"Trutg dil Flem: Seven Bridges by Jürg Conzett" by Wilfried Dechau

There can be few contemporary bridge engineers who have been as well-celebrated in photographic coffee table tomes as the Swiss designer Jürg Conzett. Indeed, the only competitor in this arena is Santiago Calatrava, who is as inappropriate a comparator as could be found.

I think Trutg dil Flem: Seven Bridges by Jürg Conzett (Scheidegger and Spiess, 2014, 192pp) [amazon.co.uk] is the third book by photographer Wilfried Dechau to depict Conzett's bridges and the landscape in which they are set. I've previously reviewed Traversinersteg and Dorfbrücke Vals, both of which are excellent.

The Trutg dil Flem is a riverside pathway, along the River Flem north of Flims in south-eastern Switzerland. The pathway is a recent project, connecting up isolated and barely-walkable sections of path. This is only possible thanks to the construction of seven new pedestrian bridges, all designed by Jürg Conzett.

These are not especially spectacular structures, ranging in length from two to eighteen metres. They are only for use by visitors on foot, with the narrowest bridge being a mere 0.7m in width. Nor do they all exhibit the innovation for which Conzett is best known. Most are simple timber beam bridges, highly economic and suitable for the context, and in no way of particular architectural or engineering interest. They enable visitors to cross the stream, and also provide vantage points from which the surroundings can be better seen.

There are three bridges of greater interest. One is a tiny oval slab, with a bare handrail on one side only, originally conceived as a stone slab but built in concrete. It's so short as to barely be a bridge at all.

A second is a simple reinforced concrete beam, spanning 3.8m. The balustrades have cranked posts, projecting horizontally from the sides of the beam, then cranking vertically. This makes the concrete appear little more than a plank, and it looks great. It's also interesting how the balustrades continue off the bridge onto the approach staircases, which rise up the side slopes away from the bridge.

The third bridge is a very slender stone arch, almost a mirror image of Conzett's famous Punt da Suransuns. This was originally proposed as an 11m span, and drawn up as an arch of varying depth, thicker at the ends. The version eventually built spans 18m, and is equally slender over its entire length. This is made possible by using the lower rail of the stainless steel balustrade as a prestressing ribbon, pre-compressing the arch and enhancing its resistance to buckling failure. It's a marvellously ingenious solution, tremendously clever engineering in the service of minimalist beauty.

The book features a number of useful, if short, essays, in both German and English, including one by Conzett on the design of the arch bridge. His beautiful original drawings for each bridge are also included.

The bulk of the volume is taken up by Dechau's photographs, in two sections. The first documents the Trutg dil Flem and the completed bridges, giving priority to the landscape itself. It would clearly be a very attractive place to visit, and it's also clear that the bridges enhance the landscape, and are appropriate rather than showy.

The second section documents the construction of the bridges, and focuses as much on the builders as what was built. I found these a real pleasure to examine.

As with previous Dechau / Conzett books, Trutg dil Flem has been produced to a very high standard, it's a gorgeous book which well befits its subject.

See also:

• Jürg Conzett: Landscape and Structures
• Traversina Footbridge

"Dorfbrücke Vals" by Wilfried Dechau

The modern bridge designer is only rarely a solitary individual. Most designers, however personally creative they may be, are part of a team, and in the case of the largest bridges, a very large team indeed. This is an inevitable feature of the complexity of both the structures designed and of the process whereby design is conceived, refined, and detailed. One result is that many fine designers are effectively anonymous – it’s rare to be able to point to a bridge and to know who the lead designer was, and particularly rare to imagine that even if you did, you have identified someone who was the key driving force behind all aspects of the design activity.

This is perhaps one reason why the Swiss bridge designer Jürg Conzett is such a significant figure. He is the descendant of a remarkable line of Swiss bridge nobility, most notably Robert Maillart and Christian Menn, men who married clear aesthetic vision to a deep intuition for structural principles, and a pragmatic taste for craftsmanship. It would not be unfair on the rest of the modern bridge design community to note that Conzett is a bridge design genius. I am sure he would be the first to admit that the bridges credited to him are also the product of considerable teamwork, but they do give the strong impression of the hands-on involvement of an auteur at every stage.

The Pontist has been fortunate enough to visit two of Conzett’s best known bridges, the Punt da Suransuns, and the Traversinersteg, both in the company of the man himself. These are lightweight, high-tensile structures, exploiting the anchorage capabilities of Swiss mountain bedrock to create undoubted masterpieces. The second of these was considered sufficiently noteworthy to be the subject of a marvellous photo-book by the excellent German photographer Wilfried Dechau, documenting its seemingly perilous construction high over an Alpine ravine.

I have not had the pleasure of visiting Conzett’s more recent structures, which include a new highway bridge in the centre of Vals village, a place best known to architecture fans as home to Peter Zumthor’s thermal baths. Luckily, it too has been documented in another splendid Dechau photo-tome, Dorfbrücke Vals – Photographic Journal (Wilfried Dechau, Ernst Wasmuth Verlag, 144pp, 2010) [amazon.co.uk].

As with its Traversinersteg sibling, the book is a delight to hold, housed in a high quality slipcase and filled with marvellous photographs. These are accompanied by several illuminating essays. Klaus Siegele discusses the centrality of water to Vals, a village built on the banks of the Valser Rhine. As well as the thermal baths, the village is also known for its mineral water. However, it is the propensity of the river to flooding which led to a decision to replace the existing river span, a life-expired metal truss.

Patrick Hannay contributes an essay which manages to put the bridge in the context of other Conzett projects, of Swiss stone, and even of Tolkien’s bridge in the Moria caverns. Ursula Baus interviews the architect Zumthor , who chose the appearance of the flood walls and set the basic parameters for Conzett’s design – that the bridge should be an arch, and that it should use local Vals stone. Conzett himself discusses the bridge’s structural engineering, as well as that of two nearby footbridges, the Milchbrücke and the Rovanadabrücke, which formed part of the same project.

I will confess that I have a general understanding how the Dorfbrücke (“village bridge”) works structurally, but am not entirely sure I understand all the details. The deck is a reinforced concrete slab, spanning transversely between two concrete edge beams, which are post-tensioned. These form the tension member, or “bow”, in what must be the world’s least conventional bowstring arch bridge. The arch is formed of radially placed stone slabs, above the deck but resting directly upon it (there’s no gap between deck and arch, because these bridge side walls also serve to hold back floodwaters and prevent it from spilling it out onto the village roads). The deck is then hung from the stone arch by means of a series of concrete “fingers” which penetrate the stonework.

The result is a bridge of exceptional structural ingenuity, but not one which has immediate visual appeal. It is certainly not elegant, with the stone side walls towering above head height – there are no views of the river from it. It is a bridge as a confining corridor, rather than as a platform from which to admire its surroundings. It channels views towards the village church at one end.

Its visual appeal is not far from that of brutalism, the 1960s and 1970s architectural trend towards robust, unadorned concrete in stark, simple geometry. It is a blunt instrument, saved mainly by the attractions of the finely cut local stone, and the general sense of craftsmanship which is one of Conzett’s hallmarks. It won’t be remembered as his finest bridge, but it is as structurally remarkable as the others.

Dechau’s photographs depict the finished bridge, but concentrate for the main part on a record of its construction, including the demolition of the old bridge, and a number of photographs of the site workers and of curious onlookers. Several photographs range beyond the bridge to depict the mountain streams which feed the river, and a nearby dam, a towering concrete monolith.

Certainly, Dorfbrücke Vals – Photographic Journal is a book for collectors and connoisseurs only. The more casual reader may prefer to await a broader overview of Conzett's career. But it is a very well-matched companion to this otherwise inscrutable bridge, bringing to life the story of its construction, and I enjoyed it.

Links:

• Conzett, Bronzini, Gartmann AG
• Wilfried Dechau

"Landscape and Structures: A Personal Inventory of Jürg Conzett"

I'd been looking to get hold of this book since I narrowly missed out on visiting Jürg Conzett's Swiss pavilion at the Venice Biennale last year. "Landscape and Structures: A Personal Inventory of Jürg Conzett" (Scheidegger und Spiess, 272pp, ISBN 978-3858813213, 2010) [amazon.co.uk] presents a travelogue of civil engineering structures throughout Switzerland, drawn from a series of joint trips by Conzett and the photographer, Martin Linsi.

I managed to get a copy from buch.ch, and it's a delightful tome. Divided into chapters both geographically and chronologically (so the early chapters begin with a winter trip, and the final ones in early summer), a wide variety of structures are selected by Conzett for their ability to exemplify successful aesthetic outcomes from an engineering process. They are pretty much all highway, railway or footway structures, from all periods of history, and several examples are of the highways themselves rather than the walls and bridges that support them.

All the structures are photographed in black and white, and accompanied by text both in English and German where Conzett explains various points of interest. A bibliography gives details of further information where it is available. The photos are generally very good, and in several cases quite beautiful, often due to the landscape as much as the structure.

The bridges include everything from historic masonry arch and covered timber spans through to the most recent designs, including several of Conzett Bronzini and Gartmann's own structures. Of the better known structures, Robert Maillart's Salginatobel Bridge is conspicuous by its absence, but it is perhaps over-exposed anyway. The joy here is in the fresh perspective and the exposure of unseen delights.

Much of Conzett's emphasis is on vision and visibility, how a bridge offers a fresh perspective along its length, or how the curve of a road is not merely an exercise in checking sightlines but the opportunity to improve the driver's perspective upon the surrounding landscape. Looking at a seemingly minor retaining wall in the Graubünden, Conzett's attention is drawn to a low-level ledge which both improves driver visibility as well as reducing the apparent height of the wall.

Similarly, the sagging deck curve on Conzett's own Traversinersteg (pictured) is both a means of stiffening the bridge (it allows the deck to react against the prestressing of the support cables) and also a way of reducing the perceived steepness of the bridge's precipitous stairway. This concern for a design that synthesises structural, perceptual, and aesthetic demands, runs through the whole book.

Another welcome aspect is the attention given to designers who have, certainly in English-speaking countries, perhaps been overshadowed by others. Three lovely bridges by Alexandre Sarrasin are included, as is the spectacular Dala Gorge Bridge by Zumofen und Glenz.

My favourite bridge in the whole book is one of the newest, Conzett's Dorfbrücke in Vals, designed with Peter Zumthor. This is a work of purest genius which on first sight appears to be a concrete decked bridge supporting unusual masonry parapets, but in reality is a masonry arch from which a concrete slab is hung, the slab also acting as the arch tie. The engineering is ingenious, but it's the bridge's juxtaposition of brute minimalism and tactile appeal that is most admirable.

This is a very unusual book. It seems at first to be too unstructured a travelogue to hold its appeal, but the combination of excellent photography with Conzett's consistently impeccable judgements makes for a very enjoyable read.

Further information:
Jürg Conzett: engineering matters - an interview about the book

"Traversinersteg" by Wilfried Dechau

One of the great footbridges of modern times was Jürg Conzett's first Traversina Footbridge, a delightful filigree timber-and-cable design that was built in Switzerland in 1996 and then sadly destroyed by a rockfall in March 1999. Luckily for pontists everywhere, it was replaced in 2005 by an equally impressive structure, also designed by Conzett. The second Traversina Footbridge is a highly unusual timber-and-steel suspension bridge, which, like its predecessor, perches high above a precipitous gorge.

I visited the bridge last November, and noted that the span was a tribute not just to its remarkable designer but also to the people who built it in such a difficult setting. The bridge's dedicated website includes many excellent photos of the construction process, and the people involved, as well as descriptions of the bridge in German (there are more construction photos online elsewhere).

I only recently discovered that there's an entire book devoted to this bridge, "Traversinersteg" (ISBN 3-8030-0662-7, Ernst Wasmuth Verlag, 2006) [Amazon UK], by the photographer Wilfried Dechau. He was also the photographer for Mike Schlaich and Ursula Baus's excellent volume, "Footbridges", which I reviewed here last year. And having just received a copy of the "Traversinersteg" book, I have to say that it's well worth getting hold of.

The photos on the website are nice, but nowhere near as attractive as when reproduced at larger scale in this gorgeously designed, large-format (27.8cm by 38.2cm), slipcased tome (Amazon has images of some of the pages).

The establishing images of the spectacular location in the Via Mala valley set the scene. The building of this bridge was at once acrobatic and heroic, and also intimate and craftsmanlike. Construction of the foundations required concrete and materials to be lifted up the hillside on an aerial ropeway suspended from trees, and the bridge span itself involved a team of specialist climbers.

The photos clearly show this range of emphasis - construction workers suspended in harnesses over the abyss, as well as close-ups of hands tightening bolted assemblies. There are several portrait images, showing a range of people involved in the scheme, not only the designers but also the workers who are so seldom credited in the creation of landmark structures. I believe one of Dechau's main concerns was to depart from the conventions of architectural photography, which fetishise the object and largely discount human involvement. If so, he has succeeded admirably.

Many of the photos are reproduced at full page size (or to fill a two-page spread), which really does them justice. Use of colour is sparing but effective. My favourites tend to be the photos that are most vertiginous, that capture what is unique about the bridge and its setting.

The book also includes short texts by Jörg Schlaich, Ursula Baus and others. Schlaich makes the point that "watching [the bridge] being built is often more interesting than admiring the finished structure", but I'd suggest the Traversinersteg is a rare case where the bridge is as impressive as its making. Schlaich and Baus both note that the bridge was built without scaffolding, that the materials required to build it mostly form part of the final structure, even to the extent of using timber from trees cut down to make space for the aerial ropeway.

There are relatively few bridges which merit a lavish book to themselves, but this is undoubtedly one. It's also a rare book where the design and imagery is as impressive as the structure it decribes. It's not going to be casual purchase for anyone, but I'm delighted with it.

Swiss Bridges: 7. Traversina Footbridge

From the Pùnt da Suransuns, we walked to our final bridge of the day, and our final bridge of the study tour. Built in 2005, the second Traversina Footbridge is another design by Jürg Conzett, and replaced his previous structure on the site (you guessed it, the first Traversina Footbridge), which had been destroyed by a falling boulder.

One thing that's impressive about Conzett is his ability to apply equal levels of ingenuity and imagination to the design of very disparate structural forms: in addition to those at Via Mala, his Coupurebrug in Belgium is another unusual example. While at first sight the second Traversina Footbridge looks like a relatively conventional suspension bridge, it turns out to be far from conventional and probably unique.

Spanning 56m across a 70m deep gorge, the levels of the hiking trail on each side are very different, and as a result the bridge is a staircase which increases in steepness towards one end. The deck and handrail are a mixture of steel and timber elements, hung from two suspension cables with a truss-like arrangement of hangers. The main suspension cables hang from abutments which are at essentially the same height, with the result that the hangers are short at the upper end of the staircase, and progressively longer towards the lower end.

The geometry and cable forces were derived using that quintessentially Swiss technique, graphic statics, specifically a Cremona diagram. Where many engineers would plunge in with the latest non-linear form-finding software, Conzett gets out a pencil and graph paper and harks back to the methods of a century ago. The trussed hangers make the structure far stiffer than a normal suspension bridge, and in practice it barely sways at all in use.

I've given links below to a couple of websites that have photos of the bridge construction, and these are well worth a look. Building a bridge above a gorge where the only access routes are steep, narrow mountain paths, is quite a challenge. As several people on the study tour noted, the people who work out how to build a bridge are often the unsung heroes of any project. All the five Maillart arches we saw relied heavily on the falsework designer to bridge the gap first, and the erection engineering at Sunniberg would have been a major design package in its own right.

To build Traversina, a specialist firm installed a "cable crane", essentially a travelling crane running on cables strung between the trees. This allowed materials and most importantly the concrete for the abutments to be brought up from much further down the hillside. The cable network and deck panels could then be assembled in mid-air using a helicopter and roped-access specialists. It's quite a feat in a place like this.

The bridge that results is magnificent but also highly peculiar. This was pretty much the only bridge we saw where I got vertigo just crossing it, let alone leaning over the side. I think this was a combination of the precipitous location and the fact that it's a staircase - you never really feel you're on a level platform, and it's mildly disorienting.

It was getting quite late by now, and much of the return journey down the hillside was in near darkness. Looking back across the Via Mala gorge, I could only just make out the bridge, a pale grey ghost amongst dark grey shadows. It did seem afterwards like something out of a dream, the genius loci returning to its home in the spirit world.

Further information:

• entry at structurae
• location on Google Maps
• Traversina Steg II website (includes concept sketches, drawings, construction photos, publications etc, in German)
• Via Spluga (Italian & German only)
• information at Kulturraum Viamala
• construction photos at Kulturraum Viamala
• Mike Schlaich and Ursula Baus's Footbridges (German edition, also available in English)

Swiss Bridges: 6. Pùnt da Suransuns

Throughout our second day of the bridge study tour, we were accompanied by Jürg Conzett. In the afternoon, we visited two of his bridges, both part of the Via Spluga hiking trail in Via Mala gorge near Thusis.

The gorge itself is absolutely stunning. At several points, you can look 80m down and struggle to see the water below in a dark crevice as little as 1m wide. And looking up there are tall cliffs for another 100m or more. Where it widens out, it's crossed by bridges including Christian Menn's Great Viamala Bridge.

We walked only a relatively short length of the hiking trail, under the Menn bridge to first see the Pùnt da Suransuns, a remarkable stressed ribbon footbridge spanning 40m across the river. I'm not entirely a fan of the stressed ribbon bridge - while they can be beautifully slender structures, the way they droop often looks unhappy - see the Maldonado Bridge in Uruguay for an example of this. They rarely meet the engineering or administrative constraints of most sites - the sag leads to slopes greater than are desirable for many users, and for the same reason they don't work where there is limited headroom below (which is the case for most footbridges). They are also almost never the most economic solution, with the costs of expensive foundation anchorages far outweighing the material savings to be made in the main bridge deck.

Suransuns, however, is a perfect example of just how a stressed ribbon bridge can work well. The river valley sides have plenty of stable rock, required for an efficient anchorage design, and the setting demands as minimal an intervention as possible. And Suransuns must be amongst the most minimal of stressed ribbon bridges you could get.

The bridge comprises granite planks, 60mm thick, 250mm wide, and 1100mm long, which sit directly on stainless steel strips only 15mm thick, and are held apart by 3mm thick aluminium inserts. That's basically the entire structural system of the bridge, and it is beautifully complemented by ultra-minimal steel handrails supported on 16mm diameter vertical rods.

Clearly, the location allowed Conzett to break many of the rules which normally bind footbridge design: minimum widths; maximum gradients; strength of parapets; susceptibility to vibration. However, it's the way he responded to some of the challenges of stressed ribbon design which was particularly impressive. Bending of the deck slab at its support abutments is a key consideration in design, which Conzett dealt with using a seemingly simple "leaf-spring" arrangement, just using more of the main stainless steel strips locally.

The elegance of the bridge's minimal silhouette is matched by the simplicity of the engineering, and for me, this was one of the best bridges we saw. Conzett, Bronzini and Gartmann are designing a very similar bridge (albeit multi-span) at Gemeinde Windisch, and it will be interesting to see how it compares.

Further information:

• entry at structurae
• location on Google Maps (satellite photo predates bridge construction!)
• Pùnt da Suransuns Pedestrian Bridge, Switzerland (paper in Structural Engineering International, 2000/2)
• Via Spluga (Italian & German only)
• Matthew Well's book 30 Bridges
• Mike Schlaich and Ursula Baus's book Footbridges (link is to German edition, also available in English)