There are two basic ways of telling that the Royal Albert Bridge between Plymouth and Saltash is the work of engineer/architect/visionary Isambard Kingdom Brunel. The first is that it looks like nothing else on the British railway network. Brunel – Benjamin ‘Dizzy’ Disraeli to Robert Stephenson’s William Gladstone – was a true one-off. He wouldn’t have recognised a conventional design solution if it had come up to him, ground his famous cigar underfoot and then jumped up and down on his top hat. Brunel seems to have been engaged in a lifelong search for the biggest, the widest, the flattest, the broadest, the most spectacular, the most unusual.
The second way you can tell is this:
…which does rather give the game away, though the inscription wasn’t there when the Royal Albert Bridge was opened in 1859.
The bridge between Plymouth and Saltash was promoted by the Cornwall Railway company, itself supported by Brunel’s Great Western Railway, which is how he came to design it, at a new location slightly further upstream than the Cornwall Railway had proposed. Before settling on the design for the bridge, Brunel had pondered on some possibly more conventional-looking timber bridges. Unfortunately for Brunel (though luckily for us), the River Tamar which separates Plymouth and Saltash was under the jurisdiction of the British Admiralty. The Admiralty is a recurring actor in the story of early railway bridges, and frequently crops up with admirable foresight demanding sufficient clearances underneath for any conceivable future warship, and a minimum of piers in the rivers being crossed.
The Admiralty rejected Brunel’s early timber bridge ideas. Then, in the face of estimated construction costs, Brunel himself had to scale back his subsequent ambitions for an iron bridge with a single main span in favour of a design with two smaller main spans and a single pier in the middle of the Tamar, which the Admiralty approved. The two large main spans were to be approached by a series of conventional metal girder approach spans, because the valley is wide between Plymouth and Saltash. Herein lay a problem, namely how to support the two long main spans, each of just under 138m in length.
Brunel had, by the time the Royal Albert Bridge was being designed, already come up with the outline design for the Clifton Suspension Bridge, which had a main span well over 200m wide (the bridge design was subsequently modified by others, and much delayed in its construction). Unfortunately, a suspension bridge wasn’t going to work for crossing the Tamar. At the risk of grossly over-simplifying the physics, if you think about a suspension bridge, the weight of the main deck is pulling down on the suspension cables hung between the towers. So those towers will collapse inwards unless the cables are secured into the ground on the outside of the towers, balancing the pull on the towers. Because the Tamar valley is wide where the Royal Albert Bridge crosses it, and the bridge is approached on a run of conventional approach spans, there is no ground to which suspension cables can be attached.
We know that Brunel was present at the construction of Robert Stephenson’s Britannia Bridge, which connected Anglesey to the mainland of Wales over the Menai Strait. Its main spans were tubular girders 140m long, so conceivably Brunel could have produced something similar. But why do that, when you could do something different? Brunel’s ever-fertile mind produced something which is now unique on the current British railway network.
Brunel’s solution for the two main spans of the Royal Albert Bridge was lenticular trusses, so named because of their lens shape when viewed from the side. It is this which gives the Royal Albert Bridge its distinctive appearance. If I understand the physics correctly, the bridge deck hangs from the lenses, the lower chords of which are made of chains, like a suspension bridge. And rather like a suspension bridge, this downward pressure might cause the vertical supports at the outer end of the lenses to collapse inwards, but in a lenticular truss the upper cord of the lenses prevents this. The upper chords are perhaps the Royal Albert Bridge’s most conspicuous design feature, being made of huge metal tubular girders (proved by the Britannia Bridge to be immensely strong). They are compressed by the inward force of the towers at either end of the lenses, but are strong enough to resist it, balancing the forces and meaning that no horizontal thrust is imposed on the piers of the bridge. Given that the approach spans of the bridge describe gentle curves and there would be a derailment risk if they were pushed out of true, this is a perfect solution.
Although the Royal Albert Bridge looks like a one-off, Brunel knew what he was about. He had already designed a railway bridge in Chepstow (since replaced) featuring a tubular girder upper section. The Royal Albert Bridge looked a lot more impressive, but the engineering was similar, if on a rather different scale. Although rare, there are other lenticular trusses around the world, though none of them are anything like as spectacular as the Royal Albert Bridge. The bridge deck is 51m above high water level, compared to an Admiralty requirement for 30m clearance.
The Royal Albert Bridge carries only a single-track railway line, meaning that trains need to be timetabled to avoid passing on this stretch of track. Track and trains go through tall elliptical arches in the towers at the ends of the two main spans. Yet although the bridge looks narrow in comparison to most modern railway bridges, which carry double track railways, the archways look slightly more spacious than they need to for a train to fit through. The bridge was originally built to carry the Great Western Railway’s broad gauge trains on track with rails 7’¼” apart, rather than the standard railway gauge of 4’8½” to which the track was eventually converted in the late 1890s, and this provides the explanation.
The bridge is a splendid symbolic gateway to Cornwall, that most independent-minded of English counties. Its dramatic shape means it attracted much attention on its construction, and it has continued to do so since it was built. It is a popular subject for photography and art, and appears several times in the work of English Primitivist artist Edward Wallis (1855-1942). More recently, it appeared on a UK £2 coin behind a portrait of its engineer/architect Brunel. It was Grade I listed in 1952.
Brunel himself died in 1859, and it is this date which is (rather morbidly; oh, those Victorians…) commemorated on the giant inscriptions at the ends of the main spans of the bridge. He had been too ill to attend the bridge’s official opening earlier the same year, which was carried out by Prince Albert, after whom the bridge was named.
For years, railway passengers could enjoy swift travel over the bridge, and feel a sense of smug superiority while peering down at car drivers below, who continued to rely on slow and infrequent car ferries to cross the Tamar. Central government appeared quite content to let this state of affairs continue, and it was left to local authorities on both sides of the Tamar to fund the construction of the Tamar Bridge, a suspension bridge which opened for road traffic in the 1960s. It blocks the view of the Royal Albert Bridge from upstream, although it’s a good way to see the railway bridge in detail if you’re driving into Cornwall.
National railway infrastructure owner and operator Network Rail carried out a comprehensive £10m refurbishment of the bridge in the early 2010s, restoring its original colour scheme (paint samples of which were collected in a positively hair-raising manner, the details of which can be found here). Network Rail had earlier removed inspection walkways, installed in the 1920s, which blocked the view of the inscriptions at the end of the main spans.
It now looks back to its glorious best, a fitting and distinctive memorial (along with several others, it has to be said) to Brunel’s individualistic approach to transport infrastructure design.
Bibliography and Further Reading
Historic England’s listing citation for the Royal Albert Bridge, here
Several original drawings for the Royal Albert Bridge, available via Network Rail’s archive shop, here
Network Rail press release detailing the restoration of the Royal Albert Bridge, here
The Royal Albert Bridge website, here
The Royal Albert Bridge at the Structurae database, here
4 thoughts on “Lens Lens (Royal Albert Bridge, Plymouth-Saltash, Devon/Cornwall, UK)”
Oh dear, you’ve called the Duchy a county….Trelawney’s army will be swarming over the barricades towards us ‘ere in Debn
But the Duchy itself refers to the county of Cornwall on its website. I am confused – but then again I’m an outsider.
Happy to take further opinions on this and amend if necessary. Certainly no offence was intended!
In light of the comments on the width of the archways, I do feel that I should point out that the relationship between track gauge and overall rail vehicle width is far ftom linear. Great Western broad gauge rolling stock was wider than other – standard gauge – railways’ trains to some extent, but it wasn’t a huge difference. Bear in mind that (to take just a couple of examples) East and South African trains run on railways, originally engineered by Brits, of metre and 3’6″ gauge respectively but their trains are both higher and wider than British ones whose dimensions are limited by older views of adequate clearance under bridges and between other bits of civil engineering.
The precise “logic” behind Brunel’s broad gauge is rather difficult to fathom out, but originally appears to have included the aim of fitting coach bodies the same width as on other railways between rather than above the wheels, which could then be larger and so rotate more slowly ay any given speed. This objective was not however actually incorporated into vehicles that were built. All most mysterious (along with the question of why Brunel, of all people, didn’t foresee improvements in bearing design allowing high-speed operation wirh small wheels…).
Reblogged this on The Bridgehunter's Chronicles.