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The Iron Bridge

2007 Schools Wikipedia Selection. Related subjects: Geography of Great
Britain; Road transport

   The Iron Bridge
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   The Iron Bridge
   The Iron Bridge
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   The Iron Bridge
   The Iron Bridge
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   The Iron Bridge

   The Iron Bridge crosses the River Severn at the Ironbridge Gorge, by
   the village of Ironbridge, in Shropshire, England. It was the first
   bridge of its size to be made out of cast iron.

Construction

   In the early eighteenth century the only way to cross the Severn Gorge
   was by ferry. However, the industries that were growing in the area of
   Coalbrookdale and Broseley needed a more reliable crossing.

   In 1773, Thomas Pritchard wrote to a local ironmaster, John Wilkinson
   of Broseley to suggest building a bridge out of cast iron. By 1775,
   Pritchard had finalised the plans, and Abraham Darby III, an ironmaster
   working at Coalbrookdale in the gorge, was commissioned to cast and
   build the bridge.

   Shares were issued to raise the £3,200 required, and Darby agreed to
   fund any overspend. Although it had been predicted that 300 tons of
   iron would be needed (costing £7 a ton), in the end 379 tons were used,
   costing Darby and his company nearly £3,000. There would be many other
   costs to bear (masonry abutments, assembly etc), so that the project
   was far more expensive than first envisaged. Darby bore most of the
   cost over-run, and was in debt for the rest of his short life.

   Being the first of its kind, the construction had no precedent. 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. 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.

   The bridge was raised in the summer of 1779, and it was opened on New
   Year's Day 1781. In 2001, the BBC screened a documentary in which a
   half-sized model of the bridge was built to test recent research over
   the construction. Instead of large timber towers, a pair of uprights
   with a crosspiece was used to erect each of the ribs in sequence. The
   abutments were built afterwards.

Repairs

   Just a few years after the construction of the bridge, cracks were
   appearing in the masonry abutments, caused by ground movement. Some of
   the cracks in the cast iron may date from this time, although others
   are probably casting cracks. They were pinned with wrought iron straps.
   By 1802, the southern stone abutment had to be demolished, and replaced
   with temporary wooden arches, before eventually being replaced by iron
   arches. Many of the cracks visible today in the bridge have been left
   untouched, however. The bridge was over-designed, and subsequent
   bridges such as those built by Thomas Telford used much less cast iron.
   For example, his cast iron arch bridge at Buildwas upstream from
   Ironbridge, used less than half the weight for a greater span (130 ft
   span , 170 tons of cast iron). However, it suffered similar problems of
   abutment movement and was replaced in 1902. The cast iron bridge at
   Coalport downstream, built in 1818, is even more impressive because of
   its lean, streamlined design, and still carries vehicular traffic. It
   was renovated in 2004.

   In 1972 a program of major repairs took place of the foundations of the
   bridge. It involved creating a ferro-concrete counter arch under the
   river. The bridge has been renovated again in 1999-2002, with
   replacement of the cast iron road plates with steel plates, and a
   lightweight top surface. Further information on the manufacture of the
   cast iron parts has emerged. While the smaller parts were cast using
   wooden patterns, the large ribs were cast freely into excavated moulds
   in the casting sand.

Ironbridge settlement

   The Iron Bridge became an 18th century tourist attraction, and the
   settlement of Ironbridge grew up beside it. Although described by many
   as a town, it falls within the parish of The Gorge.

The present day

   Vehicular traffic was stopped from crossing the bridge in 1934, but
   tolls for pedestrians were still collected until 1950, when ownership
   of the bridge was transferred to Shropshire County Council.

   The bridge is a popular tourist attraction, and part of the UNESCO
   Ironbridge Gorge World Heritage Site.

   Retrieved from " http://en.wikipedia.org/wiki/The_Iron_Bridge"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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   Documentation License. See also our Disclaimer.
