Olympic Central Park Footbridge installed

I reported over a year ago on the outcome of a competition for the design of a footbridge for the London 2012 Olympic Park. That was won by Adams Kara Taylor with Heneghan Peng.

Now, the first parts of their unusual bridge design have been installed on site by contractor Lagan Construction.

The design is for three permanent link bridges spanning 36m above Carpenter's Lock. What makes them unusual is that during the Olympics, the spaces between these structures are also filled in, creating a single bridge some 54m wide. Once the circus leaves town, the temporary infill structures are to be removed.

The geometry is such that the two edge bridges have a curved, twisting form. These two structures (each weighing between 40 and 50 tonnes) were erected in early March (see video). Structurally, they are tubular space trusses, sufficiently unbalanced in shape that they need to be temporarily propped until the third link bridge is installed between them (due to take place in April).


They are also clad in mirror-polished 4mm thick stainless steel, the fabrication of which will have been quite a challenge. I guess from below they will give the impression of some kind of giant Anish Kapoor sculptures (see picture). Building magazine has much more information on the difficulties of fabrication and construction.

Manchester Bridges: 12. Mariners Canal

Having got the two more interesting bridges at Salford Quays out of the way, I made the big mistake of venturing further, along a channel called "Mariners Canal".

This channel is a recent construction, opened in July 1989, and links Erie Basin (where the Detroit Bridge sits) with Ontario Basin to its south. To either side of the channel are low-rise residential developments. Both canal basins are used for watersports, so presumably Mariners Canal provides a useful functional link as well as increasing the amount of higher-valued waterside property.

The Canal is crossed by four bridges, three for pedestrians and one carrying the highway. Starting from the north end, the first bridge is a ghastly faux cable-stayed bridge, with masts grossly out of proportion to the bridge and its span. Indeed, the mast and stays are essentially useless, considering that the bridge spans no more than 15m, and probably less than that.

Clearly, they wanted a landmark at the end of the channel, but surely it would have been better to erect a more straightforward structure, and just add a tall sculpture beside it? Or perhaps, a large pike with the head of the designer on top?

As if its general conception were not sufficiently ridiculous, the bridge is further diminished by an ultra-cheap cable anchorage via a joist below the deck, and by bizarre circular plates at the head of each mast.

Heading south, and still in something of a state of shock, I came to the Grain Wharf footbridge. My stomach still felt slightly nauseous, but this bridge began to calm me down. The bridge is "dressed" with non-functional steel plates to look like an arch, although in fact it is a Howe truss design.

I can almost forgive the fake arches because of the effort put in to make the parapets interesting, with parapet infill bars parallel to the truss diagonals rather than in the more normal vertical arrangement. Indeed, it's actually quite an attractive idea.

The next bridge along is a highway bridge, and although rather ugly it is not without its redeeming features. Semi-circular belvederes jut out from the sides of the bridge (not because there is literally any "fair view", of course).

The underside, with its series of fanned ribs, might be thought reminiscent of the great Italian engineer, Pier Luigi Nervi. If you were very, very drunk.

The undercroft to the main bridge deck has a rather startling allure. The circular reinforced concrete support columns should by rights be highly unattractive. However, there's a mysterious, grotto-like quality to this space. I'm sure it is unintentional, but I really enjoyed it (honest, no sarcasm now).

The final of the four bridges along Mariners Canal is simply a repeat of the first, so I skipped past it quickly and took a photo of this nearby bascule bridge (across the entrance to the Ontario Basin) instead. You can see the Lowry Millennium Bridge in the background.

Further information:

• Google maps
• Salford Quays heritage trail (PDF)

Manchester Bridges: 11. Detroit Bridge

From the Lowry Millennium Bridge, it's only a short walk to Detroit Bridge, which spans Erie Basin just off the Manchester Ship Canal.

In its former life, this was a twin-track railway bridge, one of a number of swing bridges spanning across the Manchester Ship Canal. A single-track rail swing bridge at its original site was first built in 1895, but replaced in 1942 by a twin-track version weighing some 300 tonnes, built by Dorman Long.

With the decline of dock industry in Salford, the bridge became redundant in 1981, and was refurbished seven years later and floated to its current location. The refurbishment design was by Arup, and included installation of a hardwood timber deck for use by pedestrians, and the loss of all the mechanical equipment. It's no longer a swing bridge, but is permanently fixed in position.

The bridge is 80m long, 9m wide and over 10m tall above deck level. It's in the form of a balanced cantilever modified Warren truss. I would have thought a Pratt truss would be slightly more efficient for this arrangement, as it would eliminate compression in the diagonals, but this may depend on the balance between dead and live load. In its original swing configuration, the bridge acts as twin cantilevers under dead load, while under live load, the bridge behaves as a two-span continuous beam. The balance between each load determines the most efficient truss arrangement.

The timber decking and paintwork lasted 17 years before £0.5m was spent on refurbishment in 2005. The decking has been replaced with non-slip GRP planks, the bridge repainted, and flush-faced panels added to all the truss web members. These are there to prevent people climbing up onto the top of the truss and diving off, which was reported as a regular problem (although they didn't entirely solve it). The panels have also been treated with anti-climb paint. While the practicalities are unavoidable, they definitely detract from the appearance of the bridge.

It's marvellous to see an old bridge reused and treated so well. The bridge was well-used when I visited and is likely to become more so when the nearby Media City development is complete.

The most interesting feature of the bridge is the installation of an observation deck below its redundant pivot in the middle of the canal basin. This is accessed on curved staircases, and while it hardly offers a useful viewing platform, it does make the bridge experience more interesting.

Further information:

• Google maps (present location)
• Google maps (original location)
• Report on 2005 bridge refurbishment (DOC)
• Salford Quays heritage trail
• Bridges of the Manchester Ship Canal (includes photo in original location)

Knight & Helbig win at Margaretengürtel

A competition to design a 380m long footbridge at Margaretengürtel in Vienna has been won by Knight Architects and Knippers Helbig. The bridge will link recreational parkland to Bruno-Kreitsky Park, carrying pedestrians over a busy highway. The designers beat 36 other entrants [PDF, German], and win a share of a 70,000 euro prize fund.

The design proposes a startling intrusion into the historic Vienna cityscape, with its organic folds and curves oddly reminiscent of a crinkly pringle. It also makes me think of the Termite Pavilion at London Zoo, a sculptural environment built from contoured timber strata.

I’m not entirely sure that I understand the bridge’s structural concept. The larger spans are supported from concrete plinths (resisting highway vehicle impact loads), from which the timber deck appears to grow upwards like a dust cloud. Away from the highway, the supports are extremely slender steel stilts. The deck has a core of layered glulam timber (spruce), which appears to be clad with the contoured outer layer (larch). The timber is reinforced with steel rods inserted between the various layers.

It is intended to be built as a series of pre-assembled sections up to 20m long, stitched together on site. In total, there’s an estimated 960 cubic metres of timber involved. The designers state that the choice of material is far more environmentally friendly than any steel or concrete alternative, and it’s undoubtedly the case that timber is under-exploited as a material for modern bridges. In large part this is due to nervousness on the part of public bodies regarding its long-term durability, and its resistance to vandalism.

The bridge’s S-shaped curvature in plan is complemented by the creation of high, curved edge upstands. These provide a convenient space for bench seating, but have the unfortunate effect of increasing the bridge’s visual mass. They also obscure views off the structure (although they are above the highway so it’s unclear whether the view is of much interest). They also seem to offer a fantastic inclined surface for skateboarders and cyclists to try and negotiate, not unlike the banked surface of a velodrome track.

The parapets appear to be illustrated as simple stainless steel frames with an infill mesh, with a relatively transparent quality allowing the visual focus to remain on the laminated timber. The visualisations suggest a highly unusual structure with the potential to be quite gorgeous if the simple, smooth detailing can be successfully carried through into construction. Timber lends itself to the forming of such irregular surfaces, which would be far less economic in steel or concrete. As a result, the engineering, while clearly unconventional, is probably less forced in service of the architectural concept than is the case for much other modern blobitechture.

2nd prize in the contest was awarded to Luggin with Martin Kohlbauer (see Luggin website for images). 3rd place was taken by PCD ZT with Zeininger Architects (see Competitionline for images).

Updated 29 March: details of prize money corrected.

RFR/Halsall win St Patrick's Island contest

A winner has been announced in Calgary's St Patrick's Island footbridge design competition. The Calgary Municipal Land Corporation have chosen an elegant design by RFR and Halsall Associates Limited for this CAN$25m footbridge, which replaces an ageing suspension bridge link across the Bow River.

The contest was in marked contrast to the direct appointment of Santiago Calatrava for Calgary's other new iconic footbridge. It was open to any interested participants, there was plenty of public involvement, and the process for selection of a winner was relatively transparent. Given the criticism that Calatrava's appointment drew, no doubt CMLC are happy that Halsall, a Canadian firm with an office in Calgary, were part of the winning team (I predicted at the outset of this contest that two of the three shortlisted firms would feature locals, pretty much correctly).

The RFR design was the one I tilted towards out of the three finalists, and it's gratifying to see an honest, engineering-led but architecturally-refined design turn out the winner. The design has seen considerable modification since the initial entries, but it has retained its simplicity and delicacy throughout.

Related posts:

• St Patrick's Bridge - the final designs
• Calgary's bridges a-go-go
• St Patrick's Island Bridge Competition entries: Part 1
• St Patrick's Island Bridge Competition entries: Part 2
• St Patrick's Island Bridge Competition entries: Part 3
• St Patrick's Island Bridge Competition entries: Part 4
• St Patrick's Island Bridge Competition entries: Part 5
• How to win a bridge design competition
• St Patrick's Bridge design competition announced

Manchester Bridges: 10. Lowry Millennium Bridge

From Manchester city centre, I went west, to Salford Quays, to see several bridges.

This first one is a vertical lift footbridge. I've seen "Lowry Centre Footbridge", the "Lowry Bridge", "Salford Quays Millennium Footbridge", "Salford Quays lift bridge", and several similar variants on its name.

It spans the Manchester Ship Canal, linking regeneration centrepieces such as the Lowry Centre to the north, and the Imperial War Museum to the south.

It was built in 1999 by Christiani & Neilsen (the steelwork was fabricated by Fairport Steelwork and Lengthline Ltd). The main designer was Mouchel Parkman, but the superstructure at least was designed by the Spanish firm of Carlos Fernandez Casado, with the mechanical and electrical systems designed by Bennett Associates (now part of Atkins).

The main span is a steel bowstring arch, 96m long (spanning 91m between its bearings) and 11m tall. The arch rib and tie are both upside-down U-shaped girders, 600mm wide by 800mm deep, and steel hanger rods connect the two. The arch tie girders carry the orthotropic steel deck (pictured left from below). The bridge parapets are in the form of glass wind deflectors, with pedestrian lighting concealed in the handrails.

The bridge deck is suspended from four towers, each 31m tall, which support the lifting sheaves and counterweights, and the entire bridge can lift approximately 18m in 3 minutes, when required. The towers are tubular steel space frames, curved for enhanced stability against wind load at the base. While nicely shaped, they'd look better with less bracing, and I wonder whether emphasising the size of the maintenance platforms at the top was a good idea.

A visually attractive lifting bridge is a rare thing indeed; I certainly can't think of any good examples in the UK, and most of the lifting bridges in the US have a very heavy, industrial appearance. It's a type of moveable bridge generally limited to longer spans, with bascules and swing bridges being more economic and maintainable for short bridges, although there are some very large swing bridges around (most notably at El Ferdan in Egypt).

At Salford Quays, I presume there was a desire not to have a support pivot in the waterway, which would restrict its width (although the new Media City footbridge being built a short distance away will be swing bridge). So a lifting bridge makes sense as a choice, even though it doesn't look like it actually opens very often.

The wind screen parapets look a bit odd to me, their height makes the deck feel quite enclosed, and while they may be effective at shielding the worst effects of the wind, you are exposed again as soon as you step off the bridge.

But on the whole, it's a reasonably attractive bridge, well detailed and kept simple so that the arch form can provide the main visual focus.

Further information:

• Structurae
• Google maps
• Wikipedia
• Corus Construction (PDF) (lots of detail on the design and construction)
• Bennett Associates (includes video)
• Design & Technology online

Bridges news roundup

I've a bit of a backlog of news items that have been building up while I've been reporting on my Manchester visit ...

4 Mile Run bridge contest announces shortlist
This footbridge competition in Virginia has announced their three finalists:

• Grimshaw / Arup / Scape
• Olin / Buro Happold / Explorations Architecture / L'Observatoire International
• Rosales + Partners / Schlaich Bergermann und Partner / Simpson Gumpertz and Heger

That's a very high-powered list for a competition with minimal prize money, no funding in place to appoint the winning design team, and no guarantee that political sway won't beat design quality (see previous post). The finalists present their designs to the public on 27th March, and a winner will be announced at the same event.

Buro wins Portuguese bridge competition
Elsewhere, Happold have won a £0.5m footbridge contest with architect Powell-Williams.

Wilkinson Eyre’s Liverpool bridge scoops top honour at Civic Trust Awards
Paradise Street footbridge designed by Arup (more details)

$840,000 city study to weigh Johnson Street Bridge fate
More thought required on whether to replace or refurbish unusual bascule bridge (see previous post)

'Maintenance failures' found in Malahide viaduct report
Irish rail engineers accused of misunderstanding how their bridge was supported before it collapsed (formal report here [PDF] doesn't entirely bear out some of the reporting in the popular press). Engineers interested in why bridges fail may also like to seek out the recent RAIB report into the Stewarton Bridge failure, which is an astoundingly comprehensive catalogue of error: inspections not carried out properly; defects found and not acted on; critical calculations based on unverified assumptions; and many more.