Calatrava springs a surprise

It wasn't due to be made public until early August, but it has come early: the City of Calgary has published Santiago Calatrava's design for a CAN$25m new footbridge spanning 130m across the Bow River.

I've discussed this bridge before: first on the controversy over Calatrava's appointment without competition, then the attempts to have that appointment reversed, the designer's incredible fee, and most recently the foot-dragging over publishing the design.

Since then, events have moved on rapidly. First, Calgary announced out of nowhere that the bridge was to be a tribute to Canada's soldiers, something that had never been mentioned previously, and which seems to some like a cynical attempt to defuse the many critics of the bridge by placing a taboo on further dispute.

Then, the bridge's name was declared: the Peace Bridge. Again, who could possibly oppose that?

But at last the bridge itself has hoved into view, and Calgarians can finally see what they're getting for their money.

The Peace Bridge design is a radical departure from Calatrava's signature style, being a flat tubular structure constrained by height restrictions imposed by a nearby heliport (see left; click on any image for a larger version; all images copyright Santiago Calatrava). The helical truss form is obviously reminiscent of Buro Happold's bridges at Harthill and Edinburgh (precedents spotted by at least one Calgary reporter), as well as the Double Helix Bridge in Singapore's Marina Bay. It might also be seen as a distant relative of Pennsylvania's Weave Bridge, perhaps, although unlike that structure, the Peace Bridge is at heart a conventional truss, with proper top and bottom chords.

It has already been described variously as a candy cane, a "Chinese finger trap", or as resembling a stent. While the design has attracted many positive comments, it is also the focus of local discontent. Even now, with contracts awarded, some would like to halt the scheme, others fear parallels with a delayed Calatrava design in Texas. If nothing else, the intense debate over the design is already focussing attention on Calgary.

It reminds me of skeletal coral, or the cheap paper Christmas decorations I had as a child, which expanded like intricately entwined slinkies.

The colours are intended both to match the Canadian flag and also to make the bridge stand out in winter. For me, it's great to see Calatrava moving away from his more normal spartan white, and there's little doubt that if built, it will be a very striking landmark structure.

Visually, I definitely like the bridge, although the white interior has a little too much of the hospital or airport for me. Opening out the helix (compared to the other helical truss bridges) makes the bridge look far more attractive, and the use of curved glazing and the opportunities for lighting make the design visually more successful. How well it fits into its context is a different question, and one not easy to judge from the visualisations.

It's also not entirely clear why it needs to be a covered bridge. In an interesting interview with the Calgary Herald, Calatrava suggests this is to make the bridge more welcoming on a windy winter's day. As with most covered bridges, you have to brave the cold windswept approaches to get under cover, so it's unclear how worthwhile that really is.

Structurally, the bridge's distant ancestors are the Town Truss and the Howe Truss, although it can also be seen as a set of superimposed Warren Trusses. Like these 19th century designs, it uses triangulated elements in a structure which is both stiff and lightweight. These qualities are achieved because in conventional truss design every structural member only carries axial forces (compression or tension).

However, rolling the truss into tubular form introduces enormous secondary forces - bending moments because the curved truss members are eccentric to their nodal connections, and also torsional effects because the connections aren't co-planar. Because Calatrava's helix is so pleasingly open, these secondary forces will be enormous, much more than is the case on the Happold designs, which also have the advantage of much shorter spans (70m at Harthill). Having prepared a preliminary design for a tube-shaped but non-helical truss bridge on a much smaller scale than this, I can attest that the difficulties are considerable.

Is it value for money? That $25m is about £14m in Brit money, which isn't entirely beyond the pale for a major landmark footbridge. At 130m long and 6.2m wide, that works out at £17.4k per square metre of deck, a yardstick I've used here before on several occasions. The Buro Happold bridge at Greenside Place came in at £14k/sq.m , so allowing for inflation, Calatrava's design might seem to be priced about right. However, it's nearly double the span of the Harthill bridge, so you'd expect it to require up to four times as much steel in parts of the bridge (bending moment being proportional to the square of the span, with shear proportional to the span). The cost of construction over a wide river is also likely to be higher, especially if disturbance to the riverbed is unacceptable and if the heliport restricts crane heights.

The Peace Bridge's current cost estimate is right up there with London's Millennium Bridge (£12k/sq.m) or Brisbane's Kurilpa Bridge (£19k/sq.m) - bridges which are structurally incredibly inefficient but where the opportunity to create something truly unusual may well justify it. Will the Peace Bridge be as big a tourist attraction? I think it may well be.

Nonetheless, given how astoundingly inefficient a helical truss will be at 130m span (pity Calatrava's poor local partner Stantec, whose job it will be to make it stand up), Calgarians shouldn't take budget assurances at face value just yet.

Interestingly, the City of Calgary has published its own set of price comparisons [PDF], using the same yardstick as mine (their figures are a bit different, mainly because they adjust for inflation, which is of course reasonable). This is a very welcome move as there's little other way of justifying the budget at this early stage.

The City has also responded to criticism of Calatrava's fee, suggesting that "Calatrava's design fee is in line with the industry standard for architectural fees for similar projects of about 12 per cent of the total construction cost". In the real world, there are very few architects (if any) charging anything like that on a bridge with this capital budget: architects generally only earn large percentage fees on buildings work, where their input is far more significant than on a bridge, or on schemes with a much smaller budget (where design can be a larger proportion of the total cost).

However, a 12% fee offers encouraging news for prospective designers of Calgary's next landmark footbridge, which will be a larger structure promoted by Calgary's East Village development corporation. Originally, this was slated to be designed by Calatrava again, but it's now going to go out to a design competition, starting on August 17th, with proper public consultation prior to anointing a winner.

This is a complete u-turn for Calgary, who insisted that to get the quality they wanted for the Peace Bridge, directly appointing the best-known bridge designer in the world was the only sensible approach. Does this mean that quality is less important on the second bridge? Will they shoot themselves in the foot by demonstrating that in fact, bridge design competitions can get just as exciting a design? And most importantly of all, will they also be paying the competition winner a fee equal to Calatrava's?

Meanwhile, construction tenders for the Peace Bridge are reportedly to be sought this Autumn (good luck pricing that one without the detailed design complete!), with the bridge to open in 2010 (to coincide with an influx of porcine aviators, no doubt).

I'm off on holiday for a week, so feel free to comment but I won't be moderating comments until I'm back.

Bridges showcased at IStructE awards

Nine bridges have been shortlisted in the IStructE's 2009 Structural Awards.

The only candidate for the Heritage Award for Infrastructure is Canford Bridge, built in 1813, and now strengthened by Buro Happold.

The six candidates for the Award for Pedestrian Bridges are Castleford Bridge (Alan Baxter, Tony Gee, McDowell & Benedetti); Bishops Stortford Goods Yard Footbridge (Gifford, Chetwoods); Xstrata Aerial Walkway (Jane Wernick, Marks Barfield); Infinity Bridge (Expedition, Spence Associates); Cathedral Green Bridge (Ramboll); and Kingsway Pedestrian Bridge (Fast and Epp, Busby Perkins and Will).

Two bridges are in the running for the Award for Transportation Structures, Clackmannanshire Bridge (Scott Wilson / Benaim, Yee Associates), and River Elbe Bridge (Leonhardt Andrä, VBI).

Related posts:
Bridges dominate Prime Minister's Award shortlist
McDowell & Benedetti on t' Telly
Infinity Bridge opens

Bridges news roundup

Death on the bridge
Interesting article in the Scotsman on Elspeth Wills' book The Briggers

A working life: The Forth bridge painter
"It's like being an ant in an upturned bowl of spaghetti bolognese at an outsized John Cage concert"

Could You be One of the ‘Voices of the Bridge’?
People sought with memories of the Forth Road Bridge to help mark 45th anniversary

Willamette bridge design gets lukewarm reception
Donald MacDonald plans waterfalls and solar panels for light rail crossing

"Fritz Leonhardt 1909-1999: The Art of Engineering"

Without doubt, one of the greatest bridge engineers of the twentieth century was Fritz Leonhardt. While younger engineers such as Leonhardt's colleague Jörg Schlaich have won renown for their purely creative talents, Leonhardt's stature owes as much to his technological expertise and wide-ranging academic research as to his ability as a design engineer. His book "Bridges: Aesthetics and Design" is an encyclopedic classic, sadly currently out-of-print, and he played a central role in the development of prestressed concrete and cable-stayed bridge design.

A book devoted to this genuinely legendary figure has been long overdue, so it's great to see the gap now spanned by "Fritz Leonhardt 1909-1999: The Art of Engineering" (ISBN 978-3-936681-28-4, Edition Axel Menges, 2009, 216pp) [Amazon UK]. The book is published on the centenary of Leonhardt's birth, an occasion also marked by a conference and exhibition.

Leonhardt was educated as a civil engineer in Stuttgart, with his professors including the likes of Emil Mörsch , one of the pioneers of reinforced concrete design. As a student, he visited Othmar Ammann in America. Before he was thirty, he had already published one book on bridge design and prepared the design of the Cologne-Rodenkirchen suspension bridge, the first significant such bridge in Germany.

The list of his subsequent achievements is exceptional: development of his own prestressing system (and author of the seminal book "Spannbeton für die Praxis" as well as many others), research on orthotropic steel plates, design of the Stuttgart TV tower and the innovative Theodor-Heuss-Brücke, and collaboration with Frei Otto on tensile membrane structures (especially the 1972 Munich Olympics tent). He combined a highly active design career with a pre-eminent academic position and involvement in most of the major international structural engineering bodies. He was undoubtedly one of the giants amongst engineering, any kind of engineering.

How best to document the achievements of such a multi-faceted talent? "The Art of Engineering" is a collection of essays covering everything from Leonhardt's development of grillage analysis techniques, through overviews of his many bridges, to personal accounts of his time at the University of Stuttgart. Many of the essays are by people who knew him well, such as colleagues Schlaich and Holger Svensson, and academics such as Werner Sobek. The book also includes an abbreviated biography, and a lengthy bibliography listing many of Leonhardt's key writings.

The book is well-illustrated, mostly in black-and-white, although with some colour images. The most interesting of these include Leonhardt's own design sketches, such as those for the Hamburg television tower and the Kocher Valley Bridge near Geislingen. Nonetheless, it's a less lavish production than the similarly titled "The Art of Structural Engineering: The Work of Jörg Schlaich and his Team" (by Alan Holgate), from the same publisher. The emphasis is very much on the text, which is in German with a complete (and generally very readable) English translation by Friedrich Ragette.

From my perspective, an interesting contribution is Klaus Jan Philipp's "Rivets as ornament - Master builder Fritz Leonhardt", which analyses Leonhardt's long interest in the intersection of ethics and aesthetics. It shows both how Leonhardt demands a high-quality collaboration between knowledgeable architects and engineers, but ultimately remains a conservative, dismissing radical innovation in structural form for its own sake.

I also very much enjoyed the technical histories, such as Eberhard Pelke's "Early prestressed-concrete bridges", and Elisabeth Spieker's "Planning the Olympia roof in Munich". These, and several similar essays are great reading for the historically aware engineer, and emphasise to me how poor our engineering education is that there is so much to learn about such a well-known figure.

However, I found the most interesting sections were the more personal ones, by authors reflecting on their personal memories of Leonhardt. These show him to have been a thoroughly remarkable figure, able to combine a huge workrate with involvement in the wider world and a great love for the outdoors. Leonhardt was often conservative in his strict conception of ethics, to the extent of being unwilling to consider new ideas, but also adapted to suit the wider changes in Germany throughout his life, while being unafraid to challenge establishment views when it suited him. It's possible that only a fragmentary collection of essays such as this could truly capture his multifaceted achievements and character.

Modern civil engineering is short of heroes, and inspirational figures, with Leonhardt being one of the great exceptions to that rule. "Fritz Leonhardt 1909-1999: The Art of Engineering" is a fitting tribute to him.

See also:
Bridge aesthetics by numbers

Spencer Dock Bridge

I recently posted a link to an interview with Amanda Levete, whose project with Arup for a highway / light rail bridge at Spencer Dock in Dublin has recently been partially opened to road traffic [PDF].

Following the winding-up of her previous practice Future Systems, Levete has established a new practice, Amanda Levete Architects, who have recently released a delightful set of photos of the Spencer Dock structure (larger versions online here). I'll note from the outset that while AL_A are currently claiming much of the credit for the bridge, it should presumably be shared in some part with Nex Architecture, another new practice formed by Alan Dempsey, who left Future Systems after acting as project architect for Spencer Dock. Judging from his very interesting presentations online [both PDF], he played a large part in ensuring the complex geometry was actually buildable (several of the images below come from those presentations; all other images are from AL_A). I've mentioned Dempsey here previously, when he won the Ballsbridge-Dodder footbridge competition.

The bridge is a slightly asymmetric two-span, 3250-tonne post-tensioned structure, 40m in length and about 25m wide. As with many Future Systems designs, the bridge is organic in form and in this instance appears to draw inspiration from the undulating shape of a manta ray. The flowing form is a little reminiscent of their unsuccessful entry to the Glasgowbridge competition.

Designing an aesthetically attractive bridge with such a large width-to-length ratio is always a challenge, particularly considering the appearance from below. It's all too easy to create a space that's dark, forbidding and unpleasant.

At a reported €5m, the bridge is pretty good value for money (about €5k per square metre), although as far as structural or construction efficiency goes, it's an exceptionally inefficient design. To achieve the curved soffit, the canal bed was pumped dry, and 250 individually profiled polystyrene blocks were assembled on scaffolding.

Each block has been individually cut using CNC machinery, coated in polyurea and then sanded to give a smooth finish. The image on the right is from the CAD model used to work out the block profiles. The edge fascias comprise 34 precast elements, each slightly different in geometry.

It's difficult to see how else the doubly-curved shape could have been achieved, as the structure doesn't lend itself to the use of fibre-glass or ultra-high strength concrete shells. I guess it's a shame that all this advanced technology can't also be employed to make the poor reinforcement detailer and fixers' jobs easier - designing and then fitting all that curved rebar can't have been much fun.

While this is all completely at odds with the conventional wisdom amongst bridge engineers, it's a powerful lesson in what can be achieved visually using modern digital design technology with the assistance of innovative talent and a supportive client. One of the great failings of modern concrete construction is that despite its ability to create beautifully sculpted shapes, it is so rarely used in this way.

The bridge is all in white concrete, which will maximise the feeling of light underneath, although some of the preliminary visuals suggested a murky green appearance, which would have been interesting. Intelligent use has been made of recesses between the polystyrene panels to both break up the soffit and hide what would otherwise be irregular formwork joints.

Overall, has the effort been worthwhile? I'm generally no fan of blobitecture, which strikes me as a fad which will ultimately have to give way to the more efficient spaces and construction methods demanded by a low-carbon, post-crash economy. However, the photos suggest this to be an uncommonly beautiful bridge. And there are technological spin-offs from pioneering work of this kind which will prove useful elsewhere, and which will never arise from the mundane projects where boundaries are respected rather than pushed.

The bridge has been nominated for a LEAF Award.

Living bridge: alive or dead?

This whole idea of a "living bridge" across the Thames in London has something of the zombie about it. While there have been many attempts to breathe life into the idea over the years (the book Living Bridges is the best document of them), there have been two or three especially significant schemes in the last fifteen years.

First, the Peabody Trust attempted to re-establish the concept, and usher life into it golem-style. While there were few signs of movement, the idea was passed to the Royal Academy who gave it a fresh jolt of electricity with their own habitable bridge competition.

Back in May this year, mayor of London Boris Johnson disinterred one of the Royal Academy corpses, but although the concept is still shambling around London, it seems to have little future.

The most recent scheme has been the self-admittedly pie-in-the-sky ideas competition run by RIBA. This one emphasises the undead nature of the whole enterprise: any signs of life are purely illusory, the idea of a living bridge across the Thames can't possibly survive once detached from utopian voodoo.

Look at the designs that have come out of this latest exercise. The winner, Laurie Chetwood, has proposed a flourish of glazed teepees in which the eco-conscious can sip organic tea amidst a latter-day hanging gardens (see left). It responds to the context (the concrete London Bridge) by essentially ignoring it.

Chetwood is presumably more interested in the chance of publicity than anything else, as was well-demonstrated with his other, more satirical, living bridge proposal: housing MPs in tapioca-like pods on the sides of Westminster Bridge (see right).

The second placed entry, by Lawrence Friesen, again largely ignores the existing bridge by building a bridge on top of it (see left, click on this or any other image for a larger version). This design begs the question of why you wouldn't just build a new bridge further along the river, especially given the "blot on the landscape" quality of this modernist take on the Forth Railway Bridge.

Ryszard Rychlicki's third-placed design is perhaps the most practical of the three, with a series of disposable housing pods shelved in a supporting framework. But yet again, the existing bridge is largely incidental, and the design would destroy views up and down river, something that be very hard to justify in real life.

Of course, nobody should take the designs too seriously - all the bridge really does here is to introduce the constraints of a horizontal plot of land into a fairly ordinary quest for architectural fantasia. In their favour, they offer the chance to re-imagine London as a city big enough and robust enough to tolerate a corner of utopian improbability. The idea that everything conservative, orderly, and well-understood about the city might be able to cope with disruption, intrusion and playful challenge is always welcome.

To finish off, here are a couple more of the entries, and links to further information.

Some of the shortlisted entries are discussed with additional images at the Worshipful Company of Chartered Architects' blog. And anyone wondering why the only previous habitable bridge in London eventually proved a failure, can find out the results of recent historical research.

Abre Etteh & others

WDR & RT Taggart

Updated 27 July 2009
Several other entries are now shown online at RIBA's competition website

Scottish Bridges: 5. Greenside Place Link Bridge

Back in April, I wrote about the Harthill Footbridge, which spans between the two halves of a motorway service station near Glasgow. The design, by Buro Happold, was largely based on their earlier footbridge at Greenside Place in Edinburgh (designed in collaboration with Broadway Malyan). Both enclose the pedestrian walkway within a tube consisting of helically entwined steel pipes.

I’ve recently had the chance to visit the award-winning Greenside Place footbridge, and it’s interesting to see how it compares with its younger brother at Harthill.

The setting is entirely different, and this has much to do with the success of each design. The tubular structure is an odd choice for the motorway crossing, with its ends left somewhat stranded. It offers none of the visual termination that is provided by a conventional arch bridge, or a more conventional truss.

The Greenside Place bridge, however, spans a busy urban street between two relatively tall buildings, the St James shopping centre, and a new multi-storey development. At least, it does now - it hasn't been like that since it was completed in 2003 - for most of its life it connected only into a lift tower giving access to an underground car park (as well illustrated in the artists impression above right).

Where a bridge sprouts from two vertical faces, a tubular structure is visually far more satisfactory – the expectation is that it's an extension of each building, something perhaps expressed particularly well elsewhere at Manchester’s Corporation Street bridge.

While at Greenside Place that expectation generally makes the tube work well visually, it’s not entirely a success, largely because in fact it doesn’t span between two vertical faces at all. At the shopping centre end, it gingerly touches an exterior walkway (see above right), and at the car park it currently remains a dead end (presumably a temporary situation), stopping in mid-air and offering only a side exit into the lift tower (see left).

I commented on Harthill Footbridge that the helical truss form makes little structural sense for a bridge which is essentially straight in plan. The Greenside Place structure is S-shaped in plan (see right), with a significant offset between the two ends. Torsional effects are therefore significant, and the helical truss will be very efficient at withstanding these.

The other big difference from Harthill Footbridge is that at Greenside Place, there was evidently less concern about the possibility of bricks being dropped onto passing traffic. While Harthill's walkway is fully enclosed over the motorway, Greenside's is roofed but open to the sides. I think this is much preferable - the bridge user has more of an intimate sense of the enclosing steel cage. There's also a tension between the sense of comfort given by the enclosure, and the sense of vulnerability given by the low glass parapet.

The helical design is interrupted slightly by additional, vertical rings at the support positions, required to reduce stresses in the lattice members. If you didn't know they were there, you might not spot them - they certainly don't detract visually.

Of course, the bridge remains heavily over-engineered, and very expensive to fabricate (at approximately £1.8m construction cost [the original budget was £1m], that's about £14,000 per square metre of walkway). While that may have been justified by the bridge's presence within Edinburgh's World Heritage site, it seems out-of-step with the rather unattractive facade of the St James shopping centre. Perhaps it will seem more in tune with the new building on the other side of the road, once that's complete.

I was surprised by how much I liked Greenside Place bridge, after disliking its younger sibling at Harthill. The twisting latticework makes sense against the bridge's snaking plan, and the open sides give a more user-friendly feeling. It's difficult not to be impressed with the difficulties of design and fabrication that were overcome (documented with great clarity in the IStructE paper listed below). It's hardly a bridge design that will be frequently repeated, but it would be interesting to see whether a more economic version could be developed without affecting its visual integrity.

Further information:

• location on Google Maps
• page at Structurae
• page at Buro Happold
• page at Broadway Malyan
• page at Edinburgh Architecture
• LUSAS case study
• "Design and construction of the Greenside Place Bridge Link, Edinburgh", by S. Fryer, The Structural Engineer, Volume 83 Number 21, November 2005 (abstract online)

Calatrava bridge kept hush-hush

I've commented previously on the city of Calgary's extravagant scheme to build two $25m footbridges designed by Santiago Calatrava, an appointment made at great expense ($3.3m designer's fees) without any competition. I had been waiting to see what would result, with the designs originally due to be made public in May.

Two months later, and still no sign of the designs, it has become apparent that despite the city's appointment of a designer normally associated with maximising publicity, they are strangely reluctant to make the most of this opportunity for hype.

The Calgary Herald reports that unveiling of the first design has now been put back to August. The lucky few who have seen the design are quoted variously as saying:

"It's not the big bang. It's not the big statement people have come to expect from his work"

"Lovely . . . different that anything I've seen from Calatrava before"

I'm reminded of Caltrava's Ponte della Costituzione in Venice, a relatively shallow and modest arch offering a marked contrast to the designer's more usual structural acrobatics. Despite its extravagant cost, it was opened without ceremony. Initial rows over its lack of access for the disabled gave way to complaints from injured tourists.

It's unclear quite why Calgary are withholding the design, but I'd expect the bridge will be the subject of a great deal more debate once locals finally do get to see what they're getting for their money.

Elsewhere in the bridges world, a couple more brief news items rate a mention.

I've mentioned previously Glasgow's Tradeston Bridge and its vulnerability to climbing, but it seems efforts to deter the intrepid are failing.

Also the 2009 Structural Steel Design Awards include a couple of deserving bridges: the Kew Aerial Walkway, by Jane Wernick and Marks Barfield, and the Castleford Footbridge, by Tony Gee, Alan Baxter and McDowell Benedetti (covered here previously).

Bridges news roundup

Book tells story of Forth Bridge Briggers
Eslpeth Wells interviewed on her new book “The Briggers: The Story of the Men Who Built the Forth Bridge”

City architects peddle idea for cycle way over Leith Walk
Smith Scott Mullan Associates propose new bridge in Edinburgh

Olympic footbridge touches down in Stratford
1600-tonne pedestrian bridge completes launch across rail tracks

Bridge dispute moves to court
Watson and Macalloy unable to reach agreement in £1.8m "squinty bridge" case

Roads to nowhere - abandoned, ruined and unfinished bridges
Does what it says on the tin

Spencer Dock Bridge nearly complete
Amanda Levete interviewed on Future Systems bridge in Dublin

Santiago Calatrava Wins European Steel Design Award for His Bridges at Reggio Emilia
Three bridges in Italy win ECCS prize

Pedestrian and bike bridge proposed for False Creek
Gregory Henriquez designs suspension footbridge for Vancouver

Who ate all the pies?

The latest designs for a proposed iconic bridge over the River Wear in Sunderland are being made available for public consultation next week, in advance of an application for planning consent. Designed by Techniker and Spence Associates, the cable-stayed structure ranks as one of the most audacious proposals ever to come out of a bridge design contest. Plans will be on show at three local venues from 14th to 22nd July.

The projected cost of the bridge has not been made public, but Sunderland City Council acknowledge that it will cost about £29m more than a conventional girder bridge alternative, with the risk of a considerably greater funding gap (and that figure was put together before Techniker were appointed to carry out more detailed design development). Sunderland are currently suggesting that work on the bridge could start in 2012, and be complete by 2014.

I'm not sure what is expected from this latest round of consulation: a previous exercise in 2008 found that while 52% of locals wanted "a striking design", 49% wanted something "tried and tested", and 58% wanted to minimise impact on council tax payers. There's clearly a contradiction here, as a bridge of this outrageously ambitious design will inevitably cost far more than more ordinary options (indeed, either of the unsuccessful competition entries that I've seen would cost significantly less, while still being "striking").

What's most interesting about this latest round of consultation is the set of images that have been released to accompany it. Let's take a look at one of them, and compare it to a similar image used previously.

The first one is the earlier image. The new image is second.

Is it just me, or has the bridge been at the pies? The masts have put on weight, and they're also shorter and more upright. To me, it looks a lot less attractive than the design which won the competition, although this is hardly a surprise given the extraordinarily inefficient structural form which has been chosen - a cable-stay bridge without back stays or even any attempt to counter-incline the mast.

Some of this is just "design development" - contestants in bridge design competitions often tend to slim down their bridge design visually in order to get a positive reception. I've done some of this myself - not slimming it down, but omitting some of the details such as stiffeners which I know will really be there. The competition image is an aspiration, not the finished article, and hopefully the technically astute jury understands this.

But on the River Wear Bridge, the expanding waistline has as much to do with the design's conceptual difficulties as it does that art of deceptive visualisation. I can well imagine the work that has gone into reviewing the calculations in order to eliminate the lack of stiffness and potentially poor dynamic behaviour that would have been inherent in the original geometry. The reason the masts are more upright is simply because in the original concept their own self-weight was only adding to the problems, and straightening them reduces this.

What would be interesting would be to see more of the technical review brought into the public domain. Given the structure's innovative nature, who (if anyone) is peer reviewing the designer's work? Who is giving advice on its construction (e.g. have specialist contractors been brought on board for early input)? Given the scale of the mast foundations required, what are the ground risks? What key risks have the cost planners identified? Sunderland Council's stated game plan is to achieve greater cost certainty before proceeding further with the Techniker design, and these are the pertinent questions.

London living bridge result announced

Very briefly ... the winner has been announced in RIBA's "ideas" competition to adapt London Bridge into a "living bridge". Laurie Chetwood's winning design features glass spires in which organic food would be grown. The competition attracted over 70 entries, which perhaps gives an indication of how many architects are currently short of work (given that this is an entirely speculative contest with no chance of ever being built).

The bridge is shown below - I'll save comment until some of the other entries are made public.

RIBA bridge design competitions - any better?

Last August, I asked the question: do RIBA bridge design competitions work? At the time, my conclusion was that they offered a mixed bag: out of six competitions I considered, two ended going nowhere; one appeared to be going well; and three were impossible to tell. None of them had actually resulted in a bridge being built, which you might have thought was the aim of the promoters in each case.

One reason for asking the question was that at the time, RIBA-run bridge competitions were proving controversial in the engineering press. This was largely because of RIBA's insistence that entrants to their competitions must include an architect on the team, a ridiculous requirement in the bridge design field (to be clear: architects can help design great bridges; they're just not essential). However, behind the scenes, there was greater discontent, with a number of prominent designers concerned that RIBA (and other) design competitions were producing designs that were structurally bonkers, and expensive to both build and maintain.

Since then, RIBA has agreed with the ICE and IStructE to allow engineers to enter such competitions without an architect (the recent architects-only ideas contest for an inhabited London Bridge notwithstanding), and to include knowledgeable bridge engineers on all bridge design competition juries. So, the question is, have things improved?

I'll cover the same six schemes as last time, to see how they've moved on, plus the one other RIBA bridge competition held since then.

River Wear Crossing

An invitation-only competition was held in 2005, with the winner announced in September of that year as Techniker and Spence Associates (pictured right). Last August, there were moves to secure government funding, but the bridge design itself hadn't been made public. Things moved on rapidly, though. Wraps were taken off the design in September, it was subject to public consultation, and then confirmed as the preferred option, subject to further feasibility study and cost review. Sunderland Council has never made public the losing entries, but I showed two of them here in March.

Since the end of 2008, things have gone quiet, although I understand preparatory work on the Sunderland Strategic Transport Corridor, the grandly named road scheme that the bridge forms part of, is continuing. However, as it stands, Sunderland Council's support for the Techniker design is subject to further assessment of its affordability, and central government have not yet given unconditional agreement to fund the scheme. My own view is that the present cost estimates for the iconic bridge are too low (given its profoundly unusual structural behaviour) and that it will never be built.

Is that the fault of the RIBA competition process?

I think so. The design was chosen on aesthetic merit before it was subject to a technical review by engineers with appropriate expertise, and has been allowed to gather public support before any serious attempt to review its cost or feasibility has been completed. The risks inherent in the design should have been challenged robustly before a winner was chosen.

River Avon Footbridge

No change here: the competition winner (pictured left) was announced in January 2007, and the scheme cancelled in July 2008 due to rising costs. It won't be resurrected. I've covered the losing entries for this one as well.

I don't think the competition process is especially to blame - the winning design (by Schlaich Bergermann and Ian Ritchie) is attractive and the engineering risks should have been low. Lack of strong local commitment to the scheme seems to have been the main problem, although I have to say the increased scheme costs are a puzzle - they don't seem to be merited by such a simple bridge.

Leeds-Liverpool Canal Footbridge

This one was looking good last time around. The competition for a bridge in Bootle was won in February 2007 by Eckersley O'Callaghan and Softroom (pictured right), who went on to secure planning permission by May 2008, despite a near doubling of the project budget. An August 2008 start date was reported, but as far as I can find out, construction has still not started. Competition entries here.

The cost rise here seems largely attributable to the low initial budget of £400k, which is very low for a landmark structure, however short the span. It's not clear at all why this scheme has stopped. I think the competition organisers must take some of the blame - if funding is the issue, as seems most likely, they should be telling promoters upfront when their budgets and aspirations don't match. There's also a need to discourage competitions from being run when funding isn't secure, as the cost to unsuccessful competitors is an unfair burden - people compete in the expectation that the winning bridge will be built. Where that's not the case, prize money should be greater to reflect the greater fee risk.

New Islington Footbridge

Last year, it was too early to tell if this Manchester footbridge would go ahead. A winner, by Michael Hadi Associates and Gollifer Langston (pictured left) had been announced in July 2007. Since then, it became apparent that funding was no longer available to build the winning design (if it ever was). The local regeneration company has had staff budgets slashed, which means they will have little money for the bridge. However, the very latest news is that the design has been submitted for planning consent, and that efforts to secure funding are still ongoing.

As for RIBA's role, I think it's the same as at Bootle - the competition simply shouldn't have gone ahead if there was a high risk that entrants would go unrewarded. Competition entries here.

Sheffield Parkway Footbridge

In January 2008, Norlund Architects and Ramboll Whitbybird won this footbridge contest. Since then, there's been complete silence, although on the Norlund Architects website it says the bridge is due to be built in 2010. I don't really believe that, but let's be kind, give it the benefit of the doubt, and assume this bridge is still undergoing design development. Competition entries here.

River Douglas Footbridge

The proposal to span the River Douglas, near Preston, was always on the optimistic side. It was clear even at the time of the competition that there was no funding in place to actually build the bridge, and that the organisers intended to use the winning design (by Arup and JDA Architects, pictured left) to try and drum up some cash. Quite how many entrants actually realised that is a different matter, as the contest had a ridiculous 110 submissions.

So far as I can tell, the project has yet to secure funding, and once again designers have been very poorly rewarded for a scheme which seems to be going nowhere. I've previously discussed both the shortlisted designs, and shown some of the other unsuccessful entries.

River Soar Footbridge

Here's a case where it really is too soon to judge - the winner (Buro Happold with Explorations Architecture, pictured right) was only announced at the end of February. Other entries here. I don't know whether design is progressing yet, and it would be rather unfair to speculate how well it will go just yet. Compared to other recent RIBA competitions, this one seems to have been run well, with only six firms invited to submit entries, and each of them paid £6,000, which will cover a reasonable proportion of their costs.

So, what are the scores on the doors? I make it: one bridge cancelled for definite (Stratford); three stranded without funds (Bootle, New Islington, River Douglas); one still trying to prove its feasibility (River Wear); and two don't knows / too early to tell (Sheffield, River Soar).

Looked at another way, only three out of the seven have made it as far as planning consent stage (Bootle, New Islington, Stratford). None have made it as far as putting a spade in the ground. By those measures, the RIBA design competition seems a pretty good way to get lots of publicity, but not a great way to actually get a bridge built. To be fair to RIBA, past competitions prior to these seven have not always been so unlucky - they have led to bridges being built (e.g. the Infinity Bridge, although in that case only at a cost three times what was allowed for in the competition). It's also important to understand that the process of getting any bridge built can be subject to lengthy hiatuses and false starts, so some of these bridges may yet get there in the end.

The cost to the bridge design sector of these seven competitions is substantial, and certainly well in excess of £1m. The customers don't seem to worry about that: if you could get dozens of concept designs and still pay peanuts, why wouldn't you? However, the cost to the taxpayer will also be considerable, particularly on schemes like River Wear and Stratford where substantial investment has been made in the designs.

The real question is whether there's a better way to procure a landmark bridge design. Bridges at Stirling, Brisbane and Glasgow have recently been built through the Design-and-Build route, with no evident loss of design quality, and although a risky design was chosen, the Rhyl opening footbridge may well prove to be similarly successful. Other fine bridges have resulted from the promoter going it alone and organising their own competition.

Keys to success? A clear political will, with public support. Funding in place. Inviting a small number of designers and rewarding them sufficiently to spend time optioneering rather than just being obliged to draw up their first idea in order to meet the contest's deadline. Giving engineers a strong role (design-and-build normally forces this to happen, because no sensible contractor will put forward a design they aren't confident they can build for a known sum of money).

There's no reason why all of these can't be in place for a RIBA competition, but the evidence suggests that when any one of them isn't there, the scheme will fail.

Update 15 July 2009: I'm told by Prospect Leicestershire that the next stage of design of River Soar Footbridge is about to start, progressing towards a planning application.

Bridges news roundup

Top 10 bridge engineers
Courtesy of Accelerated Bridge Construction blog

Lenticular truss footbridge proposed in New York
SHoP Architects with plan for Battery Park

Chris Wise interviewed
Discusses the design of the Infinity Bridge for Stockton-on-Tees: "We drank all the beer during the course of sitting there in the sweltering heat. I doodled away and we came up with the double bow design."

Unesco listing for 19th century Welsh aqueduct
Pontcysyllte Aqueduct given World Heritage Site status

Mayor considers pedestrian-cyclist crossing parallel to Burrard Bridge
Can$45m suspension footbridge proposed for Vancouver

Open sourcing bridge design

In certain other fields of technology and design there has been a huge trend towards open-source development over the last decade or so. Embraced enthusiastically by software hobbyists, it refers to the development of software where the source code is publicly available, and which can be freely redistributed, modified and used. Open source software is usually developed collaboratively, often by unpaid volunteers.

There are few parallels in the engineering or architectural design world, but one is the design charrette. The charrette process involves a diverse group of designers working collaboratively to propose and develop ideas, with the philosophy that several heads are better than one.

I hadn't heard of it being applied to bridge design, until I stumbled across its use for a proposed footbridge in Toronto. The background is a private developer's proposal to build a new footbridge across a railway corridor and connect to the new waterfront Cityplace development. Their plan to build a relatively conventional truss structure (as pictured, above right) has sparked the ire of the city's designerati, who see the cost-conscious choice as an affront to civic aspiration.

There's little doubt that it's a challenging site, and that aesthetics may play second fiddle when the difficulties of meeting the technical constraints are considered. The rail corridor is 110m across (see image on the left showing the proposed bridge location), with only a single possible pier location due to the number of rail tracks present. The bridge must be 11.7m above the tracks due to problems with train signal visibility, which in turn leads to a need for extensive ramps to approach it from the adjoining streets. The basic site plan is available online [PDF]. Building a bridge over the railway without closing it for an unacceptable period would be by far the biggest difficulty, particularly as nearby buildings might rule out a conventional launching option.

The charrette organisers set up a dedicated website to attack what they call a "box truss" (not something I've heard of, but never mind). The briefing for the charrette simplified the difficulties of building the bridge (asking, for example, for it to be possible with "no disruption of rail service", which would be impossible at this site), but was clearly less concerned with getting a buildable design than with getting ideas which offered more inspiration than the bog-standard proposal.

It's not entirely clear if there ever really was a bog-standard "box truss" proposal - Councillor Adam Vaughan responded to a post on Spacing Toronto, stated:

"Let me be clear. It will not be a truss bridge. It will be a sculpture that functions as a bridge and a glorious gateway in and out of the adjoining communities and the city."

To be designed by an artist, no less, because clearly they'll be far better aware of the intense difficulty of securing the railway body's permissions than would the entrants to the charrette. I suspect the number of 110m long bridges over railways designed by artists could be counted on the fingers of one hand. If you chopped your hand off first, that is.

Anyway, let all that pass for a moment. How successful was the charrette initiative, and how did it really differ from a "normal" bridge design contest?

The entries are summarised on the Torontoist blog, and the full gory detail can be found at the Urban Toronto forum. A few of the entries are included below. In practice, this was indeed a beauty parade rather than a proper charrette - the entries are separate, weren't collaboratively developed, and as a result few of the participants seem to have learnt from their fellow entrants' flaws. That's a disappointment, because I think there would have been the potential for something interesting to develop in a true design charrette arrangement.

Amazingly, despite there being no prize money, fourteen entries (of varying quality) were still submitted: just how much time do some people have on their hands? This sort of contest tends to rule out anyone with real professional understanding of bridge design (either engineering or architecture), as they are likely to have paying work to occupy their time (unless they're all credit crunch victims, of course). A surfeit of time over experience shows, very painfully, in most of the submissions. That's the lavishly rendered winner there on the right, by the way, not that it really matters.

Most of the designs seem to ignore the need for approach ramps, although finding a clever way to deal with the ramps would be a key issue for any real design. Many of the entries ignore the necessity for the bridge to be fully or semi-enclosed (to prevent people dropping bricks on trains, or gaining access to the railway, see left for one inappropriate design). Of those that do consider it, they generally give no thought to maintenance, with rippling glass walls which would be a nightmare to keep clean or to repair the inevitable breakages. There's also lots of emphasis on lighting, with the winning design proposing "spectacular light shows" on its underside, something the railway signalling people would undoubtedly prohibit.

Most of the designs give little thought to what form of structure might actually be required to span 110m in two hops - several designs clearly give it no thought at all. What possible value is a gorgeous rendering of something that in reality would need to be disfigured with hundreds of tons of steelwork in order to stand up? There's at least one example of a feasible design for this sort of footbridge to be found online, so it certainly can be done.

Despite the formidable technical constraints, most of the entries would be very difficult to build over a railway, and several would involve considerable disruption e.g. cable-stay bridges with a central mast (quite how do they imagine materials would sprout from that mast?).

In fact, the entries resemble to a great extent the sort of thing which is now often submitted to proper bridge design competitions, such as the open contests run by RIBA, which similarly attract every architecture-student-and-their-dog. It's all empty style with no content, fed by the widespread notion that bridge design is essentially similar to fashion design - don't worry about the anorexic skeleton holding it up, just look at the clothes. Engineers (and wiser heads amongst architects and lay observers) who don't mind running the risk of spluttering their coffee all over their keyboards should read the comments on the Urban Toronto forum - rivers of praise for computer renderings that could never possibly be built. Not even on Pluto, where I believe the gravitational acceleration is more favourable than what we have to deal with here on planet Earth.

As a professional bridge designer, I strive not be irritated with well-meaning amateurs, particularly where they have a genuine enthusiasm for higher quality urban design. Having designed and had built several bridges in the railway environment, I clearly have a perspective that they don't (not to mention the advantage of understanding the real-world aesthetic implications of w.L²/8, and all its little brothers and sisters). But my irritation here comes from two points.

Firstly, this charrette is simply a lost opportunity. Before I saw the results, I found the initial idea very interesting: a collaborative rather than authorial vision; the opportunity to involve the public in bridge design in a more direct way; the hope of multi-mind brainstorming to create a sort of super-feasibility study. I think the idea remains interesting: there's something here to explore in the future which the Toronto contest hasn't achieved. One of the great flaws of the traditional bridge design competition format is that entrants have to settle on a "final" vision at a very early stage, and all the positive aspects of the traditional single-designer feasibility study approach are lost. The design charrette may be a way to put that right.

Secondly, the Toronto charrette makes clear in microcosm how society as a whole sees bridge design. All the things that concern professional bridge designers (buildability, efficiency, maintainability, expression and optimisation of structural form etc), are meaningless to Joe and Jane Public, let alone to Joe and Jane Student Designer. Instead, it's all about shape, material, contextual intervention - ideas that can work well in building design, where the skeleton really is largely there to hold up the clothing, but which often translate poorly to bridges. The architect as fashionista has won in the court of public opinion - if the Toronto footbridge design charrette is genuinely representative, then there's little hope of engineers ever reclaiming a serious public influence and voice in matters of landmark bridge design.

So, to return, at last, to where I began, are we ready yet to open source bridge design? If that means opening it to unpaid amateurs with no real understanding of what bridge design actually requires, then I'd say we're definitely not ready - it would be like having open source software developed by poets. (Clearly, you don't have to understand differential calculus to design a bridge: I have various architect friends and acquaintances who demonstrate both that bridge design can be learnt by the less numerate and also that a dash of poetics can often be a very good thing.) Getting the non-specialist designers and the general public to understand that bridge design is more than just the product of some fancy digital rendering software - that's the real challenge, and one it's hard to see being met any time soon.

Where next for the Cityplace footbridge itself? The "design" community seems pleased with their efforts, entrenched in their opposition to the "box truss" (ironically, the very type of bridge that those with an interest in history and understanding of bridge technology are struggling to preserve elsewhere in North America). The powers-that-be seem convinced their artist, Francisco Gazitúa, will come up with something that meets the conflicting demands of the vocal anti-trussers, the railway company, and the poor old developer, who will be paying for the final result. A design should be made public this summer. I'm not convinced those demands are at all reconcilable, so expect further contretemps in due course.