Rod Smallwood: Nether Moor Images
I think I have always been interested in bridges. They combine utility and elegance better than any other structure. I plan journeys so that they visit interesting bridges on route. I have photographed hundreds – Viaduc de Garabit, the Storebaelt Bridge, Pontcysyllte, Runcorn Bridge, the Viaduc de Millau, Ingrande Bridge, Pont de Sully, the Seto-Ohashi Bridge, Connel Bridge, Boothferry Bridge, Newport Transporter Bridge, Glenfinnan Viaduct, the Briare Aqueduct, Ganter Bridge, Eki-Narin bridge in Kyrgystan, Kvalsundet Bridge, Tjeldsundbrua, the Atlanterhavsvegen …
Here are a few of my favourites.
The earliest bridges were probably trees that had fallen across streams, and many small footbridges are still essentially a pair of trees with a plank deck. Clapper bridges could be the first constructed bridges – a rock slab laid on piers, and impossible to date. This example is in Cwmorthin, and leads to the quarry barracks in the background. It probably dates from the 19th century.
The first modern bridge was the Ironbridge across the River Severn, built in 1779 at Coalbrookdale, where Abraham Darby established, in 1709, the first blast furnace to smelt iron with coke rather than charcoal.
Although it is built with cast iron, the bridge follows woodworking practice, with the parts joined with dovetails, mortice joints, and wedges. The development of cast iron bridges was rapid – the next one to be built used about half the weight of iron. The banks of the River Severn are unstable, which has caused structural problems throughout the life of the bridge. In the early 1970s a concrete inverted arch was cast in the river to stabilise the abutments, and a major restoration has recently repaired broken joints and returned the bridge to its original condition.
Thomas Telford built more than a thousand bridges in Britain. He developed standardised designs for cast iron bridges, which his contemporaries thought were outstandingly light and elegant. The most beautiful of these bridges were at Bonar Bridge and Craigellachie. Bonar Bridge had two masonry arches and a cast iron arch, and was destroyed when it was undermined by flood water. Craigellachie Bridge across the River Spey was built between 1812 and 1814, and has been by-passed by a modern concrete bridge, from which the photograph was taken.
Telford also rebuilt the London-Holyhead turnpike, which was the strategically important route from London to Dublin, with an extension along the coast to Chester. The road engineering through North Wales is very fine, and includes two major bridges. The smaller of the two, across the Afon Conwy at Conwy, looks very similar to when it was built. It is now a pedestrian bridge owned by the National Trust who, for some reason, only allow you to cross it in summer. The bridge behind is the tubular railway bridge built by Robert Stephenson and William Fairbairn, a precursor to the now-destroyed bridge over the Menai Strait.
Telford’s masterpiece is the Menai Bridge, by far the longest single span bridge when it was built. The Admiralty requirement was that the passage through the Menai Strait by a warship should be unobstructed – hence the single span and the height above the water. Stephenson’s railway bridge – now a combined rail and road bridge after the tubular bridge was destroyed by a fire – is off the right of the picture. The water in between is the notorious Swellies. The tide runs at about 8 knots, there are numerous islands, and the bottom is very rough. The result is an exciting stretch of water – very interesting in a sea kayak.
The original bridge had a deck which was insufficiently stiff, and was destroyed on one occasion and damaged frequently by high winds – the same problem resulted two centuries later in the famous destruction of the Tacoma Narrows Bridge. A major reconstruction of the bridge was undertaken in the early 1940s. The suspension chains were replaced and a new deck was built below the old deck so that traffic was not interrupted. The trusses shown below, which separate the footway and the roadway, act as deck stiffeners. There is an excellent article in the Journal of the Institution of Civil Engineers (Telford was the first President) describing the history and the reconstruction of the bridge (G A Maunsell. Menai Bridge Reconstruction. Volume 25 Issue 3, JANUARY 1946, pp. 165-193).
Brunel built many bridges, two of which are well-known. The first is the very elegant brick bridge over the Thames at Maidenhead, which has very low rise arches. The second is the Clifton Suspension Bridge in Bristol. Brunel designed the bridge, but it was not completed in his lifetime. It was finished as a memorial to him, using chains from the old Hungerford Bridge over the Thames, when it was replaced by the present railway bridge.
There are three outstanding bridges over the Firth of Forth, two of them shown here in this panorama (the shoreline is actually straight). The first was John Fowler and Benjamin Baker’s railway bridge, the first major steel bridge.
In the past, painting the bridge was a process which went on all the time. In the image above, the covered parts of the bridge are being painted with a modern two-part paint that should last 30 years.
The view from a train of the Forth Road Bridge, before the Queensferry Crossing was built.
After the destruction of the Tacoma Narrows Bridge by wind-induced oscillation of the deck, suspension bridge construction was dominated by the American practice of stiffening the deck with large trusses. The Forth Road Bridge was the first suspension bridge to be designed with an aerodynamic deck to achieve stability, which lead to the bridge having a very slim stiffening truss – just visible in this photograph.
Because of the increase in both traffic volume and weight, a third bridge, The Queensferry Crossing, was built. This was the longest three-tower cable-stayed bridge in the world, and also the longest with overlapping cables, which give a stiffer and more slender bridge.
Following the construction of the Forth Road Bridge, the Severn Bridge had the first deck designed as an aerofoil. The result is wonderfully elegant, a blade of light across the Severn Estuary. Like the Forth Road Bridge, the Severn Bridge has had to supplemented by a cable-stayed bridge further down the estuary.
This view beneath the Welsh pylon clearly shows the deck aerofoil.
The more recent Humber Bridge has an aerofoil deck, and was briefly the longest single span bridge in the world.
Bridges do not have to be big to be beautiful – this is the Kylesku Bridge in the north of Scotland, looking east to the Glendhu Forest. It is curved in plan, and is now listed Category A by Historic Environment Scotland.
Finally, three historic bridges in Berwick-upon-Tweed. The first is the Old Bridge, built between 1611 and 1624.
The Royal Tweed Bridge, seen from the Old Bridge, was built between 1925 and 1928 and was the largest concrete arch bridge in the country when it was built. In the background is Robert Stephenson’s Royal Border Bridge (1847-50) carrying the East Coast Main Line high above the River Tweed.
Further Reading
I highly recommend David P Billington’s discussion of the genesis of beauty in structures in his ‘Tower and Bridge: the New Art of Structural Engineering’.
Image Gallery
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