28 July 2014

Yorkshire Bridges: 4. Needle Eye Bridge

Okay, I'll continue this series of posts a little further north along the M1 Motorway. I'm bypassing the Cock Inn Bridge simply because it proved impossible to get a decent photograph, which means the next bridge of interest is the Needle Eye Bridge.

This is a three-pin concrete arch "accommodation bridge", built to carry farm traffic and pedestrians. The arch spans 88m between springings, and was cast entirely in-situ in reinforced concrete.

It seems to owe more than a little to Robert Maillart's 1933 Felsegg Bridge, the first of the Swiss designer's concrete arch bridges to adopt an angle at the upper hinge rather than a continuous curve. This is a departure from pre-conceived notions of what an arch should look like, and is structurally more rational, responding appropriately to the full envelope of possible live load effects. Needle Eye Bridge lacks the sharp angle at the crown of the arch, but overall the bridge is shaped in a similar manner.

It is better than Maillart's bridge, however, in its use of prestressed suspended side spans, preserving a simple, clear geometry. Maillart's designs paired the solid main span with finicky, slender approach structures, often over-fussy in their detailing.

My sense is of a design team very aware of precedent, and enjoying the rare opportunity to experiment with form.

As with the other two M1 bridges I featured recently, at Droppingwell and Smithy Wood, I find it amazing that this bridge is not protected by any kind of heritage status. Sure, it only dates to the 1960s, but the whole set of bridges along this part of the motorway, designed by the West Riding County Council, is remarkable and worthy of wide recognition.

Further information:

26 July 2014

Pedestrian Bridges of London: A Short Guide

Updated 27th July 2014 - THIS OFFER IS NOW CLOSED (see below)

I mentioned this little booklet recently. It was given free to attendees at the recent Footbridge 2014 conference in London. It is based on (much shortened) articles about significant footbridges in London, with all text and photos contributed by The Happy Pontist.

There are twenty pages, covering the following bridges: Bridge of Aspiration; Challenge of Materials Footbridge; Millennium Bridge; Golden Jubilee Footbridges; Chelsea Bridge Wharf Link Footbridge; St Saviours Dock Bridge; Royal Victoria Dock Bridge; South Quay Footbridge; West India Quay Bridge; Plashet School Footbridge; Stratford Town Centre Link; Green Bridge; Rolling Bridge; Merchant's Square Footbridge; Sackler Crossing; Xstrata Treetop Walkway.

The booklet also provides some (very) brief details on significant bridges and structures encountered along the River Thames, the conference's Gala Dinner boat cruise route.

I have eight of these booklets left over from the conference, and I will post them to the first people to email me (happypontist at gmail dot com), having first made a donation to Bridges to Prosperity. I wrote about B2P and their excellent efforts to build low-cost footbridges in the developing world, way back in 2009.

The booklets will never be reprinted, so this is a unique chance to get a copy.

It's very simple:
  1. Donate to B2P whatever amount you wish, although an absolute minimum of US$5 please.
  2. Email me your address and a copy of your B2P donation receipt - if you want to keep any details private, just take a screenshot and cut out any private bits.
  3. This is a bit silly since I blog anonymously, but I will sign the booklet on request. Minimum US$10 donation for a signed copy.
  4. I will post you a copy of the booklet, free of charge. Please bear in mind that I am covering international postage when you decide how much to donate to B2P!
  5. I will post here when all copies are gone, but there can be no refunds - if you donate, and I've run out of copies, never mind, at least B2P will benefit!
  6. Did you attend the conference and already have a copy of the booklet? That's great, but please consider donating to B2P anyway, they're a great organisation.
Updated 27th July 2014 - THIS OFFER IS NOW CLOSED

All the spare booklets are now allocated, many thanks to those who have donated to Bridges to Prosperity! I have also made a donation myself, and together we have raised US$350 to support their excellent work around the world. I'm absolutely delighted to have helped create this opportunity.

24 July 2014

Yorkshire Bridges: 3. Smithy Wood Footbridge

I first became interested in the Smithy Wood Footbridge when Tallbridgeguy posted about it on his blog.

It's another great example of how the West Riding County Council engineers in the 1960s applied real innovation to deal with a specific technical challenge. Their concern when designing new bridges over the Sheffield to Leeds motorway was with possible mining subsidence, which could lead to foundation settlement and severe damage to their new structures.

Three new footbridges were designed as concrete Wichert trusses, possibly the first such designs in concrete, and almost certainly the first such designs in Britain. Only one now survives, the footbridge at Smithy Wood. The concept, originally developed by E.M. Wichert in Pittsburgh in 1930, is for a bridge which is statically determinate but also continuous, such that pier settlement can occur without causing damage.  It achieves this by incorporating a quadrilateral bay within the truss immediately above the support pier or piers.

Don't ask me quite how that works: any first-year structural engineering student will look at it and ask why the quadrilateral truss bay doesn't simply "squish". I look at it and I don't really know why either, although I think it has something to do with the feasible displacements of the two adjacent spans. To make it work, the designers had to undertake basic research and testing for the tri-hinge, the point directly above the pier. The upper hinge also has to be prestressed.

It's interesting to think that engineers of the time were designing structures with hinges partly to deal with settlement but also to make them determinate and hence amenable to analysis. Today's engineer would struggle to analyse this bridge: modelling it in any conventional structural analysis software would be fruitless, as the quadrilateral bay will be treated as a mechanism and the software will just output an error and come to a halt.

The bridge looks to be in much worse condition than it really is. It looks like it had a concrete coating which is now peeling away.

Perhaps the thing I found the strangest about this bridge is not its supremely odd structural system, but its incongruity. One end of the bridge is terminated with a series of switchback ramps. This gives the bridge a very urban feel, it's the sort of arrangement you often see in an urban environment. But at Smithy Wood, it's in the middle of a field, and it seems completely out of place. This is probably what I liked most about the bridge ...

Further information:

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 bridges 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: