Commonwealth Avenue Bridge

The Commonwealth Avenue Bridge are two parallel pre-stressed concrete box girder road bridges that carry Commonwealth Avenue across Lake Burley Griffin, and connect and  in Canberra, Australia.

History
The current bridge is the fourth crossing over the Molonglo River. The first Commonwealth Avenue Bridge, completed 1916, was damaged in the 1922 flood. The second, using three Leychester-type trusses, was completed in 1924 and damaged in floods a year later. The third bridge, completed in 1927, was a modification of the 1924 bridge, by raising the bridge by 1 m and adding a fourth truss. At that time, Molonglo River was not dammed to form Lake Burley Griffin. Building on the plan developed by Walter Burley Griffin, in 1957 William Holford proposed to the Federal Government that the Molonglo be dammed near Yarralumla and that Canberra's 'two halves' should be joined via a lake.

Construction of the Commonwealth Avenue Bridge began in March 1961 and the bridge was opened in November 1963. Concurrently, the Kings Avenue Bridge was opened in March 1962; and Scrivener Dam was completed in September 1963. Both bridges were built over a dry riverbed as Canberra was in the grip of drought. It took some time for the lake to fill; finally filled for the first time on 29 April 1964.

Description
Designed by Maunsell & Partners and built by Hornibrook, the Commonwealth Avenue Bridge comprises five spans of continually pre-stressed concrete, totalling 310 m. The provide an entry and exit clover leaf layout, on the bridges southern approaches, operate structures were constructed totalling 49 m each, in four approximately equal spans. The main superstructure is of multi-web box section shape, continuous over the five spans, ranging from 185 to 240 ft. The central piers, octagonal in shape, are carried on 6 ft diameter reinforced concrete cylinders. Each of the pre-cast concrete box girder sections are 10 ft each.

In 2019 a detailed analysis for the strengthening and widening of Commonwealth Avenue Bridge was presented in a business case for the project. In late 2020 the project was evaluated and accepted by Infrastructure Australia and in January 2021, the Federal Government announced funding to renew the Bridge.

That project is unrelated to the ACT Government's plan to extend Canberra light rail network from Civic to Woden.