Danube bridge competition winner announced

Marc Mimram has beaten seven other teams to design a new €60m highway and tram bridge over the Danube in Linz, Austria. The other competitors included heavyweights such as Leonhardt Andra, Flint and Neill, Knight Architects, Dietmar Feichtinger and Dissing + Weitling.

It's a big bridge, some 30m and 400m long in total, and it's perhaps surprising to see a winner which is an essentially entirely new type of bridge. Essentially, it's a steel cantilever bridge along the lines of the Forth Railway Bridge, but with a number of unusual features.

The cantilever trusses are curved rather than comprised of straight pieces, requiring significant quantities of additional steel to resist the local bending induced in the steelwork. Very limited support is provided to the deck, which therefore has to be excessively deep.

The oddest feature, however, is the fact that the cantilevers sit on single lines of bearings, so that under uneven loading, the only stability is provided by the connection between adjacent cantilevers. Those short connection pieces don't really look stiff enough to provide that stability, and I wonder quite how the engineer has persuaded the design to work.

Of the other designs, the 4th prize entry is the most ambitious, with what appears to be a 250m span network arch bridge (just shy of the existing longest span of this type), a very challenging and complex structure to build.

Winner - Marc Mimram

2nd Prize - Öhlinger+Partner ZT GesmbH, Ponting Consulting Engineers and Zeininger Architects

3rd Prize - Gruppe VCE Vienna Consulting Engineers ZT GmbH, FCP Fritsch, Chiari&Partner ZT GmbH and Quist Wintermans Architects

4th Prize -  SSF Ingenieure AG, ISP ZT GmbH and Knights Architects

Footbridge 2011: papers roundup pt 2

I've had time to jot down a few more comments on the papers presented at Footbridge 2011. Again, this is a highly selective bunch, there were many others which were interesting but which I simply won't have time to cover.

The Arganzuela helicoidal bridge over the Manzanares River, designed by MC2 Engineering Cosultants with Dominique Perrault Architecture, belongs to the increasingly popular genre of helical truss bridges, a genre I have surveyed previously. There are plenty of images online, but I've just chosen one from the conference paper.

It's actually two separate bridges, with a total length of 278m. Each is in the form of a cone, varying in diameter from 6m to 12m, and structurally they are helical trusses, with straight upper and lower chords intersected with spiral diagonals, taking the general form of a through Warren truss. This is pretty much as rational as this helical form ever gets, but as the authors noted, it still imposes significant secondary stresses on the steelwork, requiring substantially more material than would the more conventional solution.

I've included it here because while I have my doubts about the conic geometry (attractive in the widening direction, but visually constricting in the other direction), this is one of the best of its genre. This is largely, I think, because of the cladding treatment, which with its varying densities of mesh, distracts from the structural frame and uses its apparent solidity to create an object with a greater sculptural weight.

I enjoyed Andreas Keil's presentation, Passerelle sur Nanterre - spatial play of forces, on the La Defense footbridge designed jointly by Schlaich Bergermann und Partner and Deitmar Feichtinger Architectes. This is a remarkable 88m long bridge which passes around the perimeter of a curved building, without touching it, and with supports only towards the ends. This is a challenge in itself, but the choice was made to support it on only one edge using the "inverted Fink truss" typology (a system which has only limited resemblance to a genuine Fink truss).

The result is a truly superlative example of high-tech structural engineering. The main vertical support comes from the truss, which is essentially a series of successively cantilevering cable-stays. The number of cables in each bay of the truss are varied according to their order in the cantilever i.e. the number of cables used is proportional to the force to be carried. This system is assisted by a set of ring-cables offset below the deck level, which are cranked back up to deck level at the ends and hence carry a share of the vertical load in a manner similar to an external prestressing tendon. This also reduces the possibility of uplift forces on the bridge's end bearings.

The deck is a hollow steel box, providing some of the much needed torsional stiffness. However, this is far from sufficient on its own, and the lower ring-cables provide the remaining torsional restraint. The vector sum of their forces at each mast position imparts a net inwards force, which, because of its level, acts to counterbalance the torsion resulting from the deck dead and live loads only being supported on one edge. For some reason, the bridge as a whole reminds me of a set of gimbals, as in a gyroscope, possibly because of the way the whole ensemble appears to teeter on only a few pin-point supports.

It's a remarkable bridge.

Another bridge which impressed me was Link 27 - a new footbridge in the west of Vienna, Austria, presented by Rudolf Branstötter. This 38m span bridge was completed on site in September 2010, and was the end result of a student design contest which Branstötter had won. I thought this was an exceptional structure, where the structural form, although unusual, was a carefully thought-through response to the site's very specific constraints.

It spans over both a railway line and the River Wien. The different permissible clearances led to a structural form which has a low level springing on the river bank, and which is supported over the railway from above. One end resembles a concrete arch, while the other is a concrete cantilever, with fixity provided by steel tie-down bars. However, both aspects appear fully integrated. The method of construction was also unusual, with both edge girders precast on site, lying on their side, before being rotated and lifted into place.

Bridge museum in Austria

Some of my American readers may be familiar with the Calhoun County Bridge Park in Michigan, a presumably unique collection of six historic bridges in a parkland setting. Sure, there are parks with more bridges, but none quite so dedicated to the subject.

As a destination for overly enthusiastic bridge-lovers, it has now clearly been beaten by the creation in Edelsback, Austria, of a back-garden exhibit dedicated to bridges, both full-size and in Legoland-style models. Hundreds of them, apparently.

Renate Theissi, 39, who has apparently sunk £70,000 of life savings into the exhibit, comes in for quite a bit of stick at The Sun (never a newspaper afraid to stoop too low in its coverage of a story), who quote her as saying:

"I've never wasted my time with men or romance or anything like that. I'd much rather have an old timber framework bridge than a man. When my girlfriends played with dolls, I built my first bridge model. I read books about bridge construction until late in the night and constructed my bridges."

Renate reportedly has a collection of 4,000 books on bridges, and sleeps on a bed shaped like a bridge (just in case anyone is wondering, the Happy Pontist can't boast either of these things). The story is reported elsewhere on the internet with a little more sympathy, and as with anything reported in The Sun, I'd treat some of their claims with an extra-large pinch of salt.

I've tried without success to find a website for this splendid little Brückenmuseum, or contact details for Ms Theissi, but if anyone can assist, let me know.


Updated 12 July: I'm grateful to the reader who has given me links to the Brückenmuseum website, also to other sites with further information.

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.