Moving bridges

How many ways can you move a bridge to let boat traffic through? Well, you can lift it, fold it, curl it, retract it, tilt it, swing it, or submerge it.

Gateshead Millennium Bridge
Mike1024 / Public domain

Bridges are one of those items of engineering that lend themselves to creative solutions. How far can it stretch, how high can it be, can ships pass underneath it, can you make it out of iron? Suspension, cantilevers, arches… it’s engineer nirvana.

A specific subset of bridges have a very specific challenge: how do you move the bridge to make room for passing barges, boats, and ships? You’re probably familiar with the bascule bridge, which operates like two drawbridges that meet in the middle, but there are a whole range of creative and innovative solutions to this simple problem.

I could describe them all, but the Wikipedia user “Y_tambe” put together a fantastic set of illustrative GIFs and I think they’re more eloquent than anything I could write.

Bascule bridges, like the famous Tower Bridge in London, pivot upwards.

Bascule bridge
Y_tambe / CC BY-SA

Some bascule bridges – like the new Pegasus Bridge in Normandy – don’t pivot, they roll.

Rolling bascule bridge
Y_tambe / CC BY-SA

Similar to the rolling bridge is the tilt bridge, although instead of rolling up it rolls sideways. The Gateshead Millennium Bridge in England (pictured at the top of this post) is a pretty impressive example of this method.

Tilt bridge
Y_tambe / CC BY-SA

Folding bridges fold up like a concertina. The Hörn Bridge in Kiel, Germany, is a good example.

Folding bridge
Y_tambe / CC BY-SA

Instead of lifting the bridge up you could just retract it like a ship’s gangplank. The Carroll Street Bridge in Brooklyn, New York does this. It was built in 1889, and it is apparently the least used public bridge in New York City.

Retractable bridge
Y_tambe / CC BY-SA

An obvious solution to this whole problem is to lift the entire bridge up, as in the table and vertical lift bridges. These are common over the Eerie Canal in New York, for example.

Table bridge
Y_tambe / CC BY-SA

If lifting is too much trouble, you could just swing the whole bridge sideways. These bridges are everywhere; the longest one (the El Ferdan Railway Bridge) crosses the Suez Canal in Egypt.

Swing bridge
Y_tambe / CC BY-SA

Okay, so much for the common ones. Let’s get weird! How about curling your bridge up into a ball using hydraulic cylinders, like the Rolling Bridge in London?

Curling bridge
Y_tambe / CC BY-SA

Or just dropping the whole bridge down under the waterline so that ships can pass over the top, like the ones across the Corinth Canal in Greece? (That’s the canal, by the way, that arguably turns the Peloponnese Peninsula into an island.)

Submersible bridge
Y_tambe / CC BY-SA

I’ll be honest, I just find all of these GIFs extremely soothing and wanted to share them with you.

[Thanks to Shaun T. for suggesting this topic.]



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