Golden Gate Bridge: an Exceptional piece of Steel Engineering

San Francisco’s Golden Gate Bridge is one of the most iconic bridges in the world. It is a so-called suspension bridge: the deck is supported by vertical cables attached to upper larger cables, which -in turn- extend between supporting towers and are anchored at the ends.

The bridge’s construction begun in 1933 and gave chances of employment during the US’s Great Depression. The design was assigned to engineer Joseph Strauss. The constructions time took 4 years costing $35 million and featuring some extreme scenarios.

For example, 3.25 million cubic feet (92,030 cubic metres) of soil excavations were required for establishing the bridge’s anchorages and they are 12-floors tall! The divers had to submerge as deep as 90 feet (27.4 m) in the water to explode rocks and then remove the debris! Despite such difficulties, the bridge finally opened in 1937.

On-site construction of the suspension cables began in 1935. All the bridge’s cables are made of galvanized carbon steel wires and they were laid by a ‘spinning’ technique.

The two main cables alone account for 61,500 tons of weight load on the two 746-ft-tall (227 m) towers! The wires pass on top of the towers and are secured at each end in massive anchorages. The main cables measure 36.22 inches in diameter and they extend for 7,650 ft (2,332 m) each!

Such massive cables were manufactured by grouping together 61 bundles of wire. In turn, each of these is made up of 452 smaller wires, for a total of 27,572 cables! As for the vertical suspended cables, they tie the bridge’s deck to the main cables. There are 250 pairs of them; they are spaced 50 feet apart from each other and measure from 2 to 16 inches in diameter.  All of the vertical ropes were replaced between 1972 and 1976.

It is interesting how the Golden Gate Bridge ‘dances’ up and down depending on the temperature. Hot days with high temperature cause the metal to expand; steel cables elongate and the bridge’s deck lowers. This is especially visible in its central part. Moreover, painting the ‘Red Bridge’ is a non-stop task and of primary importance. In fact, the paint applied to the steel prevents both corrosion and rust that the air with high salt content in may cause.

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