Thermal movements of the existing Gateway Bridge

The Gateway Bridge, opened in 1986, is a post tensioned concrete box girder bridge crossing the Brisbane River, with a main span of 260 metres and approach spans ranging from 60 metres to 145 metres . The approach spans are twin-cell segmental box girders and the main spans are cast in-situ box girders . The approach spans have bearings at the tops and base of all piers . The twin blade piers that support the main span are integral with the superstructure . The bridge has two internal expansion joints and is tied into each abutment, preventing longitudinal movement at these locations . On the south side, the expansion joint is 376 m from the abutment . On the north side, the expansion joint is 731 metres from the abutment . The distance between the two expansion joints, including the main span, is 520 metres . The joint consists of a needle-beam type halving joint and modular expansion joint at deck level . The modular expansion joints on the Existing Gateway Bridge have reached the end of their useful life, and will be replaced as part of the Gateway Upgrade Project . As creep and shrinkage movements of the existing bridge have effectively ceased, the movement range of the replacement expansion joints will be largely determined by the thermal movements . In order to obtain a more accurate estimate of the thermal movement range, the movements at both of the existing modular expansion joints on the Gateway Bridge have been continuously recorded since September 2007 . Ambient temperature inside the bridge has also been recorded at both expansion joint locations . The paper summarises the thermal movements, and relates these to both the bridge ambient temperature, and the shade air temperature near the site, as recorded by the Bureau of Meteorology . The results are compared to the provisions of the Australian Bridge Design Code .