21 December 2012

Bridges news roundup

Time for a quick last post before Christmas ... hopefully I will get some time over the festive break to deal with a backlog of bridge visits, five from around the UK, one from Greece, and get those posted up here in the New Year. Meanwhile, here is the news:

Pedestrian Bridge / HHD_FUN Architects
Chinese footbridge. I am not sure whether all the arched steelwork on top is actually doing anything structural, or is merely decorative.

Compiegne Bridge / Explorations Architecture
An excellent highway bridge design, the Vierendeel arches are exquisite.

Transforming the Bridge Competition Winners
A variety of proposals to transform the abandoned Detroit Superior Bridge.

Melkwegbrug / NEXT Architects
I think I've mentioned this before. But here it is again. Lovely photos.

Pont de Singe Installation / Olivier Grossetête
Thoroughly delightful artwork / bridge supported by balloons. Sadly, here's how it really looked when the Pontist paid it a visit in September (click the photo to see it full size).

River Lee pedestrian crossing plans unveiled
Bridge will lift a mere 4m. Huh?

£600k bowstring design for new footbridge in Boston is backed by council
See previous Pontist report.

Bridge full of life
Contemporary Chinese bridge-cum-classroom with more than a few echoes of classic Chinese covered bridges.

China to Complete World’s First All-Glass Suspension Bridge in 2013
Anywhere other than China, I would dismiss this story out of hand.

Festina Lente / Adnan Alagić, Bojan Kanlić & Amila Hrustić

Footbridge Over the Railways / DVVD | Architectes – Designers
An interesting approach to the inherent difficulties of keeping railway authorities happy.

That's all for this year, have a Happy Christmas!

19 December 2012

Lancashire Bridges: 1. Lune Millennium Bridge, Lancaster

Opened in early 2001 at a cost of £1.8m, the Lune Millennium Bridge in Lancaster, was one of a rash of pedestrian bridge structures taking advantage of a loosening of development funding and the desire to attach the Millennial label to anything in sight. Lancaster's span across the River Lune formed part of a wider "Lune Millennium Park" project, an important link in a traffic-free coastal route.

The bridge was designed by Whitby Bird (now part of Ramboll), and built by Henry Boot Construction. Its main deck is 114m long, with a longest span of 64m. It's basic form is that of an asymmetric cable-stayed bridge, with the main support on the south side of the river, where ground conditions were apparently better. However, it's clearly much more complex than that simple description suggests.

Twin masts are poised on a conical concrete pier. A cable ties the masts together, and stays support the main span. Further stays connect to the back span and also to a 30m long "gangway" side span. This arrangement is unusual but not unique - there are other British twin-mast examples at Lockmeadow, Newport, and Ashford.

In plan, the main deck curves a little like a boomerang, connecting a high-level footpath on the river's south bank to the the river's north bank. From the bend in this path, the separate gangway drops downwards to connect to the south bank quayside. The links to Google and Bing maps below will make this clearer (at the time of writing, Bing's overhead view dates from when the bridge was still under construction, showing temporary works in the river prior to mast and deck erection).

The main bridge deck is a 4m wide, 600mm deep steel box girder, which provides the torsional stiffness necessary for the cranked span. It is suspended from 40m tall cigar-shaped steel masts of maximum diameter 1.2m. A number of features of the structural configuration seem a little puzzling, and also led to considerable difficulties during construction (the first attempt to lift in the masts by crane, had to be abandoned for example).

The load on the mast "V" comes mainly from the river span, and tends to pull the V out-of-plumb. Along the main deck axis, this is resisted by the back-stays, which are tied to the very short south span back span, rather than directly to foundations on the shore.

This results in a better balance of horizontal force within the deck, but must complicate the end-of-span support, where the south bearings have to resist uplift. Away from the main deck axis, the "V" is prevented from tilting by two cables which again are tied to the gangway rather than to the shore. Again, tie-down bars have been incorporated at the end of the gangway to resist what in this case must be a substantial uplift force. To me, it feels odd, as tying the masts directly to the foundation would appear much more straightforward.

The main deck is supported at both ends, and by the cables, but also at two other points. Twin bearings take some of its weight directly onto the gangway's tubular spine beam (presumably to provide sufficient torsional stability), and an additional pier is required at the distant end of the main span some way in front of the main abutment. Looking at the bearing on this pier, it is yet another tie-down against uplift. Having a pier here rather than another cable support also helps reduce the height requirement for the masts, while still satisfying navigation requirements. Overall, it seems to me that the designers found it quite hard work to ensure adequate stability for what at first seems a fairly straightforward and elegant conceptual layout.

I visited the bridge in October this year, and was generally impressed. The overall scale and silhouette of the bridge is not inappropriate to the surroundings, which are sufficiently level and open to give the structure space. The masts are well-formed and the cable layout pleasingly uncluttered, and the bridge offers different views and vantage points from every direction. Sometimes with a bridge of this geometric complexity, you can find a viewpoint which is visually jarring, but I didn't find that here.

Vibration is perceptible when crossing the bridge, but its magnitude under normal foot traffic was too small for me to get a useful measurement on my smartphone accelerometer, so I guess it is not enough to pose any concern. The bridge was being very well used, so it appears to have been a sound investment.

The gangway is quite different to the main span. It consists of an ovoid steel spine beam (presumably two circular sections split and joined by flat plates), supporting the deck via a series of folded-plate ribs. These give it considerable visual interest, more so than the relatively anonymous main span. They also result in significant pattern staining, where water has run through the perforated aluminium decking.

The parapet on the gangway is very different to that on the main span. On the main deck, it is an all-painted steel assemblage of vertical and horizontal steel flats, with stainless steel used only for the handrail. The gangway has steel posts, stainless steel kick and hand rails, stainless steel horizontal wires, and the upper part is a separate stainless steel assemblage which seems only to be there to provide the standard height requirement for cyclist use. Clearly there is a visual justification for emphasising the different nature of the gangway, but I wonder whether it was purely for budgetary reasons that so much stainless steel is used on this part of the bridge, and so little elsewhere.

Another very noticeable feature of the bridge is the use of conical, perforated stainless steel shrouds at the lower end of each cable. From a distance, these are not very obtrusive, but from closer at hand they seem quite unnecessary. The only engineering justification I can see for their presence is that they reduce the risk of vandalism to the cables, but this can be achieved as easily with narrower steel sheaths.

On the whole, I like the Lune Millennium Bridge. It has a few peculiar details, but they don't significantly compromise its overall clear and slender silhouette. It's not as flashy (and certainly nowhere near as expensive) as some of its Millennial brethren, and that's no bad thing either. It will not be a straightforward structure to maintain, but the local authority could certainly start by considering giving it a bit of a clean.

Further information:

17 December 2012

Bridges in Japan

I don't know how many of my readers also follow the Japanese bridge photography blog, Tabikappa, but they've covered some truly brilliant ultra-lightweight footbridges in the last few days, so I'd really recommend you take a look. I hope they don't mind me re-posting one of their photographs here as a taster! My three favourites: Monkey Nishikawa, Nishikawa / KH Masago, Nishikawa / Nagai.

14 December 2012

"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).

13 December 2012

"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)

12 December 2012

"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).

11 December 2012

"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"
"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.

06 December 2012

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.