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The Sydney Harbour Bridge is the main crossing of Sydney Harbour carrying vehicular, rail, and pedestrian traffic between the Sydney central business district (CBD) and the North Shore. The dramatic water vista of the bridge together with the nearby Sydney Opera House is an iconic image of both Sydney and Australia. The bridge is colloquially referred to as the Coathanger because of its arch-based design, although this usage is less prevalent than it once was. The iconic Bridge is celebrating its 75th anniversary in 2007.
The bridge was the city"s tallest structure until 1967. According to Guinness World Records, it is the widest long-span bridge in the world and is the largest steel arch bridge with the top of the bridge standing 134 metres above the harbour.
The bridge"s two ends are located at Dawes Point (in Sydney"s Rocks area) and Milsons Point (in Sydney"s lower North Shore area). It carries six lanes of road traffic on its main roadway, two lanes of road traffic (formerly two tram tracks) and a footpath on its eastern side, and two railway tracks and a bicycle path along its western side. The western side being 305mm larger that the east side.
The road across the bridge is known as the Bradfield Highway and is about 2.4 km (1.5 miles) long, making it one of the shortest highways in Australia. (The shortest, also called the Bradfield Highway, is found on the Story Bridge in Brisbane). At 48.8 m (151.3 feet) wide, it is the widest long-span bridge in the world (Guinness World Records, 2004). The bridge deck portion of the highway is 1.15 km (0.71 miles) long. It is concrete and lies on trimmers (beams that run along the length of the bridge). The trimmers themselves rest on steel beams that run along the width of the bridge. The trimmers and beams are visible to boats that pass underneath the bridge.
The arch is composed of two 28-panel arch trusses. Their heights vary from 18 m (55.8 feet) at the center of the arch to 57 m (176.7 feet) (beside the pylons).
The arch span is 509 m (1,559 feet) and the weight of the steel arch is 39,000 tons. The arch"s summit is 134 m (415.4 feet) above mean sea level, though it can increase by as much as 180 mm (7 in) on hot days as the result of steel expanding in heat. Two large metal hinges at the base of the bridge accommodate these expansions and contractions and thereby prevent the arch from being damaged. The steel used for the bridge was largely imported. About 79% came from Middlesbrough in the North East of England, the rest was Australian-made. The granite used was quarried in Moruya, New South Wales, and the concrete used was also Australian made.
The total weight of the bridge is 52,800 tonnes, and six million hand-driven rivets hold the bridge together. The rivets were made at the Park Bridge Ironworks in Lancashire England.
The two pairs of pylons at each end are about 89 m (276 feet) high and are made of concrete and granite. Abutments, which support the ends of the bridge, are contained at the base of the pylons. They prevent the bridge from stretching or compressing due to temperature variations. Otherwise, the pylons serve no structural purpose and are primarily to visually balance the bridge itself. They were originally not part of the design but were added later to allay concerns about structural integrity — ironically, as the pylons do not actually touch the bridge (except at road level). Although inserted into the designs for their aesthetic value, all four pylons have now been put to use: a museum and tourist centre with a lookout of the harbour is contained in the southeastern pylon. The southwestern pylon is used by the New South Wales Roads and Traffic Authority (RTA) as a base for their CCTV cameras overlooking the bridge and the roads around that area. The two pylons on the north shore are now venting chimneys for fumes from the Sydney Harbour Tunnel. The RTA maintenance shed for the bridge is contained within the bottom of the southern pylon and the traffic management shed (tow trucks and safety vehicles used on the bridge) is contained in the bottom of the northern pylon.
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