Loch Etive is a Scottish sea inlet or fjord north of Oban in the Highlands.
Back in the 19th Century it was decided to extend the railway from Oban northwards and the big issue was whether to go round Loch Etive or across it. Unlike other lochs it had a shallow part at a place called ‘The Falls of Lora’. The name was apt as when the tide comes out of the loch it produces a standing torrent of water.
The engineers (John Wolfe Barry and partners) knew it would be too difficult to place any part of a bridge directly in that part of the loch, so needed to come up with a different, not too expensive solution for the trains to cross. They decided on a single span cantilever action bridge made from steel.
What is a cantilever bridge? The most famous example then and still with us is the Forth Rail Bridge, also in Scotland, for which the huge amounts of steel were supplied, like at Loch Etive and Tower Bridge, by William Arrol and Company of Glasgow.
The Forth Rail Bridge was over-specified due to the high winds in the wide sea estuary where it was located – by contrast the bridge over Loch Etive would shorter and could be based on a simpler design, but using the same cantilever principle. The rising bascule leaves on Tower Bridge also acted as movable cantilevers, extending out from the tower bases to meet in the middle of the River Thames.
When the Connel Ferry Bridge was completed in 1903, it became the world’s longest single span cantilever bridge (the Forth Rail Bridge had double spans!). It was soon taken over by other bridges, but I feel it set a precedent and it is still with us now for road traffic only.
This is the first post in a series of 10 favourite structures featured in the book ‘Building Passions’ by Nick von Behr. The 11th post will try to rank the structures in order of appeal.