02 May 2021

"The Architecture of British Bridges" by Ronald Yee

Where does engineering end and architecture begin? That's the question I was left with after reading Ronald Yee's wide-ranging and informative "The Architecture of British Bridges" (Crowood Press, 2021, 224 pages).

Books on the bridges of Britain tend to fall into three camps: big national surveys; more selective surveys following the author's specific tastes; and studies of niche topics like railway bridges. The new book by specialist bridge architect Ronald Yee surprised me by coming closest to the first camp.

The core of the book is a survey of bridges from around the UK, not comprehensive but very well-chosen. This is bookended by an introductory chapter on the architecture of bridges, and two final chapters on bridge parapets and lighting. There is a useful index but nothing in the way of references or bibliography.

Since much of the first chapter is given over to a layperson's guide to different structural forms, there are actually only three or four pages which specifically tackle the architecture of bridges. I had definitely hoped to read more about this, given the author's own area of expertise. There is a bit of a gap in the market here, as most books and articles about bridge aesthetics are written by engineers, not the architects who now play such a key role in bridge design.

Yee's own architectural approach is one that is very closely aligned to the engineering: he is not one for the outlandish or decorative. His approach to the book's topic is to "show, not tell", allowing the idea of good bridge architecture to emerge through example rather than through a didactic approach.

The message I got from the main part of the book is that Yee sees architecture and engineering as being to some extent complementary and to some extent inseparable. Bridges from all periods are described straightforwardly, with the same attention given to how they work (structurally), as to their place in history, their visual appearance, or their local context. Yes, they may have specific architectural attributes (the description of Chester's Grosvenor Bridge includes its "archivolts of red Peckforton sandston ashlar" and "a frieze and cornice with rectangular modillions", amongst other features; Stirling's Forthside Footbridge's "visual effect is gymnastic and an undeniably spectacular sight"), but these are never anything other than part of the wider story.

This leaves many of the individual bridge entries a little dry, even where the bridges themselves can be seen to have some degree of special interest. In other cases, Yee ventures more of an opinion and I'd certainly like to have seen more of this.

The key strength of the book lies in how well the entries have been curated, and illustrated with generally excellent photographs. Given that Yee is well known for his sketches and drawings, I'd love to have seen more of those - they are few and far between.

I have read many books about bridges in Britain, but I still found plenty here that I was unaware of or which has not been celebrated previously in print. It surveys an excellent range of often exemplary bridges, at all scales great and small.

Presenting the bridges in a gazetteer format, structured by materials and bridge typology, does mean that much is left unsaid about architecture: the way in which bridge design in Britain moved through phases of craft construction, master builders, the era of "scientific" engineering, and the slow and then more rapid rise of architects as the leaders of the design narrative. Yee's book therefore leaves room for some very different treatments of the subject, and hopefully others will step into the breach.

22 April 2021

"Transporter Bridges: an Illustrated History" by John Hannavy

Transporter Bridges by John Hannavy (Pen and Sword, 268pp, 2020) is, I think, the first book to bring these unusual structures together in a comprehensive record. Subtitled "An Illustrated History", this is indeed a highly pictorial and well-detailed account of what was a very short-lived type of structure. Nineteen were built between 1893 and 1916, before the growth in motor traffic made them a less attractive form of river crossing.

The concept of a transporter bridge dated back to the mid-19th century. At a time when tall boats still used major rivers, there were essentially four ways to transport vehicles across such an obstacle. Ferry boats were common, but could only carry a few vehicles at a time, and could be unreliable. Fixed bridges were the highest-capacity, most reliable solution, but expensive both in construction and land-take. Moveable bridges were, in their earlier years, complex and expensive, and suitable only for moderate spans. The transporter bridge could cover longer spans, but carrying loads more in line with those on a ferry.

Hannavy documents early proposals for transporter bridges in detail: H.N. Houghton's idea for a railway crossing in New York (1852); J.W. Morse's plan for a similar crossing (1869); Charles Smith's proposal in Middlesbrough (1873); and others.

However, the first proposal to be built was the Viscaya bridge at Portugalete near Bilbao, completed in 1893. The designers Alberto Palacio and Ferdinand Arnodin took out patents for the transporter concept, and Arnodin went on to complete eight more such bridges.

Hannavy's history covers most of the transporter bridges with relative brevity - I say relative as they all get plenty of detail. He takes the story right up to recent decades where new transporter bridges have been proposed (e.g. at Royal Victoria Dock, Nantes, Marseilles and Brest). Of these, the Royal Victoria Dock Bridge is the only that was built, but its transporter gondola was never installed.

Beyond the basic history, the book discusses the "Systeme Arnodin" in detail, and there are chapters covering five of the few surviving transporter spans at length as fine examples of the type: the Viscaya bridge, Newport Transporter Bridge, the Tees Transporter Bridge, Crosfield's Warrington Transporter Bridge (and its now-demolished sibling), and the Rochefort Bridge. A further chapter considers the Widnes-Runcorn Bridge, which was closed in 1961. All five of the transporter bridges ever built in the UK are therefore given close attention.

Each of these is covered thoroughly, with quotes from contemporary journals and an excellent variety of historic and recent photographs. Hannavy's research has clearly been in-depth. The chapter on the Rochefort bridge is particularly interesting, as it mainly documents the massive refurbishment project undertaken to prolong the life of the bridge and to restore it closer to the original Arnodin design.

In addition to the main chapters, the book concludes with a series of one-page summaries of all the known transporter bridges both built and unbuilt.

This is, without any doubt, the definitive book on transporter bridges, and essential for anyone with an interest in them. More generally, it should appeal to those with a broader interest in historic bridges. It is not entirely faultless, unfortunately, as there is no bibliography and no referencing of any sort. This is a shame for any serious researchers, but probably not a big issue for the more general reader.

18 April 2021

"Bill Brown's Bridges" by David Boxall

I've remarked in the past how few books there are on the great bridge designers of the 20th century, other than one or two of the earliest decades such as Robert Maillart and Othmar Ammann. Even many bridge design professionals will struggle to name designers comparable with the likes of the nineteenth century's Telford, Stephenson and Brunel.

In the 20th century, the increase in scientific understanding of structural design and consequent specialisation made large projects more and more the province of a broad team rather than a singular man and his support office. This was especially the case where the scale or sensitivity of projects required decision-making to be collective rather than dictatorial.

Of course, it was always the case that the big names were often just those who fronted up the work of a broader team. That's nothing new, although it does sometimes seem as if in the late 20th and early 21st century the only entities that can be credited for a bridge design are the engineering corporation or the architect. Individual engineers, not so much.

With all that in mind, I was keen to read "Bill Brown's Bridges" by David Boxall (301 Publishing, 2015, 148pp, available from b2.co.uk), a biography of one of Britain's most successful suspension bridge engineers, who worked on the Forth Road Bridge, Severn Bridge, Erskine Bridge, Humber Bridge, two bridges over the Bosphorus straits, and on unbuilt proposals for the Messina Strait Bridge. Brown has been credited with the aerodynamic box girder design for the Severn Bridge, which radically changed the economy and feasibility of major suspension bridges.

Boxall runs a marketing and design agency, but was previously manager of Brown Beech Associates. This book is very much an "official biography", produced with the cooperation of Brown's wife Celia, and its aim is to document and cement the legacy of one of Britain's most successful bridge engineers.

Born in south Wales in 1928, Brown studied engineering at Southampton and then completed a PhD at Imperial College. His family background was technical in that his grandfather and father were both cabinetmakers. On graduating from Imperial in 1951, Brown was fortunate to go straight into employment with the engineer Gilbert Roberts at Freeman Fox.

Roberts was one of the top engineers of the day, responsible for the structural design of the Dome of Discovery for the Festival of Britain. He had worked with Sir Ralph Freeman on the design of the Sydney Harbour Bridge (1932), and on a suspension bridge on the Zambia - Zimbabwe border (1939).

Over the course of eighteen years until Roberts retired in 1969, Brown was exposed to progressively more challenging engineering and greater levels of responsibility. By the time he became a partner in the Freeman Fox firm in 1970, he had worked on some truly exceptional projects.

His early years included work on major cranes, and a major steel arch structure, Adomi Bridge in the Ghana (1957). Developments in welding and higher-strength structural steels during the 1950s were to prove essential for what would follow in the 1960s.

Freeman Fox's design team, led by Gilbert Roberts, were appointed (alongside Mott, Hay and Anderson) to develop designs for both the Forth Road Bridge (1964) and Severn Bridge (1966). These were spans well in excess of the largest suspension bridge recently built in the UK (Tamar Bridge, 1961). It had been two decades since the collapse of the ill-fated Tacoma Narrows bridge, but aerodynamic concerns remained high in engineers' minds.

Both the Severn and Forth bridges were initially designed to be built using the truss decks then seen as the norm. Fortuitously, an accident in wind tunnel testing during design of the Severn bridge led to a model being mostly destroyed. The book recounts that for the replacement model Brown sketched out a very different slender box-girder geometry, that could be built quickly out of plywood and used for the remaining testing. Severn went on to become the first large suspension bridge built using an aerodynamically stable box girder, a major innovation.

What the book doesn't say is that the slender box-girder concept was not new to the Severn crossing: German engineer Fritz Leonhardt had proposed the same idea for the Tagus suspension bridge in 1960, albeit with two separated box girders rather than just one. Indeed, much of the development of welding and stiffened steel plates for bridge construction had been undertaken in Germany.

The book goes big on Brown's role here (and elsewhere) as an innovator, but says nothing about the Severn Bridge's legacy of problems: fatigue in the inclined suspension hangers, issues with the quality of welded plate, and the need for expensive strengthening. Innovation is never without risk, and on this scale, the consequences can be significant.

Box girders were also used by Freeman Fox for the nearby Wye Bridge, the Erskine Bridge, and for the West Gate Bridge in Melbourne, Australia. The latter collapsed, killing 35 people, in October 1970, and Brown was amongst the senior Freeman Fox staff summoned to testify at the subsequent inquiry in Australia. Boxall records partner Dr Oleg Kerensky's view that the collapse was the fault of the contractors, and that the design had been sound. This is misleading: Freeman Fox's design calculations and site supervision were condemned as completely inadequate by the inquiry.

At the time the West Gate Bridge collapsed, Freeman Fox had already been working on plans for a new suspension bridge across the Bosphorus for three years. This adopted both the aerofoil deck from the Severn Bridge, and also the triangulated layout for the suspension hangers, an idea which had seen little if any use elsewhere.

Completed in 1973, the first Bosphorus Bridge was the longest span outside the USA at the time it was built, and is quite possibly Roberts and Brown's finest achievement. Freeman Fox took on significant overall responsibility for guiding and supervising the project, not just its design, and Brown relocated to Istanbul for most of the construction phase.

By the time of the even longer Second Bosphorus Bridge (1988), Brown had left Freeman Fox and set up his own firm, Brown Beech Associates (in a huff, to paraphrase the book's account). His role this time was as the client's technical advisor, rather than as designer. This bridge adopted conventional vertical hangers, unlike the triangulated ones used on Severn and the previous Bosphorus span, and a few years later the latter bridge had its hangers replaced with vertical cables as well.

In his later years, Brown worked as a consultant on a number of structures, including the Messina Strait Bridge and the Storebaelt East Bridge, both developing concept design proposals and advising on more specific issues such as cable-spinning techniques. He passed away aged 76, in 2005. The book includes a gallery of images of nine key structures that he worked on, and they truly are an incredible CV.

I think it's fair to say that this official biography is a partial account - broader and more balanced accounts of the development of twentieth century suspension bridges are available elsewhere. However, the book is well written, well illustrated and well presented. There are dozens of great photographs of some truly epic bridges, and it's great to see a twentieth-century British bridge engineer recognised in this way.

There was a period from the completion of the Severn Bridge to the completion of the Humber Bridge when it appeared that Britain had firmly re-established itself in the vanguard of long-span bridge design, and as part of the Freeman Fox team Bill Brown was clearly central to that.

13 April 2021

"Fowler's Bridges" by Aidan Bell

Sir John Fowler is best known (with Sir Benjamin Baker) as one of the engineers responsible for the Forth Railway Bridge, completed in 1890, a masterpiece of Victorian civil engineering. During his illustrious career, Fowler was responsible for many other bridges and railways, including much of what is now the Circle Line on the London Underground.

Aidan Bell's book "Fowler's Bridges" (self-published and available from biblio.com, ISBN 978-1-5272-7661-1, 190pp, 2020) deals with the engineer's most famous works only in passing. Instead it is an in-depth study of the estate that Fowler developed at Braemore, near Ullapool in Scotland, and the bridges that he built there, many with Baker's assistance.

Fowler's life story is one of almost constant upward progress. Born in 1817, Fowler set himself on a career in engineering as soon as he left school. His first few years saw him apprenticed to John Towlerton Leather, George Leather and John Urpeth Rastrick. He rapidly took on increasing responsibility, before setting up independently at the age of 26 in 1843. It was the period of railway mania, and Fowler was in the thick of it, taking on chief engineer roles and promoting schemes in Parliament.

By 1849, Fowler was elected to the Council of the Institution of Civil Engineers, going on to become its President in 1865. By that time his consulting practice had grown substantially and was working on over 70 large projects each year. Fowler's army of assistants were based at premises in London, where he also had his main residence.

Also in 1865, Fowler bought the first of two estates near Ullapool in northern Scotland, Braemore, merging it two years later with the adjacent Inverbroom estate. This was to be his holiday home, and he would spend two months of each year there. A new house was built, with innovations including hydro-electric power for electric lighting, and many improvements were made to access around the estate. Fowler had become a proper Victorian gentleman, eventually adding a Baronetcy to his Knighthood, enjoying the Highland hunting life, and entertaining guests at what must have seemed a very remote place to some.

In this painstakingly detailed book, Aidan Bell recounts the story of Fowler's life and career, and documents the Braemore estate, providing detailed descriptions of several "miniature" bridges which Fowler had installed within the landscape. The estate was very different in character to many of those of the landed gentry, with its rough terrain and steep river gorges. The only comparable landscaped Victorian estate seems to be William Armstrong's Cragside.

Two of the estate bridges are relatively well-known: Corrieshalloch Suspension Bridge, and Auchindrean Bridge. The bridge at Corrieshalloch stands out for its situation above a waterfall, allowing visitors spectacular views of the river gorge. The Auchindrean bridge spans a less dramatic location, but is notable as the largest lenticular bridge surviving in Scotland today. It has similarities to Brunel's larger Saltash bridge.

The other bridges are less spectacular, but interesting in how Braemore was treated very differently to other Victorian estates. As an engineer, Fowler seems to have had little interest in the sort of faux-classicism that decorated the property of other wealthy landowners. The Braemore bridges are economically appropriate solutions to difficult terrain, rather than ornamental. They are for the most part aesthetically unspectacular, encouraging the visitor to look away from the bridge and admire the scenic grandeur instead.

Bell's book is heavy on detail. Many of the bridges no longer exist, but each bridge site is described in detail, with photographs and even diagrams to illustrate the structural behaviour of each bridge. It is, to be fair, so much detail that it is likely to be too much for the casual reader, but I certainly enjoyed its thoroughness. The book may be best suited to anyone with an interest in Fowler himself, or Scottish historic bridges generally, or the way in which an estate's development illustrated the expertise and philosophy of an engineering owner.

For me it raises interesting questions around taste. The desire of others to ornament their lands with the mock-Palladian, columns and porticos and pediments taken out of context and plopped down amidst soft green vistas seems to be a taste that has survived today. Prince Charles is perhaps the most notorious modern proponent of a belief that beauty can be found mainly in the past, and that the tics and tropes of the classical are a timeless aesthetic, rather than a pastiche shorn of meaning when taken out of context.

As an engineer, Fowler is more likely to have seen the problem that needed solving as one of spanning an obstacle, rather than decorating a view. The functional nature of the Braemore bridges suggests a love of a more natural landscape, and a desire to make his intrusions into it as modest as was possible. It seems an aesthetic approach to admire and emulate: bridges creating new spaces to admire the surroundings rather than to function primarily as sculpture. There are designers still working today who could benefit from that philosophy.

12 April 2021

The return of the Happy Pontist

You may have spotted this blog has been a little quiet last year, and especially recently. This is the first time I've posted since the beginning of November. There haven't been many opportunities to visit bridges, and generally more pressing things to do than blogging anyway.

So ... I do have a few books about bridges that I could review, so I'll start posting some of those shortly.

And if there is something in the world of bridges that you really think I should feature here, please do let me know, via the comments.

So long as it is not this.

Or this.

Or this. Definitely not this!

01 November 2020

"Bridging: by Foot and Bicycle" by Ney & Partners

Here is an excellent book devoted to  the designers du jour in the world of bridges, Ney and Partners. Once past its ungrammatical title, Bridging. By Foot and Bicycle (Archibooks, 264pp, 2019) is an excellent and very well-presented survey of the firm's pedestrian bridge oeuvre, filled with photos, visualisations, drawings, diagrams and informative text (in both French and English). As with the firm's bridges, the book is not completely without its flaws, but I can recommend it to anyone with a serious interest in the very best bridge design.

An introduction titled "A bridge has to be designed!" by Laurent Ney sets the tone. Ney reports his experience working on a project with a large multi-disciplinary firm, who apparently responded with embarrassed silence when Ney asked "Who designed the bridge?" While this hardly rings true (such firms are obviously well populated with people who design bridges) his point is that the norm in design firms when presented with a bridge project is not to design from a tabula rasa, but to select and adapt from an existing structural typology. His argument is that there is no real "design" in this approach.

This is the very opposite of Ney's own modus operandi which is (to at least some extent), to see how context and constraints can point the way to creative opportunities, minimising preconceptions wherever possible. This book illustrates that effectively, explaining in detail the design decisions that were made on the various projects featured.

From the outset, this also highlights a lacuna that recurs throughout the book. It is the designer's perspective, and largely a history of various designed objects and why they are how they are. There is little in the way of self-criticism, and essentially no space for the voice of those who commission or use these bridges. This is not uncommon in an architectural monograph, and in this case, where much of the discussion is inevitably somewhat technical, the sense that there are people on the bridges and they may have something to tell us sometimes vanishes entirely.

The technical element in the book is inevitable given the superlative engineering at the core of many of Ney and Partners' bridges. Sometimes, their astonishing bridges seem to be the output of a designer who is operating as a naïf, ignorant of the conventions of bridge design and hence able to devise solutions that would never even enter the peripheral vision of an experienced engineer. At other times, they seem the work of an auteur, someone with an in-depth understanding of the bridge engineering craft but the desire to pursue excellence and never accept compromise.

Fellow engineers often admire Ney and Partners' bridges because this approach - creative, challenging, courageous - leads to structures which are remarkable in their geometric perfection and economy of detail, slimmed down well beyond what others ever attempt, let alone achieve. This is why the technical issues are key throughout the book and it could never be purely about the architectural aspects of design.

Although the bridge designs featured often take the idea of refinement to extremes, the bridges are only rarely completely rational in their conception. It's always clear that intuition has been applied, and subjective choices made. This is particularly the case in the first few bridges presented, which share a theme of history and context.

The as-yet unbuilt Poissy Footbridge is a proposal for a new bridge on the site of the remnants of a historic bridge across the River Seine. The historic Pont de Poissy was largely destroyed in 1944, and never rebuilt. The Ney design follows the same alignment but flies above the remaining bridge piers, supported from tetradactyl steel supports sitting in between the original masonry. The new bridge's longest span is 93m, yet the deck is formed from a single, ultra-slender folded steel plate. The impression is of a gently undulating ribbon, dancing across the river, dipping down over the existing piers but darting back away from them as if suspended on air. It is both a little incongruous, giving the initial impression of being structurally unreasonable, and also rather stunning.

Dejima Footbridge, completed in 2017 in Nagasaki is very different but illustrates some of the same aspects of the Ney philosophy. This is a cantilever bridge, arranged with one fixed end so that the "free" end imposes as little load as possible on the more archaeologically sensitive of the two river banks. The two edge girders feature multiple rows of stiffening plates, with the web perforated in a visually interesting manner. However, the stiffeners are to a great extent decorative, and the shape of the girders gives the visual impression that the bridge functions like an arch. It's a beautiful structure, but the engineering and architecture are not integrated in the way that many other Ney designs achieve.

The book's discussion of the Tintagel Footbridge serves to illustrate the point that Ney and Partners don't entirely ignore conventional typologies, but that their design process can allow them to take or adapt those standard forms in interesting and site-appropriate ways. At this site, Ney's analysis of the normal bridge forms led them towards an arch as a visually and contextually desirable proposal for the site.

A key issue at Tintagel was the difficult access for construction, leading to consideration of a bridge which was built by cantilevering from its supports (a well-trodden method for building metal arch bridges). The bridge as-built retains the cantilever form, as making it into a genuine arch would have been structurally far more challenging (a result of the sag curve of the pathway, and the consequences for thermal restraint).

It's a spectacular bridge and the engineering and architectural ideas are well-explained in this book, but very little is said about how its users find it (especially with such filigree parapets high above a chasm, and with a gap in the floor at midspan).

The same is true of a structure like the Park Footbridge in Antwerp. This is one of a number of designs where Ney and Partners apply a "subtractive process", defining a stable shape and form, generally in thin sheet metal, and then looking to see what metal is unnecessary and can be cut away (the carbon balance of reduced material versus increased fabrication process is never discussed). The structure here is a hybrid between a bowstring arch and a box girder, although, as with many architects, that's a term that's never used - after all, who would celebrate being able to walk through the interior of a girder (it's not 1850 any more)?

It's an amazing work of structural engineering, absent all the bolts and stiffeners that a normal box girder interior displays. The webs are perforated in a manner that takes account of levels of stress, but is not entirely determined by that, with far more material left in place than can be structurally necessary - compare a proper bowstring arch where a handful of cables suffice to connect the arch to the bridge deck. It looks like an amazing experience to walk through but ... why is it a covered bridge at all? Will the patterns of illumination inside be tolerated by pedestrians susceptible to flicker? And is a floor-rail, an obvious trip-hazard, really the best way to stop cyclists bashing their heads on the girder web? To me, it feels like the uncompromising desire to maintain the purity of the design object results in a design that is not completely comfortable.

This is not the only Ney bridge where this can be said. The Vluchthaven Footbridge in Amsterdam has the same sinuous deck plate as the Poissy design, and an ingenious parapet design. The client was keen to address the common Amsterdam problem where bridge parapets serve as a favoured place for bicycles to be parked and locked. Ney and Partners came up with an elegant parapet design with all verticals - no top rail or handrail. If someone were foolish enough to lock a bicycle here, it could just be lifted off. It's smart and very well detailed - but handrails are a good thing for many bridge users, especially the elderly or infirm who may want to take the opportunity to stop and briefly secure a handhold. This does not appear to a bridge for stopping on.

A very different result from the subtractive approach mentioned above is the Knokke Footbridge, which I discussed right back in 2009. This is, in my view, one of the firm's masterpieces, using one curved steel plate to satisfy the requirements both of transverse load distribution (a curved skin acting in tension) and as the primary longitudinal structure (sharing the characteristics of a suspension bridge and also of a Robert Maillart arch, inverted). The Y-shaped bridge supports, and the way they hold up the deck, are brilliant.

In writing this book review I've been drawn to writing about the flaws in these designs, because I feel that the monograph style of the book (uncritical, celebratory) and the presentation entirely from the designer's perspective (their subjective view is privileged over anything else) do beg for some degree of challenge.

However, Ney and Partners are easily one of the best bridge designers working today, bringing together a very rare blend of imagination with the superlative technical ability required to turn their audaciousness into reality. They operate way beyond the level of the vast majority of bridge designers.

The breadth and variety of their designs shows that they do take context seriously (contrast their designs, for example, with someone like Calatrava). The detailing of their bridges is frequently exquisite, and the book's photographs and technical drawings make that abundantly clear. I can't imagine a bridge designer who wouldn't enjoy and learn from this book, and non-specialists should also find their work well worth discovering in more detail.

30 September 2020

Welsh Bridges: 20. Llantysilio Chain Bridge

This bridges goes by a number of names - Berwyn Chain Bridge may be equally as appropriate. Signs at the site just call it "The Chain Bridge". It is neither a Listed Building nor a Scheduled Monument, which will only be surprising if you incorrectly imagine that our heritage bodies are competent.

The first bridge across the River Dee at this location was the work of local man Exuperius Pickering, variously described as an entrepreneur or a "coalmaster". Pickering was looking for a way to transport his coal and other materials between the Llangollen Canal (1808) and Telford's recently improved London to Holyhead Road, without paying tolls to cross Llangollen Bridge. Conceived in 1814, his bridge was completed in 1818.

This was a period of rapid development in cable or chain-supported bridges within the United Kingdom. Granted, the Winch Bridge, an iron chain catenary structure, had been built over the River Tees in 1741. However, it was the early 19th century when cable and chain bridges took off, with stayed bridges in Galashiels (1816), King's Meadow Bridge (1817) and Dryburgh Abbey Bridge (1817, rebuilt as a suspension bridge in 1818), and the Union Chain Bridge (1820, suspension bridge). Things advanced rapidly enough for Robert Stevenson to present an article surveying these and other designs in 1821, as well as proposing his own bridge at Cramond, an underspanned suspension bridge, which was never built.

Pickering's bridge sits right in the middle of this chronology. Happily for posterity, drawings of the bridge were made by the French traveller Joseph-Michel Dutens (see below). These show the bridge to be an underspanned suspension bridge, with eyebar chains supporting the deck, and an additional tension rod below this, perhaps to enhance stability. The bridges I mentioned above were well-reported, and it's often stated that Stevenson was the first to propose an underspanned suspension bridge, and James Smith's Micklewood Bridge (1831) the first to be built. In reality, Pickering got there first, although how much of an improvement his structure was over a simple catenary bridge might be doubtful.

The first drawing by Dutens shows half of the bridge (it was a three-span structure), while the second drawing gives cross-sections and details of the chains. A dozen chains passed below the bridge deck to provide support.

In addition to the drawings, photographs of Pickering's bridge survive, although showing it enhanced on one side by a timber truss.

The bridge lasted remarkably well, until it became unsafe and was dismantled in 1870. In 1876, Henry Robertson, owner of Brymbo Ironworks, rebuilt the three spans and re-used the original chains, again adopting the underspanned system (photograph below). This one was destroyed in flooding in 1928.

Roberton's son rebuilt the bridge the following year, but this time with only a single pier in the river. The chains were re-used, but now to form a suspension bridge, with three suspension chains on each edge, and two stiffening chains connected along the deck underneath.

One tower sits on an outcrop of rock within the river, and the other on the river wall at the north edge. The river tower was protected by a large concrete pier, rendering the new bridge far less susceptible to flood damage.

The chains at the south end of the bridge were anchored into the ground, while at the north end they pass over the adjacent Chainbridge Hotel and were anchored into rock high above the canal. The deck chains were anchored into the ground using an adjustable tensioning system.

A pair of bars hang downwards from each chain link, and these are connected to a triangulated system of lower hangers. These in turn carry the lower deck chains and the timber deck.

The bridge was load-tested with 45 people when it opened, and lasted reasonably well, becoming gradually more dilapidated until being closed as unsafe in 1984. In 2014-15, it was completely refurbished, with all the metalwork carefully dismantled and then reinstated.

The works were completed by local firm Shemec Ltd to a design by consultants Ramboll. The engineers completed a careful structural assessment of the bridge, determining that even if corroded ironwork was replaced, it could not carry anywhere near modern loading requirements, being limited to 1.5 kPa of load. This equates to roughly 5 tonnes of load on the 24m main span, or around 60 people. Llangollen Town Council, who had taken over responsibility for the bridge, agreed that this was sufficient. Warning signs at the end of the bridge request that no more than ten people use it at once.

The reconstruction works are well documented in a paper by Ramboll and in photos on the Chain Bridge Project website. I'm not clear what proportion of the original metalwork was preserved and reused, but new pieces were fabricated in mild steel to match the existing details and dimensions wherever any piece could not be reused. All the chain pins had to be replaced. Nonetheless, in the rebuilt bridge it is claimed that these are the oldest bridge suspension chains in Britain to remain in use.

Prior to the refurbishment, there was no parapet remaining on the bridge. The reconstruction introduced a series of new parapet posts, a tensioned upper cable, and a mesh infill system. I'm not sure how well these match any parapet that had been there in the past, but I doubt the new system is compliant with normal modern standards.

Indeed it's interesting to compare the refurbishment work at Llantysilio with what was done at Brabyns Park Bridge in Marple, which I discussed in a recent post. The chain bridge project is an exemplary piece of conservation engineering, where even though the structure is not Listed, it has been treated with integrity and the original details preserved as closely as possible. The engineers sensibly recognised that compliance with modern standards would have been entirely inappropriate. By contrast, the Marple structure is Listed Grade II, but senseless attempts to impose modern standards on it have largely ruined its appearance (although thankfully not irreversibly).

The Llantysilio Chain Bridge is unique both in the complex history of its surviving structural fabric, and in its form and details. It is well worth visiting, in a setting within view of two other fine bridges, and with plenty more to see within walking distance.

Further information: