03 October 2015

Welsh Bridges: 4. Penmaenpool Bridge

This privately owned timber road bridge dates from 1880, when it was constructed by the Penmaenpool Bridge Company Limited, under agreement with the Barmouth Harbour Trust. It crosses the River Mawddach in Wales, and provides a useful short cut between the coastal towns of Barmouth and Fairbourne during its opening hours.

Most spans are 20-feet, but the central span is 30-feet. This span was designed for possible conversion into an opening bridge span, in case a disused boat-building yard upstream of the bridge was ever re-opened, but this was never required.

The structure is a series of straightforward braced timber trestles, with a heavy deck of diagonally arranged baulk timbers. It appears to be generally in good condition, although several of the deck timbers are loose.

The bridge is operated as a private toll bridge, with prices of 20p for a pedestrian, or 70p for a motor vehicle not exceeding 1.5 tonnes in weight. The bridge is only open between 8.30am and 6.30pm, with tolls being collected from the southern end, adjacent to the bridge-owner's cottage.

It's a lovely spot to visit. The abandoned railway line on the southern edge of the river has been converted into a cycle and walking trail, Llwybr Mawddach. The former signal box is now a bird-watchers' hide, while the old railway station and platform are now part of the nearby George III Hotel. It's a splendid spot from which to admire the historic structures, landscape and wildlife.

Further information

21 September 2015

Bath Quays Footbridge Competition entries published

These came out a few days ago now, but I've only just had time to look at them properly.

This is a contest for a new £2.5m pedestrian bridge across the River Avon in Bath, organised by Bath and North East Somerset Council.

In May, six teams were shortlisted, and each given £5000 and eight weeks to develop a design. The teams are:

  • AL_A / AFA Consult
  • Flint & Neill / Moxon Architects
  • Grimshaw / Buro Happold
  • Heneghan Peng / Ove Arup
  • Marc Mimram / Webb Yates
  • Price & Myers / McDowell & Benedetti

Now, all six entries have been released, although anonymously. You can have fun, if you wish, trying to guess the designers! A winner was originally scheduled for August, but this is now expected to be in November.

Entry 1
This is a very curious design, a propped cantilever bridge (intended to minimise physical impact on the historic south bank of the river) fabricated from a series of extremely lightweight trusses. It's fiddly to the point of being finicky, and would make a fantastic climbing frame for the locals to explore. The truss members are all of stainless steel, but painted, which is a genuinely baffling idea.

Entry 2
Again, this is a structurally bold design, and one which makes use of the same basic principle: support the bridge from the north bank so as to reduce impact on the south bank. It's an unusual "cable-stayed" bridge, with a steel box girder deck which is boomerang shaped in plan, and supported by a mast on only one side. The normal cables are replaced by steel ribbons. I especially like the detailing of the balustrades on this design.

Entry 3
This entry comes with a name, the "zig-zag bridge", which describes its profile in plan. Architecturally, it is extremely restrained, so modest that the zig-zag is the barest nod to the need for the bridge to express something, anything. The money here has gone into expensive materials: stainless steel box girders and balustrades, a Bath Stone handrail, and a "precast granite" deck. I'm not quite sure what precast granite is, but it sounds expensive, anyway.

Entry 4
Captioned "Between history and modernity", the fourth design takes the idea of responding to a propped cantilever moment diagram as seriously as did the first, and with much the same logic. The bridge curves gently in span, and is supported by two Vierendeel girders, one on each edge of the bridge. These are shaped to provide almost a hinge at the point of structural contraflexure. They remind me a little of the Vierendeel ribs on Paris's Pont de Solferino, a Marc Mimram design. The designer has tucked the main supports away behind the edge girders, which would be implausible on anything other than a short footbridge.

Entry 5
Now here's a design that I quite dislike. I loved the basic image, an elongated Ikea-like picture frame, with ancient Roman ivy already growing over it, but I think the design fails under closer examination. It's a bridge with a tall central timber truss with footways either side, possibly intended as a Vierendeel but that's clearly impossible in timber at any useful scale. Diagonal steel bars and a support framework for the vegetation fill in the truss bays, making it impossible to cross from one side of the deck to the other.

Entry 6
The final entry is the most intriguing, at least in terms of its engineering. It's a half-through girder bridge, with twin steel girders constructed from perforated weathering steel plate. The perforations are layed out to suit the stress patterns in the girder, which is constructed of a series of steel segments. The segments are stressed together using stainless steel prestressing cables. It's technically fascinating, although I think it's perhaps the least sympathetic bridge to this particular site, and a concept which may be more appropriate elsewhere.

For your amusement, here are my guesses at the various designers. I'm not going to forecast the winner, but if I had a vote, it would go for Entry 6.

  1. AL_A / AFA
  2. Flint & Neill / Moxon
  3. Grimshaw / Happold
  4. Mimram / Webb Yates
  5. Henneghan Peng / Arup
  6. Price & Myers / McDowell + Benedetti

03 September 2015

Tintagel Castle: Shortlist announced

The organisers of the design competition for a new footbridge at Tintagel Castle in Cornwall, England, have shortlisted six out of one hundred and thirty seven entries. A winner is due to be announced early in 2016.

  • Dietmar Feichtinger Architectes with Terrell (France)
  • Marks Barfield Architects with Flint and Neill (UK)
  • Ney & Partners Civil Engineers with William Matthews Associates, Ettwein Bridges and Waagner Biro (Belgium)
  • Niall McLaughlin Architects with Price and Myers, and Max Fordham (UK)
  • RFR and Jean-François Blassel Architecte, with Engineers HRW, and WSP (France)
  • Wilkinson Eyre with Atelier One (UK)

They seem to have assembled some (mostly) impressive contestants, although a number of well-known bridge design specialists are notable for their absence. I certainly look forward to seeing the various designs unveiled in due course.

11 August 2015

10 essential bridges books: Conclusion

Attentive readers will notice I've actually discussed twenty "essential bridges books" here in recent posts.

Older posts

Recent posts

But now it's your chance to tell me: what did I miss out? What is your own "essential" bridges book? Answers in the comments, please!

10 essential bridges books: 10. The Architecture of Bridge Design

I struggled over my choice of the tenth and final book in this series, and am not entirely sure that David Bennett's The Architecture of Bridge Design (1997, Thomas Telford Publishing, 200pp) [amazon.co.uk] can rightly be described as "essential". However, it's a book that had quite a significant impact on me as a designer, and so I'm including it here.

The book was intended as a "state-of-the-art" survey of bridge design by both engineers and architects at a time when there had been a prolonged period of intensifying activity between both types of designer working more closely together, on projects which were of considerable public interest and often of high design merit. The author brought together a wide variety of designers to describe their projects in their own words, and the reason I still enjoy the book today is the manner in which it captured a certain zeitgeist.

Bennett dates the period of interest to the beginning of the 1990s, with Santiago Calatrava's (unbuilt) East London River Crossing proposal from 1990, and Cezary Bednarski's Bloomers Hole Bridge, an unbuilt competition winner from 1992. It's a period that was probably at its peak when a fever for millennial footbridges took over, and I think it's a period from which designers and their clients are still suffering from a bit of a hangover.

Re-reading Bennett's book now is an exercise in nostalgia. It's quite remarkable how bad some of the designs featured are, coming from an era when pretty much any ropey old visualisation could make a bridge look contemporary. Cases in point include Rodolphe Luscher's awful Pont Devenir and Budapest proposals, both included here and showing quite a staggering lack of respect for context or scale. Other poor designs include the Japan Bridge, and the East Bridge at l'Parc de la Villette, both in Paris. It's interesting to contemplate quite how these bridges were considered worthy of inclusion, but I think that then, as now, there was too little genuine criticism of such ventures.

There are other designs where reading the designer's own ideas and justifications is a little depressing. Examples here include the Royal Victoria Dock footbridge, which seems even more of a white elephant when the author makes clear its reliance on the transporter gondola element, which was never installed.

In other instances, it's interesting to read numerous "what-might-have-beens", for example not only Foster and Partners' early ideas for the Millau Viaduct, but also those of Alain Spielmann, an opposing competitor. Similarly, you can contrast the Royal Victoria Dock footbridge as built with the design by Cezary Bednarski which was not. There's a degree of poignancy here, and throughout the volume, huge quantities of passion and creativity devoted to structures which would never get built. As an industry, this represents many lifetimes of talent and hard work which appear to be wasted. However, with their preservation in this book, perhaps there are still ideas which can form seeds for further development.

In a few of the better contributions, the designers offer genuine illumination on how their structure was conceived. A bridge like the South Quay Footbridge can't properly be understood without this background, I think.

I'd like to see more books like this about bridges: argumentative, speculative, informed and informative. It would be interesting to look back on such a book again, in ten or twenty years time, and see how the bridge-design zeitgeist has evolved.

24 July 2015

10 essential bridges books: 9. Calatrava Bridges

And so, we come to Santiago Calatrava.

Calatrava is something of a phenomenon in modern bridge design, and is often cited, quite wrongly, as being singlehandedly responsible for making bridges architecturally interesting. His designs are often immediately recognisable - his combined training as both an architect and as an engineer has led him to produce structures which combine visual drama with structural rigour, a kind of spacial poetics, usually writ large in tons of carefully balanced steel.

Calatrava Bridges (Tzonis and Donadei, Thames and Hudson, 272 pp, 2005) is ten years out of date now but remains the most up-to-date guide to this superstar's bridges, both built and unbuilt. As with most other books about the Spanish designer, it is in no sense a critical work, but is a celebration of his P.T. Barnumesque showmanship.

Calatrava's work is much-derided by other architects and engineers, if supposedly much loved by the public. Even the latter appears less true now, as he has a growing reputation for budget and programme over-runs as much as anything else. Fellow designers criticise the way that his bridges rarely respond to context, instead taking a signature style (white, generally steel, a cat's cradle of cables, hi-tech detailing) and dropping it into whatever setting is currently to hand. His bridges are bombastic, grandiose, sometimes over-wrought to the point where they become almost hysterical. Modesty and restraint are never Calatrava's watchwords.

However, as this book makes clear, Calatrava's work is also often geometrically fascinating, spectacular, and informed by a deep love of engineering craftsmanship and technology. That they are instantly recognisable puts other designers to share: he is the supreme bridge design stylist, happy to provide his signature wherever his clients are willing to pay for it. Few designers have been so prolific or so consistent, and if Calatrava has many unbuilt projects to his name, he also has far more completed works than most rivals.

Tzonis and Donadei's book is well illustrated, with plenty of beautiful photographs and quite a few diagrams and architect's sketches. It is not thorough in this regard - this is a good summary of the designer's work but certainly not the definitive encyclopaedia.

Reading through the book today, I am actually most struck by Calatrava's facility for concrete design. His unbuilt Vecchio Bridge would have been a particularly elegant, Maillart-esque concrete arch, while his 9 d'Octubre Bridge in Valencia features some exquisitely shaped curved concrete.

He is also occasionally capable of surprise, with his grey Oberbaum Bridge in Berlin and red-ribbed Ponte della Costituzione in Venice both being fine designs which are all the better for their departures from his usual palette.

A properly critical study of Calatrava's bridges has yet to be written, but until that happens, this book is at least a useful compendium of his work, and one that I am quite happy to recommend.

22 July 2015

Nine Elms - Pimlico Bridge Design Competition: Stage 2 Designs

Ok, here are the Nine Elms / Pimlico Bridge Design Competition Stage 2 designs in full. Click on any image for a full-size version, or visit the project gallery.

Ove Arup & Partners Ltd with AL_A, Gross Max, Equals Consulting and Movement Strategies

There has been a great deal of NIMBY-ish wailing from residents on the north bank of the Thames (and also from their political representatives), concerned that the bridge may wreak havoc upon one of the few public riverside green spaces in London, Pimlico Gardens. These complaints ignore the fact that this is a contest to select a team, not a design, and that no location for the bridge has been confirmed as yet. However, there's little doubt that an alignment between Pimlico Gardens on the north bank, and the new US Embassy on the south bank, is the most sensible.

Arup's design tries really, really, really hard to minimise harm to the gardens, siting the bridge's necessary cycle ramps in the river rather than on land. This makes for great public space, but is something of an imposition on the river, and it's hard to see how Arup deal with the inevitable issue of boat impact. As shown the ramps are structurally sketchy at best, slender loops of something-or-other with no visible means of support.

It's not an unattractive design, but, having visited the site, I don't think it is best served by having a tall structure mid-river, the riversides shouldn't be so visually dominated by a bridge. It's also not a straightforward bridge to build, with multiple angled and criss-crossing hangers, potentially requiring a great deal of temporary supports within the river.

Ove Arup & Partners Ltd with Hopkins Architects and Grant Associates

Arup, again, this time with a suspension bridge solution. This should, in theory, be much more respecting of the river environment, but for reasons that seem obscure, the designers have chosen to stretch the pylons far taller than is actually necessary, taller even than some pretty tall trees in Pimlico Gardens. By also painting them red, there seems to be an unnecessary dash of "look-at-me" all over this.

The ramps are, again, in the river, although the connection to the Gardens is less well detailed, punching through the middle rather than tucked discreetly into the corner as was the case for the previous design. However, this is the only design that recognises that the route is not fixed, showing clearly in the plans how the same bridge can be adapted to any number of alternative locations without affecting the structure's logic.

The circuitous ramps at least have some means of support, with cable stays radiating from the main pylons, but again they are vulnerable to boat impact and visually intrusive.

I'd also question the choice of deck structure, a steel multi-cellular box girder which seems unnecessarily expensive to me for a bridge of this span with suspension cables on both sides of the deck.

Bystrup Architecture Design and Engineering with Robin Snell & Partners, Sven Ole Hansen ApS, Aarsleff and ÅF Lighting

Bystrup's design shares the first two designs' offshore ramps, but does at least trouble itself to consider boat impact protection, with an "eco-pontoon", a planted floating fender, shown as a possible solution.

It's a cable-stayed design with an S-curved deck supported on opposite sides from the two towers, but I think the curvature of the deck is too slight, and this renders the cable and tower arrangements somewhat inert.

As with the second Arup design, a multi-cellular box deck is shown, symmetrical in cross-section, which make no real sense for a structure with cables on one side only at any given point - too much of the section's capacity is used to restrain its own self-weight torsion.

Buro Happold Ltd with Marks Barfield Architects, J&L Gibbons Landscape Architects, Gardiner and Theobald

Structurally, the Buro Happold design is by far the oddest of all these conceptions. It's an asymmetric cable-stay bridge, but the deck seems to be supported from a suspended cable net rather than from the usual array of stay cables. I found this baffling when the designs were first announced at Stage 1, and I find it baffling now. It seems to add a great deal of complexity for very little benefit, and it would be a nightmare to install and to maintain.

Even Happold's own construction diagrams make clear quite how unbuildable it is, with the main part of the deck requiring temporary props to actually hold up the cable net, even at at point when the cable net is doing nothing to hold up the deck. The deck is therefore temporarily supported along its entire length before being whizzed into position on a barge. This is simply not sensible or economic, given the alternatives available if a conventional cable-stay design were chosen.

It's the only design to dare to antagonise the NIMBYs by putting the ramps onshore, and I admire this. Pimlico Gardens is not, at present, a particularly impressive space, nor is it especially well-used, so it seems to be ripe for re-imagining, if, as this design suggests, the trees can be left largely untouched.

According to the competition website, design teams are now due to enter into "competitive dialogue" with the judging panel, and to submit final tenders (including a fee for their services) in early September. A winning team should be declared in October.