Wednesday, April 14, 2010

An iron bridge

The first arch bridge in the world made out of iron spans the Severn River at, well, Ironbridge. It was started in 1779 and opened in January 1781.
Being the first of its kind, the construction had no precedent; the method chosen to create the structure was therefore based on carpentry. Each member of the frame was cast separately, and fastenings followed those used in woodworking, such as the mortise and tenon and blind dovetail joints. Bolts were used to fasten the half-ribs together at the crown of the arch. Very large parts were needed to create a structure to span 100 feet rising to 60 feet above the river. The largest parts were the half-ribs, each about 70 ft long and weighing 5.25 tons. The bridge comprises more than 800 castings of 12 basic types. (Wikipedia)
It's a very stylish bridge. We were able to walk across it because it's closed to vehicle traffic now. We didn't have to pay any tolls.

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