A loch, some falls and a bridge #buildingpassions #10favstructures

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 in Scotland (Wikimedia Commons)

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.

Why study great engineers of the past?

I’m reading a biography of the 19th Century Scottish engineer William Fairbairn. It has been very well researched with hundreds of references to primary and secondary materials. Personally, I find it a fascinating read, but I could imagine it doesn’t appeal to many. Too technical and detailed they might say.

That’s where the challenge comes along to those who would like to spread the lessons from historical biography. These are case studies of significant individuals who have clearly made a difference to an area, a sector, a technology, a community, a nation, a world etc.

As Roma Agrawal has shown with her book BUILT, people are interested in stories about other people. This allows us to entice them in the direction of more scientific and technical issues which have traditionally scared them away.

Even though William Fairbairn didn’t have a proper education, he learned by doing and by reading voraciously in his little spare time. He was driven by a bigger purpose than making money for himself and his family. He wanted to change society for the better. This is surely a reason for knowing a little more about him and his personal and physical achievements.

A Benjamin Baker’s dozen

There are 13 days until we commemorate the death of Sir John Wolfe Barry, one hundred years ago.

The play on words in the title of this blog is obviously to do with the number thirteen, but also allows me to tell you a bit about Sir Benjamin Baker.

Baker was a close friend and business associate of Wolfe Barry and like John was also President of the Institution of Civil Engineers. He is most famous for designing and building between 1883 and 1890 with Sir John Fowler the iconic Forth Rail Bridge in Scotland, which still stands and functions as it was intended.

The steel for the bridge was supplied by William Arrol, who also provided the steel for Tower Bridge and the Connel Bridge, both built by Wolfe Barry.

Benjamin Baker went on to design and construct a number of docks with Sir John including the Royal Edward at Avonmouth near Bristol. Subsequently heĀ  built the new Aswan Dan in Egypt to tame the Nile, no doubt well informed about the nature of river currents and movement of sediment.

Like Barry, Sir Benjamin has a stain glass window commemorating him in Westminster Abbey.