Sydney Harbour Bridge
When the Sydney Harbour Bridge was opened by the Premier of New South Wales, Mr Jack Lang on the 19th March 1932, the Harbour Bridge was one of the greatest engineering masterpieces of its time. Port Jackson (Sydney Harbour) had an impressive and instantly famous landmark made in a style that reflects the end of an industrial era.
The bridge joined the city of Sydney (at Dawes Point) to the North Shore (at Milsons Point) obviating the need to travel by ferry or make a substantial trip around the harbour foreshores towards Parramatta and back.
As early as 1815 Francis Greenway proposed the building of a bridge from Dawes Point to the northern shore of Port Jackson, to Governor Macquarie.
Many years were to pass before the vision became a reality. Around the time of Federation there was a well-recognised need for a bridge crossing and design submissions were invited in 1900, all were deemed inappropriate or unsatisfactory for one reason or another and the momentum lapsed.
Serious initiatives started after the end of World War I. Tenders were called for in 1923 either an arch or a cantilever bridge would meet the requirements. Dr J.J.C. Bradfield was responsible for setting the parameters of the tendering process. He and his staff were to ultimately oversee the entire bridge design and building process. The Bradfield Highway, which is the paved section of the bridge and its approaches, still bears his name to this day.
The tender of Dorman Long and Co. Ltd., of Middlesborough England for an arch bridge was accepted. The Dorman Long and Co’s Consulting Engineer, Sir Ralph Freeman, carried out the detailed design of the bridge. The design was similar to New York’s Hell Gate Bridge built 1916. The Hell Gate Bridge was a little shorter in span but was much lighter in construction as it only carried four railway tracks.
Work first began on the Sydney Harbour Bridge in 1924, with construction of the bridge approaches and the approach spans. As many as 800 families living in its path were displaced without compensation.
During this time the foundations on either side of the harbour were prepared to take four steel thrust bearings.
The foundations, which are 12 metres (39 feet) deep, are set in sandstone. Anchoring tunnels are 36 metres (118 feet) long and dug into the bedrock at each end. Large bolts and nuts are used to tie the thrust bearings onto their supports.
It is interesting to note that the four pylons are actually placed mainly for aesthetic reasons on each corner of the bridge. The pylons are about 90 metres above the average water level. The Sydney Harbour Bridge design had to perform functionally and be pleasing to the eye as well. The pylons are made of concrete that is covered by grey granite from Moruya on the south coast of New South Wales.
When the bridge was constructed the use of reinforced concrete was in its infancy. Today the Harbour Bridge ranks second or third in the world in terms of span but it is still considered to be the greatest of its type in the world because of its load bearing capacity and width of nearly 50 metres.
Known locally as the ‘coat hanger’ and now more commonly as ‘the bridge’, the bridge was manufactured in sections on a site on the western side of Milsons Point. About eighty percent of the steel came from England while the remaining twenty percent was manufactured here in Australia. The construction of the arch was begun from both sides of the harbour with cable support for the arches. In 1930 the two arches met. The construction of the deck then proceeded from the middle outwards towards each shore as this was easier than moving the construction cranes back to the Pylons.
In 1932, when the Sydney Harbour Bridge was opened, it was the longest single span steel arch bridge in the world. The main span is 503 meters (1,650 feet) across it consumed more than 52,800 tonnes of silicon based steel trusses. The plates of steel are held together by around 6 million steel rivets. It originally carried road transport, trains and pedestrians. From start to finish, the bridge and its approaches it took eight years to complete.
The two eastern lanes were originally tram tracks . They were converted when Sydney abolished its trams in the 1950s. Today it carries eight traffic lanes and two railroad lines. One of the eastern lanes is now a dedicated bus lane. The bridge is often crowded, and in 1992 the Harbour Tunnel was opened to help carry the traffic load. The traffic levels were substantially reduced compared to the period before the tunnel opened.
In 1932, the original cost of the Bridge was several million Australian pounds. This debt was eventually paid off in 1988 but the toll was then used for maintenance.
Before the Harbour Bridge opened, it was completely packed with railway carriages, trams and buses to stress test its load bearing capacity. While it has had many traffic jams since and half a million people walked across it on its 50th anniversary it has probably never been asked to carry that much of a load since.