Izmit Bay Suspension Bridge – Main Cable Anchorages

This paper describes the concept development and subsequent detailed design of the anchorages for the Izmit Bay suspension bridge with a main span of 1550 m. The significant variation in foundation conditions at the two ends of the bridge required completely different concepts for the anchorages. In particular at the south end of the bridge an innovative solution was developed where the main part of the anchorage was built within a huge excavation pit shaped like a "guitar" formed by 30 m deep diaphragm walls. As explained in the paper this solution was driven by the aim to safeguard against a potential secondary seismic fault occurring in the ground just below the anchorage. The long term durability and in particular the corrosion protection of the large number of post-tensioning tendons used to transfer the main cable tension to the bottom of the anchorages was a major concern. The paper describes an innovative solution based on use of dehumidification to deal with this challenge.