Low-impact cable system adopted for the Awa Shirasagi Ohashi Bridge, Japan

The Awa Shirasagi Ohashi Bridge is located at the tidal estuary of the River Yoshino in Japan, adjacent to wetlands where migratory birds such as snipe and plover congregate. As the wetlands form a unique and invaluable ecosystem, an environmental conservation group expressed serious concerns over the construction of the bridge. A long-span bridge with low visual intrusiveness to avoid any negative impacts on the ecosystem associated with the wetland was required. To satisfy the requirements, a unique type of cable trussed system termed a ‘cable egret’ structure was designed. The proposed structural form enabled a 260 m long span with pylons only extending 29·6 m above the deck and a minimum number of cables, minimising impacts on the ecosystem associated with the wetland. In the span between the two pylons, the main girders made composite with the sandwich slabs are propped by intermediate under-slung supports, which are in turn suspended by a cable truss system. This paper describes details of the cable egret system and the construction method adopted for the bridge, which allowed the environmental impact to be minimised.