Replacement of the stays on a major cable-stayed bridge

The bridge discussed in this paper was completed in 1985 and is part of a vital sea crossing. The main cable-stayed bridge has a span of 225 m with side spans of 107·5 m. The bridge carries two three-lane carriageways. The bridge cables comprise lengths of coupled high-yield bars within a grouted steel tube. An assessment of the structure in 1996–1999, using modern design standards, identified large overstress in the shortest cables anchored close to the pylons. Other cables were also found to be overstressed, but to a lesser degree. Bearings were thus installed at the piers to relieve load from the shortest cables and the second shortest sets of cables were replaced. An acoustic monitoring system was also installed on all cables to detect any problems. Since then, two bar breaks were detected in other cables, which have been replaced. Inspection and testing showed fatigue of the couplers to be responsible for the breaks. Following the first bar break detected in December 2004, an additional assessment was completed by Atkins. This paper describes the assessment of the bridge cables, examines the consequences of cable failure and discusses the reasons why the decision to replace all the cable stays was made. It also describes the specification for the new replacement stay system and its advantages over the old system.