Road Trip: The Tower Bridge Is Weird

by Don Friedman on May 19, 2016

Another snap from London:

IMG_1353

That’s the Tower Bridge as seen from the walkway to the Tower of London. Structurally, we’ve got a double bascule roadway at the center span, a truss walkway high above (so that pedestrians can walk across even when the road span is raised), and suspended side spans with inverted three-hinged arch trusses as the catenaries. It’s like a scrapbook of 1880s bridge ideas.

I can partly understand the thought process that leads to this result: this was the farthest-downstream bridge over the Thames when it was built and is still the farthest downstream except for two modern, high-level highway bridges. So using the bascule span meant that it wouldn’t block river traffic. The bascule span and high span needed the big towers, and suspending the side spans meant that the towers would be the only waterway obstruction.

It’s bizarre and, in engineering terms, non-elegant, but those features are what make it an international icon. It’s a shock, but fame and elegant engineering don’t entirely overlap.

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