Characteristics and Applicability of Four-Span Suspension Bridge

A four-span suspension bridge which has two main 2,000 m spans is investigated with respect to the deformation characteristics. Generally, deformation behavior of the four-span suspension bridge is mainly influenced by rigidity of the center tower. This study is focused on properties such as bending and torsional rigidity of the girder, sag ratio, and dead load. The result of this investigation clarified that the lower rigidity under live load than the three-span bridge is caused by the smaller cable spring coefficient of the main span, which is 1/6 of the side span. Nevertheless, the tendency is stable and can be assisted by stiffened rigidity of the center tower. Live load deflection of the girder can be reduced to less than 1/200 of the main span length, which is useful and economical, by stiffening the bending coefficient of the center tower. Moreover, relatively lower rigidity of the center tower is sufficient for the 2,000 m span suspension bridge than for the 1,000 m span case, keeping the same deflection ratio. Three-dimensional sag geometry of the main cable is effective in limiting the torsional deformation, which is an especially important issue for the four-span suspension bridge caused by twist of the center tower.