e-mosty March 2019 Long Span and Multiple Span Bridges - Page 51

Multi-span suspension bridges are appropriate for deeper water crossings, and can be more economic than very long spans. Proposals for their use with multi-span suspension bridges have been made (Figure 13). The robustness of suspension bridges is a key criterion. The size of the foundation for the intermediate towers is a key aspect of this bridge form. Conventional single or 3-span suspension bridges are often used to span major rivers, estuaries or fjords with the towers located on or as close as possible to the land. One of the largest bridge foundations constructed to date are the 80m diameter, 70m deep caissons of the 1991m span Akashi Kaikyō Bridge. Slightly smaller multiple deep-water foundations were also used on the Rion Antiron multi span cable stay Bridge. For multi-span suspension bridges with one or more towers in the river or sea they will potentially have shipping lanes either side of one or more towers and so it is vital that the foundations and lower parts of the tower below the deck are protected against the possible ship impact. The large caissons required for the Taizhou Three- Tower Bridge are shown in Figure 12. Gravity platforms for the offshore oil industry have developed from the Ekofisk platform in 96m of water to the Troll A platform in 305m of water. Figure 12: River caisson for the Taizhou Bridge 1/2019 3