Cantilever  Bridges  over  the  River  Severn

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Haw  Bridge

Haw1.jpg (38141 bytes)The first steel road bridge upstream from Gloucester is the Haw bridge, a haunched cantilever carrying the B4213.  Placing a beam across a narrow support is a classic way of generating a stress concentration.

Bringing the lower edge of a beam down to a point spreads the load into the beam in a controlled manner.  When Brunel designed his timber viaducts in the south-west of England he employed a fan of timber struts to achieve the same effect, at the same time decreasing the effective span of the viaducts.

HawPlaque1.jpg (85205 bytes)   HawPlaque2A.jpg (166580 bytes)

Upton-on-Severn  Bridge

The bridge at Upton-on-Severn is a haunched cantilever of riveted construction, with a 200 foot span, completed in 1940.  The plaque points out that this method of connecting members together was hardly ever used again again for a large bridge in this country.

There is a plaque high up at the south-east end of the bridge, facing outwards, and another at the same end, facing the road.  Pictures are shown below.

UptonBigU.jpg (226458 bytes) Upton1.jpg (66896 bytes) Upton4.jpg (36564 bytes)

UptonOnSevernBigX.JPG (193294 bytes) UptonPlaque1940.jpg (88230 bytes) Upton2.jpg (38297 bytes)

UptonFlanges.jpg (81343 bytes)UptonFlowers1.jpg (65215 bytes)These pictures show details of the two sets of I-beams that form the major parts of the bridge.  The road is set about 1.5 metres below the top of the beams, which form  barriers between the road and the footpaths.  In the second picture we see the power of living things to find places to grow.

UptonUnder.jpg (75411 bytes)Here is a view of a part of the under side of the bridge.  Points to note are the cantilevered footpath, cross I-beams with triangulation, carrying corrugated supports for the road, the variation in thickness of the bottom flange, also shown in the next picture, and the pigeons that make use of the structure for shelter.  In addition to the road, the bridge carries pipes across the river.

UptonPivot.jpg (66975 bytes)Most of the weight of the bridge rests on four pivots, which look very small, though the load is spread into the masonry piers by larger supports.  Pivots are adequate supports for most cantilevers, because the position of an object in a plane is completely determined by two points:  any extension of the fixtures would result in over-determination.  The central tower of the Forth railway bridge is not hinged - it is so wide that the structure cannot overturn with any feasible load.  This construction was needed because the central cantilever is free at both ends.  In fact the other two towers are not hinged either, even though the outer ends are pulled down by massive weights.  The width of these towers reduces the size of the weights, and makes the bridge more rigid.

AnglerUOS.jpg (50153 bytes)BushCricketFE.jpg (57338 bytes)Near Upton-on-Severn, anglers pass many a peaceful hour, using their long, thin cantilevered rods to sense the presence of the fish.  The antennae of the bush cricket serve a similar purpose.

UptonPlaque2000.jpg (130431 bytes)CholeraUOS.jpg (77398 bytes)Here are two plaques recalling previous bridges at Upton-on-Severn, and an outbreak of cholera.

Queenhill  Bridge

QueenhillHH.jpg (112676 bytes) QH.jpg (21973 bytes) QP.jpg (46075 bytes) QX.jpg (37517 bytes) QV.jpg (32339 bytes)

The Queenhill Bridge, completed in 1961, takes the M50 motorway over the Severn, a few miles north of Tewkesbury.  A total length of about 2500 feet was needed to cross the flood plain. To find good rock, the caissons had to go down about as far below the surface as the height of the bridge above.  Numerous concrete spans on concrete piers lead to a steel cantilever bridge on steel piers, with a centre span of about 240 feet.

Massive spreading concrete piers separate the steel cantilever bridge from the approach viaducts, contrasting oddly with the slender steel piers of the cantilever.  On the other hand, if a number of heavy trucks are on the centre span, a large counterweight is needed to keep the bridge in place.  The white drain pipes detract from the appearance of the bridge.  Nevertheless, the bridge is an impressive sight from the river bank.

 

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Visit Severn bridges book for details of a very useful book by Chris Witts, who has spent much of his working life on the River Severn.    This book, called "A Century of Bridges", includes information, a grid reference, and a drawing by the author for every bridge, even including notes about demolished bridges and some history.  A Century of Bridges, ISBN 0 9532711 0 2, is published by River Severn Publications, Gloucester.

Another very interesting book by the same author is called "Along the Severn from Source to Sea", ISBN 1 873877 31 5.  This book is published by Reardon Publications, Leckhampton, Glos.

Haw Bridge - http://www.s-y-c.freeserve.co.uk/haw_bridge.htm

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