31 March 2010

Maribor footbridge competition winner announced

I've got a real backlog of posts building up here: lots of things I want to write about, and a couple more posts still to come to finish off my Manchester series. So bear with me, I'm going to have to pick and choose what to cover and when, and some bridge-related news may come pretty late as a result.

Back in November, I mentioned a footbridge design competition being held in the town of Maribor, Slovenia. This is part of a trio of contests seeking enhancements to the townscape in advance of Maribor becoming European Capital of Culture in 2012. I complained at the time that the competition was open only to registered architects, although I believe they did reverse that ruling before entries had to be submitted in February.

Anyway, results have now been announced. It was a popular competition, with 124 entries (even more for their contest for a new art gallery, which garnered 217). Three entrants have been given a share of the prize fund, with two others singled out for honourable mentions. Click on any image for a larger version.

Burgos & Garrido Arquitectos / Idom (Spain)

This design is a three-span girder bridge, with timber-clad steel edge girders, and arrays of inclined stainless steel tubular piles forming the piers. The spans seem to be sympathetic to the existing three-span arch bridge a short distance away, and it seems a modest but well-detailed proposal.

2nd prize
Viktor Markelj and others (Slovenia)

This is a single span steel box girder arch bridge, with semi-glazed balustrades. Again, it's attractive and almost utopian in its simplicity, although I wonder whether the ground conditions are suitable for an arch of this span, with the foundations illustrated looking somewhat unconvincing.

3rd prize
José María Sánchez García and others (Spain)

I find it hard to believe there weren't more convincing entries than this, a tall, presumably steel, truss structure with walkways on three levels (including high-level links further into town away from the river banks). The illustrations are unconvincing, structurally, and it's hard not to think it spoils the views of the existing bridge.

Honorable mention
Gentiane Desveaux and others (France)

This is a two-span steel space truss supporting an interestingly shaped promenade. I like the organic, flowing form, but the choice of span arrangement seems as arbitrary as the deck geometry.

Honorable mention
Gašper Premože / Andraž Tarman (Slovenia)

So far as I can tell, this is actually a boat platform connected to a control rope, essentially a variant on the traditional idea of a rope ferry. It's always good to see a brief being challenged: is a bridge really the right answer? But it's also hard to see this as the sort of permanent addition to the town that best exploits the opportunity for European funding.

30 March 2010

Waiwhakaiho Update

Roughly a year ago, I discussed Novare Design's proposed footbridge in New Zealand. It's a 69m span bridge, part of an extension to New Plymouth's coastal walkway. The steel bowstring arch spans diagonally across the span, resulting in a rather unusual appearance for the structure.

Now, the bridge is getting closer to completion, with the main structure having been installed in mid-February in an operation that must have given a few locals cause to wonder exactly what they were seeing (all photos are courtesy of Novare Design).

The 83m long superstructure was ferried for 1.5km, with the final stage seeing one end sitting on two excavator bases coupled together, and winched across the river.

I think it looks pretty good, and it will be nice to see the finished structure.

29 March 2010

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.

26 March 2010

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:

25 March 2010

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:

24 March 2010

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.

23 March 2010

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:

21 March 2010

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:

18 March 2010

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.

17 March 2010

Manchester Bridges: 9. Corporation Street Footbridge

On 15 June 1996, an IRA bomb went off in Manchester, on Corporation Street, between the Arndale shopping centre and a branch of Marks & Spencer. It was the largest peacetime bomb to be exploded in the UK, and even though the neighbourhood had been evacuated beforehand, over 200 people were injured, and about £700m of damage caused.

Extensive redevelopment followed, including the construction of new Arndale and M&S buildings. The old buildings had been linked by a covered footbridge, and a £600,000 new bridge was put back in its place in November 1998. The new structure was designed by Arup, with Hodder and Partners as architect, and built by Severfield Rowen for main contractor Bovis.

The new bridge is, as far as I know, unique in conception and form. Its glazed enclosure takes the form of a hyperboloid of revolution, a geometry best known to structural engineers for its use in thin shell power station cooling towers. I'm not aware of any examples (other than the Corporation Street Bridge), where it has been turned on its side.

Link bridges between buildings are often visually awkward. There are few structures which can bridge between flat building facades without looking at odds with the environment. Not far from Corporation Street, I walked under the three bridges pictured on the right, typical examples of an often shabby genre. I've discussed Edinburgh's Greenside Place Link Bridge here previously, but other recent examples which try to get away from cliche include the Paradise Street bridge in Liverpool, and Cabot Circus bridge in Bristol.

The Corporation Street footbridge is essentially a giant tubular truss, 18m long and 6.2m in diameter, consisting of eighteen 114mm diameter steel tubes alternating with 28mm diameter prestressed tie rods. Each main member is straight (a feature of hyperboloid geometry which makes it easier to describe and set out), and these members are interlinked with a series of circular hoop frames at intervals.

The hoop frame support a grid of steel beams which forms the sloping walkway, which is finished with oak plank flooring. The whole steel assembly weighs 28 tonnes. It's supported from the buildings via circular end frames, which have differing geometry to take account of the fact that the crossing isn't perpendicular to the buildings, nor are the building facades parallel.

The glazing consists of triangular panels, with ten different sizes and shapes of triangle required in total. These are fixed to the structural frame with cast stainless steel nodes, each of which clamps together six glazing panels. It's nice to see the numbering of the glazing panels still there a decade after it was built.

The glass is now somewhat grimy, and this isn't the only maintenance problem for the bridge. Between the walkway and the glazing, there is a small gap, and dirt, debris and litter has passed through, coming to lie on the glass panels forming the bridge's underside. I've read that the lower panels are designed for higher loads so that maintenance workers can access the space below the walkway, but there's little sign that anyone has done so for some time. That's a shame, because the impression of neglect definitely detracts from the bridge.

However, it still retains some capacity to enchant. The geometry of the bridge, which as seen on the right creates a star-shaped pattern when viewed end-on, creates a sense of occasion and an experience quite unlike any other shopping centre bridge that I've used. It has a nicely crystalline quality which would only be enhanced if it were to be cleaned up. I hope it will remain unique: it would be cheapened if it were to be repeated elsewhere.

Further information:

14 March 2010

Manchester Bridges: 8. Trinity Footbridge

From Castlefield I headed into Manchester city centre. First stop, Trinity Footbridge.

This is Santiago Calatrava's only bridge in the UK (his only structure of any type, I think). Manchester (or to be precise, it's close neighbour Salford) should be proud to have attracted the world's most prominent bridge designer, and to get one of his better designs.

The £1.9m footbridge, named for the nearby Trinity Church, was opened in 1995. Like several of the bridges I've already covered, it was part of a regeneration initiative, in this case intended by Salford City Council to draw development funding out of Manchester City Centre and across the River Irwell into Salford. The structure is therefore required to act both very much as a landmark ("here be development") and as a gateway ("enter our City here").

Calatrava's design is a 79m long asymmetric cable-stayed bridge, in his trademark white-painted steel, with a main span of 54m and a 41m tall inclined pylon. The 210 tonnes of structural steel were assembled by main contractor Dew Group, having been fabricated by Spanish steel specialist Urssa (who had experience on other Calatrava bridges).

The bridge's key feature is the cable geometry with a conventional arrangement on the main span paired with two hyperbolic crossed fans on the twin back spans, each of which curves away from the main bridge deck (see aerial photo on Google maps linked below). It's not the most efficient cable arrangement, but pure efficiency is of less relevance at this span, and the result is undoubtedly spectacular. The asymmetry is justified both by the general spatial constraints of the site, and by the marked level difference between the two river banks, which requires the bridge to rise up from west to east.

The pylon is tilted at 60°, and is attractively cigar-shaped (varying from 0.55m to 1.22m in diameter, and hence efficient at resisting buckling), and the 4m wide triangular box-girder deck profiled to appear more shallow than it really is. The little triangular fins where the main span cables attach to the deck are nicely done (although the attachments of the back-span cables are less visually successful). The pier below the pylon is also carefully shaped, and looks good in profile, although a bit more peculiar from close-at-hand.

The cables are anchored in recesses in the pylon, presumably to hide the cable anchorages and give a cleaner visual effect. I think it looks very good, although the downside is that maintenance of the anchorage has been made much harder.

Judging by the bridges already visited in this series, maintenance seems to be a big problem for Manchester's bridge authorities. It seems easy to find the funding to erect a monument, but harder to find the cash to look after it.

According to a report in the New Civil Engineer magazine, Salford City Council didn't even carry out a full Principal Inspection of the bridge until 2006, eleven years after construction (the normal interval would be 6 years), although admittedly the bridge was refurbished in 2002 (re-tensioning the cables and replacing end joints). The inspection in 2006 was prompted by corrosion appearing at end tie-downs and cable connections, although it's unclear if these relate to poor design detailing or a poorly applied protective paint system.

The NCE has used this as evidence that clients are using design competitions to select "complex, high maintenance" designs, but there's little about Trinity Footbridge which should make it much harder to maintain than any other cable-stay footbridge. Indeed, an extensive article they published on the subject in 2006 offers a set of more balanced points of view (including one from a designer opposed to "the Calatrava route" which makes for particularly ironic reading).

The bridge is now in reasonable condition, but there's still plenty of rust and grime visible at the back-span tie-downs. My photo of these also shows the awkward bearing arrangement, with its mixture of tie-downs, vertical and horizontal bearings indicating that the bridge relies on substantial restraint here.

Since the bridge was built, there seems to have been a limited spread of development radiating out from it into Salford, consisting of flats, offices and the Lowry Hotel, which overlooks the bridge. However, the development doesn't extend very far into Salford, presumably because unlike the Manchester side of the river, there's nothing else in the immediate vicinity to attract investment, no obvious hinterland.

The result has compromised the setting of the bridge, which seems caged in by tall surrounding buildings, also restricting what can be done to make the most of the open space around it. There's a walkway along the river to the north, but not to the south, and the area seems barely half-finished.

This detracts from the bridge, restricting views of it and making its scale seem more overly intrusive than may originally have been intended. Nonetheless, it's a spectacular structure, and in my one view, one of Calatrava's best designs.

Further information: