Strengthening of the West Gate Bridge steel box girder

The West Gate Bridge is a key transport link to Melbourne's western suburbs. The 2.6 km long bridge crosses the mouth of the Yarra River and comprises two concrete box girder approach viaducts either side of the 850 m long cable stayed steel box girder main spans. The recent West Gate Bridge Strengthening Project was undertaken to; ensure the long term sustainability of the bridge for current and future traffic demands, reduce congestion by increasing the capacity of the carriageways from 4 to 5 lanes, controlled with a freeway management system, and improve public safety on the bridge. This paper describes the treatments developed to strengthen the steel bridge including props for the cantilevered portions of the deck, additional plates at the base of the towers and on the pier diaphragms, bolt replacement and splice strengthening, and a range of details used to strengthen internal members. In addition, public safety barriers have been added to the bridge. A major influence on the design of strengthening elements was constructability, and during the construction phase strengthening details were continually being reviewed as new information on the existing structure became available. The complexity of the project, however, was not limited to the design of strengthening elements. The project was undertaken without peak hour lane restrictions and over the entry to Australia's busiest port. In addition, strict controls were required over the staging of the works to ensure the structural integrity of the bridge at all times.