"Christian Menn: Bridges"

I recently reviewed Philip Jodidio's Calatrava: The Complete Works, a shallow but brain-poundingly flashy review of the Spanish engineer / architect's grandiloquent oeuvre. Now here's a similarly weighty coffee-table recap of Swiss engineer Christian Menn's career. How do they compare?

Christian Menn: Bridges (Scheidegger and Spiess, 2015, 350pp) [amazon.co.uk] is in matching German and English throughout, so a good chance to find out more about the man who is generally recognised as one of Switzerland's finest bridge designers. The previous monograph, Christian Menn - Brückenbauer (2007) was in German only.

The book covers pretty much all of Menn's significant designs, interspersed with various essays, an interview, and tail-ended with a short biography, list of works and the like.

Menn explains his own philosophy of bridge design, which is also a philosophy of bridge procurement, with some thoughts on design competitions and design standards. For Menn, bridge design must be led by engineers, as structures must satisfy all applicable standards and be economical as well as beautiful. His view is that design is the art of achieving an appropriate balance, with economy and aesthetics apparently incompatible, but to some extent reconciled in the choice if appropriate structural form.

I've discussed Menn's philosophy in detail on a previous occasion, so won't repeat that here.

Menn's signature bridge design was the concrete arch, especially in its deck-stiffened guise as pioneered by Robert Maillart. The first project in this book is the magnificent 72.5m span Crestawald Bridge, and there are many more similar examples. They have been beautifully photographed by Ralph Feiner (all the photos I've used here are by Feiner), and generous space is given over to these images, as well as technical diagrams for each bridge in plan, elevation and cross-section.

With the exception of the Crestawald arch, most of Menn's bridges of this type use a polygonal arch, the engineer's rational alternative to a pure curve. The bridges therefore have a Germanic austerity to them which generally sits well within the mountainous Swiss landscape. I particularly admire the way in which they rely on the strength and purity of their structural form: the concrete finishes are sometimes poor and the detailing negligible, but that's simply not what they are about.

Menn has also been responsible for a number of admirable post-tensioned concrete box girder designs, again most notable for their simplicity and clarity of intent - no fussy cross-sections or pier sculpting, they rely on their visual directness for effect.

After a while, it's hard not to feel bludgeoned by repetition - most of Menn's career has been distinguished by monotony, and a number of basically very similar bridges are presented in perhaps more depth than is merited.

I also occasionally find myself doubting his aesthetic judgements. He is highly self-critical, an admirable trait, but is he always right in his view of his own work? He complains that the twin-legged piers of the Felsenau Bridge would have been better as single legs, but I find this hard to credit, as this is a very high quality bridge as built.

In the later years of his career, Menn's work was sometimes uneven. I greatly admire the elegant cable-stayed Sunniberg Bridge but find the Ganter Bridge to be over-rated in the extreme, with its stiff rectangular piers and their clumsy connection to concrete fins in which its support stays are embedded.

The Leonard P. Zakim Bunker Hill Memorial Bridge in Boston, USA, is for the most part a fine design, but it is cursed with a gargantuan 56m wide deck and I can't help wondering whether it would have been better as two smaller, parallel bridges.

Similarly, some of Menn's unbuilt designs in the middle-East show significant departures from the clarity of his earlier work. The pylon for the cable-stayed Al Showah Island Bridge consists of a spindle braced by concrete fins, and seems over-wrought, as does an arch design for the same scheme, where the rise of the arch is much greater than structurally necessary.

Setting all that aside, this is an excellent and well-produced book, and overall Menn's oeuvre certainly deserves this degree of attention. The details of his individual designs are not necessarily something to emulate, but this is largely because few readers will be designing works for the Swiss landscape, and most will be working in forms other than solely reinforced and prestressed concrete. What stays with me the most is his disciplined approach in finding the most appropriate structural form, and in then keeping it simple and unembellished. From experience, that's nowhere near as easy as it sounds, and something that few have achieved as successfully and consistently as Christian Menn.

"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

Swiss timber bridges

I'm preparing various new posts, but while that happens, I thought I'd post a link to a great website I stumbled across: Swiss timber bridges. Written by Werner Minder, this is a catalogue of some 1,481 timber spans in Switzerland, with plenty of pictures.

Unsurprisingly the website majors on covered wooden bridges, some 520 of them, but has space for structures as varied as suspension bridges, timber falsework, and even a tiny bridge for rabbits. It's the kind of detail-obsessed labour-of-love that I love finding on the internet.

"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

I'll huff and I'll puff and I'll blow your bridge up

New Civil Engineer reports that Swiss architects have created an inflatable bridge. Philipp Dohmen and Oscar Zieta have built a 6m long steel-skin balloon that can hold a load of up to 1800kg, according to load test at the Swiss ETH institute.

It's all very exciting, but not really news as such - the ETH's department of Computer Aided Architectural Design (CAAD) has been working on this system for some time, with their so-called FIDU-Brücke having been load-tested in December 2007 (FIDU stands for FreieInnenDruckUmformung, or internal pressure forming). Essentially, it's a prestressed steel shell structure, where the internal pressure prestresses the skin (maintaining it in tension even when subject to applied compressive stress) and hence prevents it from buckling, even in the absence of stiffeners.

Although Zieta's website shows lots of clever applications in product design, including furniture, it's hard to see how any inflatable structure can be robust enough to act as a real bridge, with the danger that any escape of air (e.g. due to failure of a seam or accidental puncture) would immediately eliminate all the structural resistance. The advantages, of course, include the extremely light weight of the structure, which also allows it to be readily deployable in difficult locations.

Nor is ETH-CAAD the first to develop an inflatable bridge.

The US Army has a deployable air-inflated system which can carry military vehicles weighing as much as 80 tons. This however, is really a causeway system rather than a bridge as such: unlike the FIDU-Brücke, it isn't subject to bending.

The University of Maine has also used inflatable plastic arches in bridge construction, although these are filled with concrete after inflation.

More pertinently, the "tensairity" system promoted by Airlight has been proposed for a number of bridges, and applied to some. I wrote about this previously because an Airlight bridge was one of the entries to the Leamouth Bridge Design Competition (pictured left).

The tensairity system uses inflatable plastic beams shaped a little like cigars. These are inflated under relatively low pressure, and the system relies on the use of struts and cables fixed to the inflatable membrane to carry most of the load: the balloon only carries shear and compression between these, and stabilises the whole system against buckling.

An 8m span test bridge was built and shown to be capable of carrying a 3500kg test load [PDF], easily putting the Dohmen / Zieta span in the shade, and with a structure lighter in weight as well. Unlike the metal-skin solution, a further advantage of the Tensairity beams is their translucency, allowing them to be lit internally for architectural effect.

The Airlight website illustrates a number of projects for which tensairity beam bridges have been proposed, but not built. As well as Leamouth, these include footbridges in France and Switzerland, such as the one at Giubiasco shown on the right. They have also been proposed for temporary use to support construction vehicles.

The most significant bridge to be completed is at Val Cenis ski resort in France, a 52m footbridge for skiers (also carrying substantial snow load) - pictured below. This is essentially a timber frame bridge with steel bars providing the suspension cable below - the two elements are separated by the Airlight balloons which hold the main structural pieces in place. It was designed by Charpente Concept, who provide further details of the design and construction on their website.

See also:

• Student tensairity bridge project at ETH
• Greenline blog discusses the tensairity Tubaloon

"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.

"Vom Holzsteg zum Weltmonument" by Andreas Kessler

A mere two months after visiting the amazing Salginatobel Bridge itself, I was delighted to get a book on it for Christmas: "Vom Holzsteg zum Weltmonument - Die Geschichte der Salginatobelbrücke" (ISBN 3 9520963 1 8, Verlag AG Buchdruckerei Schiers, 1996) [order from the author]. The title roughly translates as "From the boardwalk to the World Monument - The history of Salginatobel Bridge".

It's not the easiest book to get hold of. The Prättigauerhof hotel in Schiers didn't have any copies when I visited, and the local publisher communicates only in German. My copy was purchased directly from the author - follow the link above to email Mr Kessler. It can be paid for either with international bank transfer (expensive) or simply by posting cash. It's definitely best to email first as postage rates may vary and I don't know how many copies he has left.

If ever there were a labour of love, this 232-page book is it. The village of Schiers has a population of roughly 2500, yet this locally-published book is nonetheless an unexpectedly lavish tribute to one of the world's greatest bridges. To my knowledge, it's the only book devoted entirely to this very singular structure.

The book is in ten chapters, mostly written by Andreas Kessler, but with contributions from Jürg Conzett, Duri Prader (son of the bridge's builder, Florian Prader), and others. There is also an extensive bibliography, several pages of the original bridge design calculations, and three fold-out construction drawings showing the general arrangement of the bridge, the concrete reinforcement, and the timber falsework.

The book explains the difficult site on which Salginatobel Bridge was built - a deep ravine between the small village of Schiers and the tiny hamlet of Schuders. Before the bridge was built at high level, a number of low-level crossings of the Salgina existed, generally of timber, prone to flood damage, and providing access only to a steep path leading up to Schuders.

The book discusses the key figures reponsible for the design and construction of the bridge: Robert Maillart, the structural engineer (pictured); Richard Coray, who designed the falsework; Peter Lorenz, the district engineer; and Florian Prader, the contractor. Jürg Conzett explains the state of the art in arch bridge design at the time, and compares Maillart's various designs both built and unbuilt from the Stauffacher bridge of 1899 to the Lachen bridge of 1940, with the help of an excellent scale drawing showing them all. While the Salginatobel bridge is one of Maillart's most spectacular achievements, he proposed far greater arch bridges at Schaffhausen, Bern and elsewhere.

The book covers various proposals for a new Salgina crossing from 1914 onwards, including a suspension bridge design proposed by Richard Coray. Eventually, a competition was held to obtain design-and-build proposals, with Prader & Cie's tender (designed by Maillart) proving to be the least-cost design. The construction of the bridge during 1929 and 1930 is documented in detail, including a series of photographs which show the difficult cantilevering construction of the falsework very clearly. In the steep rocky terrain, the timber centering (pictured, in model form!) was a major achievement in its own right.

The book goes on to address the bridge's history since it was opened, including the period in the second world war when plans were made to install explosive charges for the bridge's possible destruction. There is also an extensive chapter discussing the bridge's growing reputation as a work of art or historical importance, citing the writings of architecture critic Siegfried Giedion in the 1930s, Max Bill's book on Maillart in 1949, the substantial writings of David Billington, and many less well known authors.

The bridge's award in 1991 of the status of an International Historic Civil Engineering Landmark by the ASCE (American Society of Civil Engineers) is also covered, including descriptions of the other IHCELs declared up to 1995.

Throughout, the text is supported by excellent black-and-white photographs and diagrams, many unavailable readily in print elsewhere, making this book a very fitting tribute to a marvellous bridge.

The only problem, for me at least, is that it's all in German, which I can't read. So I must apologise that I can't comment in detail on the text at all! Even with this somewhat major handicap, it looks to me to be an excellent book, with high production values and a welcome thoroughness. Expect a fresh review if my German is ever up to it!

Swiss Bridges: Epilogue

So that was that, the end of the IABSE Study Tour in Switzerland, and very much back down to earth afterwards.

One of the main things I took away from the trip was how much can be achieved by engineers when they are confident in their creativity, skilled in their art, and (relatively) unimpeded by bureaucracy. Few if any of the bridges we saw had the involvement of an architect, or if one was involved, the structural engineering was central to the design process. Much of this is down to the challenges set by the remarkable Swiss landscape rather than anything else: the engineering absolutely has to take precedence.

That most of these bridges are also aesthetically successful is far from a foregone conclusion. Several of Robert Maillart's bridges are visually clumsy (including one that we visited, Traubach Bridge). These bridges are masterpieces because of the deep involvement and care lavished upon them by their designers. I think bridge designers anywhere can learn what can be achieved when they have a strong vision and can minimise the need for compromise.

David Billington has suggested that all engineers should consider making a pilgrimage to the Salginatobel Bridge. Before this trip I'd have dismissed that as daft idealism, but now I'd quite happily go along with it. There's plenty to learn technically from structurally challenging historic bridges such as these, but more important is what they offer in both inspiration and aspiration.

I know I'm already looking forward to the next study tour!

While in Epilogue mode, can I take the opportunity to ask for more feedback from anyone reading this blog? I'd be keen to hear comments on the bridges, opinions, news or anything else; it would be good to know that someone is reading, and I'm particularly open to discussion, debate or even dispute!

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)

Swiss Bridges: 5. Sunniberg Bridge

From Salginatobel, we drove south towards Klosters and by far the biggest bridge on the study tour. Christian Menn's Sunniberg Bridge is, to my mind, his finest work, and since its completion in 1998, it has been a major landmark in the Landquart River valley.

The bridge is part of the Klosters bypass scheme, but at CHF 17m, its cost is dwarfed by the CHF 345m cost of the 4km long Gotschna Tunnel, which the highway enters at the south end of the bridge. Nonetheless, the bridge design was (rightly) chosen in place of a cheaper box-girder option because of the environmental sensitivity of the landscape.

Bizarrely, the bridge was opened seven years after completion, in 2005, by Prince Charles, that notorious foe of modern architecture. Prior to opening, the bridge had provided the construction access for the tunnel works. I find it hard to imagine the opening ceremony: "Yes, one is proud to open this monstrous carbuncle if it makes it ten minutes quicker to get to one's skiing holiday."

Approaching the bridge from the south, we drove down towards it from higher in the valley. From here, the bridge looked small, minimal, barely present in the landscape. It was only once we approached it from ground level that its scale became apparent. 526m long, 12m wide, with a longest span of 140m, and pylons up to 77m above ground level, it's a bridge on the heroic scale.

Menn's adoption of the extradosed bridge form allows the deck to be more slender than in a conventional box girder bridge (because it's supported by cables from above), while the overall bridge doesn't compete unduly with the mountain landscape (because the cables are at a much shallower angle than a conventional cable-stayed bridge). The extradosed bridge is really a special case of a post-tensioned bridge, where the cables are lifted out of the deck to allow the overall bridge deck to carry higher bending moments and shear forces at pier positions. Essentially, it's more complex and expensive than a post-tensioned bridge, but less efficient than a normal cable-stayed bridge. But when done well, it can certainly look very impressive indeed.

The bridge was designed without any expansion joints, which means that under temperature variations, the deck "breathes" in plan i.e. sways sideways. The piers are designed with relatively slender bases to be flexible enough to withstand this movement, and along with the need to maintain highway headrooms, this leads to their distinctive and elegant Y-shape. Everything about the piers and pylons is well thought out - their gentle curves, echoing the tall trees nearby; the way the bridge deck nestles between their arms; their continuity (many cable-stayed bridge have very different pylon forms above and below deck); the clever way the massive steel cable anchorages are hidden within them; and their delicate but robust proportioning.

Unfortunately, we spent so much time tramping around admiring the bridge from below, that we had no time to stop at deck level. However, a pretty good idea of the appearance can be found from this advertising poster, which I spotted when arriving at Zurich airport. Good to see the Swiss pride in this monument to engineering heroism.

Later in the day, we'd see one of Menn's concrete arch bridges at Viamala gorge, but it wasn't really flattered by the viewpoint, and certainly didn't compare well to Sunniberg. Sunniberg Bridge is a proper engineer's bridge - all the key elements of the design have a sound technical rationale, but the combination of choices made and the way they are each worked out is absolutely exquisite.



Further information:

• entry at structurae
• entry at wikipedia
• location on Google Maps (satellite photo predates bridge construction!)
• information posters for Klosters bypass (in German)
• project newsletters (see number 17 for the alternative design options; see number 33 for bridge design & construction details)
• Sunniberg Bridge, Klosters, Switzerland (paper in SEI by Menn et al)
• analysis of the Sunniberg bridge (student paper, PDF)
• Matthew Wells's book 30 Bridges
• David Billington's book The Art of Structural Design - A Swiss Legacy

Swiss Bridges: 4. Salginatobel Bridge

The first day of the IABSE study tour had been pretty marvellous - great scenery, great bridges, great company. But it was very much run into second place compared to the excitements of the second day.

As with the first day, there was plenty to see from the coach to indicate that the Swiss have engineering accomplishments to be proud of. Driving from Zurich to Schiers, we passed below the 1965 Bircherweid stressed ribbon footbridge designed by René Walther, for example. Driving from Schiers towards Klosters, we stopped at a reinforced concrete vierendeel truss bridge (apparently the only one of its type in the country) for a quick look. And of course the Alps are riddled with spectacular road tunnels, avalanche shelters, funicular railways etc.

The first stop of the day, Robert Maillart's Salginatobel Bridge, was the only structure in the entire trip to be properly signposted, with brown tourist signs (Rossgraben did have some less visible signs, and both it and Schwandbach have tourist information boards). It was also the only bridge that seemed to have an entire cafe dedicated to visiting pontists: the Prättigauerhof in Schiers. You can stay overnight, eat pizza, drink coffee in this 1627 building.

Or just admire the various artefacts on display. Tourists stopping off en route to the bridge can examine detailed construction drawings, a model of the formwork, souvenir lumps of concrete taken from the bridge (presumably during its refurbishment), and inspect an original section of the bridge parapet. Sadly the Prättigauerhof didn't have any copies of Andreas Kessler's locally published book Vom Holzsteg zum Weltmonument - Die Geschichte der Salginatobelbrücke, let alone any souvenir t-shirts. I had to settle for a postcard.

Writing about the Salginatobel Bridge when it was presented with an International Historic Civil Engineering Landmark plaque in August 1991, David Billington said:

"Such structures remind us that in this fragmented world, a highly rational, deeply educated engineer can integrate utility and beauty and bring into being objects to which all engineers must make at least one pilgrimage in their lifetimes." (Structural Engineering International 4/91)

So: a marvellous mecca for engineers, or just a nice lump of concrete neatly set off by the lovely landscape?

It took some time to get around Salginatobel Bridge. For one thing, there were plenty of places to view and photograph it from - on top, underneath, from the road at one end, and from a viewing platform at the other end. But no amount of rushing around could distract from a palpable sense of awe that grew the longer I stayed there. Billington is right: this was an almost religious experience, which caught me quite by surprise.

The design of Salginatobel bridge is undoubtedly excellent (although not quite perfect - see below). And the setting, 90m above the bottom of a deep valley, with forest to one side and gnarled rock to the other, is magnificent. Photos struggle to do justice to its promethean splendour - you have to be there with the mountains to all sides to really understand how great this bridge is. Many photos of the bridge nestling amongst the forested hillsides fail to give any idea of its scale - it's a big bridge in this context, making it even more remarkable how good it looks.

It's a great example of how the introduction of a bridge can transform relatively ordinary scenery. Sure, it's grand scenery, but there are far more spectacular gorges and mountains throughout the rest of Switzerland. Without the bridge, this would just be one of many pretty mountain valleys. Salginatobelbrücke literally makes concrete the pervading spirit, the genius loci, of this particular valley, as if rocks layed down a hundred million years ago had just been waiting patiently for a bridge to one day vault majestically outwards.

Like many great bridges, what you can see is only half the true story. Excellence in bridge design is as much about how a bridge will be built as how it will look. Without Richard Coray's audacious timber centering, the 90m span of Salginatobel Bridge could never have been built. In 1930, Maillart won the job because his was the most economic solution, and it's unfortunate that this would no longer be the case. Now, a prestressed concrete structure or welded steel bridge would be much cheaper, and both lead to structural forms suited to factory production or repetitive site assembly, certainly not an arch requiring major temporary works. A bridge like this is unlikely ever to be built again.

So where are its flaws? The masonry abutments certainly detract, and the solid concrete parapets give a heavier appearance than at Rossgraben (but not terribly so). However, I think it would be quite frightening standing on Salginatobel and looking down 90m if the parapets were only of the post-and-rail type (it's okay less disconcerting at Rossgraben because the drop is only about 12m).

Of course, although the arch shape looks like it has been precision-engineered to match the bending moment diagram for a three-hinged arch (see diagrams linked below), it's the perfect shape just for one very specific (and unlikely) arrangement of loads. Robert Maillart realised this and changed the shape of his later three-hinged arch bridges, but the less logical shape at Salginatobel undoubtedly looks more beautiful.

As at Rossgraben, if you look along the arch at an acute angle, there seems to be a reverse curve towards the springings, an illusion created by the way the arch widens at its ends.

The original bridge design also dates from a time before concrete's long-term durability was well understood - there was no waterproofing, minimal cover to reinforcement, poor quality concrete and inadequate drainage. These were all put right with repairs in 1975/76 and a US$1.3m refurbishment completed in 1998, including complete replacement of the parapets (which is why there's a section of parapet outside the Prättigauerhof). The engineers did a remarkable job on the repairs, blasting off and then shotcreting most of the concrete surface. Unusually, formwork boards were then applied to the shotcrete to reinstate the original appearance.

The flaws are pretty irrelevant. It's as much the glorious setting as the bridge itself, but Salginatobel Bridge remains Maillart's masterpiece, a truly singular sculpture in reinforced concrete that must rarely, if ever, have been equalled. We had a busy day ahead and were already running late, but it was difficult to tear ourselves away - I would have been quite happy just to stay there for another hour drinking in the view, or exploring the bridge more closely.

It was lucky the bridges still to be seen would prove to be Salginatobel Bridge's equal, in their own ways.

Further information:

• entry at structurae
• entry at Wikipedia
• location on Google Maps
• Schiers tourist information (including picture of scaffolding)
• Prättigauerhof information (including more pictures of scaffolding)
• photos of refurbishment (in French)
• diagram of bending moments explaining shape of bridge
• The Salginatobel Bridge (student paper, PDF)
• David Billington's b0oks Robert Maillart's Bridges; Robert Maillart and the Art of Reinforced Concrete; and The Art of Structural Design - A Swiss Legacy
• Heinrich Figi's paper Rehabilitation of the Salginatobel Bridge (Structural Engineering International 1/2000)