The Iron Bridge over the Severn River in Shropshire in England is the first cast-iron arch bridge in the world, a revolutionary building of its time. It is protected by UNESCO as a World Heritage Site .
The construction of a metal bridge was made possible by the presence of John Wilkinson blast furnaces in the area. The bridge construction initiative and its project belonged to architect (c. 1723 - 1777). Casting large parts of the bridge required a number of innovative solutions. The bridge was built in the summer of 1779 and was commissioned on the first day of 1781.
In the image and likeness of the first bridge, several more cast-iron bridges were built in England at the end of the 18th and beginning of the 19th centuries. When casting new bridges, much less metal was required. Already at the beginning of the XIX century, the bridge began to be covered with cracks, it has to be repaired regularly. In 1934, the building was put on state guard and closed for vehicles.
Content
Construction
At the beginning of the XVIII century, it was possible to cross the Severn Gorge only by ferry . A more reliable crossing was required.
In 1773, T.F. Pritchard proposed to local steelmaker John Wilkinson to build a cast iron bridge. By 1775, Pritchard completed the design of the bridge, but died in December 1777, a month after the start of work. Abraham Darby , the owner of the iron foundry, was instructed to cast and build a bridge.
Shares were issued to finance the construction, but there weren’t enough of them, and Darby agreed to partially finance the missing (a total of £ 3,200). According to preliminary estimates, 300 tons of pig iron (worth 7 pounds per ton) was required for the construction, but 379 tons were actually spent. Given the additional costs (installation, support, etc.), the project was much more expensive than originally expected, and Darby suffered heavy losses, remaining in debt until the end of his life.
The bridge was the first of its kind, the construction did not have a precedent, so the design was based on the methods used in carpentry. Each element of the bridge frame was cast separately, and thorn-groove and dovetail articulations were used, which adapted as necessary to the properties of cast iron. Bolts were used to fasten the halves of the ribs to the top of the arch.
Large parts were needed to create a structure that was about 30 m high (up to 20 m above the river). The largest in construction were half the ribs, each of which was about 70 feet (over 20 m) long and weighing 5.25 tons. The bridge consisted of more than 800 separately cast elements of 12 basic types. All the castings took about 380 tons of cast iron.
The dimensions of the bridge: length - 60 m, the length of the central span - 30.5 m, height 13.7 m [1] .
The construction of the bridge was erected in the summer of 1779, and it was opened on the first day of 1781.
Already in 1784, cracks were noticed in some structures due to stresses associated with shifts of the coastline and massive stone coastal supports. In 1821, the southern stone support was replaced by lightweight cast iron.
In 1935, the bridge was closed to traffic [2] .
Miscellaneous
The half-sized bridge was built in 2001 as part of a study for the BBC television program Timewatch , which was shown in 2002.
Notes
- ↑ Iron bridge .
- ↑ Conservation and Restoration (unavailable link) . Date of treatment February 6, 2015. Archived October 24, 2015.
Literature
- Neil Cossons, Barrie Trinder . The Iron Bridge: Symbol of the Industrial Revolution. - 2nd ed. - Phillimore & Co Ltd, 2002.
Links
- BBC about the stages of construction
- An online walk on the bridge on the BBC website
- “Is this Britain's most influential bridge?” - BBC review article