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Construction
Construction of Sydney Harbour Bridge
bridge crossing Sydney Harbour in Australia
- 19 March 1932
- Oceania
Construction
bridge crossing Sydney Harbour in Australia
Fetching the article from Wikipedia…
The Sydney Harbour Bridge is a steel through arch bridge in Sydney, New South Wales, Australia, spanning Sydney Harbour from the central business district (CBD) to the North Shore. The view of the bridge, the harbour, and the nearby Sydney Opera House is widely regarded as an iconic image of Sydney, and of Australia itself. Nicknamed "the Coathanger" because of its arch-based design, the bridge carries rail, vehicular, bicycle and pedestrian traffic.
Under the direction of John Bradfield of the New South Wales Department of Public Works, the bridge was designed and built by British firm Dorman Long of Middlesbrough, and opened in 1932. The bridge's general design, which Bradfield tasked the NSW Department of Public Works with producing, was a rough copy of the Hell Gate Bridge in New York City. The design chosen from the tender responses was original work created by Dorman Long, who leveraged some of the design from its own Tyne Bridge.
It is the eleventh-longest spanning-arch bridge in the world and the tallest steel arch bridge, measuring 134 m (440 ft) from top to water level. It was also the world's widest long-span bridge, at 48.8 m (160 ft) wide, until construction of the new Port Mann Bridge in Vancouver was completed in 2012.
The road over the bridge is currently owned by the state government through NSW Motorways.
The southern end of the bridge is located at Dawes Point in The Rocks area, and the northern end at Milsons Point on the lower North Shore. There are six original lanes of road traffic through the main roadway, plus an additional two lanes of road traffic on its eastern side, using lanes that were formerly tram tracks. Adjacent to the road traffic, a path for pedestrian use runs along the eastern side of the bridge, whilst a dedicated path for bicycle use runs along the western side. Between the main roadway and the western bicycle path lies the North Shore railway line.
The main roadway across the bridge is known as the Bradfield Highway and is about 2.4 km (1.5 mi) long, making it one of the shortest highways in Australia.
The arch is composed of two 28-panel arch trusses; their heights vary from 18 m (59 ft) at the centre of the arch, to 57 m (187 ft) at the ends next to the pylons.
The arch has a span of 504 m (1,654 ft), and its summit is 134 m (440 ft) above mean sea level; expansion of the steel structure on hot days can increase the height of the arch by 18 cm (7.1 in).
The total weight of the steelwork of the bridge, including the arch and approach spans, is 52,800 tonnes (52,000 long tons; 58,200 short tons), with the arch itself weighing 39,000 tonnes (38,000 long tons; 43,000 short tons). About 79% of the steel, specifically those technical sections constituting the curve of the arch, was imported pre-formed from England, with the rest being sourced from the Newcastle Steelworks. On site, Dorman Long & Co set up two workshops at Milsons Point, at the site of the present-day Luna Park, and fabricated the steel into the girders and other required parts.
The bridge is held together by six million Australian-made hand-driven rivets supplied by the McPherson company of Melbourne, the last being driven through the deck on 21 January 1932. The rivets were heated red-hot and inserted into the plates; the headless end was immediately rounded over with a large pneumatic rivet gun. The largest of the rivets used weighed 3.5 kg (8 lb) and was 39.5 cm (15.6 in) long. The practice of riveting large steel structures, rather than welding, was, at the time, a proven and understood construction technique, whilst structural welding had not at that stage been adequately developed for use on the bridge.
At each end of the arch stands a pair of 89-metre-high (292 ft) concrete pylons, faced with granite. The pylons were designed by the Scottish architect Thomas S. Tait, a partner in the architectural firm John Burnet & Partners.
Some 250 Australian, Scottish, and Italian stonemasons and their families relocated to a temporary settlement at Moruya, 300 km (186 mi) south of Sydney, where they quarried around 18,000 m3 (635,664 ft3) of granite for the bridge pylons. The stonemasons cut, dressed, and numbered the blocks, which were then transported to Sydney on three ships built specifically for this purpose. The Moruya quarry was managed by John Gilmore, a Scottish stonemason who emigrated with his young family to Australia in 1924, at the request of the project managers. The concrete used was also Australian-made and supplied from Kandos.
Abutments at the base of the pylons are essential to support the loads from the arch and hold its span firmly in place, but the pylons themselves have no structural purpose. They were included to provide a frame for the arch panels and to give better visual balance to the bridge. The pylons were not part of the original design, and were only added to allay public concern about the structural integrity of the bridge.
Although originally added to the bridge solely for their aesthetic value, all four pylons have now been put to use. The south-eastern pylon contains a museum and tourist centre, with a 360° lookout at the top providing views across the harbour and city. The south-western pylon is used by Transport for NSW to support its CCTV cameras overlooking the bridge and the roads around that area. The two pylons on the north shore include venting chimneys for fumes from the Sydney Harbour Tunnel, with the base of the southern pylon containing the Transport for NSW maintenance shed for the bridge, and the base of the northern pylon containing the traffic management shed for tow trucks and safety vehicles used on the bridge.
In 1942, the pylons were modified to include parapets and anti-aircraft guns designed to assist in both Australia's defence and general war effort.
There had been plans to build a bridge as early as 1814, when convict and noted architect Francis Greenway reputedly proposed to Governor Lachlan Macquarie that a bridge be built from the northern to the southern shore of the harbour. In 1825, Greenway wrote a letter to The Australian newspaper stating that such a bridge would "give an idea of strength and magnificence that would reflect credit and glory on the colony and the Mother Country".
Nothing came of Greenway's suggestions, but the idea remained alive, and many further suggestions were made during the nineteenth century. In 1840, naval architect Robert Brindley proposed that a floating bridge be built. Engineer Peter Henderson produced one of the earliest known drawings of a bridge across the harbour around 1857. A suggestion for a truss bridge was made in 1879, and in 1880 a high-level bridge estimated at £850,000 was proposed.
In 1900, the Lyne government committed to building a new Central railway station and organised a worldwide competition for the design and construction of a harbour bridge, overseen by Minister for Public Works Edward William O'Sullivan. G.E.W. Cruttwell, a London based engineer, was awarded the first prize of £1,000. Local engineer Norman Selfe submitted a design for a suspension bridge and won the second prize of £500. In 1902, when the outcome of the first competition became mired in controversy, Selfe won a second competition outright, with a design for a steel cantilever bridge. The selection board were unanimous, commenting that, "The structural lines are correct and in true proportion, and... the outline is graceful". However due to an economic downturn and a change of government at the 1904 NSW State election construction never began.
A unique three-span bridge was proposed in 1922 by Ernest Stowe with connections at Balls Head, Millers Point, and Balmain with a memorial tower and hub on Goat Island.
In 1914, John Bradfield was appointed Chief Engineer of Sydney Harbour Bridge and Metropolitan Railway Construction, and his work on the project over many years earned him the legacy as the father of the bridge. Bradfield's preference at the time was for a cantilever bridge without piers, and in 1916 the NSW Legislative Assembly passed a bill for such a construction, however it did not proceed as the Legislative Council rejected the legislation on the basis that the money would be better spent on the war effort.
Following World War I, plans to build the bridge again built momentum. Bradfield persevered with the project, fleshing out the details of the specifications and financing for his cantilever bridge proposal, and in 1921 he travelled overseas to investigate tenders. His confidential secretary Kathleen M. Butler handled all the international correspondence during his absence, her title belying her role as project manager as well as a technical adviser. On return from his travels Bradfield decided that an arch design would also be suitable and he and officers of the NSW Department of Public Works prepared a general design for a single-arch bridge based upon New York City's Hell Gate Bridge. In 1922 the government of George Fuller passed the Sydney Harbour Act 1922, specifying the construction of a high-level cantilever or arch bridge across the harbour between Dawes Point and Milsons Point, along with construction of necessary approaches and electric railway lines, and worldwide tenders were invited for the project.
As a result of the tendering process, the government received twenty proposals from six companies; on 24 March 1924 the contract was awarded to Dorman Long & Co of Middlesbrough, England well known as the contractors who later built the similar Tyne Bridge in Newcastle Upon Tyne (opened 4 years before Sydney Harbour Bridge), for an arch bridge at a quoted price of AU£4,217,721 11s 10d. The arch design was cheaper than alternative cantilever and suspension bridge proposals, and also provided greater rigidity making it better suited for the heavy loads expected. In 1924, Kathleen Butler travelled to London to set up the project office within those of Dorman, Long & Co., "attending the most difficult and technical questions and technical questions in regard to the contract, and dealing with a mass of correspondence".
Bradfield and his staff were ultimately to oversee the bridge design and building process as it was executed by Dorman Long and Co, whose Consulting Engineer, Sir Ralph Freeman of Sir Douglas Fox and Partners, and his associate Georges Imbault, carried out the detailed design and erection process of the bridge. Architects for the contractors were from the British firm John Burnet & Partners of Glasgow, Scotland. Lawrence Ennis, of Dorman Long, served as Director of Construction and primary onsite supervisor throughout the entire build, alongside Edward Judge, Dorman Long's Chief Technical Engineer, who functioned as Consulting and Designing Engineer.
The building of the bridge coincided with the construction of a system of underground railways beneath Sydney's CBD, known today as the City Circle, and the bridge was designed with this in mind. The bridge was designed to carry six lanes of road traffic, flanked on each side by two railway tracks and a footpath. Both sets of rail tracks were linked into the underground Wynyard railway station on the south (city) side of the bridge by symmetrical ramps and tunnels. The eastern-side railway tracks were intended for use by a planned rail link to the Northern Beaches; in the interim they were used to carry trams from the North Shore into a terminal within Wynyard station, and when tram services were discontinued in 1958, they were converted into extra traffic lanes. The Bradfield Highway, which is the main roadway section of the bridge and its approaches, is named in honour of Bradfield's contribution to the bridge.
Bradfield visited the site sporadically throughout the eight years it took Dorman Long to complete the bridge. Despite having originally championed a cantilever construction and the fact that his own arched general design was used in neither the tender process nor as input to the detailed design specification (and was anyway a rough copy of the Devil's Gate bridge produced by the NSW Works Department), Bradfield subsequently attempted to claim personal credit for Dorman Long's design. This led to a bitter argument, with Dorman Long maintaining that instructing other people to produce a copy of an existing design in a document not subsequently used to specify the final construction did not constitute personal design input on Bradfield's part. This friction ultimately led to a large contemporary brass plaque being bolted very tightly to the side of one of the granite columns of the bridge to makes things clear.
The official ceremony to mark the turning of the first sod occurred on 28 July 1923, on the spot at Milsons Point where two workshops to assist in building the bridge were to be constructed.
An estimated 469 buildings on the north shore, both private homes and commercial operations, were demolished to allow construction to proceed, with little or no compensation being paid. Work on the bridge itself commenced with the construction of approaches and approach spans, and by September 1926 concrete piers to support the approach spans were in place on each side of the harbour.
Text from the Wikipedia article “Sydney Harbour Bridge”, available under CC BY-SA 4.0.