Conceptual Design of a New Three-Tower Cable-Stayed Bridge System with Unequal-Size Fans

Abstract

Multitower cable-stayed bridges with three or more towers often have economic advantages over ultralong-span double-tower cable-stayed bridges or suspension bridges, in situations when deep foundations are not required. However, the internal towers of multitower cable-stayed bridges are not connected to stiff supports or foundations, and therefore the stiffness of the internal towers is lower than the side towers. As a result, when unbalanced live loads are applied to one main span, the deformation and internal forces of the internal towers and the main girder can be excessively large. Therefore, solving the low stiffness problem of the internal towers is an important issue for multitower cable-stayed bridges. In this paper, a new type of three-tower cable-stayed bridges is proposed. Since the stiffness contributed by the flanking towers is much greater than the central tower, the proportion of the main span supported by flanking tower cables can be increased, while the span supported by the central tower can be reduced. This can be achieved by modifying the design of the three fans, which originally had equal sizes. This new system is therefore called a three-tower cable-stayed bridge with unequal-size fans. The stiffness, internal forces, and cost of the new system were compared to the conventional three-tower cable-stayed bridges with identical fans, and it was found that this new system could be an excellent alternative to the conventional designs.