25 July 2008
Apparently Sunderland Council have even turned down a Freedom of Information request to reveal the design. Spence states:
"You see so many schemes that never even materialise in which they proudly
show the designs. Here we have a lot of the money secured but no
That hardly seems unreasonable. The local regeneration company, Sunderland Arc, seemed to be using the competition as a way to get wider publicity for their local schemes, but it's hard to see how this can be achieved without actually letting anyone see the winning design.
What caught my eye, as may be obvious from the cover image, was an absolutely outstanding footbridge, designed by Juan Miró (architect) and Chuck Naeve (engineer). This private structure spans 80 feet (24.3 metres) over part of Lake Austin in Texas, and connects a guest house to the owner's main home. It's an ultra-slender arch comprising five 125mm steel tubes, with the decking and parapets both formed by bending 12mm plain steel bars. It's designed to mimic the lake's natural reed vegetation, and is the sort of one-off masterpiece that could only ever be built for a private client, free from the constraints of disability compliance or crowd loading.
This book / journal has eight pages of photographs, text and drawings of this magnificent bridge, but also devotes plenty of space to several other recent structures. None of these are quite as great, and indeed some are rather mediocre. The bridges include Marc Mimram's bizarre Feng Hua Bridge; Atkins and Grimshaw's derrick-like Newport City Footbridge; an unusual and interesting distorted lenticular truss from Vienna; Thomas Heatherwick and SKM Anthony Hunt's Rolling Bridge; Arup and Wilkinson Eyre's lavish but visually incomprehensible tensegrity bridge; and others. Most of these are simply too recent to have been covered widely elsewhere.
None of the other bridges are anywhere like as glorious as the Lake Austin footbridge, which is a superb piece of engineering and architecture. But they do include several structures worth looking at.
There's plenty more in the magazine, but as it doesn't relate to bridges, I'll say no more here!
22 July 2008
17 July 2008
This one can be found at the Yorkshire Sculpture Park, about 50m south of the main visitor centre. The artist responsible is Brian Fell, but YSP haven't been able to tell me who the bridge designer was.
I like the assymmetry, the way it's like a giant stencil split in half, an idea crying out to be used somewhere else on a more "serious" bridge.
I'm not 100% convinced by the rust colour - it doesn't look in photos quite like weathering steel and even if it was, the detailing would lead to significant corrosion over time in the various sharp corners. It would also have been nice if the side panels actually held up the bridge - from the photos it looks like the deck is strong enough to be self-supporting.
For non-UK readers, a "ha-ha" is essentially a posh ditch. Well, there's more to it than that, but that's the basis of the bridge-as-pun that has been sculpted here.
[Photos from Flickr used with permission]
15 July 2008
The project to build a new footbridge in Stratford-upon-Avon has come to an unhappy end, and one not entirely untypical of bridge competitions. It has been cancelled due to "spiralling costs".
In 2006, RIBA ran a bridge design competition for a new footbridge over the River Avon in Stratford, garnering over 60 entries. Five entries were shortlisted in November 2006, and the winner announced as Schlaich Bergermann & Partners with Ian Ritchie Architects, with a super-slender steel arch design (pictured). This was an interesting reaction against a trend towards structurally gymnastic cable-supported bridges which had dominated high-profile footbridge design.
The promoting authorities' support for the bridge always seemed to be in doubt. It was promoted by Warwickshire County Council, but there was considerably opposition in the local press to what was seen as an unnecessary scheme, and the council's lukewarm attitude was reflected in consultation after consultation, with associated feasibility reports and pedestrian studies. Most of these were prepared after the competition had already begun, suggesting that a genuine need for the bridge was never conclusively demonstrated.
The original scheme budget was £2m, which is ample for a bridge that is 50m long, and is 3.71m wide. That works out at over £10,000 per square metre of deck, which is plenty for almost any footbridge, however unusual (for dimensions, see the original design submission at Warwickshire's website).
Now, however, Warwickshire have spent £312,000 on getting the bridge to planning submission stage, and have in the process re-estimated the bridge's budget cost at £3.3m, an increase of over 50% and equating to over £17,500 per square metre. Not unsurprisingly, the project has been cancelled, with the council quoted as saying "neither the County or District Councils are in a position to fund the shortfall so we have reluctantly decided to remove the bridge from the World Class Stratford programme." Given that Warwickshire were only going to stump up £0.2m of the original budget (the rest coming from external development funding), it's easy to understand their decision.
So what really went wrong?
The council's original budget certainly wasn't at fault, for what should have been a fairly straightforward and simple river footbridge. There are several competitions where the budgets are unrealistically low, certainly in comparison to the effort expected from entrants. The need for repeated studies and consultations, as well as the low budget contribution from the main stakeholder suggest a lack of commitment which won't have helped. Surely a proper feasibility study prior to holding an expensive competition would have helped establish a firmer case for the bridge (or led to its cancellation prior to spending so much money)?
The council has chosen to blame construction price inflation, particularly steel prices, but any sound project should assess risks such as this at the outset and take them into account throughout. Steel price inflation wasn't an unknown when the winner was chosen in late 2006.
Was there something particularly risky about this design that the council could have spotted and dealt with? The "glasgowbridge" competition was one high profile case where the winning design came in well above budget (like Stratford, subsequently cancelled), and where it was apparent that the design was structurally challenging, to say the least. Was that the case here?
The Stratford design was an arch that was both very slender (50m span and only 350mm thick at midspan, a span-depth ratio of 142), and with a very shallow rise. The former will have made it susceptible to dynamic excitation, and the latter will have created an unusually large horizontal thrust on the abutments, but it's hard not to think that these could both be addressed within the original budget.
The council also cites "additional flood mitigation measures" as increasing the cost, and it may be the case that there are issues beyond the bridge itself affecting the scheme.
I'd ask whether a RIBA competition was the right approach to such a minor structure. The Stratford bridge isn't the only RIBA competition to go nowhere due to uncertain funding and commitment from the promoter - another happened at River Wear in Sunderland.
One lesson perhaps is that ambitions should be scaled to match the resources really available (including the willingness to deal with risks); another could be that the conventional non-competition design process (feasibility study, preliminary design, detailed design etc) may uncover problems at an earlier and more cost-effective stage.
11 July 2008
First there was "Neptune's Way" (shown above right), winner of a lavish competition for a new footbridge between Broomielaw and Tradeston, which was cancelled when the contractor's bids came in well over the council's budget.
Then there was the failure of a hanger on the Clyde Arc (locally nicknamed the "squinty bridge"), resulting in its closure for over 5 months.
Now there seems to be a problem with slopes on the deck of the Tradeston Bridge (locally nicknamed the "squiggly bridge", and shown on the right). This is the proposed footbridge that replaces the failed Neptune's Way project. According to both the Evening Times and the Herald, there are slopes of up to 15cm on a full-size mock-up of the deck prepared by fabricator Steel Engineering, and these may cause problems for some bridge users.
The reports aren't very clear, but they seem to me to imply a transverse crossfall (i.e. a drop of 15cm parallel to the river). If it were longitudinal (parallel to the bridge span), then it should be straightforward to get up and down 15cm, given sufficient length of bridge. But if it is the crossfall, it's easy to see why it might be difficult for some pedestrians to negotiate - not just the mobility-impaired but people with pushchairs might also find it awkward.
It's odd that this was in the Glasgow press two-and-a-half weeks ago, but doesn't seem to have been picked up in the national civil engineering press. As with many non-technical press reports on bridge problems, it's hard to figure out what's really going on. It may be a storm in a tea cup, a perfectly good design misinterpreted by the fabricator. But I'm sure Glasgow city council would be much happier if the Squiggly Bridge was the one crossing of the Clyde that had gone forwards without any problems at all.
05 July 2008
Of course, the internet is beginning to diminish these difficulties. I've been aware for a while that Google Books contains scanned versions of several key books of interest, which can be read online or downloaded as PDFs. These include:
- Charles Stewart Drewry's "A Memoir of Suspension Bridges" (1832)
- Samuel Smiles' "Lives of the Engineers" (1862)
- James Finley's "Description of the patent chain bridge" (in the Port Folio, 1810)
- Thomas Pope's "A Treatise on Bridge Architecture" (1811)
There are dozens of others, many of them great early documents of the pioneering 19th century.
I was unaware until very recently that bibliophiles can get much of the same material in print, thanks to Kessinger Publishing and the University of Michigan's Scholarly Publishing Office. In addition to some of the titles mentioned above, you can find otherwise long out-of-print books by David Steinman, John Roebling, Squire Whipple and many others. Several are unavailable through Google. They can be ordered either through the publishers or through Amazon.
Great for the happy pontist's bridges bookshelf; very, very bad for his wallet.
01 July 2008
In large part that's because coauthor Mike Schlaich is a practising bridge engineer, son of the more famous Jörg Schlaich, but also a widely recognised and respected figure in his own right. In many ways, "Footbridges" is the glossy layperson's companion to the more technical "Guidelines for the design of footbridges" (Fib, 2005), for which Mike was the lead author, and which spotlights several of the same structures.
The book includes a lengthy (40-page) history of footbridge design and construction, covering key figures such as Jean-Rodolphe Perronet, Ulrich Grubenmann, Guillaume Henri Dufour and the ubiquitous Robert Maillart. This is no small thing, as the history of footbridges is to a great extent the history of bridges - the earliest timber, stone and rope bridges were all footbridges, and many of the great experimental developments in bridge engineering were first attempted on footbridges, particularly the earliest suspension bridges. This historical survey introduces several great structures both well-known and little-known, with great photographs, such as the Seguins' pioneering Annonay bridge, now in a state of seemingly terminal disrepair. I particularly enjoyed the coverage of vernacular bridge designs that were unremarkable historically but widespread, such as David Rowell's suspension bridge at Ilkley, one of a number of similar structures that dot the British Isles (and beyond).
The bulk of the book is taken up with descriptions and photographs (all taken specially for this book) of selected modern footbridges around the world. These include elegant designs by several of the greatest bridge engineers, such as Riccardo Morandi, Fritz Leonhardt, Ulrich Finsterwalder, René Walther and Jiri Strasky, those five just from an early 18-page stretch. There are bridges that are remarkable, beautiful, puzzling and inspiring, as well as one or two (such as Arup's Kingsgate Bridge) where the merits are much less clear. There are several works of sheer genius (including three by Jürg Conzett and several by Schlaich's own firm, SBP). There's an obligatory Calatrava (Campo de Volantin) and a good sampling of Wilkinson Eyre's oeuvre, but my favourites include a selection of relative obscurities - a delightful spider-web suspension bridge over the River Esk in Scotland; a glass garden bridge near Nice in France; a combination bridge and park bench in Baruth in Germany formed from curved oak slats; and an ultra lightweight suspension bridge over the Maggia valley in Switzerland.
Schlaich and Baus have identified so many great footbridges that there's an entire chapter devoted to dozens of shorter portraits, including older structures, many of which would have merited three or four pages if space permitted, being every bit as good as the bridges given full coverage. Unfortunately the space restrictions limit the photographs in these pen-portraits to very small monochrome images, which struggle to do justice to several excellent structures.
Although the authors initially seem to have a good critical eye, I think they are too restrained in many instances, with bridges ripe for criticism given the kid-gloves treatment. For example, London's Millennium Bridge, so often described as a "blade of light", is suggested here to be "probably the most delicate suspension bridge of our time". Am I the only person who finds it an over-engineered throwback to 70s high-tech architecture, marred by an ungainly and arrhythmic array of outriggers, dampers and cable fixings? Or that the Royal Victoria Dock bridge is a white elephant which struggles to match its remarkable superstructure to an appropriate means of support below? There are numerous other bridges where gentlemanly restraint has triumphed over the possibility of a less deferential critique.
Spliced in between the bridge portraits are a series of short pieces on key issues in the design of modern footbridges - stress ribbon structures; dynamics; curved ring girders; and moveable bridge types. I find it hard to judge how informative these will be to the non-technical reader, as they don't entirely manage to avoid mathematical formulae and force diagrams, but they do at least attempt to explain that the better bridges are the product of the careful consideration both of structural behaviour and construction methods, rather than just a pretty curve or gesture.
Overall, "Footbridges" is an excellent survey of a wide range of interesting structures, many of them not covered in other recent coffee-table assaults on the contemporary bridge (by Wells, Arcilla, Pearce and others), with plenty of excellent photographs that make you want to grab an atlas and plan your next holiday itinerary accordingly. For the professional bridge designer as well as the lay bridge enthusiast, this is not a book to sit proudly on the shelf, but to keep well-thumbed and close at hand.