Coalbrookdale  Bridges

June 2003

Coalbrookdale

Coalbrookdale is famous as one of the places where the industrialising process began.  In the course of a day or two, you can walk around a large number of museums and gain insight into the early machines, and the lives of the people who lived and worked among them.

The bridges are listed in order, going with the flow of the River Severn, which here, as in many other of its reaches, possesses bridges which are either famous, technically interesting, or just good to see.

Official Ironbridge Web-site

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Buildwas bridges

Buildwas1992.jpg (90114 bytes)Should you decide to walk from Ironbridge up to Buildwas, you will take, as you approach your destination, a trip back in time.  The first thing you see is this bridge of 1992, a simple beam.

BuildwasPiece2.jpg (113340 bytes)Next, on the right, in front of the pub, you will see this small piece of a bridge, and on the wall above it, a plaque, explaining that this is a piece of the bridge of 1905.

BuildwasAllA.jpg (334343 bytes)As you approach the road junction, you will see a large memorial tablet, which includes several plaques, and a piece of the first Buildwas bridge, that of 1796.  And not any old bridge, either, for that bridge was the first cast iron bridge designed by Thomas Telford, already a great builder in masonry.  His Buildwas bridge was unusual in having intersecting arches of differing curvature, perhaps to increase rigidity in this unfamiliar material.  In later years, Telford was to design superb arches in cast iron, achieving the required rigidity by the use of trussed arches.  Pictures of two of these can be found elsewhere in this web-site.  It is a great pity that the original bridge was not retained when the next bridge was built in 1905 to 1906.  All you can see here is one piece of Telford's bridge, bearing the date.

Here are some pictures of the monument -

BuildwasLeft.jpg (85723 bytes)  BuildwasRight2.jpg (165665 bytes)  BuildwasAllB.jpg (147424 bytes)

Not enough care was taken in these pictures to get verticals and horizontals correct.  This is not easy to achieve, especially with a wide angle lens.

Severn bridge builders

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Three  Awkward  Bridges

CBDOldTrussA.jpg (87842 bytes)CBDOldTrussB.jpg (114803 bytes)The next bridge downstream from Buildwas is a disused truss.  On the far side, the track rests on a series of piers based on arches.  It is not possible to get a good view of the entire bridge.

Next comes a concrete beam belonging to an electricity generating company.  It, too, is impossible to see clearly unless you can stand on something to look over a hedge.  

AlbertEdwardBr.jpg (97810 bytes)From the concrete bridge, if you can get permission to walk on it and take a photograph, you can see an old arch bridge, inscribed "Albert Edward Bridge, 1863, John Fowles, Engineer".  Trains still rumble slowly across it, going to and from the power station.  It would probably be a slightly easier to see in winter.

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Ironbridge  in  Coalbrookdale

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The abutments are asymmetrical: on the north side the footpath passes under a stone arch: on the south side, inaccessible to the public, there are two iron arches.

CBDale1.jpg (48902 bytes) IronBridge6X6B.jpg (370369 bytes) IronBrSignBig.jpg (113807 bytes) IronB2002PS.jpg (50404 bytes)

This very famous bridge was built between 1777 and 1779, and is reputed to be the first cast iron bridge.  The detailing is perhaps more like that of carpentry than that of modern metalwork, but perhaps it is enough to be innovative in material without the added risk of using new ideas in assembly.  At any rate, the bridge still stands.  

It may be that the give in the joints has helped the bridge survive the distortions, given the weakness of cast iron in tension.  Glues have sometimes been advertised as being stronger than wood, but that is not in all cases desirable.  See also Attachments, Cracks and Indeterminacy.  Perhaps there is a lesson here for people who make model bridges for school projects and competitions.

A plaque states that the bridge was built to advertise the skills of the workers in cast iron, and that in this it succeeded brilliantly.

IronB2002L.jpg (98018 bytes) IronB2002M.jpg (78557 bytes) IronB2002N.jpg (114535 bytes)

Under the river, an inverted arch prevents inward movement of the abutments, which evidently push inwards more than the bridge can withstand, probably because the river is in a steep valley.  Although built in a brittle material, the bridge has survived the insidious thrust, but the orange lines in the fourth bridge picture above - repeated here IronB2002D.jpg (199469 bytes) - suggest that distortions have occurred.  But look very carefully at the picture.  Can the bridge really have changed its shape?

Ironbridge Museum - http://www.ironbridge.org.uk/

Ironbridge - excellent pages

Free map of Ironbridge area

A large area of the valley is given over to industrial museums, which are all well worth visiting.  You probably need more than one day if you want to visit all the sites.

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Jackfield  Bridge

Not far downstream from the famous Ironbridge, the Severn is crossed by a much newer structure - a cable stayed bridge.  Here are some pictures.  As the plaque states, an earlier bridge, known as the Free Bridge, because the other bridges were tolled, was built in 1909, in the early days of reinforced concrete.  The famous name of Hennebique appears on the plaque.  In 1994, an asymmetrical cable stayed bridge was built as a replacement.  The second picture shows a small segment from the old bridge.

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Cable stayed bridges are apt to look somewhat angular and highly stressed.  This design makes no attempt at disguising anything: all the parts are so clearly visible that the bridge could be used as a textbook example.  In the last picture we see the cable anchorages, the terminal deck pin, and the foot of one strut, which is tapered to the point where it is more or less a pivot.  The last picture but one shows that the tower, except for the upper segments, is not in a vertical plane.  Can you account for all these features?

The tower is essentially an A-frame or shearlegs, but instead of continuing to an apex, it is truncated, rigidity being provided by the ring, which also supports the two vertical cable supports.  These supports continue above the cable attachments, tapering to provide a neat finish to the tower, which otherwise might have looked somewhat stubby.  If you approach Ironbridge from the east, intending to park in the Ironbridge car park, you will cross this bridge.  You can walk easily from the Ironbridge to the Jackfield bridge along the south bank of the river Severn.  On the way, you may see this exhibit -

SpiralBowlsPlaque.jpg (61216 bytes) SpiralBowlsA.jpg (148379 bytes) SpiralBowlsB.jpg (100279 bytes)

The thick orange deposit in the bed of the stream shows the presence in the rocks and soil of iron , the basis of industry in Coalbrookdale, though in fact it was the presence of easily won coal that made the region so successful.  

In the earth's crust, iron makes up about 4.8 % by weight, or 1.8 % by number of atoms, though deep inside the earth, iron and nickel are probably the most common elements by far.  Dense metals like iron perhaps owe their existence near the surface of the earth to their combination with light elements such as oxygen.  But why is there so much iron in the earth as a whole?  A glance at a table of nuclear binding energies reveals that the region of minimum energy lies broadly around the position of iron.

But that doesn't mean that it is easy to make heavy elements.  The search for controlled nuclear fusion has not yet resulted in a commercially viable means of releasing energy from fusion, though great progress has been made in prolonging the life of the necessary hot plasmas.  Temperatures above 100 million degrees are needed.   The natural existence of heavy elements at all is perhaps the result of supernovae, exploding with great energy, fusing light nuclei and spewing the results out into space

 

Across the river you will see the ruined Bedlam furnaces.

BedlamA.jpg (75609 bytes)   BedlamB.jpg (84852 bytes)

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Jackfield  Memorial  Bridge

JackfieldMemA.jpg (83356 bytes)  JackfieldMemB.jpg (99876 bytes)  JackfieldPlaque.jpg (116635 bytes)

This bridge can be found downriver from Jackfield Bridge.  It is a bowed Pratt truss.

Coalport  Bridge

CoalportMP.jpg (123211 bytes)This iron bridge is rather like a smaller version of the famous Ironbridge.