[below: Sydney Harbour Bridge at night]
It took 8 years to build - from 1924 to 1932; the contractor was Dorman Long, of England. The bridge was designed with strength in mind - it carries six lanes of road traffic plus two train tracks. This is a weight loading in excess of, say, the Golden Gate Bridge's design. And a stronger bridge means a heavier bridge - it weighs 53,000 tonnes before any vehicle gets on it.
The design choosen is a single arch - an ancient design which you have seen in door arches and domes of cathedrals.The weight of the bridge is 'funnelled' along the arch into the supports at either end, producing a stable structure. The bridge deck is then attached (suspended) to the arch to result in a strong crossing.
Steel is a strong, yet flexible building material, but it's main disadvantage is that it expands with heat. On a hot day in Sydney, the bridge can 'grow' by 180mm. To allow for this the engineers designed hinges at the four corners of the main span:
Did I say 'hinge'? This is not something that you would hang a door on - they each weigh 300 tonnes and can support a weight of 20,000 tonnes:
[below: installation of one of the bridge arch hinges]
The bridge, including the approach ramps, contain approximately 6 million rivets. That's a lot of rivets.
The four concrete and stone towers (called 'pylons') are not part of the structural integrity - they are just for show. And what a difference they make to the visual impact of the bridge, giving it a solidity and grandeur it deserves.
If you want to have a look at the bridge yourself there is a webcam (best to view either early in the morning or late at night since they are 10 hours ahead of us).
