22 July 2014

Footbridge 2014

I thought I'd try to write a brief summary of Footbridge 2014, held over three days last week at Imperial College in London.

Much of the conference was in the usual format: a series of plenary sessions with twelve keynote presentations (substantially more than Footbridge 2011), accompanied by various themed parallel sessions where the bulk of the papers were presented. These ran in triplicate, so I almost certainly missed more amazing presentations than I saw. If I get time, I'll write here about a few of the particularly interesting presentations. I also barely scratched the surface of the exhibition, which was a shame as there were some interesting products and companies on show.

The conference was very busy: I had time to visit a handful of London bridges the day before the event, but once it started there was so much of interest to see, and so many interesting people to meet, that I never had time to go off-campus.

One of the undoubted highlights was the first night, which featured "Footbridge 10-20", a session where presenters had to speak over only ten slides, each shown for exactly 20 seconds. This is a variant on the PechaKucha presentation format, but half the length, and all the better for it. It really forced speakers to be concise, and if they were boring, well, they were gone quickly and on to the next. The four highlights, for me, were presentations on Thomas Heatherwick's absurd Garden Bridge ("Boon or boondoggle?" - I don't think there's much doubt which it is); "freaky London bridge facts" (one of few presentations not by a bridge designer, builder or client); a comparison of the love of "sexy" (i.e. "iconic") bridges with scopophilia, in its sense as a sexual perversion; and a much-applauded tour of bridges in Hollywood action films, particularly science fiction and fantasy films, discussing how they tend to defy the laws of physics. The last was supported by a paper in the main body of the conference, from which this picture of Asgard's rather improbable Bifrost Bridge is taken.

The second night of the conference was the Gala Dinner, a cruise down the River Thames on a glass walled boat. I know London well, but this was a marvellous night, great company, great sights, and the chance to experience very different characters of the city as daylight faded into night.

The keynote presentations were generally of a very high standard, thought-provoking and wide-ranging. Several showed concern with the philosophy and ethics of design, with Andreas Keil, Marc Mimram, Jürg Conzett, Laurent Ney and Martin Knight all addressing the "why" and "how" of footbridge design as much as the "what".

Keil presented ten objectives for a designer, drawn from the vocabulary of a product designer, and illustrated them with examples from the Schlaich Bergermann and Partners portfolio. My favourite objective was to employ "as little design as possible", illustrated by the Bleichwiesesteg (pictured, right).

Conzett's talk addressed the question of how engineers could draw on "inspiration" without having to compromise their essential character and become "artists". Conzett's inspirations are often historic, such as Brunel's Chepstow Railway Bridge, and he often uses images from the past to provide the key to modern design problems, whether of broad conception or with regard to details. Conzett's timber Murau Bridge (pictured, left), was shown as one structure inspired by the Chepstow span. The approach is like that of a detective, treating historical artefacts as clues to discover a hidden and unsuspected new design solution.

Laurent Ney offered nine design principles, developed in collaboration with Chris Poulissen. These were broadly aligned with Vitruvius's famous three principles of Utilitas, Firmitas and Venustas. Many of Ney and Poulissen's principles are primarily ethical: relating to social integration, minimal waste, recognition of diversity, shared ownership ahead of ego. One principle, "towards an appealing creation narrative", asks for design and construction to embody the culture within which they operate, to create stories with a wider social resonance beyond the specifics of the project.

The conference closed with Martin Knight's talk, "Bridges for places, bridges for people". Like Ney, he was concerned with the role a bridge plays in society beyond the purely functional. The rebuilding of the bridge in Mostar (pictured, right) was offered as an example of a bridge playing both a practical and also a symbolic role, an act of rehabilitation and a site for celebration. He urged designers to "zoom out" and look beyond the bridge itself to its place in a wider context.

I can only scratch the surface of the conference here. Several of the other keynotes were highly informative, and indeed two lectures on footbridge dynamics were both quite amusing, not something often said about this topic. If time permits, I'll pick out a few further papers and projects from the conference, and post here again.

19 July 2014

Footbridge Awards 2014 winners

The winners of the 2014 Footbridge Awards were announced a few days ago at the Footbridge 2014 conference in London. I'll hopefully have more to say about the conference soon, but for now, here are the winning bridges. I posted the full shortlist previously.

I will keep my own comments to a minimum, but would welcome further opinions via the blog comments facility.

Short span
Winner - Smedenpoort Twin Bridges, Bruges, Belgium - Ney and Partners
This is a truly flabbergasting design. I doubt that many engineers other than Ney and Partners would have had the faith that they could make such slenderness work.

Highly Commended - Bleichwiesensteg, Backnang, Germany - Schlaich Bergermann and Partners
I keep staring at this bridge design and wondering about its peculiarly upside-down quality - the compression strut and tension hinge look like they should be a tension tie and compression hinge.

Highly Commended - Campusbrücke Opladen, Germany - Knippers Helbig / Knight Architects
I'm not 100% sure that I understand this bridge, which is geometrically complex and difficult to "get" from just one image, but I do love the use of simple patterns to generate considerable visual interest.

Highly Commended - Vluchthaven Bridge, Amsterdam, Netherlands - Ney and Partners
I'm not sure what I like better about this, the rail-less balustrades, or the folded steel plate deck.

Medium span
Winner - Jarrold Bridge, Norwich, UK - Ramboll
Discussed here back in 2012.

Highly Commended - Geniedijk Bridge, Netherlands -
I can't find a lot of information on this bridge on the internet. The V-shaped theme and use of weathering steel are attractive, as is the detailing, but I do dislike bridges with 3m tall anti-vandal barriers - are they really necessary, or did the client only think they would be?

Highly Commended - Slinky Bridge, Oberhausen, Germany - Schlaich Bergermann and Partners / Tobias Rehberger
When I first saw pictures of this bridge, I found its frivolity, particularly the "slinky" spiral itself, somewhat garish and dispiriting. Closer examination reveals a very well detailed stressed ribbon bridge, and what looks to be an attractive and jolly combination of colour and shape.

Highly Commended - Media City Footbridge, Salford, UK - Wilkinson Eyre / Ramboll
I visited this bridge in 2011.

Long span
Winner - Bow River Bridge, Banff, Canada - StructureCraft
This was up against some pretty impressive competition on the long span shortlist. It's unusual to see timber in bridges this long (an 80m central span), certainly of the beam type.

Highly commended - Peace Bridge, Londonderry, UK - AECOM / Wilkinson Eyre
Sometimes it seems there is little more to be said in the hi-tech, modernist style which Wilkinson Eyre have made their own, but the Peace Bridge is something new within that space (overlapping self-anchored suspension spans), and also a very well detailed example of how it should be done.

Winner - Mala Panew River Bridge, Poland
The write-up in the Awards booklets indicates this to be an exemplary restoration and strengthening of a historic bridge, built in 1827. A paper was presented at the conference, but I can find no useful information on the project online.

Jonathan Speirs footbridge lighting award
Winner - Castle Green Bridge, Taunton, UK - LDA Design / Moxon Architects / Flint and Neill
This strikes me as the sort of design that the late Dan Flavin would have put forward if he were designing visitor access ramps rather than minimalist art installations. That can only be a good thing, in my opinion.

16 July 2014

Pontist in print

I'm currently visiting Footbridge 2014, and very pleased to note that the Happy Pontist is now in print for the first time. All the attendees at the event are being provided with a short guide to the pedestrian bridge of London in booklet form, with all the text and images provided from past blog posts here (edited for length!)

If you're attending the conference, and want to read more about any of the bridges featured in the booklet, just google "Happy Pontist" and the name of the bridge, and you should find a link to the relevant post.

07 July 2014

Yorkshire Bridges: 2. Droppingwell Footbridge

The Wentbridge Viaduct is only one of a number of aesthetically forthright, highly ingenious bridges to be built by the West Riding County Council during the 1960s as the motorway network was progressively expanded, forming what is now parts of the M1 and M62.

Under the ambitious County Surveyor, Colonel Stuart Maynard Lovell, the bridge team at West Riding was led by Norman Buchi. Colleagues in the team included Bill Varley, Ron Bridle, Sri Sriskandan and F.A. ("Joe") Sims. The team was responsible for the introduction of a great deal of new computing technology into bridge design, as well as for some of the most imaginative bridge engineering going on anywhere in the country. Their design efforts were supported by close involvement in research and testing work, for example, on half-joints and concrete hinges. All the above named engineers went on to considerable seniority, some in the Department of Transport, and Sims and Bridle in particular have published various papers and contributed to books on the history of Britain's motorway development.

Nonetheless, I'd be surprised if many of my readers have heard of them, which is a shame, as they deserve to be recognised for the many interesting and in some cases spectacular bridges that they designed. I'm going to cover several in the course of this series of posts, but there are many more in the area which I haven't yet had time to get to. In particular, I'll highlight the Brodsworth and Sprotborough Footbridges, built for the Doncaster Bypass, which are magnificently slender, with a span to depth ratio of an incredible 94:1. Perhaps I can cover those another time.

Droppingwell Footbridge spans 52m across the M1 between Sheffield and Leeds. The land to the east of the motorway sits above the roadway; while on the west it sits below, and the bridge therefore has to facilitate a very large change in level. It does this first with a gradient of 1 in 10 (described at the time as "for the easy pushing of prams", but far steeper than would now be allowed), and then with a spiral ramp at its western end.

The bridge is a 3-pinned reinforced concrete arch, broadly of the Maillart Tavanasa Footbridge type, although with an elongated profile more closely resembling the Swanscombe Cutting design built perhaps a year or two earlier in Kent.

The arch sections are hollow where they are thick, and solid where they are slender. The arch leg at the western side splits in two, for lateral stability. The hinge at the crown of the arch is prestressed, to assist with lateral stability and to prevent the hinge opening up under wind load.

Considering the severe geometric constraints placed upon the bridge, that it manages to retain a degree of elegance is a commendable achievement. Viewed along the motorway, the profile of the bridge is very fine, although sadly for reasons of health and safety I was unable to photograph the bridge from this direction (you may wish to try Google Street View).

It's less successful in many other ways, however. The forked pier, with its stiff triangular form, lacks the curvature and flow of the bridge's elevation. This detail has been done better elsewhere, and I think it's the forces from the ramp that led to the fork being so wide in this instance.

The side spans are on half-joints, and look a little clumsy, especially at the junction with the ramp structure, where the soffit line kinks in elevation. This whole area is badly detailed.

The positioning of one of the ramp's four concrete piers between the forked legs of the main span is also visually quite awkward - the two elements needed to be kept apart.

The similar bridge at Swanscome is Listed, Grade II, whereas the Droppingwell Footbridge, along with the other bridges I'm about to feature, has no heritage status. This is a sad omission, as these bridges are unique and innovative, and if not always beautiful, they were clearly designed with a strong aesthetic sensibility.

Further information:

04 July 2014

Yorkshire Bridges: 1. Wentbridge Viaduct

I spent a day earlier this year in the area between Sheffield and Leeds, touring a number of very interesting bridges, principally under and over the local motorways. I've been to some interesting modern bridges in Yorkshire before (the York Millennium Bridge and the Castleford Footbridge), but this was a chance to take more of a trip back in time, roughly half a century to be precise.

Wentbridge Viaduct was built as part of improvements to the A1 in 1961. It cost £320,000 when built, and has a central span of 94m (between the pier bases). Design is usuallly credited to the West Riding County Council's County Engineer, S. Maynard Lovell, although the lead designer was more probably F.A. Sims.

The deck is of post-tensioned concrete, with six box cells, and sits on inclined cellular reinforced concrete legs which are pinned at top and bottom, with precast concrete hinges. The prestressing cables are external to the box webs, and are continuous over the full 143m length of the deck. This was the first use of external prestressing in the UK. Additional internal cables are provided in the top slab over the piers, and vertical prestressing is used to counteract shear in the side spans.

The bridge was recognised for its significance at the time it was built. It was one of only two British bridges selected to feature in the Twentieth Century Engineering exhibition at New York's Museum of Modern Art (the other was the Hammersmith Flyover). The image on the left was taken shortly after the bridge was built, and shows it at its majestic best.

Concrete Quarterly was almost rhapsodic:
"At last Britain has a bridge to show which, by virtue of its dramatic impact, its taut, pared-down elegance, its sheer size, can hold its own with any of the great bridges on the Continent - a bridge of a Maillart-like excitement, that even the Autostrada del sole cannot better".

Since 1998, its significance has been recognised by its status as a heritage-protected Listed Building, a rare accolade for such a modern structure.

It's difficult to see a bridge like this being built again, certainly in Britain. Much of the cost will have been in the temporary works, particularly the forest of scaffolding required, which was pictured in Modern British Bridges, and is shown here. Any bridge of this scale would almost certainly now be built in steel, and probably on much cheaper vertical concrete piers, regardless of the aesthetic merits.

I didn't visit on the brightest day, and growth of vegetation in the river valley over time has made the bridge hard to photograph in its entirety. The bridge is massive in size and presence, but delightful in its stark lack of embellishment. Only a subtle curvature to the underside of the deck, and the minimal taper of the pier legs, give any sense that the bridge is more than a series of giant, monolithic paving slabs propped against each other.

A caged walkway has been added to the east face of the bridge, with very little care taken over its appearance. In parts, it projects below the deck soffit, so it can be seen from the other side of the bridge, spoiling the deck's clear lines. I guess this must have been installed before the bridge was Listed, because I can't see how it would be an acceptable addition to a Listed Building.

Further information:

30 June 2014

Bridges news roundup

I'm preparing some posts on groups of bridges I visited earlier this year in Yorkshire and in Lancashire, as well as on the Foryd Harbour Bridge. Meanwhile ...

Footbridge 2014
The Happy Pontist will be attending this conference from July 16-18 in London. The final programme has been released, and looks really interesting, so I'm looking forward to it.

Tees Transporter Bridge
A new book is being published on this bridge, and you can read a short sample online. I visited the bridge last year.

Very thorough website telling you more than you could possibly want to know about what will apparently be Europe's longest arch bridge, currently under construction.

New St Elmo Breakwater Footbridge
Of various bridges showcased on architectural websites recently, this one stood out for me as one of the most interesting.

London's Garden Bridge: "It feels like we're trying to pull off a crime"
It feels like that because you are trying to pull off a crime. Please hand yourself into the authorities immediately! The planning application is available online, and reveals the bridge to be a steel truss wrapped in ultra-expensive bronzed steel, rather than the pair of concrete flower-pots that I had expected. Please place some cushions on the floor around your chair before you read it.

26 June 2014

Sydney Harbour Bridge

What can I possibly add to the volumes that have already been written about the Sydney Harbour Bridge?

Well, I have selected nine photos from when I visited, so here are nine thoughts (in no particular order, and not especially related to each photo!)

Completed in 1932, spanning 503m, Sydney Harbour Bridge was never the longest arch bridge in the world, but it was by far the widest and heaviest. It was pipped to the record by the Bayonne Bridge, opened in 1931, and which spans 25 inches longer. However, Sydney's bridge is probably still the most iconic of the world's long span arch bridges, situated in a beautiful harbour, and forming a key landmark visible from much of the surrounding city.

Sydney's chief engineer, J.J.C. Bradfield, had originally proposed a cantilever bridge for the site. A tour of bridges around the world convinced him that a steel arch might be more efficient, and he prepared alternative plans based on the Hell Gate Bridge in New York. Both bridges are two-pinned trussed arches, with monolithic and essentially non-structural pylons abutting the steel arch.

There are subtle differences. The Hell Gate Bridge has a more visible reverse curvature towards the upper ends of the arch, and its top chord disappears within the bridge pylons, rather than stopping short as is the case in Sydney. The upper chord carries no significant force at its ends, so the Sydney Bridge is more honest in this respect, but I think it looks quite odd.

A further difference between Hell Gate Bridge and the Sydney Harbour Bridge is in the approach spans. Hell Gate has girder spans of similar depth to the main span, with a continuity of road deck line which the pylons don't greatly interrupt. Sydney's bridge has very deep deck trusses for the approach spans, and its pylons serve a useful purpose in distracting the eye from the very different structural forms on either side.

The bridge arch is two-pinned, quite literally supported on a pin at each end. The entire weight of the bridge and the road, rail and pedestrian traffic that it carries is passed through the bottom chord into these pins. What then, is the point of the upper chord of the arch truss? The deep trusses are needed to stiffen the arch against buckling, particularly from unevenly distributed loading. However, they could converge to a point at the ends, a "crescent arch", as was the case for the much smaller Tyne Bridge, built by the same contractor, Dorman Long, in 1928.

I think the reason for the difference lies in the method of construction. Sydney Harbour Bridge was built by cantilevering from each bank of the harbour, with the steelwork tied back by massive arrays of temporary cables anchored into bedrock. 

In its temporary state, the bridge doesn't behave as an arch at all, but as a cantilever bridge of the type that Bradfield eventually rejected. As such, it relies on its strength in bending to stand up, and this is why the arch truss is so deep towards its ends. It had to resist enormous bending during construction, even if this meant that the top chord at the ends became largely redundant in service. While a crescent arch might be strong enough to be built by cantilevering at smaller spans, it would simply not be deep enough and strong enough for a span of this magnitude.

The entire form of the iconic Sydney Harbour Bridge bridge is therefore essentially a relic of its process of making.

The debate on the type of arch which should have been used was rehearsed by other engineers at the time, and I'd thoroughly recommend the discussions of the papers presented to the ICE. These cover a wider variety of procurement and technical issues which remain relevant today.

Cantilever construction of large arch bridges was a common method at the time (and since), although now it would be recognised as highly inefficient (a cable-stay bridge uses its temporary erection cables as part of its permanent structure, so is almost always more efficient, as is a suspension bridge at longer spans). Indeed, other engineers commented on this at the time. David Steinman, who had submitted a design for a losing tenderer, considered that a suspension bridge should have been cheaper, and noted that Dorman Long were reported to have lost a million dollars on the contract, suggesting the arch option was under-priced.

Steinman also commented that the heavy temporary cables would have been sufficient to build a suspension bridge. Ironically, some of the temporary cables were indeed used for precisely that purpose, to build the Walter Taylor Bridge at Indooroopilly in Brisbane in 1936. Again ironically, this was one of the very few bridges in the world to copy Steinman's "Florianopolis" bridge design, an unusual trussed suspension bridge which never gained wide favour.

The design of the Sydney Harbour Bridge was controversial. A huge disagreement arose between J.J.C. Bradfield, who had conceived the bridge, and Dorman Long's designer Sir Ralph Freeman, who was responsible for the detailed design and for all the construction drawings. Bradfield claimed to be the designer, and went so far as to entirely omit any mention of Freeman in various articles, including his technical paper for the Proceedings of the ICE. Freeman, in turn, campaigned in the Sydney press for his role to be recognised, with the full support of Dorman Long. The contractor even threatened to sue the New South Wales government if Freeman's role wasn't properly credited on a plaque to be placed on the bridge.

The entire controversy is discussed in great detail in Peter Lalor's excellent book, The Bridge. In the discussion in the ICE Proceedings on the various technical papers by Bradfield and Freeman, Oscar Faber is recorded making the point that Freeman appeared to have received too little credit. Faber and several others also spoke against the design of the bridge pylons, which were regarded by many as an unnecessary extravagance.

The bridge must be one of few large bridges in the world where the public can gain access to climb the structure, albeit for a hefty fee. BridgeClimb is one of the most popular tourist highlights in Sydney, and I took advantage of it when I visited. It must make considerable profit for both the bridge owner and for BridgeClimb, as when I was there, at the height of the Australian summer, groups of visitors could be seen walking up the bridge on a very regular basis.

The BridgeClimb experience is very well organised: visitors are thoroughly briefed on what to expect, and even get to climb a trial set of staircases before being allowed onto the bridge itself. The safety arrangements are impressive, with "climbers" hooked onto a static line constantly from the beginning of their experience to the end. The scariest part of the experience is passing across the approach spans towards the pylon, where the proximity of the roadway directly below the catwalk is a little disconcerting. Once past the main pylons and onto the main span, the climb is straightforward, and not at all terrifying. The large width of the main arch chords is such that you never feel close enough to an edge to feel at all worried.

For anyone wanting to know more about the bridge, I can recommend Peter Lalor's book (see below), which is from the perspective of a journalist, concentrating on the human-interest stories, and Peter Spearritt's (also see below), from the perspective of a historian, very well illustrated and placing the bridge narrative in more of a social context.

Further information: