Tag: July

The Iron Bridge in Shropshire, England is a historical marvel and engineering feat. It was built in the late 18th century and was the first arch bridge in the world to be made out of cast iron. Before the rise of blast furnaces, cast iron was far too expensive to use for large structures. However, a new blast furnace nearby lowered the cost of cast iron and encouraged local engineers and architects to find a solution to the long-standing problem of a bridge crossing over the River Severn.

Abraham Darby III, the grandson of the first foundry owner and an ironmaster working at Coalbrookdale in the gorge, was chosen to cast and build the bridge. Darby agreed to fund any overspend and shares were issued to raise the £3,200 required to fund the project. It had been predicted that 300 tons of iron would be needed at a cost of £7 per ton. However, in the end, 379 tons were used, costing Darby and his company nearly £3,000. The costs of the project were higher than first envisaged due to the need for masonry abutments, assembly, etc., and Darby bore most of the cost over-run.

Being the first of its sort, the construction of the Iron Bridge in Shropshire, England had no precedent. The method chosen to create the structure was based on carpentry as a result. Every 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 necessary to create a structure that spanned 100 feet and rose to 60 feet above the river. The largest parts were the half-ribs, each about 70 feet long and weighing 5.25 tons. The bridge is comprised of over 800 castings of 12 basic types.

The Iron Bridge was raised in the summer of 1779 and was opened on New Year’s Day 1781. As a result, it played a crucial role in Industrial Revolutions worldwide.

Posted by alanhitchcock49 on 2012-07-09 20:04:00