- Publication no: ABC-CAS009-11
- Published: 31 October 2011
Westgate Bridge is the largest bridge in Melbourne. The main span over the Yarra river is 336m long and made of a cable stayed steel box girder. The approach viaducts are made of prestressed concrete multicell box girders. The Western viaduct consists of 10 spans at 67m each and the Eastern Viaduct consists of 13 spans at 67m each. The traffic loading is to be increased by converting the outer shoulders into typical traffic lanes. Accordingly, the entire bridge is to be strengthened to enhance its structural capacity. The Western viaduct has already been partly strengthened in 2002. Strengthening is made of carbon fibre strips outside of the box girder, and additional external prestressing inside the box girder. Freyssinet Australia was awarded the installation of external prestressing tendons in both Eastern and Western viaducts. It consists of 300 tons of strands in both viaducts. Tendons are made of bare strands injected with cement grout in HDPE ducting. Straight 13C15 tendons are installed at midspan in the Western viaduct and 19C15 deflected tendons are installed in the Eastern viaduct. Deflector and end blocks are made of cast-in situ reinforced concrete blocks stressed to the webs with 50mm diameter Freyssibar. They are fitted with flared shape diabolos to allow for tendon misalignment and deviation. Tendons are deviated across pier diaphragms with a double formed diabolo (no steel tube). Freyssinet Australia also carried out the jacking of the bridge to relocate the deck at the abutment.