Welsh Bridges: 5. Barmouth Bridge

This is described as the longest estuarial bridge in Wales, and it's certainly the longest timber bridge in Britain, being a total of 731m long. It has carried the Cambrian coast railway across the mouth of the Mawddach Estuary, between Barmouth and Fairbourne, since 1867. There are 113 timber spans, comprising braced wooden trestles, and five metal truss spans at the northern end.

Originally, an opening span was included of so-called "cock-and-draw" construction, which reportedly took some 37 minutes for two men to open. This was replaced by Cleveland Bridge in 1900 with the present arrangement. The timber trestles have been entirely replaced at least once in their history, and were most recently refurbished by Network Rail the early 1980s.

The metal spans are an interesting arrangement. There are two bowstring trusses, which at first glance appear identical. However, one is a simply-supported span, and the other is a swing bridge supported from its centre on a pivot pier. Closer examination reveals that the swing span has vertical members above its pier which are not present on the other span, as you would expect, and I expect the detailed build-up of steel sections is also different.

The bridge has clearly not opened for some time (there's a photo of it open here). The opening mechanisms are in a state of considerable disrepair, and the rails across the bridge are now continuous across the span joints.

Only a single rail track passes over the bridge. The bulkhead rails are supported from longitudinal baulk timbers, which are held at the correct spacing by a series of metal struts and ties. Metal cleats hold the timbers in position on the main timber decking. On the metal spans, short lengths of longitudinal timber sit within "bath-tubs" in the metal bridge deck.

A timber footway passes along the eastern edge of the viaduct. This is a very pleasant walk, with fine views of the Mawddach estuary, but also a vital link between Fairbourne and Barmouth. There is an occasional passenger ferry between the two towns, but after the rail viaduct, the next crossing upstream is the toll bridge at Penmaenpool, which is only open during the daytime, and beyond that, the road bridge near Dolgellau.

A toll was levied on the footway since the early twentieth century, but this has recently been abolished.

At the south end, the footway slopes steeply up to the nearby highway, and Barmouth residents have established a campaign for a better footway connection.

The timber parts of the bridge are in fair condition, although there are a number of holes in the trackside decking which have been covered over with metal or GRP plates. From below, isolated areas of rotted or damaged timber can be seen, and metal fixings are severely rusted, as is only to be expected in a tidal estuary.

The condition of the metal spans is of greater concern, being extremely poor with little or no worthwhile protective treatment, and extensive corrosion. Network Rail have plans for a full refurbishment of the metal elements, which appears to be long overdue. This is not a busy railway line, and it must be difficult to justify the expense that properly maintaining this type of bridge should entail.

Walking over the bridge, it's hard not to speculate about the possibility of building a highway bridge nearby. When the Penmaenpool toll bridge is closed, the highway journey between Barmouth and Fairbourne takes about 17 miles, and even when its open it's still 14 miles. As the crow flies, the actual distance is only 2 miles, so a highway bridge would be of considerable benefit both to local residents, and to others passing north and south along the coastline. It would be an expensive endeavour, due to the need for lengthy highway improvements approaching from the south, and potential conflict with Barmouth harbour at the north end.

Meanwhile, the local council, which essentially "rents" the walkway from Network Rail for £30,000 per year, is under severe pressure to reduce costs and is considering closing the footpath. It's hard to argue that it should be more of a priority than many other hard-pressed council services, but unsurprisingly there is a great deal of opposition to closure, including an online petition with over 40,000 signatures.

I think this is a lovely bridge, of great engineering, historic and social value, and it would be a shame to see it closed or not maintained. It's not far from the site of Pont Briwet, another timber viaduct which, despite its Listed status, was recently demolished and replaced with a new concrete bridge. It would be a terrible shame for Barmouth Bridge to ever follow suit.

Further information:

• Google maps / Bing maps
• Wikipedia
• British Listed Buildings
• Structurae
• Transport Heritage
• Engineering Timelines
• Timber railway viaducts in Wales
• Description of viaducts across the estuaries on the line of the Cambrian Railway (Conybeare, Proc. ICE, 1870-71) (and Discussion)
• British Railway Bridges and Viaducts (Smith, 1994)
• Civil Engineering Heritage: Wales and West Central England (Cragg, 1997)
• The Bridges of Wales (Breese, 2001)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

Welsh Bridges: 4. Penmaenpool Bridge

This privately owned timber road bridge dates from 1880, when it was constructed by the Penmaenpool Bridge Company Limited, under agreement with the Barmouth Harbour Trust. It crosses the River Mawddach in Wales, and provides a useful short cut between the coastal towns of Barmouth and Fairbourne during its opening hours.

Most spans are 20-feet, but the central span is 30-feet. This span was designed for possible conversion into an opening bridge span, in case a disused boat-building yard upstream of the bridge was ever re-opened, but this was never required.

The structure is a series of straightforward braced timber trestles, with a heavy deck of diagonally arranged baulk timbers. It appears to be generally in good condition, although several of the deck timbers are loose.

The bridge is operated as a private toll bridge, with prices of 20p for a pedestrian, or 70p for a motor vehicle not exceeding 1.5 tonnes in weight. The bridge is only open between 8.30am and 6.30pm, with tolls being collected from the southern end, adjacent to the bridge-owner's cottage.

It's a lovely spot to visit. The abandoned railway line on the southern edge of the river has been converted into a cycle and walking trail, Llwybr Mawddach. The former signal box is now a bird-watchers' hide, while the old railway station and platform are now part of the nearby George III Hotel. It's a splendid spot from which to admire the historic structures, landscape and wildlife.

Further information

• Google maps / Bing maps
• British Listed Buildings
• The Bridges of Wales (Breese, 2001)

Bath Quays Footbridge Competition entries published

These came out a few days ago now, but I've only just had time to look at them properly.

This is a contest for a new £2.5m pedestrian bridge across the River Avon in Bath, organised by Bath and North East Somerset Council.

In May, six teams were shortlisted, and each given £5000 and eight weeks to develop a design. The teams are:

• AL_A / AFA Consult
• Flint & Neill / Moxon Architects
• Grimshaw / Buro Happold
• Heneghan Peng / Ove Arup
• Marc Mimram / Webb Yates
• Price & Myers / McDowell & Benedetti

Now, all six entries have been released, although anonymously. You can have fun, if you wish, trying to guess the designers! A winner was originally scheduled for August, but this is now expected to be in November.

Entry 1

This is a very curious design, a propped cantilever bridge (intended to minimise physical impact on the historic south bank of the river) fabricated from a series of extremely lightweight trusses. It's fiddly to the point of being finicky, and would make a fantastic climbing frame for the locals to explore. The truss members are all of stainless steel, but painted, which is a genuinely baffling idea.

Entry 2

Again, this is a structurally bold design, and one which makes use of the same basic principle: support the bridge from the north bank so as to reduce impact on the south bank. It's an unusual "cable-stayed" bridge, with a steel box girder deck which is boomerang shaped in plan, and supported by a mast on only one side. The normal cables are replaced by steel ribbons. I especially like the detailing of the balustrades on this design.

Entry 3

This entry comes with a name, the "zig-zag bridge", which describes its profile in plan. Architecturally, it is extremely restrained, so modest that the zig-zag is the barest nod to the need for the bridge to express something, anything. The money here has gone into expensive materials: stainless steel box girders and balustrades, a Bath Stone handrail, and a "precast granite" deck. I'm not quite sure what precast granite is, but it sounds expensive, anyway.

Entry 4

Captioned "Between history and modernity", the fourth design takes the idea of responding to a propped cantilever moment diagram as seriously as did the first, and with much the same logic. The bridge curves gently in span, and is supported by two Vierendeel girders, one on each edge of the bridge. These are shaped to provide almost a hinge at the point of structural contraflexure. They remind me a little of the Vierendeel ribs on Paris's Pont de Solferino, a Marc Mimram design. The designer has tucked the main supports away behind the edge girders, which would be implausible on anything other than a short footbridge.

Entry 5

Now here's a design that I quite dislike. I loved the basic image, an elongated Ikea-like picture frame, with ancient Roman ivy already growing over it, but I think the design fails under closer examination. It's a bridge with a tall central timber truss with footways either side, possibly intended as a Vierendeel but that's clearly impossible in timber at any useful scale. Diagonal steel bars and a support framework for the vegetation fill in the truss bays, making it impossible to cross from one side of the deck to the other.

Entry 6

The final entry is the most intriguing, at least in terms of its engineering. It's a half-through girder bridge, with twin steel girders constructed from perforated weathering steel plate. The perforations are layed out to suit the stress patterns in the girder, which is constructed of a series of steel segments. The segments are stressed together using stainless steel prestressing cables. It's technically fascinating, although I think it's perhaps the least sympathetic bridge to this particular site, and a concept which may be more appropriate elsewhere.

For your amusement, here are my guesses at the various designers. I'm not going to forecast the winner, but if I had a vote, it would go for Entry 6.

1. AL_A / AFA
2. Flint & Neill / Moxon
3. Grimshaw / Happold
4. Mimram / Webb Yates
5. Henneghan Peng / Arup
6. Price & Myers / McDowell + Benedetti

Tintagel Castle: Shortlist announced

The organisers of the design competition for a new footbridge at Tintagel Castle in Cornwall, England, have shortlisted six out of one hundred and thirty seven entries. A winner is due to be announced early in 2016.

• Dietmar Feichtinger Architectes with Terrell (France)
• Marks Barfield Architects with Flint and Neill (UK)
• Ney & Partners Civil Engineers with William Matthews Associates, Ettwein Bridges and Waagner Biro (Belgium)
• Niall McLaughlin Architects with Price and Myers, and Max Fordham (UK)
• RFR and Jean-François Blassel Architecte, with Engineers HRW, and WSP (France)
• Wilkinson Eyre with Atelier One (UK)

They seem to have assembled some (mostly) impressive contestants, although a number of well-known bridge design specialists are notable for their absence. I certainly look forward to seeing the various designs unveiled in due course.

10 essential bridges books: Conclusion

Attentive readers will notice I've actually discussed twenty "essential bridges books" here in recent posts.

Older posts

• Chinese Bridges
• Leicht Weit / Light Structures
• An Encyclopaedia of Britain's Bridges
• Footbridges
• Traversinersteg
• Von Holzsteg zum Weltmonument
• Bridges of Britain
• Footbridges: Small is Beautiful
• Failed Bridges: Case Studies, Causes and Consequences
• Bridges in Slovakia

Recent posts

• Bridge Engineering: A Global Perspective
• Living Bridges
• The Architecture of Bridges
• Highland Bridges
• Bridgescape: The Art of Designing Bridges
• The Work of Jörg Schlaich and his Team
• 30 Bridges
• Robert Maillart: Bridges and Constructions
• Calatrava Bridges
• The Architecture of Bridge Design

But now it's your chance to tell me: what did I miss out? What is your own "essential" bridges book? Answers in the comments, please!

10 essential bridges books: 10. The Architecture of Bridge Design

I struggled over my choice of the tenth and final book in this series, and am not entirely sure that David Bennett's The Architecture of Bridge Design (1997, Thomas Telford Publishing, 200pp) [amazon.co.uk] can rightly be described as "essential". However, it's a book that had quite a significant impact on me as a designer, and so I'm including it here.

The book was intended as a "state-of-the-art" survey of bridge design by both engineers and architects at a time when there had been a prolonged period of intensifying activity between both types of designer working more closely together, on projects which were of considerable public interest and often of high design merit. The author brought together a wide variety of designers to describe their projects in their own words, and the reason I still enjoy the book today is the manner in which it captured a certain zeitgeist.

Bennett dates the period of interest to the beginning of the 1990s, with Santiago Calatrava's (unbuilt) East London River Crossing proposal from 1990, and Cezary Bednarski's Bloomers Hole Bridge, an unbuilt competition winner from 1992. It's a period that was probably at its peak when a fever for millennial footbridges took over, and I think it's a period from which designers and their clients are still suffering from a bit of a hangover.

Re-reading Bennett's book now is an exercise in nostalgia. It's quite remarkable how bad some of the designs featured are, coming from an era when pretty much any ropey old visualisation could make a bridge look contemporary. Cases in point include Rodolphe Luscher's awful Pont Devenir and Budapest proposals, both included here and showing quite a staggering lack of respect for context or scale. Other poor designs include the Japan Bridge, and the East Bridge at l'Parc de la Villette, both in Paris. It's interesting to contemplate quite how these bridges were considered worthy of inclusion, but I think that then, as now, there was too little genuine criticism of such ventures.

There are other designs where reading the designer's own ideas and justifications is a little depressing. Examples here include the Royal Victoria Dock footbridge, which seems even more of a white elephant when the author makes clear its reliance on the transporter gondola element, which was never installed.

In other instances, it's interesting to read numerous "what-might-have-beens", for example not only Foster and Partners' early ideas for the Millau Viaduct, but also those of Alain Spielmann, an opposing competitor. Similarly, you can contrast the Royal Victoria Dock footbridge as built with the design by Cezary Bednarski which was not. There's a degree of poignancy here, and throughout the volume, huge quantities of passion and creativity devoted to structures which would never get built. As an industry, this represents many lifetimes of talent and hard work which appear to be wasted. However, with their preservation in this book, perhaps there are still ideas which can form seeds for further development.

In a few of the better contributions, the designers offer genuine illumination on how their structure was conceived. A bridge like the South Quay Footbridge can't properly be understood without this background, I think.

I'd like to see more books like this about bridges: argumentative, speculative, informed and informative. It would be interesting to look back on such a book again, in ten or twenty years time, and see how the bridge-design zeitgeist has evolved.

10 essential bridges books: 9. Calatrava Bridges

And so, we come to Santiago Calatrava.

Calatrava is something of a phenomenon in modern bridge design, and is often cited, quite wrongly, as being singlehandedly responsible for making bridges architecturally interesting. His designs are often immediately recognisable - his combined training as both an architect and as an engineer has led him to produce structures which combine visual drama with structural rigour, a kind of spacial poetics, usually writ large in tons of carefully balanced steel.

Calatrava Bridges (Tzonis and Donadei, Thames and Hudson, 272 pp, 2005) is ten years out of date now but remains the most up-to-date guide to this superstar's bridges, both built and unbuilt. As with most other books about the Spanish designer, it is in no sense a critical work, but is a celebration of his P.T. Barnumesque showmanship.

Calatrava's work is much-derided by other architects and engineers, if supposedly much loved by the public. Even the latter appears less true now, as he has a growing reputation for budget and programme over-runs as much as anything else. Fellow designers criticise the way that his bridges rarely respond to context, instead taking a signature style (white, generally steel, a cat's cradle of cables, hi-tech detailing) and dropping it into whatever setting is currently to hand. His bridges are bombastic, grandiose, sometimes over-wrought to the point where they become almost hysterical. Modesty and restraint are never Calatrava's watchwords.

However, as this book makes clear, Calatrava's work is also often geometrically fascinating, spectacular, and informed by a deep love of engineering craftsmanship and technology. That they are instantly recognisable puts other designers to share: he is the supreme bridge design stylist, happy to provide his signature wherever his clients are willing to pay for it. Few designers have been so prolific or so consistent, and if Calatrava has many unbuilt projects to his name, he also has far more completed works than most rivals.

Tzonis and Donadei's book is well illustrated, with plenty of beautiful photographs and quite a few diagrams and architect's sketches. It is not thorough in this regard - this is a good summary of the designer's work but certainly not the definitive encyclopaedia.

Reading through the book today, I am actually most struck by Calatrava's facility for concrete design. His unbuilt Vecchio Bridge would have been a particularly elegant, Maillart-esque concrete arch, while his 9 d'Octubre Bridge in Valencia features some exquisitely shaped curved concrete.

He is also occasionally capable of surprise, with his grey Oberbaum Bridge in Berlin and red-ribbed Ponte della Costituzione in Venice both being fine designs which are all the better for their departures from his usual palette.

A properly critical study of Calatrava's bridges has yet to be written, but until that happens, this book is at least a useful compendium of his work, and one that I am quite happy to recommend.