Hobart, Tasmania
The second bridge across the River Derwent at Hobart, and the design and fabrication of all the land and marine temporary works, were undertaken in joint venture. The requirement for this bridge arose from the need to have two crossings of the river following a barge collision, with the first bridge causing partial collapse.
FEATURES:
The second Hobart Bridge is 976m long, with an overall width of 21.4m. The bridge is of twin box girder construction, comprising 8x109m spans, with end spans of approximately 50m. The contract specified the precasting of 594 match-cast box segments, to be erected using the balanced cantilever system. An alternative foundation design, utilising 14m diameter rings with a mass of up to 320t, was adopted for the construction of the pier cofferdams, the deepest being 45m below river bed level. The first three bridge segments above each pier were assembled in the casting yard into a single 300t unit and then placed on the pier bearings by derrick barge. All remaining segments were lifted separately into place by overhead gantries, travelling on the previously erected segments.
BENEFITS:
The cofferdam design facilitated the river pier construction and provided a dry safe working environment. Match casting of the cantilever segments ensured a high standard of production and ease of erection. The joint venture's own heavy duty plant enabled construction methods to be devised which could make use of large components resulting in a saving in construction time.
CLIENT: Main Roads, Tasmania
