21 October 2010

Entries invited for Footbridge Awards 2011

Entries for the 2011 Footbridge Awards have been invited by Bridge design & engineering magazine.

Bridges opened to the public during 2008, 2009 or 2010 are eligible. Entries must be submitted by 21 January 2011. The winners will be announced on 7 July 2011 at the Footbridge 2011 conference. The full entry form is available online.

Astoundingly, the Happy Pontist isn't one of the judges. If I were, who would I be voting for? My shortlist might include:
Out of that lot, the question would be which bridges don't merit an award, not which ones do!

I am open to further suggestions. What have I forgotten (probably plenty!) Which footbridges do you think should be up for these Awards? Should your bridge be on the list?

19 October 2010

"An Encyclopaedia of Britain's Bridges"

It's not long since I was waxing lyrical over several of the books that have been published documenting the bridges of Britain. At the time, I noted that a new addition to the pile was due soon, and indeed, here it is, arriving in late October.

David McFetrich's "An Encyclopaedia of Britain's Bridges" (Priory Ash, ISBN 978-0-9566387-0-0, 2010, 352pp) is easily the largest and most comprehensive book on the subject. The main A-Z section covers 1,350 bridges from England, Scotland and Wales (no Northern Ireland - an Encyclopaedia of Bridges of the United Kingdom is still awaited).

The book's introduction includes a very short history of Britain's transport infrastructure, explanations of basic structural behaviour, and a helpful glossary of terms. I would say that the book is mainly aimed at the non-specialist reader, but contains plenty to keep the more dedicated bridgespotter happy. McFetrich was at one time a civil engineer, and this ensures the Encyclopaedia finds a balance between history and technology not always achieved in such books.

There are several things that the book is not: it doesn't offer a history of bridge building in Britain, nor any detailed coverage of bridge builders and designers. For the most part, it tries to remain factual and straightforward, offering little in the way of critical opinion on any of the bridges (although the Gateshead Millennium Bridge merits a well-deserved "superb"). It treads a middle path, between the rambling anecdotes of certain bridge historians and the overly technical. In these respects, it's complementary to other books already available, but in its sheer scope, it offers something unavailable elsewhere.

Before I opened it, I wondered a little about the place of the print Encyclopaedia in the Wikipedia age. Surely there's less need for a traditional reference work like this when Google can tell you all you need to know? Well, the reality is that many of the bridges featured here have little or no information available online.

The curatorial aspect is also significant: even an ardent Pontist can't fail to find dozens of structures here which are not only unfamiliar, but also often remarkably interesting, and the Encyclopaedia format naturally leads to providential juxtaposition. You go looking for the Iron Bridge, Shropshire, and become intrigued by the Iron Bridge in Exeter. A chance meeting with David Rowell's Llanstephan Bridge is the result of a search for the Llanrwst Bridge of Inigo Jones.

Not all the entries are accompanied by a photograph, but the book remains very well-illustrated, mostly with recent colour images but also a few paintings and other images. Most bridges get a reasonable paragraph or two of detail, with references to other publications - the book is a copious compendium of secondary sources, with a marvellous bibliography.

I managed to find a few bridges of interest that aren't included, but I had to try quite hard, and was constantly surprised to find it included bridges that I knew were interesting but had thought quite obscure. It was intriguing to find not only the many bridges I had visited, but also several that I have worked on one time or another. I didn't spot many errors either, although there certainly were a couple (e.g. the inclusion of Hadrian's Bridge, which was never built).

The main A-Z is supplemented by several further sections. A "bridge miscellany" offers short entries on subjects such as "Aesthetics of bridges", "Collapses and failures of bridges", "Cornes-de-vache arch bridges" and "Lenticular bridges". Although the author downplays the level of detail offered, this section offers a host of interesting information, as do several pages of lists of record-breaking structures of various kinds.

A geographical index is provided, including map references and information on which bridges have Listed status (Grade I and A only). There's also a fine general index, making it easier to track down groups of bridges according to their designer, railway, canal, highway or river.

Overall, it's a marvellous addition to the literature on British bridges, and being published at a very handy time for Pontists preparing their Xmas present lists. The book can only be bought direct from the publisher (price £45 inclusive of p&p) and is not available in shops (it's listed by Amazon but don't hold your breath waiting for them to supply it). The publisher can be contacted at Priory Ash, 2 Denford Ash Cottages, Denford, Kettering, Northants NN14 4EW, by telephone at 01832 734425, or by email to wadams1907@aol.com.

It's also now available in the ICE Bookshop and through a dedicated website.

18 October 2010

Bridges news roundup

Scottsdale's Soleri Bridge project becoming a reality
The first of 91-year old Paolo Soleri's bridge designs to be built nears completion.

Sheikh Zayed Bridge to open soon
Zaha Hadid's iconic structure may open on October 20th, after seven years of construction.

MediaCity footbridge put in place
£11m swing footbridge in Manchester has been installed and will open early next year.

Poole's Twin Sails bridge open days start
Now this one isn't ready to open, it has only just started.

Bridge referendum heats up
Victoria, Canada, prepares for a vote to borrow CAN$49m to replace the historic Johnson Street Bridge with a new Wilkinson Eyre design.

Design revealed for Weymouth's Newstead Road footbridge
I really hope the final design looks better than the visualisations currently on offer.

Floating bridge over the Strait of Messina: why?
Thanks to Bridge Design & Engineering magazine for spotting this one, a totally mad idea realised by its proposer in exquisite detail.

The Birth of a Modern Marvel
The new Hoover Dam Bridge opens later this month, but here's an awe-inspired preview.

13 October 2010

Manchester Bridges: 16. Manchester Curve

A recent day trip gave me the chance to visit one more bridge in Manchester. There can't be many more left in the city that will be of interest here!

Manchester Curve must be one of Wilkinson Eyre's least well known bridge designs. It's a 35m span footbridge built as part of a new office development, and spanning a city centre highway. It was built by CTS Ltd. Apparently, it carries 3.5 million pedestrians every year.

When it first opened, there were concerns about its proximity to overhead tram power cables, but I don't know whether any changes have been made in response.

The structural form, with two inclined arches, is very similar to Wilkinson Eyre's much earlier Butterfly Bridge. That spanned a river in Bedford, but the shape works just as well in the dense urban environment of Manchester.

The Bedford Bridge had more interesting parapets, with kinked posts which first incline outwards parallel to the cables before kinking back inwards.

The Manchester Curve has a box-beam deck with elliptical cut-outs, similar in style to the Whatman's Field Downstream Bridge. These serve a dual function of breaking up what would otherwise be a very dull underside, as well as preventing the box from becoming a closed beam inaccessible to maintenance. It's an attractive detail, the only concession to texture in a bridge which is generally no more than it has to be.

The least successful detail of the bridge results from the way that it passes above the highway at quite a high skew angle. Unfortunately, the supports have not been angled perpendicular to the bridge, but parallel to the highway, with the result that the two arches don't both spring from the same point on the support structure.

This is compounded by the fact that the bridge bearings are hidden behind a rendered facade, such that the bridge seems to be partly embedded in concrete. It all looks terribly awkward, although I imagine there's a good reason.

The Manchester Curve is simple, elegant, and contemporary. It's good to see that some of the many footbridge forms generated in the last couple of decades have the potential to be reused and reinterpreted, rather than just being developed for novelty's sake.

Further information:

11 October 2010

IABSE Symposium Venice 2010

This was my second time at an IABSE Symposium, and the first where I had time to sit back properly and take in as much of the conference as possible. The event was held in the Casino building on Venice Lido, an interesting venue with considerable historic charm, some of the rooms featuring unusual lighting, a copper ceiling, and wall mosaics.

The papers presented were widely varied in both quality and content. There were one or two where the engineering principles seemed surprisingly lightweight. Many of the papers were also quite esoteric, by academics for academics, and very few tackled the Symposium’s ostensible theme ("Large structures and infrastructures for environmentally constrained and urbanised areas").

The guest and keynote presentations were generally of high quality, but the conference format, which gave each speaker about 8-9 minutes for their presentation, actively discourages discussion and debate. Most of the best discussion took place over coffee or meals.

There were, however, moments when a greater level of interaction broke through. The design for the new Bundek Bridge in Zagreb (pictured, left) was presented, and it was difficult if not impossible to see how it actually stood up. It seemed to comprise an organic, curved gridshell frame suspending a highway deck, something that might work well as a building roof supported on all edges, but made little sense for a bridge spanning end-to-end. When this was queried (by the famous Swiss engineer Jürg Conzett, who wondered where the top flange of the lattice truss was), the speaker had no real answer, and I can’t find any in the full paper either. Conzett’s own Traversina Footbridge was presented in the same session, and offered the perfect counter-example, true structural art rather than a fantasy.

The Zagreb structure wasn’t the only example of a design where any engineering rationale had been submerged (drowned, even) by the architectural vision. One voice which clearly articulated the opposing view came in a paper "on the development of structural criticism through case studies", a topic dear to the heart of the Happy Pontist. The author, Ignacio Payá-Zaforteza, compared two large cable-stayed bridges in Spain, Calatrava’s Serreria Bridge (image courtesy of e.phelt on flickr), and Troyano’s Bridge over the Lérez River. The presenter took as his critical frame the criteria of David Billington: economy, efficiency and elegance, and unsurprisingly came out very much against the Calatrava design, which has as its major sin the use of a 155m main span to cross a redundant river bed, something more readily achieved with a multi-span viaduct.

While I’m all in favour of more open criticism of structural design, this paper veered too close to the puritan orthodoxy for my taste, citing with approval Schlaich and Menn’s contentions that an appropriate price premium for a more attractive bridge is of the order of 5-20%, and absolutely never more than 50%. This sort of dogma ignores the fact that bridges (and even giant sculptures disguised as bridges) have a value too, not just a cost.

Among the many other papers, one that stood out was Yoshiaki Kubota’s "Systematization of structures and forms of truss systems", which presented an elegant framework showing how five basic transformations can be used to generate the geometry of most or all known truss systems, as well as many more types not already known (just one of the transformation diagrams is pictured here). This formed part of a wider framework emphasising the continuity between the traditionally separate bridge forms of beam, truss, arch and suspension bridge.

With a total of 378 papers included in the conference proceedings, it's impossible here to do more than scratch the surface. As with any conference, there was as much value in the opportunity to "network" than in the technical material presented. In Venice, that also mean the opportunity to explore and enjoy the city itself, including both the bridges already featured here and the Pier Luigi Nervi exhibition previously mentioned.

The next IABSE Symposium is in London, in September 2011, which should be particularly interesting as it is being jointly organized with the International Association for Shell and Spatial Structures (IASS).

09 October 2010

Venice Bridges: 5. Miscellaneous

Okay, I'm nearly done with reporting on my trip to Venice. In this post, I've got a few photos of the more ordinary bridges encountered there, generally without comment. These give some idea of the range of structural forms used on the smaller spans in the city. Click on any image for a larger version. In the next post, I'll say a few words about the IABSE Symposium that prompted my trip.

In addition to the four bridges previously blogged, Venice's most famous span is the Ponte dei Sospiri ("Bridge of Sighs"). This is a covered bridge originally used to transfer prisoners to and from interrogation rooms in the Doge's Palace. It's not a particularly interesting structure, only spanning 11m, but given its fame I was surprised to find it almost hidden behind huge advertising hoardings.

And I'm not the only one, with Lord Foster and others protesting against this bizarre defacement of a UNESCO World Heritage site. The adverts help to pay for the building restoration work, but it's a little like sticking a giant MacDonalds logo across the Taj Mahal, I think.

07 October 2010

Calatrava's Peace Bridge delayed

I interrupt my posts from Venice for a short diversion. Many thanks to Tallbridgeguy for spotting that Calatrava's Peace Bridge in Calgary, originally predicted to open this month, has been delayed until January 2011.

Calatrava's bridges are no strangers to cost and programme overruns, so this should surprise no-one, including the client project manager, who said "It doesn’t come as a surprise to us. This is a piece of art, in a huge scale that is hugely demanding". But surely if the duration of the construction was no surprise, the later end date would have been the one originally predicted?

The project manager is also quoted as saying: "The contractor (now) fully realizes the complexity of assembling that structure will put a huge demand on their time and effort". They only realise that now? With the steelwork sections fabricated and just having arrived in Canada after their ocean voyage from Spain?

I am being unfair, as innovation does often bring increased uncertainty, to an extent that people accustomed to the conventional often fail to allow for.

06 October 2010

11 firms shortlisted for Providence bridge competition

The City of Providence, Rhode Island, USA, has chosen 11 designers out of 47 submissions to prepare designs for the next stage of their pedestrian bridge design contest. They have until 29 October to submit their designs, which must reuse the existing stone bridge piers from a redundant highway bridge.

The shortlisted firms are:
  • !melk / Balmond Studio / Robert Silman Associates (New York City)
  • Endres Ware (California)
  • H2L2 / Arup (Philadelphia)
  • inFORM studio / Buro Happold (New York City)
  • La Dallman Architects (Milwaukee)
  • McDowell + Benedetti Architects LLP (London)
  • RFR (Paris)
  • Rosales + Partners / Schlaich Bergermann and Partner (Boston)
  • Studio Providence, LLC (Providence, Rhode Island)
  • William D. Warner Architects and Planners Ltd. (Exeter, Rhode Island)
  • WXY architecture + urban design (New York City)
I'd say there are some very heavyweight entries there for a contest with such limited funding, suggesting that the attractions of the footbridge design competition remain strong.

05 October 2010

Venice Bridges: 4. Ponte della Costituzione

The Ponte della Costituzione ("Constitution Bridge") is the most recent bridge to be built across the Grand Canal, and may seem to be the most controversial due to a number of complaints that I’ll come to in a moment. However, it should be noted that the other crossings were also controversial when first built. Antonio da Ponte’s Ponte di Rialto was the source of criticism from rival designers who felt its single span was over-ambitious. Alfred Neville’s iron truss Ponte dell’Accademia was seen as an affront to the traditions of Venetian architecture.

The fourth bridge was built to replace an existing ferry, or traghetti, which linked Venice’s Piazza Romale bus terminal to its Santa Lucia rail station. At this point, the Canal is considerably wider than is the case further south along its length. The design contract was awarded to Santiago Calatrava in November 1999, an audacious choice for a city presumably afraid to tamper with its heritage for fear of alienating the visitors who provide much of its revenue. The bridge was built by Cignoni, and opened in September 2008.

Traditional Venetian arch bridges never venture beyond a span to rise ratio of about 7:1, as beyond this the horizontal thrusts to be carried by the foundations become very difficult to accommodate, and even below this it can be a problem. Shallower arches have been built elsewhere, but generally on firmer ground.

Calatrava’s proposal was for a steel arch footbridge spanning 80.8m, and with a total rise of 4.76m, a ratio of 16:1. The rationale would seem to be entirely straightforward: it avoids supports within the Canal, with their consequent disruption to navigation. It achieves the required navigation clearance while minimising the slopes that users have to climb, something of a relief compared to its steeper forebears.

The bridge is carried by a ribbed steel spine, consisting of five steel boxes linked by ribs in a configuration which is star-shaped in section. Within the vertical plane, the ribs form a Vierendeel truss, with the truss web members set off-vertical in a radial arrangement. The steelwork is painted red rather than Calatrava’s characteristic white. The bridge deck (which varies from 6.5m wide at the abutments to 9m wide at midspan) is constructed in reinforced concrete, with some glass panels at the edges. The parapets are in structural glass, with bronze handrails.

I think that in overall form it is very much an excellent response to its context. The low-profile arch is a great complement to the other Venetian spans. The arch springings are very beautifully shaped, and there are nice little details like the ornamentation at the ends of the handrails, which nicely subverts Calatrava’s traditional purity of form.

Seen in person and up close, it is however peculiarly disappointing. I think much of this is due to the fact that it is already rather dirty, with the red steelwork taking on a distinctly faded appearance. While this brings it in line with the dilapidation seemingly normal to Venetian bridges, it reduces the bold visual impact considerably.

I think the parapets are great, but the bridge deck less so. This is mainly because of the steps, which vary in tread length significantly as the bridge is climbed. Traditional Venetian arch bridges manage to avoid this by not having the steps follow the arch profile too closely. On the Ponte della Costituzione, the effect is quite disconcerting, and it’s unsurprising that a number of legal claims have been made by bridge users tripping on the steps. The problem is enhanced by the lack of any kind of visibility measure on the step edges (such as the yellow border often used to make them clearer to the visually impaired). I don’t think this would have greatly upset Calatrava’s design vision, as colour contrast can be used as effectively as very bright colours.

The glass decking has also been alleged to be slippery when wet (not for the first time on a Calatrava bridge). However, the biggest criticism of the bridge’s accessibility is simply that the use of steps is inappropriate in the modern age, as making access very difficult for the mobility impaired. As a result, a disabled access lift is currently being added to the north face of the bridge (the face probably least often viewed or photographed), and criticism relates to the fact that it is apparently an afterthought and didn’t form part of the original project.

However, I have some sympathy with Calatrava, as few if any of the other Venetian bridges I saw are accessible in the modern sense, and his shallow slopes make the bridge far less strenuous to cross than the others. Why should disabled access be such a big issue here but not at Rialto or Scalzi? This is a Venetian problem, not a Calatrava problem.

The bridge has also been criticised for its structural behaviour. The star-shaped cross-section can only be stiff torsionally if diagonally braced, which it isn’t, with the result that twisting behaviour was a major design concern. The huge horizontal thrusts generated by such a shallow arch (roughly seven times the vertical thrust, according to the authors of a paper listed below), also require huge foundations, and it is essentially impossible to prevent the foundations from moving over time, such that the bridge’s arch behaviour would reduce, and it would behave more like a beam (as it already does to some extent). To address this, Calatrava has provided jacking facilities at the end(s) of the bridge, such that as the foundations move over time, the bridge can be jacked back to its original profile.

Many of these criticisms are hinted at in the paper on the bridge’s engineering, and while I pretty much agree about the torsion, I think the arch thrust issue is simply an engineering challenge which had to be met if the bridge’s architectural conception was to be respected. So long as the foundation movements don’t affect adjacent structures, the jacking solution seems a reasonable one.

Calatrava himself is on record as saying "This is my most beautiful bridge", and blaming the bridge's problems not on his design, but on the contractors.

The bridge received perhaps its greatest criticism for its cost, which escalated considerably as the project progressed. The final cost is reported as being €7.3m for the bridge contract, or €11.3m including other costs such as surveys (up from €6.7m when estimated in 2002). A formal opening ceremony was cancelled for fear that it would be disrupted by protesters.

Overall, it’s a fine bridge, far better than the criticism would suggest, which would benefit greatly from being kept clean, bright, and properly illuminated at night.

Further information:

04 October 2010

Venice Bridges: 3. Ponte degli Scalzi

The third bridge to be built over the Grand Canal in Venice was an iron truss structure built near the Venice railway station in 1857. As with the truss structure of the same vintage at Ponte dell'Accademia, it was replaced in the early 1930s with a new arched bridge, the Ponte degli Scalzi ("bridge of the barefoot").

The new structure was built between 1932 and 1934 to a design by Eugenio Miozzi. It is a stone arch span of 40m, rising 6.75m. The bridge is only 0.8m thick at its crown, which is remarkable slender for the type and age of the bridge. Stone was chosen instead of reinforced concrete to avoid future corrosion problems. The construction cost 2.55m lira.

Miozzi adopted an unusual technique in construction of the arch, which he called the "compensatory systematic lesion" method. This involved leaving open joints at the crown and springing, which would close as the bridge's formwork was removed. This ensured that in the dead load condition, the arch was subject to minimal bending effects, greatly reducing the adverse stresses in the stonework.

As with all Venetian arches, containment of the arch thrusts is the key engineering problem, and the bridge is supported on 0.3m diameter concrete piles, both vertical and inclined, along with timber piles. These were tested with horizontal loads prior to construction of the arch.

Today, the bridge may appear at first sight the least distinguished of the four bridges over the Grand Canal. There are, after all, roughly 300 arch bridges in Venice, most of them in stone. However, its attraction is in its simple elegance, especially its slenderness at midspan. It's both beautiful and durable, an illustration that older technologies are often still of great value.

Further information: