Some recent books about bridges

I have a couple of posts on recent bridge visits in preparation, but meanwhile here's a quick round-up of a few books about bridges that have recently arrived at Pontist Towers ...

From Brycgstow to Bristol in 45 Bridges by Jeff Lucas and Thilo Gross (Bristol Books, 144pp, ISBN 978-1-90944-618-2, 2019) is a catalogue of all the bridges spanning Bristol's main waterways (at least, those that can be crossed by foot), presented in the order of a possible walking tour (albeit quite a long walk). The city is mentioned as Brycgstow in the Anglo-Saxon Chronicle, translated as "place by the bridge", sited at the confluence of the Rivers Frome and Avon. Over the years, it expanded as a port, especially after the creation in the early 19th century of the New Cut to divert the main river, turning the remainder into the "Floating Harbour".

Inevitably, a profusion of bridges resulted, and Jeff Lucas shares their stories with his own photographs in this book. It's a general interest book, so more of a travel guide or social history than a book on architecture or engineering, which is fine. The idea to write the book arose from an article by mathematician Thilo Gross applying the Königsberg Bridge Problem to Bristol, and a chapter by Gross explains this topological network puzzle in more detail.

Thomas Telford's remarkable bridge over the Menai Straits was opened in 1826, so to find an excuse for a bicentennial history, Menai Suspension Bridge: The First 200 Years (Menai Heritage, 206pp, ISBN 978-0-9932351-3-9, 2019), the author Bob Daimond has had to date events to the laying of the first stone, in August 1819. Spanning 176m, this was the longest bridge in the world when completed, a tremendous achievement given the state of engineering knowledge at the time.

Daimond's book is a definitive history of Telford's masterpiece, and very well illustrated with extracts from archive drawings, photographs etc. It discusses in detail the planning, testing, design and construction of the bridge, and its subsequent history including storm-induced failures, alterations and eventual reconstruction in the mid-20th century. As a history of engineering it is exemplary; my only complaint would be that it has little to say beyond that, on the bridge's cultural status, on the people who use it, and on its place in the wider history of suspension bridges.

Bridges by David Ross (Amber Books, 224pp, ISBN 978-1-78274-576-1, 2018) is essentially just a coffee-table photo book, a collection of photographs (with short descriptive text), arranged chronologically. The bridges are from all around the world and the photos are from a variety of photographers, so there's no special theme or style. Nonetheless, I found it a very enjoyable book. The photos are very well-chosen, and well presented, often across two pages. There are plenty of familiar bridges, plus quite a few that are less well-known, or were to me, anyway. A real effort has been made to span the globe, and the result is a fine reminder of the variety and ingenuity that bridge-builders have brought to their art over many centuries.

Ann-Mary Paterson is the great-grand-niece of William and Murdoch Paterson, two of the engineers responsible for construction of various railway lines radiating from Inverness in Scotland in the late 19th century. Her 2017 book, Spanning the Gaps: Highland Railway Bridges and Viaducts (Highland Railway Society, 96pp, ISBN 978-0-9927311-1-3; my copy was purchased from Old School Beauly) describes the history of the Highland Railways, with a focus on the structures that carried traffic through often quite difficult terrain.

The book is very well illustrated, with a mixture of historic and modern photographs, and several historic drawings. There are some informative photographs of construction, and some following various disasters, such as the 1989 collapse of the Ness Viaduct. There are some fascinating and impressive bridges along these railway routes: Culloden Viaduct, William Fairbairn's box girder bridges across the Rivers Findhorn and Spey; the timber Aultnaslanach Viaduct; Findhorn Viaduct; swing bridges over the Caledonian Canal; ornate castellated viaducts at Blair Atholl and elsewhere; and many more.

Bristol Bridges: 4. Meads Reach Bridge

This bridge was another early morning visit, to an award-winning span which is probably unique in Britain.

Built in 2009 for £2.4m, the 55m long bridge is a rare all-stainless steel structure. It was designed by Price & Myers with Níall McLaughlin Architects, and built by M-Tec. You'll see it described on the internet as a "stressed skin" bridge, to make it sound like it's using aircraft technology, but to bridge engineers it's simply a twin half-through box girder bridge, conventional enough except for the geometry and material.

The two edge girders hold up the bridge and also double as parapets. They consist of continuously welded, perforated Duplex 2250 stainless steel plate (supplied by Outokumpu), wrapped around triangular diaphragms. A series of cross-beams and bracing frames are hidden within the deck, which is surfaces with perforated stainless steel planks (of which, more later). The entire bridge weighs about 75 tonnes, and sits on four hidden stub "legs", one at each corner.

The extensive use of stainless steel is a bold, and presumably expensive, choice. The bridge's skin is punctured with thousands of small holes, arranged in size according to the calculated level of stress at each point of the girder surface. The process of analysing the bridge, determining acceptable levels of perforation, and translating that back into a fabrication model, will have been complex and demanding, and is an impressive achievement.

Luminaires are located within the girders and below the bridge's floor, and the perforations allow the structure to glow from within at night.

The bridge won the IStructE Structural Award for pedestrian bridges in 2010, and I think justifiably so, as it is highly innovative and geometrically challenging. I haven't seen it illuminated at night, but in daylight, sunlight reflects off the skin in a very attractive manner. However, the bridge is not without its critics.

The main complaint appears to relate to the deck panels, which are clearly very slippery, to the extent that the bridge is disfigured by prominent warning signs at each end advising users to cross with care. Reportedly, bridge users who do slip and fall have frequently been injured by the "cheesegrater" quality of the decking. In one month, over 600 people signed a petition asking for the bridge decking to be replaced.

However, as with the nearby Valentine Bridge, this is a public amenity which is privately owned. Although the decking is clearly not fit for purpose, the public may find it hard to force change.

Further information:

• Google maps / Bing maps
• Exploded diagram
• Mondo ARC
• Meads Reach Footbridge, Bristol (BDOnline, 2010)
• Oasys Software case study

Bristol Bridges: 3. Valentine Bridge

I'm nearly caught up on a backlog of bridge visits. The next two are both in Bristol, where I've previously covered Clevedon Pier (yes, I know that stretches the definition of "Bristol" and "bridges") and Pero's Bridge.

Valentine Bridge was built in 2000 by Alfred McAlpine, to a design by Atkins. The steel cable-stayed bridge carries pedestrians and cyclists across Bristol's Floating Harbour close to Temple Meads railway station.

As with the nearby Meads Reach footbridge (for which, see the next post), the bridge was privately funded and is privately owned.

The structure is S-shaped in plan, with a triangular cross-section framed truss deck. The upper and lower chords are circular steel tubes, connected by I-section struts in a Vierendeel arrangement.

This is not a good bridge.

It seems evident that the client must have wanted a "landmark" bridge of some sort, hence the mast, cables, and general layout. However, little effort seems to have been put into creating an efficient or well balanced structure. Of the four back-stay cables, two are so slack as to appear un-stressed, presumably a result of a cable layout which appears baffling when viewed from overhead. A balanced layout could have been achieved with fewer cables working more effectively.

Some of the cable detailing also looks a little awkward, perhaps cheap, especially the anchor detail to the deck.

The curved stainless steel parapets seem to be trying a little too hard, with an over-pronounced arc to the parapet posts. The abutment at one end, a mix of bold brick and prison-fencing (to guard the bearings), is quite unfriendly, as are the (pointless) anti-cycling barriers which block the walkway entrance.

Most annoying of all is the decking, which seems to have been fixed incorrectly, making a pronounced clattering sound each time someone crosses the bridge. If you watch the video below carefully, you can see the deck planks actually bouncing up and down.

Further information:

• Google maps / Bing maps
• Structurae

The great debate: Who owns bridge design?

I've been in Bristol and took the opportunity to attend this debate, held at the Arnolfini as part of the Architecture Centre's Bridge150 season, celebrating 150 years since the inauguration of Brunel's Clifton Suspension Bridge.

The debate was set up as architects against engineers, but from the start you could tell there would be a happy ending and both parties would make the case for living happily together ever after.

On the side of the engineers were Ian Firth, of Flint and Neill, and Julia Elton, engineering historian and proprietor of Elton Engineering Books.

Firth has been responsible for a significant number of innovative and architecturally interesting bridges. He introduced most of the key points that would recur throughout the debate. He noted the different involvement of the professions in projects of different scale, with the architect's role diminishing in inverse proportion to the size of the bridge. He was clear that both architects and engineers can be responsible for bad bridges, and that this usually occurs where one party fails to properly challenge their co-designer (River Wear and Glasgowbridge were offered as two examples). He tagged badly run design competitions where the engineering was sidelined or the client badly advised.

Firth identified the cult of the celebrity as one recent phenomenon which worked against engineers receiving proper recognition. Architects tend to be better known, and better at presenting themselves, and therefore are sometimes the only designer credited for a structure, however significant the engineer's role may be.

I was most pleased when he noted that good engineers could design very good bridges without architects involved, citing the work of Schlaich Bergermann und Partner in the present day, and Robert Maillart in the past. However, I was left with the impression that engineers should better aspire to working in collaboration with good architects, and that this was where good design was more likely to arise. Firth noted that the engineering education did not produce design-led, creative types, and that architects could contribute a better-trained imagination.

Elton also focused on education, citing a series of innovative engineers in the past who were perfectly capable of designing excellent structures with only minimal architectural assistance. She decried the lack of awareness amongst engineers about their forebears, suggesting this was why modern-day engineers lacked the confidence and context in which to be creative in their own right. Jean-Rodolphe Peronnet was offered as an example: few in the audience had heard of one of the greatest structural engineers of the 18th century. In contrast, architects understand their history very well, and see themselves as part of a tradition of productive, creative personalities.

I have a lot of sympathy for this point, seeing it in both colleagues and students. I see it as an issue of aspiration: designers need role models to learn from and to set scales of ambition. Many engineers simply fail to understand how great they could be, and along with an education which concentrates on analysis to the almost total exclusion of communication, presentation and creative design, this really does hold them back. I don't personally think we need to develop engineers who are good collaborators with architects - I think we need engineers who can be great designers in their own right, and they will then be successful both alone and in collaboration.

The architectural side of the debate was presented by Jim Eyre, of Wilkinson Eyre, and critic Hugh Pearman. Eyre addressed many of the same points, and presented a few quite ugly examples of what an engineer could produce alone, citing Maillart's Zuoz Bridge as the start of an era of boring engineer-designed bridges. Eyre noted that an architect's training made them far more aware of issues of context, culture, the experiential rather than solely functional side of a bridge, and that engineering training produced people ill-suited to addressing these issues.

He highlighted a period post-Zuoz when the engineer became king, and poor quality visual design resulted: the age of the motorway expansion, where least-cost no longer meant least-material (i.e. elegant), but fastest-to-build, and dull identikit concrete structures resulted.

Eyre also highlighted the key role that the procurement process plays in determining the success of design. Projects are increasingly led from a commercial rather than design perspective, with the contribution that design can make devalued. The increase in contractor-led design, in particular, has led to a focus on value-engineering which often reduces cost while simultaneously diminishing genuine value.

These are fair complaints, but appeared to attack the symptoms rather than the cause. Why do clients not value design? I think that both fee-paying clients and end-users, the public, share a lack of understanding of quality, and hence of value. Put simply, they do not know what a good bridge is, particularly where "good" is defined by engineering attributes. This even extends to visual aspects, where a widespread lack of visual literacy leads to some really spectacularly ugly architect-led designs being lauded as if they were actually good. The internet is full of such designs, and design competitons attract them like super-magnets. Instead, clients and the public often fall back on more straightforward yardsticks such as least-cost, or false signifiers of value, such as celebrity (the "it's Zaha Hadid so it must be good" syndrome).

Pearman did draw attention to the role of the public, who would not normally care about who "owns" bridge design. Architects were simply better at articulating their vision, at explaining design, but even they remain for the most part un-named and unknown to the general public.

I think this issue of "credit" for design is, or should be, a red herring. It seems to exercise many engineers who feel their contribution is often ignored, and while this is true, I think back to the motorway era. Although Jim Eyre suggested this period was the nadir of low-visual-quality, engineer-led design, I think there were also some very creative engineers at work during this period, highly innovative, and visually aware. I've recently posted a series of examples from the Sheffield-to-Leeds and Leeds-to-Manchester motorways on this blog: remarkable, sometimes beautiful structures, where no architect was involved, and where the engineers were not seeking any special recognition, but content to serve the public with humility.

I think it's vital that we train better-rounded engineers, who aspire to emulate the great engineers of the past. It's vital that we train people who can explain and articulate their designs. We should aim to encourage great designers who can transcend their training, from whichever background they come. But the relative roles of different designers only serve as the means towards an end, which is producing great bridges. More effort is require to explain to clients and end-users what "great" actually is, and why it can mean structures without flash, bling or spectacle. Only then can the people who use and pay for our bridges be in a position to "own" bridge design, and allow the designers to slip happily back into the shadows.

Bristol Bridges: 2. Pero's Bridge

I've badged this and the previous post as "Bristol Bridges", as if you're going to get a whole series of bridges in the area that I've visited. Well, actually only the two, for now anyway. But I do plan to make a return visit to the area and cover a few more.

Pero's Bridge is a relatively recent addition to Bristol's scenery, having opened in 1999. It spans an inlet of Bristol Harbour, and undeniably improves pedestrian access in a very busy part of the city. Designed by Arup with artist Eilis O'Connell, it features an 11-metre long bascule span, flanked by two fixed spans.

Visually, the most obvious feature of the bridge is the two large "trumpets" forming the rear half of the lifting deck. These provide a counterweight mass to balance the main deck, so that minimum force is required to open or close it.

The bridge is unusual in being a modern implementation of the rolling bascule, which rocks back onto its supports like the exaggerated motion of a rocking chair. Teeth are provided on the support beams to ensure it does not move out of tolerance when it does so. Bridges of this type were once common: I've visited those at Queensferry and Liverpool previously. One advantage of the form is that the centre of gravity of the rolling span can be positioned so that it lies to the span-side of the centre of rotation when the bridge is down, but so that it moves to the rear-side of the centre of rotation when the bridge is up; in both cases, it holds the bridge secure in the rest position.

The bridge is operated by a hydraulic piston below deck level, which remains above the water level at all times (the level being constant in Bristol Harbour). In the photograph on the right, it can be seen that the deck is a box girder with strutted cantilevers. Much of the detailing below deck level is visually awkward, particularly the main pier supports for the roll path, including their uneven relationship with the other pier.

I find the bridge unconvincing overall. It's a reasonable engineering solution, but the counterweight trumpets seem awkward to me. To some extent their shape is compelled by the engineering demands - the bulk of the weight has to be high up so as to balance the main deck properly. Other elements of the bridge are over-fussy, such as the parapets, which with their complex array of posts, bars, rails, and mesh panels, offer little in the way of elegance.

The bridge is named for an African slave, Pero Jones, brought to Bristol in 1783 by a local merchant.

Further information:

• Google maps / Bing maps
• Wikipedia
• Structurae
• National Archives (information about Pero)

Bristol Bridges: 1. Clevedon Pier

The pier at Clevedon is one of my favourite bridges to nowhere. Built in 1869, its elegant iron arches make me think of the Pont des Arts in Paris. There are eight spans, each 100 feet in length, comprising a wrought-iron superstructure supported on cast iron screw piles. It seems impossible that such spindly supports could both carry crowds of Victorian pleasure-seekers and withstand the force of storm-tossed waves.

However, other than various minor alterations, they did indeed withstand them, and the collapse in 1970 of the seventh and eight spans from the shore was man-made rather than due to the forces of nature. The bridge was being load-tested for insurance reasons, with water tanks providing a load of 2 kPa, and while the first six spans passed the test, the seventh failed, dragging the eighth down with it. This seems a very low load capacity when you consider that a modern pedestrian bridge would be designed for 5 kPa loading, plus a safety factor (so, typically 7.5 kPa), but this simply highlights the conservatism of current codes.

Another aspect of the pier which would not comply with current codes is the presence all along both edges of continuous bench seating. This is prohibited on any modern footbridge because a child can stand on the seating and no longer has safe containment. At Clevedon, a sign simply asks visitors to supervise their children; it should also be noted that the pier is a private space, with a toll paid for access, rather than a public “crossing”.

When built, the pier took advantage of the availability of “top hat” section Barlow rails, surplus stock from the South Wales railway. These were riveted back to back to form columns and longitudinal arches, supporting wrought iron plate girders along the edge of the deck. They're easily visible in the photograph on the right, showing the original pier construction.

Although the reconstructed spans match the general elevation of the original spans, both the girders and support framework are in modern welded steel, and to my eye look out of place on a Grade I Listed structure. If you compare the photograph on the left with the previous one, you can see some of the differences: the column and arch sections are cleaner, with no rivets and less interesting shapes.

Another photograph of the original construction shows further differences. The trestle supports have different horizontals at mid-height, with a straight bar on the new sections (above left) in place of lenticular struts on the old sections (right). The new trestles have a horizontal cross-beam at the top, while the old sections are arched at the top. Coupled with the loss of detail in the main deck girders, I find the pier reconstruction disappointing in its lack of adherence to the original construction. You wouldn't realise this from most websites or texts, which give the impression the pier was rebuilt exactly in its original form.

As with Southport Pier, after the load testing collapse the local council at Clevedon proposed to demolish the pier, but public outcry eventually won a reprieve. Some of the funding for rebuilding, and further refurbishment, was provided by many individual donations, commemorated with plaques inlaid into the deck planks and mounted on the rear face of the benches. This crowd-funding was supplemented by grants, and I think it's a great way of raising money and demonstrating popular support for a project.

Although this is a pier, not a bridge, it clearly has many similarities. I wanted to feature it here because it's such a supremely elegant structure, with a slenderness and loveliness of form that few such structures can match. Poet Sir John Betjeman described it as "the most beautiful pier in England", and it recently won the "Pier of the Year Award" for 2013. Money is currently being raised to fund construction of a new visitors centre.

Further information:

• Google maps / Bing maps
• Wikipedia
• Structurae
• Engineering Timelines
• British Listed Buildings
• Clevedon Pier and Heritage Trust
• National Piers Society
• The Heritage Trail
• Civil Engineering Heritage: Wales and Western England (Cragg)

Did Brunel design the Clifton Suspension Bridge?

Can this be true? A new book by Adrian Vaughan on the famous engineer Isambard Kingdom Brunel is reported to claim that he didn't even design one of his best known structures, the Clifton Suspension Bridge (pictured right, courtesy of Damien Everett on Flickr).

Vaughan's earlier book, "Isambard Kingdom Brunel: Engineering Knight-errant", was a revisionist critique of the widespread view of Brunel as not merely a giant amongst engineers, but very nearly the greatest Briton ever. It drew extensively on archive research to depict a designer who was confrontational, dictatorial, and prone to making over-quick decisions which frequently led to his projects going well over budget. It sought quite consciously to provide a counter-balance to the widely read LTC Rolt biography of Brunel, which by all accounts bought quite deeply into the mythology of a Victorian hero.

The new book that has provoked the headline is Vaughan's follow-up, "The Intemperate Engineer: Isambard Kingdom Brunel in His Own Words". I haven't seen it, but understand it includes many of Brunel's letters and seeks to depict both his genius and his fallibility.

It's certainly not news that the Clifton Suspension Bridge wasn't entirely Brunel's design. His initial 1831 proposal didn't start on site until 1836, and money ran out in 1843. Work on the bridge only restarted in 1862, three years after Brunel's death, with the design revised by William Henry Barlow and Sir John Hawkshaw. In part, changes were made to the bridge width and suspension chain arrangement to make use of chains that became available from the recently dismantled Hungerford Suspension Bridge. Changes were also made to the tower design. But the span and general conception remained as Brunel had proposed.

This situation is hardly unusual even today. Is Stonecutters Bridge the design of Halcrow and Flint and Neill, who (like Brunel) won the design competition and developed the basic concept, or of Arup, who completed the detailed design and made various changes to the scheme? And even if one engineer at any of these firms were put forward as the key engineer responsible, how much did they personally contribute?

The modern era, with design tasks shared across a diverse team, is not that different from the Victorian period. Identifying, and lionising, the big names may help personalise history, but essentially it's the engineering version of the lamentable tendency to see national history as the history of royalty. Suggesting that Brunel designed the bridge at Clifton pays proper tribute to the central figure in its creation, while obscuring a more complex reality.

It's also worth considering to what extent Brunel's present-day reputation is based on his forceful personality as much as on his actual engineering achievements. Was he a better engineer than Thomas Telford, Robert Stephenson, or lesser known contemporaries like Thomas Kennard? There seems to me to be an almost willful desire in the popular media to treat Brunel as heroic in the manner of a great general, to gloss over his many flaws and the fact that many of his enterprises were disasters. Like Stephenson, his greatest bridge designs were spectacular and perhaps revolutionary, but rarely of such importance that they became templates for wider adoption.

It's interesting, perhaps, that most popular histories relating to civil engineering are of the royalist type: biographies of the famous names. I can't think, off hand, of any popular books that get to grips with the wider social aspects of the 19th century revolution in scientific bridge design, although there are certainly specialist histories that address it.

Of course, a headline that simply stated "new biography confirms what we already knew in old biographies" is neither going to sell newspapers nor justify a journalist's time and expenses. The need to manufacture controversy is understandable. What I'm less clear on is the underlying need to propagate a heroic mythology, and to defend it against any inquisition, however plausible.

Bridges news roundup

Floating footbridge that can sail down the river unveiled
Bristol proposes to draw on West India Quay footbridge as its inspiration. It's not clear what this means for the competing scheme to build a footbridge at the same site using the old disused Brunel span from Cumberland Basin.

Pyramids and Taj Mahal to have a new arch rival – the Forth Bridge
Forth Rail Bridge to be put forward as World Heritage site (again). Note that despite the article's claim, it is clearly not the world's first major steel bridge, as residents of St Louis would undoubtedly attest!

Titanium bridge design competition for University of Akron narrowed to five finalists
Designs chosen from amongst the weird and wonderful. Well, mainly just weird.

Calgary's Peace bridge contract skirted policies
Audit report finds that the sole-sourcing of the Peace Bridge to Calatrava was symptomatic of a far wider lack of open tendering, and a failure to seek best value for the local council. Rick Bell offers a more pungent editorial at the Calgary Sun. See also previous post here.

Referendum to refurbish or replace Victoria’s Johnson Street Bridge likely for November
Mammoth exercise underway to rethink the decision to go with a Wilkinson Eyre designed replacement bridge (see previous post).