31 October 2008

River Soar Footbridge competition announced

RIBA have announced a new competition for the design of a £1.5m foot and cycle bridge in Leicester, connecting the National Space Centre to a new residential development on Wolsey Island. They are seeking expressions of interest from suitable designers with a view to shortlisting six teams to produce entries, each of whom will receive a £6,000 honorarium.

The shortlisted firms should be announced in December, with a winner known by March 2009.

The jury panel includes experienced bridge architect Jim Eyre, with an engineering adviser yet to be confirmed (although I hear that it is likely to be someone with similar experience, suggesting along with the £6k payments that RIBA is gradually improving the way they run bridge design competitions).

27 October 2008

River Douglas Bridge competition winner announced

The title says it all: Arup & JDA Architects have won the River Douglas footbridge competition. As predicted here in September, the winning design is a stressed-ribbon footbridge supported on an arch.

The bridge has a structural steel arch, with the deck made from precast concrete segments hung on steel tendons. The competition entry [PDF] suggested that struts between the ends of the ribbon and the arch springings will provide self-anchoring and balance internal load effects, but in this type of design there are still substantial vertical forces at the ends which have to be anchored into the ground.

The £3m bridge's next challenge is for the promoters to actually find the money to build it.

The Curious Case of the Invisible Back-stays

There are two new iconic bridge proposals in the news this week, both unusual variants on the classic cable-stayed bridge form, one an innovation which makes structural sense, and one a carbon copy of a better-known design which makes very little structural sense.

A planning application has been submitted for a new swing footbridge over the Manchester Ship Canal (shown left). It connects the Imperial War Museum North on the south bank of the canal to the Media City development on the north side, which is to become home to several departments of the BBC in a few years time. The Canal is navigable, and therefore the bridge has to be moveable, in line with the Lowry Footbridge and Centenary Bridge nearby, both of which are lifting bridges.

The planning drawings are available online from Trafford Council's planning website (search for application H/70299), and make interesting reading, as they include a fairly thorough explanation of why this particular design was developed by Gifford and Wilkinson Eyre. The bridge is an asymmetric harp-style cable-stay bridge, swinging on a pivot located below the mast. The back-span is weighted to counter-balance the fore-span.

The bridge's details (e.g. the parapets and decking) borrow heavily from Wilkinson Eyre's previous work elsewhere, such as the Gateshead Millennium Bridge and Swansea Sail Bridge. However, the bridge's unusual feature is without doubt its striking central mast, which comprises eight circular poles fanning out from a concrete base. The geometry of these has been generated from two constraints: the harp layout of the cables (which means each pole must be taller than its neighbour), and a desire for the deck cable anchorages to be tangential to the deck's curve in plan (which means the points of support must be spread out horizontally at height). Personally, I think the mast looks unecessarily fiddly, and wonder to what extent it may come to be compared to a giant skeletal hand (particularly when painted grey-white, as intended).

The other new bridge design I've noticed this week is in marked contrast to the Manchester footbridge. The Narrow Water Bridge (shown left) is to be a new highway bridge linking Ireland to Northern Ireland across Carlingford Lough. 280m long, it comprises a large cable-stayed span, with a shorter rolling bascule span opening to permit river navigation.

The image released to the press shows a design drawing heavily on Santiago Calatrava's Alamillo Bridge, although with paired masts instead of one. Like Alamillo, the masts are inclined away from the deck, so that the weight of the mast to some extent counterbalances the tension in the cables. Like Alamillo, there are no back-stays, the far more obvious and economic way of balancing out these tension forces. Because the live load on the highway is variable, the balance can never be perfect, with the result that the mast must resist enormous bending forces and is therefore both massive and expensive. Its other major disadvantage is that it needs substantial temporary propping during construction (or to be built incrementally simultaneously with the deck, as Alamillo was), which again adds considerably to the cost compared to the more conventional vertical mast.

This case of the invisible (or just plain missing) back-stays is curious because it indicates a trend which is difficult to explain. While Calatrava has had several cable-stay bridges without back-stays built (Alamillo, Sundial Bridge, Puente de la Mujer, Chords Bridge), there are very few other examples (Puente Atirantado, Mariansky Bridge, the unbuilt River Wear Bridge). This is largely because however sculpturally striking the concept may be, few schemes come without the need to match expenditure to value. As the Narrow Water scheme is still at an early stage, it's entirely possible that an entirely different design may eventually be built, but the River Wear case shows how readily public enthusiasm for an "iconic", aspirational statement can build. It's great that the Irish authorities have ambitions beyond the humdrum, but it will be interesting to see whether they can raise the budget that would be required for their current design.

25 October 2008

Bridges news roundup

Steel? Psshaw. Concrete is best for iconic bridges

The new chairman of the Concrete Bridge Development Group, David Ball, reckons concrete is under-utilised in British landmark structures, pointing to the material's now much improved durability. Maybe so, but steel remains popular for landmark bridges because it's far easier to erect, and in many cases more compatible with lightweight and geometrically unusual structural forms.

Glasgow bridge in trouble. Not quite

It seems there's always a bridge in Glasgow in trouble of some kind. And now the virus is spreading, as the completion of the Forthside Footbridge in nearby Stirling will apparently be delayed until next year. The Sunday Herald speculates idly on possible common factors, noting the presence of cable supplier Macalloy and main contractor Nuttall both on Forthside and on the unlucky Clyde Arc bridge. (Fortunately for Nuttall, the Herald hasn't recalled that they are also building Glasgow's Squiggly Bridge, which like Forthside has also suffered delays.) Nuttall state that stressing the Forthside Footbridge's stays is proving difficult, something which was acknowledged in the designers' paper at the Footbridge 2008 conference this year (see PDF).

Personally, I think it's entirely to Nuttall's credit that they have taken on several ambitious bridge schemes. Difficulties and set backs aren't entirely unexpected on innovative designs, and perhaps engineers should make more of the opportunity to explain this to their clients, and the public in general.

Weave Bridge to open in November

Cecil Balmond's colourful Weave Bridge is nearing completion at the University of Pennsylvania. Balmond seems to have little sympathy for the conventions of bridge design, taking standard concepts like the arch or truss and transforming them into stained-glass geometric puzzles. In his use of colour and advanced computer geometry, he's an engineer with a distinctive style, a refreshingly eccentric contrast to normal engineering methods.

The Weave Bridge looks from the pictures to be a Warren truss with overhead bracing - a design that's essentially about 160 years old. Balmond's design seems to arise, however, mainly from playing with geometry on a computer, rather than from the purely structural imperatives which drove James Warren's solution. Similarly, Balmond's Coimbra footbridge looks in elevation like an arch, but in reality it's a twin cantilever bridge whose main purpose is to offer a platform for Balmond's complex, startling glazed parapets.

17 October 2008

Bridge competition debris part 4: River Douglas

This is the fourth (and, for now, final) post in a series collecting together entries to recent RIBA footbridge design competitions. The other posts have covered New Islington, Leeds-Liverpool Canal, and Sheffield Parkway.

At the time of writing, the winner of the River Douglas competition hasn't yet been chosen (although the announcement is due imminently). Seven entries have been shortlisted from a total of 110. I've discussed the shortlisted entries before, so the present post will only cover entries from designers who didn't make the shortlist.

One thing noticeable about the unsuccessful entries is that they have a less clear idea of structural form than those that were shortlisted. Perhaps this has something to do with the presence of respected bridge engineer Roger Buckby on the jury panel.

As ever, click the image for a larger version, and the name of the designer for a link to any relevant details on their website.

PS: I'm away for a week so won't be posting or moderating comments until I return.

Not shortlisted

A+J Burridge

Architects in Residence

Peter Barber Architects

Designer unknown (image from Realise3d)

Shuichiro Yoshida

Added 22 December 2008
Amenity Space

Burd Haward

Added 27 January 2009
Feix and Merlin

Added 5 May 2009
Frederic Schwartz Architects

15 October 2008

Bridge competition debris part 3: Sheffield Parkway

This is the third in a series of round-ups of RIBA bridge competition entries, following on from ones for New Islington and Pennington Road.

The Sheffield Parkway footbridge competition attracted 109 entries, but nonetheless I found it very difficult to find many of them online.

This scheme offered a fairly open brief with a relatively flat and unrestricted landscape, with the footway carried over a dual carriageway. Judging from the images below, that's again a license for every furniture designer or frustrated sculpture to try their hand at bridge-as-blob. I know that sculptor Richard Serra was a big admirer of bridge designer Robert Maillart, but here we're seeing bridge designers taking their inspiration from the likes of Serra.

As ever, click the image for a larger version, and the name of the designer for a link to any relevant details on their website.

Ramboll Whitbybird + Norlund Architects

Also shortlisted
Satellite Architects + Elliott Wood Partnership

URB Architecture + Ove Arup & Partners

Arup Associates

DLG Architects

Not shortlisted
Edgley Design

Leit-werk [PDF]

Juhana Marttinen + Markus Wikar

David Narro Associates + A+J Burridge

12 October 2008

"Understanding Bridge Collapses" by Björn Åkesson

"Understanding Bridge Collapses" (ISBN 0-415-43623-6), Taylor & Francis, 2008 [Amazon UK] seems to be a very timely book, published as it is following what seems like a spate of often catastrophic bridge failures.

There are several books available offering case studies of engineering failure: examples include "Why Buildings Fall Down" by Salvadori and Levy; "Design Paradigms" by Henry Petroski; and more structure-specific titles like Peter R Lewis's books "Beautiful Railway Bridge of the Silvery Tay" and "Disaster on the Dee". Most of these are a pleasure to read for engineer and layperson alike: Salvadori and Levy's book is a personal favourite thanks to its clear illustrations and explanations. Although both it and the Petroski book cover plenty of bridge failures between them (Tacoma Narrows, Point Pleasant, Mianus River, Schoharie Creek, Hatchie River, Dee Bridge, Britannia Bridge), I'm not aware of a book until now that has focussed exclusively on bridge-related case studies.

Åkesson, a former lecturer in Sweden, used case studies of failure to help explain complex structural phenomena to students. His aim with "Understanding Bridge Collapses" is to share some 2o examples of bridge failure with practicing engineers, enabling them both to learn from history and also to understand how the history of bridge failure is also a history of increased technical understanding.

The book covers the following collapses dating from 1847 to 2003: Dee, Ashtabula, Tay, Quebec, Hasselt, Sandö, Tacoma Narrows, Peace River, Second Narrows, Kings, Point Pleasant, Fourth Danube, Britannia, Cleddau, West Gate, Rhine, Zeulenroda, Reichsbrücke, Almö and Sgt Aubrey Cosens VC Memorial. In each case, copious technical detail is provided, including detailed formulae, calculations and diagrams describing the failure mechanism and showing why an insufficient factor of safety was present. In this respect, it's a very welcome book because nowhere else is this level of technical detail brought together in one place.

One thing to note is that the book's title is exactly correct; it's about bridge collapses rather than failures more generally. There were several early suspension bridges (e.g. Union Bridge and the Menai Bridge) which suffered terribly due to aerodynamic excitation, but didn't actually fall down (although many of their contemporaries did collapse), and the book also omits examples like the London Millennium Bridge, which suffered a performance failure but again didn't collapse. The latter omission is particularly interesting because the author quotes with approval Sibley and Walker's 30-year cycle of major bridge failures, each of which represented a major turning point in the development of bridge engineering:

Åkesson and Petroski both suggest that on the basis of this pattern the time was ripe for a major cable-stayed bridge collapse around the turn of the millennium. Well, of course, that hasn't happened yet, but the Millennium Footbridge fits the 30-year cycle perfectly, providing a classic example of innovative bridge design pushed beyond the boundaries of current knowledge, and leading to much fruitful research following its failure.

Not all of Åkesson's explanations agree with other authors. Taking Stephenson's Dee Bridge, Petroski blames lateral torsional instability, while Åkesson suggests the culprit is localised plastic deformation of a pin-connection detail. I don't feel that this matters: there's plenty to learn even from an incorrect explanation.

One problem with the book is that there are so many specific details that it doesn't really step back and offer a proper overview. There is very little attention given to the non-technical reasons for failure, Pugsley's "engineering climatology of structural accidents".

The biggest flaw, however, is the seemingly complete absence of an editor - Åkesson's English is far from perfect, and seems not to have been edited at all. At times it's just awkward, but at others it's genuinely difficult to understand some of the points being made. For any book of this sort to get to print with this little intervention is frankly baffling, and it's a constant source of irritation as you read through it.

So do the good points outweigh the problems? I'd have to say I found the book so badly marred by the imperfect English that I can't really recommend it. It's unique, and a very interesting read, but I find myself constantly regretting what I paid for it. Caveat emptor!

08 October 2008

Bridge competition debris part 2: Leeds-Liverpool Canal

Here's the second roundup of RIBA bridge competition images, following on from those for New Islington. This time it's the Pennington Road Footbridge competition, for a replacement bridge over a canal in Bootle, Liverpool, which gathered 88 entries.

Again, click on the image for a larger version, and on the link for any relevant information at the designer's website.

Themes this time around? I don't think there are any clear ones. The site's geometry was quite restrictive, and anyone who thought seriously about mobility-impaired access will have had to think hard about how to fit in the ramps, but otherwise there was considerable freedom.

There are some covered bridges (which seems fairly pointless given that the approaches are uncovered). One attempt to reuse and redecorate the existing structure. And one or two tall landmarks which tower over the adjacent housing developments or (in the case of Parklife) look to be a cable short of a full spool.

Also shortlisted

The following were all shortlisted but I've not found any images of their designs online: Arca / Martin Stockley Associates; B&C Associati; Chris Curtis / Elliott Wood Engineers; Julian Hakes Associates / Alan Baxter Engineers; Youssef Ghali.

Not shortlisted

Post edited 13 October 2008

Here's another one:

Juhana Marttinen + Markus Wikar

06 October 2008

Bridges news roundup

Trips to Venice end in trips in Venice
Apparently Santiago Calatrava's controversial new Constitution Bridge in Venice is injuring tourists. If that makes you think of a steel-and-glass monster rearing up and lashing out at wide-eyed visitors, Godzilla-style, the truth is sadly more prosaic - inconsistent glass stair treads creating a trip hazard. I especially liked Venice's daft solution:
"We'll intervene with some sort of signalling system for distracted tourists, perhaps with stickers on the ground," Salvatore Vento, Venice's head of public works, told Corriere.
Even Calatrava himself, who is notorious for fighting against proposed alterations to his bridges, has suggested some of the steps could be modified.

Helical bridges are the new black
The Harthill Footbridge was lifted into place over the M8 motorway in Scotland at the beginning of October (albeit late and over-budget). The design is a lattice truss comprising intertwining helical loops. It must be intended to be eyecatching, because it's certainly not structurally optimum. It is glazed inside the truss which will make repainting difficult - there's also no evidence of how the outside of the glass will be cleaned (e.g. a maintenance walkway). It seems to be part of a trend: similar bridges include the nearly identical Greenside Place Link Bridge in Edinburgh; and the Marina Bay Bridge in Singapore (inspired, like the Amgen Bridge in Seattle, by the shape of the DNA double helix).

To infinity and beyond
The iconic North Shore Footbridge, designed by Expedition Engineering, has had its two arches installed (using the same crane as at Harthill, incidentally) and is now named the Infinity Bridge. The bridge occasioned some controversy last year with a war of words between Chris Wise and Stephen Spence (also of River Wear bridge fame) as to who actually came up with the design.

04 October 2008

Bridge competition debris part 1: New Islington

I have an ongoing interest in RIBA bridge design competitions, as may be obvious. To round off previous posts, I'm going to offer a series of posts bringing together in one place lots of the competition entries; both the winners and the losers. Noting that there have been several unsuccessful outcomes with the RIBA competition winners (e.g. Stratford and River Wear), I think it's interesting to consider whether the available pool of entries might have led to a different outcome.

Looking through both the successful and the unsuccessful designs for the New Islington footbridge competition, three immediate thoughts come to mind.

One is that despite the competition brief very clearly calling for a "sketch" design, many of the submissions were complex computer visualisations, no doubt with the aim to catch a judge's eye, but representing a level of effort entirely disproportionate to the odds of getting shortlisted.

The second is that the geometrical problem (to link five paths at different levels and in different directions) led to many variations on a small number of basic ideas: the ring and the starfish being the most popular. So: does the client really benefit from so many entries (87)?

The third is the distinct impression that many of the entrants would be better off with a career in furniture design than bridge design; they seem to think (and the judges seem to share this view) that the same principles can apply to both. Most of the entries shown below offer little or no evidence that basic structural concerns have been given even a passing thought. Which, for a bridge, is odd.

I intend to offer the entries without further comment. I'm limited to what I can find online, so I don't know how representative a cross-section of the entries these are. In general, clicking on the image should take you to a higher resolution version; clicking on the entrant's name should take you to any further information on the design available at their website.

Michael Hadi Associates & Gollifer Langston

Also shortlisted
Gunning Groothuizen Architects

McChesney Architects & Atelier One

Techniker + Glowacka Rennie

Not shortlisted

David Narro Associates + A+J Burridge

Arup + David Miller Architects

Buro Happold + FoRM Associates

Flower Architects

Hot Architecture

ROEWU Architecture


The Space Studio

Urban Future Organisation

West Architecture

Working Architecture Group

Added 5 May 2009:
Guy Nordenson Associates