Abraham Darby IIIs most famous achievement was the Iron Bridge. He was only24 when the idea of an iron bridge was first proposed. There are 378 1/2 tons ofcast-iron in the Bridge. To produce it he first had to re-build and enlarge the OldFurnace in Coalbrookdale in 1777. The Bridge was completed in 1779 andopened to traffic on 1 January 1781.The first iron bridge erected was constructed by John Wilkinson (1728-1808) and Abraham Darby (1750-1791) in 1773-1779 at Coalbrookdale over the Severn (fig. 27). It had five cast iron arched ribs with a centre span of 100 ft. This curious bridge is still in use. Sir B. Baker stated that it had required patching for ninetyyears, because the arch and the high side arches would notworktogether. Expansion and contractionbrokethe high arch and the connexions between the arches. When it broke they fished it. Then the bolts sheared or the ironwork broke in a new place. He advised that there was nothing unsafe; it was perfectly strong and the stress in vital parts moderate. All that needed to be done was tofishthe fractured ribs of the high arches, put oval holes in the fishes, and not screw up the bolts too tight.

Read more:http://chestofbooks.com/reference/Encyclopedia-Britannica-2/History-Of-Bridge-Building-Part-8.html#ixzz27P1suMC3

Close-up of bridge joints.In 1779 Darby's grandson, Abraham Darby III (1750-91), completed the world's first cast-iron bridge (at present-day Ironbridge, near Coalbrookdale.) The bridge's semicircular arch spans 100.5 feet (30.6 m) and has five arch ribs, each cast in two halves.

The world's first cast iron bridge was built over the River Severn at Coalbrookdale in 1779. Not only iron founders and industrial spies flocked to see this wondrous bridge, but also artists and travellers. The Bridge had a far reaching impact: on local society and the economy, on bridge design and on the use of cast iron in building. The story of the bridge's conservation begins in 1784 with reports of cracks in the Southern abutments, and is brought up to date with the English Heritage sponsored work of 1999.

Why build an Iron Bridge in Coalbrookdale?It seems strange that a world famous symbol of the Industrial Revolution stands in rural East Shropshire. Why were pioneers in the use of iron working here, and why build an Iron Bridge?

View of a coal pit near Broseley

East Shropshire was an important industrial area thanks to coal deposits near the surface. By 1635 annual production from Broseley and Benthall was around 100,000 tons per year mainly for export, but also for fuelling local clay industries and lead.View of the mouth of a coal pit near BroseleyAcc No: AE185.770Chesham, Francis (engraver)Robertson, George (artist)

Act to build a bridge received Royal Assent

In 1776 the nearest bridge was 2 miles away at Buildwas. A ferry crossing carried people and goods over the river, but was difficult and dangerous, especially in winter. The Act to build a bridge remedying the situation received Royal Assent in March 1776.An Act for building a Bridge across the River Severn from Benthall, in the County of Salop, to the opposite shore at Madeley WoodAcc No: 1991.785

The Tontine family and Commercial Hotel

The Tontine Hotel next to the bridge opened in 1784 and was extended in 1786, and a number of bridge trustees owned shares in the hotel too. As soon as the Bridge was built, tourists were encouraged to come from far and wide to see it.The Tontine Family and Commercial HotelAcc No: 1984.6350.13

Iron bridgeA view from the River Severn

Local printer J. Edmunds of Madeley issued this print, probably immediately after the bridge was constucted as it shows the bottom section of the outer ribs still missing. The bridge stands an 'indisputable proof of the abilities of our mechanics and workmen', a superb advert for Coalbrookdale.A View of the Iron Bridge erected over the River SevernAcc No: 1973.132Edmunds, J. (printer)

Iron Bridge cast at Coalbrookdale

Some of the most notable early engineers including Telford, Boulton and Watt and Trevithick were connected with the Ironbridge Gorge. To underline the technical achievements of the bridgebuilders, this engineering drawing was supplied with prints of the Bridge.The Iron Bridge cast at CoalbrookdaleAcc No: 1973.200Ellis, William (engraver)Rooker, Michael Angelo (artist)

Shrewsbury architect Thomas Farnolls Pritchard first suggested to John Wilkinson in 1773 that an iron bridge be built over the Severn. Pritchard later designed the bridge but died in December 1777, only a month after work began.Building the Iron BridgeThe full story of how the bridge was built will probably never be known - only one image of work in progress survives, a watercolour on display in a Stockholm museum. Some of our questions about the building of the bridge are answered here.

Thomas Farnolls Pritchard

Shrewsbury architect Thomas Farnolls Pritchard first suggested to John Wilkinson in 1773 that an iron bridge be built over the Severn. Pritchard later designed the bridge but died in December 1777, only a month after work began.Thomas Farnolls PritchardAcc No: 1978.218.1anonymous (artist)

Iron Bridge design

The third design is most like the bridge that was actually built, differing in allowing for a towpath alongside the river.Design for an Iron BridgeAcc No: 1986.8609

Share certificate

The earliest estimate of costs for building the Iron Bridge drawn up by Abraham Darby and Thomas Farnolls Pritchard was 3200. The Rev. Edward Harries contributed 525 in a share subscription of 1777 which raised 3,150.Iron Bridge Share CerificateAcc No: 1972.90

Smelting House

Molten iron runs from the furnace into a sand pig bed. It is uncertain whether the parts for the Iron Bridge were cast directly from the furnace, or a stock of pig iron was made like this to be remelted and cast into the correct shapes.Inside of a smelting house near BroseleyAcc No: AE185.762Lowry, Wilson (engraver)Robertson, George (artist)

Sunderland Bridge

Sunderland Bridge was a much larger undertaking than the Iron Bridge. Scaffold was used successfully to construct the bridge without obstructing the heavy traffic on the river, and may have been used in the construction of the Iron Bridge.East view of the Cast Iron Bridge over the River Wear at Sunderland in the County of DurhamAcc No: AE185.411Raffield, J. (aquatinter)Clarke, Robert (artist)

Blind dovetail joint

Darby's workers adapted woodworking techniques to take into account the different properties of cast iron. Blind dovetailed joints, where only half the thickness of the iron is in the shape of a dovetail, join the arched ribs to the radials.Blind dovetail joint on the Iron BridgeAcc No: F20.28Conservation and RestorationThe constantly shifting river banks and the weight of stone in the abutments squeeze the Bridge, cracking ironwork and buckling the deck. The first reports of cracking in the Bridge abutments were made as early as 1784, and repair and maintenance has been necessary and regular ever since.

Stone Abutments

This view of the bridge clearly shows the massive stone abutments, the weight of which cracked the ironwork when the river banks shifted. The south abutment was demolished in 1802, long before this view was published in 1823.Cast Iron Bridge over the River Severn near CoalbrookdaleAcc No: AE185.771Dubourg, M. (engraver)

Wooden Side Arches

This sketch from the north bank of the river looking towards Benthall shows the wooden side arches that replaced the stone abutment between 1802 and 1821.Iron Bridge, ColebrookdaleAcc No: 1978.225.3Holdsworth, Arthur Howe (artist)

Iron Land Arches

Iron land arches were built on the south side of the river in 1821 to reduce the weight of the abutment. A heavily laden cart makes its way up Tontine Hill and three men weigh wool on the north bank.IronbridgeAcc No: 1978.73Fidlor, J. (attrib.) (artist)

1935 after closure to traffic

The Iron Bridge in 1935 just after closure to traffic and scheduling as an ancient monument. The buildings next to the Bridge were demolished in May 1946 to make way for a planned replacement bridge.The Iron BridgeAcc No: 1976.28Temple, Vera Louise (artist)

During restoration

Work in progress in September 1973, a year after the northern abutment was emptied of rubble and strengthened with concrete. A concrete strut to keep the abutments apart was built below water level, within the safety of a coffer dam.The Iron Bridge during restorationAcc No: 1987.597

Damage to the Iron Bridge

Bank movement has resulted in over 70 fractures in the Bridge ironwork. English Heritage carried out a full survey during 1999-2000 to record and photograph the entire Bridge.Damage to the Iron BridgeAcc No: F22.11

'The Cast Iron Bridge over the River Severn near Coalbrookdale', 1823.

Science Museum / Science & Societyimage detailsDescriptionColoured engraving, by M Dubourg. This bridge, completed in 1779, was the first in the world to use cast iron structurally and was commisioned because ferry traffic on the River Severn had become busy and expensive. It was 40 feet tall and the span of its single arch was 100 feet 6 inches. It was originally designed by Thomas Farnolls Pritchard (1723-1777) and built by Abraham Darby III. The combination of its reserves of coal, iron ore and the proximity of the busy River Severn made Coalbrookdale the cradle of the Industrial Revolution in Britain. Today Ironbridge Gorge is a World Heritage Site.ArtistDubourg, MImage Ref.10322967

Iron Bridge,CoalbrookdaleJuly 15, 2007 inArchitecture,Art,TechnologyThe worlds first cast iron bridge was built over the River Severn in Coalbrookdale, Shropshire in 1779. It attracted visitors from all over the world, not just engineers and bridge builders but artists and tourists in general. The technique of smelting iron with coke was perfected nearby by Abrahm Darby who used the product to build the bridge.

This is a picture of the bridge in about 1800. You can see the large stone pillars either side supporting the bridge. As early as 1784 there were reports of the iron cracking as a result of the movement of the banks and the pillars or abutments sqeezing the bridge. These were removed in the early part of the 19th Century.As soon as the bridge was built, a community started to form around it and the town of Ironbridge was born. Another one of my seven wonders and its just as pleasing to the eye, which is the main criteria!

Designer:Abraham Darby III

Location:Over the Severn River, near Coalbrookdale, England.

Built:1779

Type:Circular arch

Dimensions:Main span: 100 feet

Material:Cast iron

Ironbridgeis a settlement on the River Severn, at the heart of the Ironbridge Gorge, in Shropshire, England. It lies in the civil parish of The Gorge, in the borough of Telford and Wrekin. Ironbridge developed beside, and takes its name from, the famous Iron Bridge, a 30 metre (100ft)cast ironbridgethat was built across the river there in 1779.Contents History Present day Flooding References and notes

HistoryThe area around Ironbridge is described by those promoting it as a tourist destination as the Birthplace of the Industrial Revolution. This description is based on the idea that Abraham Darby perfected the technique of smelting iron with coke, in Coalbrookdale, allowing much cheaper production of iron. However, the industrial revolution did not begin in one place, but in many. The growth of railways, spinning machines, weaving and other industrial inventions and activities were going on all over the country. Smelting iron by Darby was but one small part of this generalised revolution and was soon superseded by the great iron-smelting areas. However, the bridge being the first of its kind fabricated from cast iron, and one of the few which have survived to the present day remains an important symbol representative of the dawn of the industrial age.The grandson of the first Abraham Darby,Abraham Darby III, built the famous bridge originally designed byThomas Farnolls Pritchard to link the two areas. Construction began in 1779 and the bridge opened on New Year's Day 1781. Soon afterwards the ancient Madeley market was relocated to the new purpose built square and Georgian Butter Cross and the former dispersed settlement of Madeley Wood gained a planned urban focus as Ironbridge, the commercial and administrative centre of the Coalbrookdale coalfield. The Iron Bridge proprietors also built the Tontine Hotel to accommodate visitors to the new Bridge and the industrial sights of the Severn Gorge. On the hillside above the river are situated the stone-built 16th century hunting Lodge at Lincoln Hill, many 17th and 18th century workers cottages, some imposing Georgian houses built by ironmasters and mine and canal barge owners, and many early Victorian villas built from the various coloured bricks and tiles of the locality.St Luke's Church (1837) in simple Commissioners' Gothic by Samuel Smith of Madeley, has stained glass by David Evans of Shrewsbury. The living was endowed as a rectory when the parish was created from Madeley in 1847 and is now a united with Coalbrookdale and Little Wenlock, in the Diocese of Hereford. The former Iron Bridge and Broseley railway station, on the Severn Valley line (GWR) from Hartlebury to Shrewsbury, was situated on the south side of the Iron Bridge until 1966. It was the birthplace of England National Football Team captain Billy Wright.Present day

The Iron BridgeBy the 19th century, Ironbridge had had many well-known visitors, including Benjamin Disraeli, but by the mid-20th century the village was in decline. In 1986, though, Ironbridge became part of a UNESCOWorld Heritage Site(which covers the wider Ironbridge Gorge area) and has become a major tourist attraction within Shropshire. Most industries in Ironbridge are now tourist related; however, the Merrythought teddy bear company (established in 1930) is still manufacturing in Ironbridge and has a small museum there too. Amongst other things, the village is still host to a Post Office,pharmacy, various pubs, cafs and many successful small shops.On Thursday 10 July 2003 The Queen and Duke of Edinburgh made a visit Shropshire which included a visit to Ironbridge, and a walk over the bridge itself.[2]An annual Coracle Regatta is held in August on the River Severn at Ironbridge, along with many other events throughout the year. This is mainly due to the fact that the coracle making family of Rogers lived in Ironbridge for several generations. Just outside Ironbridge in Coalbrookdale is the Ironbridge Institute, a partnership between the University of Birmingham and the Ironbridge Gorge Museum Trust offering postgraduate and professional development in heritage.FloodingIronbridge has an annually recurring problem of flooding from the River Severn, as do many other parts of Shropshire. Flooding has previously caused much damage and disruption to the Wharfage, which accommodates both The Swan and White Hart pubs, and various private homes. Starting in February 2004, DEFRA in association with the Environment Agency implemented a portable barrier which is erected at times of floods. At its peak, the flood water has reached a depth of one metre against the barrier.

Iron Bridge, CoalbrookdaleBuilt by Abraham Darby in 1779 over the River Severn in Shropshire. The bridge is an advert for the cast iron works of Coalbrookdale which lie just upriver on the side of the gorge. The multiple arches are a demonsration of the serial potential of cast iron.

Iron Bridge, CoalbrookdaleBuilt by Abraham Darby in 1779 over the River Severn in Shropshire. The bridge is an advert for the cast iron works of Coalbrookdale which lie just upriver on the side of the gorge. A lot of repair work visible here, but I like the simplicity of this connection to the stone base.

Iron Bridge, CoalbrookdaleBuilt by Abraham Darby in 1779 over the River Severn in Shropshire. The bridge is an advert for the cast iron works of Coalbrookdale which lie just upriver on the side of the gorge. The section in this photo is at one side and shows the three different arch types on the bridge: on the left, broad arches made up of small pieces jointed together (and including Gothic style pointed arches); in the middle, a short span with a few connected pieces; on the right, another small arch made of a single piece of cast iron. It's a sort of catalogue of ironwork.

Iron Bridge, CoalbrookdaleBuilt by Abraham Darby in 1779 over the River Severn in Shropshire. The bridge is an advert for the cast iron works of Coalbrookdale which lie just upriver on the side of the gorge. Struggling a bit with evening light and cloudy sky. Unfortunately there's no way of looking at the bridge head-on except from a boat, but it really looks amazing from any angle

The Iron Bridge

Carriespedestrian traffic

CrossesRiver Severn

LocaleIronbridge GorgenearCoalbrookdale

Designcast ironarch bridge

Total length60 metres (200ft)

Longest span30.5 metres (100ft)

Clearance below18 metres (59ft)

Construction begin1775

Construction end1779

Opened1781-01-01

TheIron Bridgecrosses theRiver SeverninShropshire,England. It was the firstarch bridgein the world to be made ofcast iron, a material which was previously too expensive to use for large structures. However, a newblast furnacenearby lowered the cost and encouraged local engineers and architects to solve a long-standing problem of a crossing over the river.In 1934 it was designated aScheduled Ancient Monument[1]and closed to vehicular traffic.Tollsfor pedestrians were collected until 1950, when ownership of the bridge was transferred toShropshire County Council. It now belongs toTelford and WrekinBorough Council. The bridge, the adjacent settlement ofIronbridgeand theIronbridge Gorgeform theUNESCOIronbridge GorgeWorld Heritage Site. The bridge is a Grade Ilisted building, and a waypoint on theSouth Telford Heritage Trail.Contents[hide] 1Construction 2Repairs 3Gallery 4See also 5References 6Further reading 7External links

[edit]ConstructionIn the early eighteenth century, the only way to cross theSevern Gorgewas byferry. However, theindustriesthat were growing in the area ofCoalbrookdaleandBroseleyneeded a more reliable crossing.In 1773,Thomas Farnolls Pritchard[2]wrote to a localironmaster,John WilkinsonofBroseley, to suggest building a bridge out ofcast iron. By 1775, Pritchard had finalised the plans, but he died in December 1777, only a month after work had begun.[3]Abraham Darby III, who was the grandson of the first foundry owner and an ironmaster working atCoalbrookdalein the gorge, was commissioned tocastand build the bridge. The iron for the new bridge was cast at his foundry.Shareswere issued to raise the 3,200 required, and Darby agreed to fund any excess. Although it had been predicted that 300tonsofironwould 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 overrun, and was in debt for the rest of his life.Being the first of its sort, the construction had no precedent; the method chosen to create the structure was therefore based oncarpentry. Each member of the frame was cast separately, and fastenings followed those used in woodworking, such as themortise and tenonandblind dovetailjoints, adapted as necessary to the different properties of cast iron. 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 70ft long and weighing 5.25 tons. The bridge comprises more than 800 castings of 12 basic types.The bridge was raised in the summer of 1779, and it was opened on New Year's Day 1781.[edit]Repairs

Crack and repairs in bridge

Cracked supportsJust a few years after the construction of the bridge, cracks appeared in the masonry abutments, partly caused by ground movement. Some of the present-day cracks in the cast iron may date from this time, although others are probably casting cracks from defects such as blow holes. Some cracks were pinned withwrought ironstraps, but others have been left free. By 1802, the southern stone abutment had to be demolished and replaced with temporary wooden arches before eventually being replaced by iron arches. However, many of the cracks visible in the bridge today have been left untouched. The bridge was over-designed and subsequent bridges, such as those built byThomas Telford, used much less cast iron. For example, his cast iron arch bridge atBuildwas, upstream from Ironbridge, used less than half the weight for a greater span (130 foot span, 170 tons of cast iron). However, it suffered similar problems of abutment movement and was replaced in 1902.The cast iron bridge atCoalportdownstream, built in 1818, is much more impressive because of its lean, streamlined design, and the higher quality of the cast iron arches. Thus it still carries vehicular traffic, albeit as a single carriageway. It has about half the weight ofcast ironas the original Ironbridge, and is longer than the earlier iron structure. It was renovated in 2004 including replacement of the cast iron pavement by lighter equivalents.More information about how the bridge was built came from the discovery in 1997 of a small watercolour by Elias Martin in a Stockholm museum. This showed the bridge under construction in 1779.[4]In 1972, a programme of major repairs took place on the foundations of the bridge. It involved creating aferro-concretecounter-archunder the river. Inward movement of the bridge abutments had compressed the bridge and caused the centre of the arch to rise by a few feet.[5]This counter-arch resists this compressive force from the abutments.In 1999-2000, the bridge was renovated again, with replacement of the cast iron road plates with steel plates, and a lightweight top surface.These renovations, together with recent research, revealed more about the building process and the manufacture of the cast iron parts. While the smaller parts were cast using wooden patterns, the large ribs were cast into excavated moulds in the casting sand. It is now known that 70 per cent of the components were made individually to fit, and as a result each is slightly different from the others. English Heritage, together with the Ironbridge Gorge Museums Trust, carried out a full archaeological survey, record and analysis of the bridge in 19992000. A half-size replica of the main section of the bridge was built in 2001 as part of the research for the BBC Timewatch programme which was shown in 2002.[6][7]

We now know that all the large castings were made individually as they are all slightly different. The joints would all be familiar to a carpenter - mortise and tenons, dovetails and wedges - but this was the traditional way in which iron structures were joined at the time.

Today the bridge is recognised as a key monument to the Industrial Revolution - the River Severn Gorge and several other local sites form part of aWorld Heritage Site; the Iron Bridge isGrade 1 Listed; a Scheduled Ancient Monument; and anASCE Historic Civil Engineering Landmark. But even when it was first built, the 30m span bridge was recognised as a marvel.

Darby's workers adapted woodworking techniques to take into account the different properties of cast iron. Blind dovetailed joints, where only half the thickness of the iron is in the shape of a dovetail, join the arched ribs to the radials.

a bolt fitted to one of the rings in the 1920sA construction mysteryDespite its pioneering technology in 1779, as the first structural use of cast iron, no eye witness accounts are known which describe the Iron Bridge being erected. However, recent discoveries, research and experiments have shed new light on the mystery of exactly how it was built, challenging the assumptions of recent decades. In 1997 a small watercolour sketch by Elias Martin came to light in Stockholm. Although there are a wealth of early views of the Bridge by numerous artists, this is the only one which actually shows it under construction.A watercolour of the Iron Bridge under construction in 1779, by Elias Martin. In October 2001 a half-size model was built to reproduce the watercolour and test its credibility as an engineering solution. Meanwhile, a detailed archaeological, historical and photographic survey was done by the Ironbridge Gorge Museum Trust, along with a 3D CAD (computer-aided design) model by English Heritage.The results of these discoveries and experiments tell us a lot more about how the Bridge was built. We now know that all the large castings were made individually as they are all slightly different. The joints would all be familiar to a carpenter - mortise and tenons, dovetails and wedges - but this was the traditional way in which iron structures were joined at the time.TopBuilding beginsStage 1: The building of the half-scale model begins. The derrick poles and brace lift a rib from a barge. In 2001, a half-scale model of the main section of the Bridge was reconstructed as part of an experiment. Armed with old ledger entries and 18th century lifting manuals, advice from a range of experts and a recently discovered painting of the Iron Bridge under construction, the engineer Jamie Hillier and a labour force provided by the Royal Engineers built the model using only 18th century techniques.As a result of the reconstruction, it is now believed that the Bridge was built in the following stages:Stage 1Stone footings were built using local sandstone, and topped by iron base plates. The rest of the massive abutments were not built at this stage. A pair of 21m (70ft) wooden derrick poles were stood in the river bed, which acted as cranes. They were angled slightly towards the middle of the river and were stiffened near the top by a horizontal timber brace which provided further lifting points. The whole arrangement could be lent over in either direction, upstream or downstream, to reach different positions. Castings were brought to the site by boat, probably having been cast at Bedlam Furnaces located on the north bank of the Severn just 500m downstream.Stage 2During the building of the half-scale model, two half ribs were joined at the crown to complete the first of five arches. The arch has five parallel iron frames, built starting with the upstream one and working back towards the centre. The first pair of Inner Verticals was slotted into the base plate, one on either bank. A Lower Rib was lifted from a barge until its bottom end sat on the southern base plate and rested against the Inner Vertical. The top end was raised to the correct height, and the same process was repeated from the other bank until the two halves lined up.The two arcs were joined at the Crown by a sophisticated scarf joint, which was secured by three large nuts and bolts. Balancing on a slender timber brace, this was a job for men with steady nerves and no fear of heights. Ropes stopped the castings tipping over at this delicate stage. According to a newspaper report, the first arch spanned the River Severn on 2nd July 1779.TopArches and ribsStage 3Stage 3: The three upstream arches are erected. Using the same scaffold frame but leaning it over slightly less each time, two more arches were completed in the same way. Temporary timber braces made the structure rigid, and these were later replaced by iron castings.Stage 4Stage 4: The lower ribs of all five frames are erected, with bracing added to the Inner Verticals to make the structure more rigid. The derrick poles were next lent in the downstream direction allowing the remaining two ribs to be erected, starting with the one furthest away. All five frames were then braced by diagonal and horizontal castings, which straddled the uprights. The arches and the uprights were also tied together near the base plates by short horizontal braces. With all five Lower Rib arches in place, the ironwork was free-standing and strong enough to be used as a scaffold for lifting lighter castings. There were still no abutments at this point.Stage 5The rest of the middle frame was built next, starting with the Middle Ribs, followed by the Outer Verticals, then the Outer Ribs, all held the correct distance apart by a series of decorative radial castings. Finally the decorative Circles and Ogees were added at the upper levels. The abutments were built up to their final height behind the Outer Vertical during this process. The scaffold was dismantled and the derricks re-sited so the same sequence could be repeated for the remaining frames.TopDeck bearersStage 6The Deck Bearers were brought in at high level from the now completed abutment on the north bank, probably having been cast in a temporary furnace in The Square next to the Bridge. Each one was different and made to measure. Each pair of straight Deck Bearers was linked at the centre by a 5m long curved casting, the Crown Bearer, which gripped and tightened the Crown Joint. All the joints on the Bridge were then packed with iron blocks and wedges, which were sealed in with lead.Stage 7Stage 7: The cast iron deck plates and their locating wedges were revealed in 1975 while laying a new road surface. Deck plates were probably cast in The Square and levered into place, starting with the centre one. They were located along the Deck Bearers by cast iron wedges and were topped by a road surface of clay and blast furnace slag.TopFacts and figuresAbraham Darby commissioned this painting by William Williams in 1780 to promote the Bridge. There are 482 main castings, but with the deck facings and railings the number rises to 1,736. There were no injuries during the construction process, which took three months during the summer of 1779, although work on the approach roads continued for another two years. The Bridge was opened to traffic on 1st January 1781. Abraham Darby III promoted the Bridge by commissioning paintings and engravings, but he had lost a lot of money on the project, which had cost nearly double the estimate.Movement in the south abutment was severe and it had to be demolished in 1802 and replaced by two timber side arches, which in turn were replaced in cast iron in 1821 and remain to this day. In 1934 the Bridge was closed to vehicles and scheduled as an ancient monument, but pedestrian tolls continued until 1950.Universally recognised as the symbol of the Industrial Revolution, the Iron Bridge stands at the heart of the Ironbridge Gorge World Heritage Site.

The Iron Bridge's builders used the technology that they knew. They joined the sections of the bridge with woodworking joints. Here is a dovetail..

Another of the Iron Bridge's joints. This one is complete but shows a crack.

and here, a through housing. Notice how a piece of the iron has cracked away - showing how cast iron is brittle.

The Iron Bridge had been "cast into the proper pieces in open sand upon the spot". As the members were so large and heavy, a closer location is favoured as it would have been extremely difficult to transport large loads over unmade surfaces by horsepower alone. Whatever the case it must have been a tremendous feat to cast, transport and raise these enormous structures.

The Iron Bridge has become a symbol all over the world and reinforces the belief that Ironbridge is indeed the "Birthplace of Industry".

Ironbridge 17.3.12 - 015The iron bridge in Ironbridge, completed 1779.Source: Wikipedia - The Iron Bridge crosses the River Severn at the Ironbridge Gorge, by the village of Ironbridge, in Shropshire, England. It was the first arch bridge in the world to be made out of cast iron, a material which was previously far too expensive to use for large structures. However, a new blast furnace nearby lowered the cost and so encouraged local engineers and architects to solve a long-standing problem of a crossing over the river.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 Farnolls 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, but he died in December 1777, only a month after work had begun.Abraham Darby III, who was the grandson of the first foundry owner and an ironmaster working at Coalbrookdale in the gorge, was commissioned to cast and build the bridge. The iron for the new bridge was cast at his foundry.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 got into debt for the rest of his short life.Being the first of its sort, 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.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.

They didn't understand the properties of cast iron:- good in compression weak in tension, quite a few of the joints have failed and have been repaired with steel plates and bolts but the bridge is in good nick considering its 230 years old.