Study on the Design of an Extradosed and Suspension Hybrid Bridge with 800 m Span of Butterfly Web Girder

Abstract

In general, to design a large span bridge, cable-supported bridges are utilized with high towers and stiffened by steel girder since it is flexible and lightweight. In addition, to increase the stiffening against aerodynamic stability, a hybrid cable-supported bridge which combines both suspension and cable-stayed structure has been proposed. However, the hybrid system inherently comes with higher towers in comparison to the conventional suspension system. Consequently, the angular change of the main cable at the tower saddle could be larger which causes increasing secondary stress in the main cable and the cable becomes more critical in fatigue.

It is well known that extradosed bridge employs a structure with deeper girder and lower tower than that of a conventional cable-stayed bridge. Therefore, in this study, to deal with the secondary stress in the main cable and enhance the aerodynamic stability, the authors aim to develop a long span concrete box girder bridge which is a hybrid between an extradosed structure and a suspension structure. Incidentally, in order to reduce the weight of the girder, the butterfly web girder in which the web was replaced by thin panels with a butterfly-wing shaped was adopted.

As a case study, herein a hybrid of extradosed and suspension bridge with 800 m span of concrete butterfly web girder was suggested. The towers are considered to be 100 m in height as well as the girder is set to 7 m deep. After describing some assumptions of construction sequence for the structural analysis, three different extradosed spans of the proposed hybrid bridge are comparatively designed and discussed to confirm their structural behaviors in this paper. As the results, it is confirmed that this new type of hybrid bridge can be designed and moreover, it is found that the system with extradosed span to main span ratio 61% is the most efficient system than others.