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Extradosed bridges

1. Overview

  • The term "extradosed” in extradosed bridges is derived from “extra” (outside the range (outside of the main girder)) combined with “dosed” (reinforced). In other words, it is a structure which uses an arrangement of PC steel members to provide reinforcement outside of the main girder. That fact on its own makes it hard to differentiate this type of bridge from a cable-stayed bridge, and when considered in terms of elements strongly associated with landmarks (e.g., sightseeing spots), some people may come to the conclusion that “cable-stayed bridges = extradosed bridges” due to the many points of similarity; however, extradosed bridges have the following notable characteristics.

  • In general, this form is adopted for bridges with span lengths shorter than cable-stayed bridges, and the height of the main tower installed atop the pier is approximately 1/2 the height. Also, for extradosed bridges, the overall rigidity of the bridge is secured by the rigidity of the diagonal members and the main girders; hence, it is a structural form which is between a normal PC girder bridge, whose rigidity is secured solely by the main girders, and a PC cable-stayed bridge, whose rigidity is secured by the tension in its diagonal members. Extradosed bridges are therefore characterized by strong overall rigidity with little flexure. Various construction methods are utilized, including cantilever erection and stationary scaffolding.

  • Also there are extradosed bridges known as “skew bridges” where the diagonal members are covered in concrete, resulting in very little vibration and making these bridges suited as railway bridges.


View of the completed Komono No. 2 Viaduct


2. Key Features

  • A suitable bridge type for bridges of an intermediate size between a PC girder bridge and a PC cable-stayed bridge.

  • Because the rigidity of the main girders is higher than that of a cable-stayed bridge, a cantilever erection method of construction can be used with the same control method (flexure control) as for a normal girder bridge.

  • Because stress variation for the diagonal members due to live load is small compared with a cable-stayed bridge, the diagonal members can have a larger stress limit.

  • Because the main tower is comparatively lower than that of a cable-stayed bridge, this type of bridge offers excellent wind resistant stability.



3. Our Construction

  • Shin-Meishin Expressway Komono No. 2 Viaduct

  • Minamichiku Bridge

  • Kyushu Shinkansen Sendai River Bridge


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