Feature Article - The Tasman bridge
Plans for a bridge to link the Derwent River’s two shores near Hobart date back to 1832. It was not until 1943 that the first bridge was completed, the Hobart floating bridge and lift span. The bridge was of unique design and construction, the first of its type anywhere in the world. A large portion of the bridge was a floating concrete structure curved upstream in the form of an arch. Following completion of the bridge, the population on the eastern shore of the Derwent grew, and the bridge was unable to adequately manage the increased traffic flow.
In 1956, the Department of Public Works Tasmania commissioned the consulting engineers Maunsell & Partners Pty Ltd to report on a suitable replacement bridge. Their report concluded that a low-level bridge with a lifting span similar to the existing bridge would be little cheaper than a high-level bridge enabling the clear passage of passing ships. In May 1960, construction of the Tasman Bridge commenced and the bridge was completed in December 1964.
The bridge is constructed of pre-stressed concrete, with the major parts composed of precast sections. The bridge comprises a total of about 61,000 cubic metres of concrete, about 5,200 tonnes of reinforcing steel and 117 kilometres of prestressing cables. The total cost of the bridge was approximately £7,000,000. The bridge had an estimated peak capacity of 4,000 vehicles per hour across four lanes and the navigation span had a minimum clearance of 45.7 metres above mean sea level to enable the largest ships to pass through.
On 5 January 1975, the Lake Illawarra, with a cargo of 10,000 tonnes of zinc concentrate bound for the Elecrolytic Zinc Company, collided with the Tasman Bridge and sank. Two piers of the bridge were demolished, and three spans of deck supported by them collapsed. Twelve people died in the accident. In March 1975, a Joint Tasman Bridge Restoration Commission was appointed to restore the Tasman Bridge. The reconstruction of the bridge included the modification of the whole bridge to accommodate an extra traffic lane to allow for a peak period tidal flow system of three lanes for the major flow and two for the minor.
After the bridge collapse, eastern-shore residents were suddenly isolated from the city. The trip to Hobart by road was now a fifty-kilometre trip. A number of ferries immediately began operating and by June 1975 it was estimated that 25,581 people were travelling across the Derwent by ferry each day. A positive aspect of the bridge collapse was the development that occurred on the eastern shore. Prior to the disaster many services, such as banking, medical, legal and insurance, were severely lacking. New developments that occurred included the Eastlands shopping complex, a new highway connecting Lindisfarne to Brighton and the opening of many business services in Bellerive.
Approximately one year after the bridge collapse, the Bailey Bridge, linking the eastern and western shores of the Derwent, was opened. The Tasman Bridge was re-opened on 8 October 1977, nearly three years after its collapse. In 1975, the Commonwealth Government agreed to fully fund a new bridge; the Bowen Bridge, linking the eastern shore with Hobart’s northern suburbs, was officially opened in 1984.
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