"Kurilpa Bridge" by H Beck & J Cooper: Part 4

This is the final part of a 4-part review of the book Kurilpa Bridge. For some of the context, see Part 1.

The book's final main chapter offers a history of bridges, attempting to place Brisbane's Kurilpa span in a wider context. This is pretty well informed for a text aimed at the general reader.

The book notes that considering the long-term, design of vehicular bridges is a relatively recent phenomenon. Indeed, the history of bridge engineering is to a great extent a history of footbridges, with most new technologies and structural types pioneered in such structures. It's proposed that bigger spans and the commercial requirements of private funding led to an obsession among engineers with economy as their key yardstick during the industrial revolution. In time, economy became synonymous with engineering elegance, and the paring down and exposure of material became the engineer's aesthetic.


The authors contrast the 19th century development of bridge design in the UK and the USA to note that stylistic preferences are to some extent culturally determined - the Brits were "rhetorical", with gestures such as Telford's castellated towers, while the Americans were "utilitarian". Different preferences for craftsmanship as against mass production resulted mainly from differing availability of labour and material resources.

The Tacoma Narrows bridge is identified as both the epitome and failure of "Functionalist Modernism", the implication being that engineers who still adhere to this philosophy are following a failed tradition. Some of the book's comments are somewhat unfair. For example, Leon Moisseiff's Deflection Theory is depicted as "hunches and hypotheses dressed up as theory", which is absurd. For one thing, Deflection Theory had been devised decades before Tacoma's designer Moisseiff came along (he simple extended Josef Melan's theory and gave it a name), and for another, it was a well-developed analytical method, significantly more accurate than its precursors.

The book notes that the modern reintroduction of cable-stayed form has liberated engineers from the purely functionalist aesthetic - "a poetic genie was let out the bottle". This is clearly true - the form's inherent adaptability has triggered an explosion of creative design, especially for footbridges.

Kurilpa Bridge also includes texts from the bridge's designers, contractor and client, and a wide variety of generally excellent photographs of the bridge. Some of these reveal how the bridge's aesthetic vision has been compromised. There are balconies or belvederes at intervals, which to me don't visually cohere with the bridge's main identity, and the way the overhead canopy changes in its method of support at odd locations is visually disconcerting.

There are woven steel mesh side panels above a riverside highway which stop very abruptly, in an area where the canopy looks like it could have been hung from the bridge's tensegrity masts, but has not been.

Although the bridge is not entirely visually successful, it is undoubtedly a considerable engineering achievement. Beck and Cooper's book is also an unusual attempt amongst bridge architecture monographs to consider more widely the philosophies that can be applied by both designer and critic to evaluating the aesthetics of an engineered structure. For students of architecture, it may help shed some light on how engineers generally think. For students of engineering, it might perhaps prompt them to re-evaluate some dearly held principles and understand how to consider their work from a different perspective. I enjoyed reading it.

(Images of Kurilpa Bridge courtesy of Sankarshan Mukhopadhyay).

"Kurilpa Bridge" by H Beck & J Cooper: Part 3

This is the third part of a multi-part book review, see parts 1 and 2.

The second chapter of "Kurilpa Bridge" discusses "Hybridity and chaos". The authors suggest that a key design heuristic for engineers is the avoidance of hybridity, and a preference instead for structures which express a single form as purely as possible. This is to some extent a straw man - few engineers fail to understand that there are many simple but visually unappealing bridges.

The book suggests that the engineering "fear" of hybridity partly arose as a response to structural indeterminancy - until recently, hybrid structures (e.g. those which combine cable-stay and suspension systems, rather than being one or the other) were difficult if not impossible to analyse accurately, and may therefore have been seen as lacking in robustness. If the designer does not know what proportion of the load each structure will bear, it is difficult to assess how safe each system is.

There are counter-examples. One that the authors acknowledge is the use by Roebling and others of hybrid cable-stay and suspension bridge systems (most famously in the Brooklyn Bridge), where the cable-stays provide essential stiffening but also carry a share of the load.

Indeed, counter-examples are more common than the book accepts. On one hand, there are a number of cases where hybridity has been embraced through the trial-and-error process applied by untutored, experimental pragmatists, such as John Justice Jr or James Dredge. On the other, hybridity has resulted from hard-headed rationalism, where it offers an elegant way to separate out different functions - Robert Maillart's deck-stiffened arches seem to me a prime example of the rational development of a hybrid design, where the deck is a relatively deep beam used to stiffen a slender arch, analogous to the use of truss-stiffening in suspension bridges.

The authors also suggest that a taboo against hybridity is part of a wider cultural taboo. Given how puritan many engineers appear to be in their aesthetic outlook, I can understand this, but I think that if it is true at all, it is driven by simple economics. Even if a distaste for hybridity is part of the wider culture, you would have to ask why it persists so strongly in engineers and not, for example, in architects. Hybrid forms are less straightforward to build, a point well-proven by Kurilpa's complex erection engineering. They may be less safe, economic or reliable, and these are the engineer's primary concerns.

The third chapter is one with more questions than answers, asking whether a bridge can be art. The book asks whether Kurilpa Bridge can be seen as the distillation of a cultural zeitgeist, and point that it may be an exemplar of the digital age, a period where our culture has become dependent on tools that few of us understand or can make. That sounds about right for the Kurilpa bridge, where even the specialist bridge engineer has to undertake considerable head-scratching to understand quite how it actually stands up. The bridge, however, is not like the mobile phone, which must provide good value at low cost or fail in the marketplace - with major infrastructure like this, a clearer understanding of whether the cost is reasonable is harder to obtain.

I suggest there's also a political zeitgeist at work here, the way the complexities of democratic government can severe any clear connection between value and cost. The less an organisation directly experiences the financial consequences of its activities (for example, where it relies on external development funding), the less interest it shows in measuring the outcome of its expenditure. The result is the flashy monument predicated on an assumption that it brings value, without ever understanding whether the same value could have been purchased at a lower cost. This disconnect bedevils consideration of all iconic footbridges.

Other zeitgeists which might be thought relevant to the Kurilpa Bridge are the concepts of celebrity and bling - conspicuous consumption as a way to deal with status envy.

Returning to the question of whether the bridge is art, the book makes comparisons with land art, particularly Walter de Maria's Lightning Field, or the work of Kenneth Snelson (pictured, right). Clearly, there is some relationship there, which might support the idea that Kurilpa Bridge's aesthetic is on a higher level than merely a bridge. What is left largely unsaid is that art is defined by being non-functional - the less utilitarian an object is, the more it aspires to the status of art. I'm not convinced that this way of thinking does the bridge any favours, but I'm glad to see the authors aren't seeking a definitive answer either.

To be continued ...

(Images of Kurilpa Bridge courtesy of Jan Smith; image of Kenneth Snelson sculpture courtesy of Barbara Eckstein)

"Kurilpa Bridge" by H Beck & J Cooper: Part 2

This is the second post in a multi-part review. See Part 1 for an overview of this book.

The book has four main chapters. The first of these offers a discussion of the context of the bridge, how it was designed and built, and what it signifies about Brisbane as a place. The chapter opens with another quote from my blog post, this time unattributed, and this issue persists throughout the book - very little is referenced and it's therefore often impossible to decide how much credence to give to various strands of the narrative.

I haven't seen any of the other entries to the original Tank Street Bridge design competition from which Kurilpa Bridge emerged, but the genesis of Kurilpa's unique form is well-explained. Alternative options like a suspension, cable-stayed or arched span were rejected by the design team, until a tensegrity structure was put forward, initially as a question rather than necessarily a serious proposition. The two design aims driving the team were the need for as slender a deck as possible, to minimise ramp length at the bridge's southern end, and the desire to support a canopy of some sort, to provide shade from Brisbane's intense sun. Taken together, these make the tensegrity option more rational than it may otherwise appear.

However, it's also noted that the team rejected other options because of their lack of "wow! factor" or "originality". Beck and Cooper fail to comment on the very different heuristics at work here. The desire for something iconic was driven by the ultimate client, and "originality" plays a part in satisfying that desire - no municipality, paying the kinds of money involved here, wants something that their competitor cities already have.

Deyan Sudjic's Edifice Complex is at work: a giant pissing contest played out through the medium of architecture. Engineers respond to this sort of thing by asking: is the search for novelty enough to justify the monsters that may result, bridges which may be the equivalent of the genetically engineered luminous fish? It's only where this motivation is particularly strong that initially "crazy" ideas like a 128m span tensegrity bridge have any chance of being taken seriously. Even the authors can see some element of self-conscious absurdity to the structural form, referring to "the structural histrionics of the bridge", for example.

The authors extol the bridge's "signature spiky cloud" as being "exuberant and expressive". It "transcends the utilitarian, to celebrate both the act of crossing the river and the city it ties together". Of course, any landmark bridge would probably do the same. The question, which here as in most architectural criticism is left unasked, is whether this design in particular is better than any imaginable alternatives.

I am happy enough to throw off my habitual engineering biases and recognise that the pursuit of the most efficient engineering solution does not always result in a solution which satisfies wider criteria. The value that an iconic bridge provides to a community and economy has no clear relation to the quantity of steelwork and concrete employed in its construction. Instead, a unique and instantly recognisable silhouette can be an immensely valuable thing for a city, a readymade logo writ large on the landscape. Brisbane only needed to look south towards Sydney and its Opera House, another structure with a flagrant disregard for the principles of structural efficiency.

In short, I support the book's main argument, that there must be more to life than the "Functionalist Modernism" that serves both as an engineer's aesthetic and ethic.

To be continued ...

(Images of Kurilpa bridge under construction courtesy of Margaret Donald).

"Kurilpa Bridge" by H Beck & J Cooper: Part 1

Way back in July, I posted here my surprise and delight at seeing this blog cited prominently in the preface to Haig Beck and Jackie Cooper's book, Kurilpa Bridge (Images Publishing, 2012, 100pp) [amazon.co.uk].

I think this may be the only book in print to use The Happy Pontist as a key point of reference. The book is in part a fairly conventional piece of architectural criticism: a discussion of the titular bridge, its merits, and its place in a wider context of bridge-building. More interestingly, it's an attempt to understand how the bridge can appear as "controversial" to engineers, how it ignores the ideas of aesthetics common in the bridge engineering community, how those ideas came to be and remain in place.

The point of departure for this is a post I wrote in 2009, part of a series of posts on "tensegrity bridges". As I noted at the time (and the authors of this book acknowledge), Brisbane's $63m Kurilpa Bridge is sometimes described as a tensegrity bridge, but isn't really such a beast. As coined by Buckminster Fuller, the term refers to a structure where the compression elements are "islands" in a sea of tension, i.e. struts are connected to ties, but never to other struts. Completed in 2009, Kurilpa is a cable-stayed bridge, albeit an exceptionally complex one. The deck is sheltered under an awning, which is supported by pure tensegrity elements over part of its length.

In my post, I suggested that Kurilpa Bridge is:

"irrational, visually chaotic, disruptive, and possibly one of the most expensive fixed footbridges ever built"

The authors see this as a complaint, and one common to engineers, who see order and simplicity as both economically attractive as well as defining an aesthetic good.

They also take issue with my judgement on its expense (indeed, my original post did get some of the figures for the bridge wrong), although I'd note that any evaluation of the bridge's cost is skewed by the length of its approach ramps, which are clearly of much cheaper construction than the main river spans. Brian Duguid's moderately-definitive 2011 study of landmark footbridge costs puts Kurilpa as equivalent to €77k per metre span, which is about twice the median for landmark pedestrian bridges. So, maybe not one of the most expensive footbridges, but clearly a Porsche rather than a Nissan.

Beck and Cooper also draw attention to this quote from my post:

"Like many bridge engineers, I like a bridge where the structural principles are clear and comprehensible"

They see this as a heuristic, a rule-of-thumb which can be used to form value judgements. Their book sets out to explore this clear expression of engineering values, to demonstrate that it is a specific cultural artefact rather than (as engineers often think) an absolute, and hence to attack the idea that Kurilpa Bridge's higgledy-piggledy appearance is in any way a bad thing.

I think it's only fair to point out that my views on the merits of Kurilpa are not as straightforward as these quotes suggest. In the same post, I also said:

"I do admire its audacity, the willingness to install something that works against the orthogonality of its surroundings, a provocation which offers restlessness in place of reassurance"

and:

"it's undeniably a landmark, an innovation and a substantial technical accomplishment"

Indeed, I have in the past taken the same side as Beck and Cooper, critiquing the tendency of many engineers to treat their modernist aesthetic as a matter of morality rather than simply one of several possible philosophies. The engineering community's puritan distaste for flamboyance is something I've covered extensively on this blog in the past.

Okay, I'll stop there for now. It turns out this book review is getting pretty long, so I'll split it into parts, and continue in another post.

China bridge tour 2013

Eric Sakowksi, the man behind the highestbridges.com website, is planning another 3-week bridges tour in China, from 3rd to 24th August 2013. Participants will visit 12 of the 13 highest road bridges in the world; the sites of what will be the world's new highest road and rail bridges, currently under construction; the world's two largest rail viaducts; an exceptionally long span footbridge; and many other marvels.

Anyone interested can find out more online. For a taster of what is in store, Eric has recently added some photo albums from his 2012 China bridge tour to his site, and the 2011 China photo album is still there as well. Both are highly recommended.

"In the Wake of Tacoma" by R Scott

I've often been disappointed by what is available for students of bridge engineering history. Most of the books on the shelves relate to engineers long-dead, the Brunels, Telfords, Roeblings and the like. While there are a number of books on Robert Maillart, the closer you get to the present day, the less there is to read. Compare the field of architecture, which is well served with histories and monographs, including designers active today.

One book which helps to fill this void is In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stability, by Richard Scott (392pp, ASCE Press, 2001) [amazon.co.uk]. This is a book which takes the collapse of the Tacoma Narrows Bridge as the departure point for a wide-ranging, very thorough history of twentieth-century suspension bridge design. Its particular focus is the way in which engineers responded to Tacoma in ensuring their subsequent suspension bridge designs would not be susceptible to aerodynamic excitation.

The author is neither an aerodynamicist nor an engineer (he's an environmental planner). The result is a book which extensively discusses bridge aerodynamics without ever explaining it entirely satisfactorily. There are no equations, no graphs, and only a single air-flow diagram. This is therefore a book which talks around its central theme, somewhat like a book on evolution which mentions but never really explains the process of natural selection.

However, In the Wake of Tacoma more than makes up for these omissions with a wealth of detail.

It opens with the early history of suspension bridges, the work of James Finley, Samuel Brown, Guillaume Henri Dufour, Joseph Chaley, the Seguin brothers, Charles Ellet, the Roeblings and others. In the 19th century, a number of early suspension bridges failed under wind loading, before the provision of greater deck stiffness became a common solution.

The early suspension bridges of the twentieth century are covered in more detail, along with the design theories of the period. Josef Melan's Deflection Theory led not only to far more economic designs but also to a return to more and more slender bridge decks, at the same time as longer and longer spans were attempted, such as Othmar Ammann's 1100m span George Washington Bridge, and the 1280m span Golden Gate Bridge. Further advances in theory, such as Leon Moisseiff's 1933 Theory of Elastic Distribution encouraged the acceptance of plate girders rather than trusses for suspension bridge construction. Examples included David Steinman's Deer Isle Bridge and Thousand Islands Bridges, both of which experienced wind-induced oscillation soon after completion, resolved with a number of measures including the addition of stiffening stays.

These and other bridges pushed the drive for slenderness beyond previous limits, but in 1940 Moisseiff's Tacoma Narrows design went further still, with a span-to-depth ratio of 350:1, and a span-to-width ratio of 72:1. Some concerns were raised regarding regarding these unprecedented proportions, but Moisseiff's status as an authority in bridge design ensured that the project went ahead. Deck undulations became rapidly apparent, and despite installation of restraining cables, the bridge collapsed following severe torsional and vertical oscillations on 7th November 1940.

Scott gives a satisfyingly detailed account of Tacoma's birth, death, and the subsequent autopsy, a report completed by Ammann, bridge engineer Glenn Woodruff, and aerodynamics specialist Theodore von Kármán. The latter linked the bridge collapse to the phenomenon of vortex shedding, but found the bridge engineers to be resistant to this conclusion, later writing: "Bridge engineers, excellent though they were, couldn't see how a science applied to a small unstable thing like an aeroplane wing could also be applied to a huge, solid, nonflying structure like a bridge". Nonetheless, the Tacoma failure was to be a watershed: the lesson that had been painfully learned in the 19th century, that wind could dynamically excite a bridge in a disproportionate manner, had to be re-learned, and the field of bridge aerodynamics developed rapidly.

In time, this would lead to revolutionary new technologies for the suspension bridge, as well as the ability to tackle far longer spans than would previously have been economic. First, however, there was a period of retrenchment, both in America and elsewhere, with deep stiffening trusses adopted as the simplest way to avoid aerodynamic instability. Scott covers this period in a level of detail that begins to get tiresome later in the book: every major suspension bridge design is discussed over several pages, with mind-numbing facts about rejected design options, costs and funding, weight of foundations, records broken etc. This makes the bridge frequently a chore to read, but very useful as a reference. You certainly won't find this level of information on Wikipedia, for example.

The detail also leads to some of the book's strongest features. A number of major arguments between engineers such as Ammann, Steinman, and Germany's Fritz Leonhardt are covered, dispelling the casual reader's notion that engineering is in any way a dispassionate science. For me, this is the best thing about the book: many twentieth century engineers are little-known, and the debates and controversies that have passed between them even less so.

Discussing the revolutionary Severn Suspension Bridge, opened in 1966, which introduced the aerodynamically stable box girder to the field, Scott covers personalities like Gilbert Roberts and William Brown, hugely significant pioneers who will undoubtedly be key figures in bridge engineering histories yet to be written. Brown, in particular, went on to be involved in several other significant suspension bridges. The Severn bridge's span-to-depth ratio of 324:1 was remarkable, with the trapezoidal shape of the deck eliminating the vortex shedding problem which had affected Tacoma Narrows and other bridges.

Scott offers copious detail on the post-Severn generation of bridges, both box girders and other forms. Although the book, unsurprisingly, is dominated by American bridges, it reserves plenty of space for European, Scandinavian, and Japanese developments. Less attention is given to modern Chinese suspension bridges, although it's now the Chinese who are leading in creating long-span bridge history: 4 of the 10 longest suspension spans in the world are in China, and this figure is likely to increase.

The book continues with a look at bridges which at the time of writing were under development, not all of which have gone on to be built, including the 3300m-span Messina Strait Crossing. As with several other record-breaking spans, the Messina design features split box girders, reducing aerodynamic susceptibility. A number of other advances are under discussion, including the use of passive damping and computer-controlled active damping, which may offer the further economy needed to make ultra-long spans more viable.

In the Wake of Tacoma concludes by discussing both advances in the understanding of bridge aerodynamics, and specifically the understanding of the Tacoma Narrows collapse. It isn't clear whether the bridge's traumatic behaviour has ever been fully explained, with engineers now tending towards the view that vortex generation from the leading-edge rather than trailing-edge girder is most likely to have caused large torsional undulations.

While this book is an extremely valuable contribution to the history of bridge engineering, verbosity and an obsession with facts and records aren't its only flaws. Perhaps the major difficulty is the lack of illustration. There are quite a few bridge photographs, but nowhere near enough to show all the bridges discussed, and precious few diagrams which might help to explain how the bridges work and behave. These combine to make it a tough slog of a read. Despite this, I learned a great deal from it, and would recommend it to any bridge engineer interested in the subject.

Bridges news roundup

I'm still not having much time for blogging, so ... here is the news ...

Winners of the IStructE Structural Awards 2012 announced
Supreme award for West Gate bridge strengthening. Prizes for Crystal Bridges at the Museum of American Art, Jarrold Bridge in Norwich, and for Compiègne Bridge. Commendations for the Derry Peace Bridge, and Poole's Twin Sails Bridge.

Footbridge in Ljubljana
Not sure what minimal means? You do now.

Planning approval for Torrens footbridge short-circuited
$40m bridge in Adelaide to avoid the normal planning review.

Award for Europe's most beautiful pedestrian bridge
In the eye of the beholder, and all that.

In Paris, A Deliberately Wobbly Bridge
Silly season.

Four bidders in for New Wear crossing
Contractors keen on the chance to build £133m icon. The tender process is expected to take about six months.