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Connecting the ancient capital of Scotland with the new

Connecting the ancient capital of Scotland with the new

 

There are three iconic bridges crossing the Firth of Forth.  The 4th of March 2020, marked the 130th anniversary of the opening of the first one, the Forth Bridge.  This cantilever railway bridge is regarded not only as a symbol of Scotland but is also a World Heritage Site.

In 2015, UNESCO, the United Nations Educational, Scientific and Cultural Organization, inscribed the bridge as Scotland’s sixth World Heritage Site, recognising it as “an extraordinary and impressive milestone in bridge design and construction during the period when railways came to dominate long-distance land travel”.  In 2016, a Visit Scotland survey voted the Forth Bridge as “Scotland’s greatest man-made wonder”, beating off competition from Stirling Castle, the Caledonian Canal, the Scott Monument, Bell Rock Lighthouse, and Melrose Abbey.

Postcard of Benjamin Baker’s human cantilever bridge model.

 

The original (above) and final (below) designs of the Forth Bridge
Date: 1890

The designers of the Forth Bridge, Sir John Fowler and Sir Benjamin Baker, took advantage of the structural principle of ‘cantilevers’. Basically a horizontal beam is attached at a single point, to a vertical support. The beam, on which the rails were placed, essentially dangles from each of these supports. Think of a flag pole attached to a wall of a building. A series of trusses add extra support and help handle the forces of tension and compression. A pair of cantilevers, sharing a single upright support is known collectively as a ‘balanced cantilever’ and are often used to help anchor a bridge that needs to span even greater lengths. The bridge is made by connecting two separate cantilevers (one on each side of the bridge) which in the case of the ‘Forth Bridge’ is further supported by a series of trusses. This is important taking into account it had to support a rail system. So the ‘Forth Bridge’ is a Cantilever Truss Bridge and at the time, in 1890 when it opened it had the longest single cantilever bridge span in the world with a span of 1,709 feet (521 m). The Forth Bridge held this record until 1919 when the Quebec Bridge in Canada was completed. It continues, today, have the world’s second-longest single cantilever span.
 

The Prince of Wales drives home the last rivet, ‘Illustrated London News’, 8 March 1890.

Some interesting facts:

  • The bridge was the first major structure, not only in Scotland but the United Kingdom as a whole to be constructed of steel.
  • The bridge is made up of 55,000 tons of steel.
  • The bridge was officially opened by the Duke of Rothesay, the future Edward VII when he hammered in the last rivet.
  • In the First World War British sailors would time their departures or returns to the base at Rosyth by asking when they would pass under the bridge.
  • The first German air attack on Britain in the Second World War took place over the Forth Bridge, six weeks into the war, on 16 October 1939.
  • The bridge has featured in a number of TV programmes and movies. One of the first was Alfred Hitchcock’s ‘The 39 Steps’ in 1935.

 

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