DESIGN AND DESIGNERS

by Michel VIRLOGEUX

fib Honorary President ABSTRACT: Engineers have lost a great part of their influence on large projects, and even bridge design – the essence of structural engineering – is more and more attributed to architects. In this situation it is important to remind what is the real field of structural engineering, and to show that progress and architectural achievements in this field are due to great engineers who also were frequently great characters. This paper, revised and adapted for the Dundee conference, gives a special attention to concrete constructions and to the designers who pioneered and created in this domain.

1. INTRODUCTION 1.1. In the last ten or fifteen years the design of more and more bridges has been given to architects with very diverse results. In most cases – specially after a design competition limited to architects – the bridge concept has been developed without any consideration for structural aspects; even the balance of loads and the flow of forces have been ignored, not speaking of erection techniques. This resulted in major construction problems, with high costs for owners and contractors who had to suffer enormous losses. When more delicate problems occurred, involving dynamics or aerodynamic stability, it could even result in a serious misbehaviour. Everybody knows that two pedestrian bridges, one in Paris and one in London, had to suffer from some Parkinson decease due to a very low rigidity (at least in some direction) which favoured vibrations induced by what Jörg Schlaich calls the sailor’s walk; a third one – in Paris again, but still a paper work – might suffer even more severe dynamic effects. Some of these architects are really gifted sculptors and produce nice shapes despite the structural non-sense of the concept and the high cost. They are the more dangerous for structural engineering as their shapes can be considered attractive and some might think them worth the corresponding cost; we have to fight them to promote structural logics, structural ethics, and also to prove that elegance and beauty can be produced at reasonable and sometimes low cost.

But the majority of architects are not so gifted, and this policy produced ridiculous structures, pretentious bridges and sometimes very ugly ones. Even more, a design created by an engineer is frequently attributed to the architect who had been associated to the project – and who in some cases improved it significantly –, a situation which is unacceptable from a simple ethical point of view. It happens to me more and more frequently: I am not always cited as the designer of the Normandie Bridge, even in specialized books, and practically nowhere I am recognized as the designer of the Millau Viaduct to take only these two examples; being clear that in all cases I recognize the major input from the architects in the final result, Charles Lavigne for the Normandie bridge and Lord Foster for the Millau viaduct. 1.2. The reason of this incredible situation is partly due to the evolution of our society, which is sensible to mediatic impact more than to real facts. Words and show-off have more influence than real work and competence. But engineers also have a great responsibility in it:

- too many of us are only interested in computations, in cost, and in construction details. Of course cost, construction aspects, analyses… have a great importance, but they have to come after the development of a good concept, structurally intelligent and efficient, elegant and well integrated in the site and landscape; a poor design produced by an engineer is not better than a poor design produced by an architect, even if the bad aspects are generally different.

- Owners – who frequently are engineers – consider more attractive to show an

architect than a designer. This is a direct result of the greater influence of media and communication, but also of the fact that even the best of engineers are not known outside their circle.

- Engineers and engineering associations frequently work against their own interest,

placing the architects in the front row, sometimes because they are jealous of their colleagues who are more famous or because they don’t want to cite some engineers. Since many years – 20, 30 perhaps – the leitmotiv is that a design is developed by a team; clearly, a good team is needed to develop a good project; but any team has a team leader and we shall see that in design the major progress came from individuals more than from teams. This “team policy”, strongly promoted by large companies – administrations, design offices and contractors –, prevented the best engineers to receive some recognition outside their circle and helped the pre-eminence of architects – in a domain where they are not qualified – when personalisation, the “star system”, is of major importance.

- But also we must recognize that many

engineers have a limited interest for culture and beauty; even if once a philosopher told me that the notion of beauty is highly questionable. If we look back to the 18th century, engineers learnt at school some architecture; at the Ecole des Ponts des Chaussées they had to produce a project of bridge decoration and even to present the map of an imaginary country and pure artistic drawings (figure 1). Architecture, imagination, arts in all aspects were their concern. All of them did not become great designers, far from it, but the best of them received an education much more favourable than now.

Figure 1 : A drawing by a student at the Ecole des Ponts et Chaussées in

the 18th century (from 17).

1.3. I should like adding some words about the “academic style”; more and more scientific and technical journals adopt this convention. To be very clear the reason for this evolution is the promotion system in universities : to develop a “neutral” promotion system, professors and researchers are mainly evaluated through their publications in journals with a scientific publication committee. This is progressively transforming journals from an information system into an academic promotion channel, with very severe drawbacks.

I have been said frequently by reviewers: take out all personal names and names of companies, and give references in a bibliography. No ! Life cannot be reduced to academic literature. Facts and truth are not limited to references; companies might develop ideas and techniques and deserve being cited; those who design structures are not always those who write papers; some who gave good ideas or took part in a design or in a research, and are not authors, deserve being cited for their participation… The academic presentation might lead to real spoliation when a paper describes ideas or structures which are not from the author but from somebody else who never published; and it happens rather frequently in the construction industry.

Some might also express their doubts on a theory or on some specific problem without being able to give scientific evidences or demonstrations. But the most severe drawback is the loss

in free expression, in direct and personal thoughts. We are human beings, each with some personality, and cannot be reduced to formal and rigid literature. This is in my opinion an important factor in the de-personalisation of our profession.

And the last word will be the strongest: the industry and the profession are not to serve universities and academicians, but universities and academicians are to serve the industry and the profession. The goal is not to publish, not even to teach nor to research: the goal is to build in the best way; teaching, researching is only a way – a good way – to improve construction, but not the goal. 2. FROM SCIENCES TO ARCHITECTURE A designer has to master a very wide domain, from sciences to architecture, to be able to develop a really good design; of course with his team, including specialists, architects, landscape architects etc… He cannot be a specialist in each field, but he has to master all of them to really master the design; in opposition to the idea which exists in some countries that a design has to be developed by a commission. As frequently reminded by René Walther, a camel is a horse designed by a commission. 2.1. Sciences are more important than codes; codes are only practical and legal ways to base projects on construction sciences. But for very large projects – as well as for a good understanding of any construction – we have to go back to the sciences themselves.

- A good example is given with seismic designs. Due to the large development of softwares, very sophisticated analyses can be performed and they help designing structures which can resist to extreme earthquakes. Japanese bridges are a good illustration in the domain, as well as the Rion-Antirion Bridge with its deck totally suspended to four pylons installed on large offshore structures.

- Aerodynamic stability and resistance to turbulent winds are now very well mastered,

and extremely efficient structures can be designed, like the Normandie and Tatara bridges.

- Cable-vibration is another domain, not yet completely mastered. Many phenomena

can induce cable-vibrations: direct vortex shedding; wake effects from pylons or other cables; aerodynamic instability produced by ice deposits in Winter, by helical stranding in lock-coil cables, or by the action of rain flowing along the cable-stays; parametric excitation coming from the structure vibrations… In fact we are more able to prevent or eliminate undesired cable-vibrations than to predict them, or even sometimes to prove their precise origin.

Finally, we have to be conscious that we are asking more and more from designers: the development of computers and softwares have considerably simplified analyses as well as the production of drawings; but in the same time the demand is higher and higher. The public now considers that construction can and must be totally mastered, and does not accept accidents or even operation limitations. Under this pressure codes are more and more demanding and the volume of computations increases year after year… not always for higher quality and safety.

But it is clear that if projects are more and more ambitious – as shown by the fantastic progress in span length for each bridge type or in the size of structures –, this is due to a much better understanding of physical phenomena and to the development of computational capacities; in fact to the scientific progress. 2.2. Construction techniques It is unserious to design a bridge without an analysis of its construction steps; the poet Paul Valery wrote that he cannot separate a structure from its erection, a sentence placed by Jacques Mathivat at the front of his book devoted to the balanced cantilever method [5], though its real meaning might not be exactly the one suggested by Mathivat1. If classical erection techniques are very well known – and sometimes have been used centuries ago in very similar conditions for other types of structures –, there is a permanent evolution, specially for the construction equipment. The most recent evolution came with the development of heavy prefabrication initiated by the Japanese steel industry and by Ballast Nedam for concrete structures. Large concrete bridge elements – up to about 7 000 metric tons – have been lifted, moved and installed by a specific ship, Swanen, for the Storebelt western bridge in Denmark, the Confederation Bridge in Canada and the Oresund link between Denmark and Sweden; the lighter Rambiz was used for the Vasco de Gama Bridge in Portugal… We can also evoke the increasing use of computation, information and automation techniques. Computers have been first used to analyse structures, but progressively computers entered fabrication shops, specially in the steel industry. We are not very far to day of computer-aided-fabrication: the designer prepares drawings, and the computer prepares the steel procurement documents, optimises the division of steel plates in elements, and drives practically all shop works, tracing, cutting, handling, welding… Sites and constructions are levelled with the help of satellites, and geometry adjusted and controlled with the same type of equipment; datas are directly sent from sites to design offices, from computer to computer… In a forty years time, construction has completely changed, from manpower to a very advanced technology. 2.3. Materials If main construction techniques have been developed long ago, the major progress is due to the evolution of materials. Steel strength and quality have been increased gradually since the middle of the nineteenth century, from “mild” iron to high tensile steel. Thermomechanical steel with a yield stress of 460 MPa is now currently used, easing welding on site; steel plates of variable depth help limiting welds… As regards concrete, the recent progress is even more surprising. If a strength of 50 to 60 MPa could be obtained in the fifties by some contractors – like Freyssinet –, the classical value was reduced to 35 or 40 MPa during the sixties and seventies. But with the development of high performance concrete – in the USA, in Norway, in Japan, in France … -

1 Je ne sépare plus l'idée d'un temple de celle de son édification.

a strength of 80 or 100 MPa is now almost classical. And some special concretes – ultra-high-strength concrete – can reach a strength of 150 or 200 MPa. But special concretes can also have other goals than strength: high compactness (for durability), high resistance to abrasion, low shrinkage… Concrete can now be specifically designed, as well as structures. 2.4. Technology Technology keeps a great importance: bearings, joints, need a specific design when loads and length variations reach high values, not forgetting the conditions of a possible replacement. Cable-stays give a very good example of the influence of technology on design. We cannot speak any more of cables, but of cable-systems ; with the cable itself, the anchorages, the protective envelope, the devices to limit wind effects – such as dampers –, and all provisions to provide a high protection against corrosion (and vandalism) and to allow for cable adjustment and replacement. Much has changed during the last twenty years, when we progressively passed from lock-coil cables to parallel wires, and now to parallel individually protected strands. Just some more work is needed for a greater elegance of anchorages and additional devices. 2.5. And finally architecture Those who are recognized as great engineers always attached a major importance to bridge architecture. Once I gave a lecture on bridge architecture, Fritz Leonhardt – who was attending the conference – told me that I made a mistake. He told me that we have to speak of bridge aesthetics, not of bridge architecture, since politicians and the public might think that we need to give the design to architects if we speak of bridge architecture. But for once I shall not follow him, and I prefer to refer to Luigi Nervi and his “structural architecture”, and to David Billington and his “structural art”. Structural architecture is the architecture of structural engineers, who alone can create logical, efficient and elegant shapes, mastering all conceptual aspects, from sciences to construction, materials and technology; the most gifted of them can also produce an elegant architecture. This is exactly the goal of this lecture, and in addition we shall show that developing new concepts and new structures elegantly also calls for a very strong character. Great engineers are very often great characters, since they have to fight for their ideas, and sometimes to resist to adversity when they happen – as everybody – to make an error or have to pass hard times.

3. GREAT ENGINEERS I have selected some famous engineers, from the 18th century to the present time, to support these ideas and to show that the major progress in our domain and the most elegant constructions are due to individuals, to their creativity and character. Louis Alexandre de Cessart (1719-1806) I desired beginning with a French engineer of the 18th century directly connected with the Ecole des Ponts et Chaussées, founded in 1747 and considered as the first place where a rational education in civil engineering was given. I could have selected Jean Rodolphe

Perronet, its first director who kept this position until his death in 1794. But I prefer Louis Alexandre de Cessart for his greater originality (figure 2).

Figure 2 : Louis Alexandre de Cessart (from 22)

He began as soldier during the war in Flanders, and took part in the famous battle at Fontenoy. Due to his health he had to resign and he entered the Ecole des Ponts et Chaussées the year it was created, in 1747. Sent as engineer at Tours he built the Saumur bridge over the river Loire, using for the first time in France wooden caissons for the foundations; he developed a special saw to cut wooden piles below water, after they have been driven. He then passed to Alençon and later to Rouen where he devoted most of this time to marine constructions, adapting the caisson concept to the erection of embankments and locks. His most famous project is the erection of the Cherbourg dike, built to protect the military harbour form the English fleets. He designed a dike 4000 metres long, made of 90 enormous wooden cones, built on-shore and then shipped and sunk on the sea bed to be filled with stones. These cones were 50 metres in diameter and 20 to 24 metres high, a prefiguration of our modern heavy prefabrication and of off-shore structures. Erection began in 1783, but heavy tides and tempests damaged some of the first cones; other marine engineers altered the project by increasing the distance between cones; high costs produced delays and the dike was not finished when the revolution came, and the project could not be completed (figures 3 and 4).

Figures 3 and 4 : The Cherbourg dike project (from 22).

Cessart was of course extremely disappointed, but he had a last occasion to evidence his creativity when Bonaparte decided to erect a cast-iron bride to follow the new technique developed in England, and entrusted him with the design of the famous Passerelle des Arts in Paris; a pedestrian bridge which has been unfortunately destroyed in the seventies, after two ship collisions, and replaced by a copy which slightly longer spans. Thomas Telford (1757-1834) If the 18th century has certainly been dominated by French engineers and the creation of the Ecole des Ponts et Chaussées, the first half of the 19th century is without any doubt English, and the most famous engineer Thomas Telford.

In fact, everything began in the last decades of the 18th century with the erection of the Coalbrookdale bridge by Abraham Darby III (1779). Cast-iron and iron then became construction materials with a very rapid development, and were soon used for the erection of suspension bridges. To be honest, suspension bridges had already been built for many centuries in Tibet and China, but this was ignored in the western World (figure 5).

Figure 5 : The suspension bridge over the river

Dadu. In China, built in 1706 with a span of 103 metres (from 11).

The great step forward is due to Thomas Telford who designed the Menai Bridge, in Wales, built between 1819 and 1826 with a main span 177 metres long (figure 6). The suspension was made of a series of the so-called eye-bars, based on an invention by Hawks (1805) and Brown (1808 – 1818). Thomas Telford was the son of a Scottish shepherd and began his carrier as stone-cutter. In 1780 he works as such at the erection of large buildings in Edinburgh, and of Somerset House in London. Between 1784 and 1786 he works as architect for the construction of a house and for the rehabilitation of Shrewsbury castle; very soon recognized he becomes in charge of larger and larger projects such as the Ellesmere canal (1793) and the Caledonian canal (1803), and is even consultant for the Gotha canal in Sweden (1808-1822).

Figure 6 : The bridge over the Menai Straights (from 8).

Figure 7 : A meeting at the Institution of civil Engineers with Telfors,

Stephenson and Brunel (from 15). From 1803 to his death, he directed the erection of more than 1000 bridges, 1920 kilometres of roads; numerous harbours, churches and docks. During his life he had very diverse activities : he developed a kind of standardization of arch bridges in cast-iron, building them from standard truss panels ; he participated in the drainage of marshes, in the improvement of river navigation and in the development of water supply in London, Liverpool, Glasgow and Edinburgh. Finally, he has been one of the founders of the Institution of Civil Engineers of which he became the first President, and received many honors, the greatest of all being to have been buried in Westminster Abbey (figure 7). Later he gave his name to the publishing company of the Institution of Civil Engineers, which is the editor of the fib Journal.

Isambard Kingdom Brunel (1806-1859)

I could have selected Robert Stephenson (1803 – 1859) who erected the famous Britannia tubular bridge in 1850, after the Conway tubular bridge (1848). Or later Sir John Fowler and Benjamin Baker who built one of the most famous bridges in the world, the great tubular bridge which crosses the Firth of Forth. But I prefer Isambard Kingdom Brunel (figure 8).

Figure 8 : Isambard Kingdom Brunel (from 23).

Isambard is the single son of Marc Isambard Brunel, a French engineer who settled in Great Britain in 1799. Isambard is sent to France in 1820 to complete his education, and when back to London in 1824 he works with his father for the construction of the famous tunnel under the river Thames.

Very soon he designs the Clifton suspension bridge above the river Avon, near Bristol, which would have been the world record if the construction had not been delayed until after his death (1860-1864), with some alteration of his project (figure 9). We can note – in the line of this presentation – that he choose a long suspended span, with the chains directly anchored in the rock on each side, to eliminate any pier in the gorge for the preservation of the site.

Figure 9 : The Clifton Bridge (from 15).

Becoming the engineer of a railway company – the Great Western Railway – he selects a specific width for the track (2,10 metres in place of 1,45), limits the slopes to increase speed, designs large wheels for the travelers comfort and specific engines (figure 10); then he turns to ship construction, with the SS Great Western, then the SS Great Britain – with a steel hull and one propeller, a very new solution –, and finally the Great Western with a double steel hull, a ship six times bigger than any other ship at her time (figure 11).

Figure 10 : The engine designed by Brunel (from 1).

Figure 11 : The Great Western, the biggest ship of its time (from 1).

He designed many bridges, basing his approach on empirism and tests, avoiding cast iron which is too brittle and developing the use of puddled iron. But he also used stone and timber. He is one of the best examples of engineering creativity and innovation; his ideas have not been always successful, sometimes because he was too much in advance on his time, but he was respected and honoured as one of the men who produced the fantastic development of engineering and construction in Great Britain and the world. Gustave Eiffel (1832-1923) Gustave Eiffel is one of the rare French who could make a name in steel construction when it was dominated by English engineers. More than an engineer he was a contractor, creating his own company when he was 32 years old. He is famous for his tower (1889), but – as well as Cessart, Telford and Brunel – he worked in many very different domains. He erected the central part of the main gallery for the world exhibition in Paris in 1867, churches, factories in Paris area; a series of small railway bridges, and two large viaducts across the river Sioule, at Rouzat and Neuvial (figure 12). Due to his reputation and activity he obtains contracts all over Europe, being a real pioneer at a time when contractors were limited to their own countries: he built bridges in Romania, Spain, Portugal (the famous bridge over the river Douro in Porto), Peru and Bolivia.

Figure 12 : The viaduct over the river Sioule

(from 16).

Figure 13 : The Eiffel Tower during erection in 1880 (from 16).

He is then very successful, erecting many buildings, including the steel structure of the Statue of Liberty in New York, the famous Garabit viaduct over the river Truyère and the Tower (figure 13). Just the same year he takes part in the adventure of the Panama canal with Ferdinand de Lesseps, which ends with a financial collapse and a political scandal which stopped his contractor’s career.

Eiffel never used steel, which appeared and developed progressively during his life, and preferred iron which he considered safer due to its greater ductility. He created a system of “transportable” bridges, fabricated in elements to be exported and erected far away; the company which kept his name maintained this system very lately, even after the Second World War when the development of local companies gave an end to this activity.

After the Panama scandal he devoted his time to sciences and research, mainly to preserve the Eiffel Tower which was supposed to be dismantled after 20 years. The three domains in which he was interested were all related to the Tower : aerodynamics and meteorology, in direct relation with his passed construction activity, and radiotelegraphy. He built in 1911 the first French wind tunnel, at Auteuil, which still exists and was used mainly for the development of aeronautics (figure 14). And this is not a hazard if the Eiffel Tower is now used as a meteorological station, and that the first television emission was made from it in 1934.

Figure 14 : The Eiffel’s wind tunnel (from 16).

The Roebling family: John Augustus (1806-1869), Washington Augustus (1837-1926) and Emily Warren-Roebling (1844-1903). This is now the right time to cross the Ocean to the United States and John Roebling. But in this case it will be more attractive to refer to the family, wholly involved in the erection of the Brooklyn bridge (figures 15, 16 and 17).

Figures 15, 16 and 17 : The Roebling family; John, Washington and Emily (from 13).

John Roebling was German, born in Mühlhausen and educated at the Royal Polytechnic Institute in Berlin where he was graduated in 1826. He also studied there philosophy under Hegel, who considered him as one of his best students. He settles in the United States as farmer in 1831, in Pennsylvania, but he soon accepts to become engineer in the State administration. He works on roads and canals, and from this experience decides in 1841 to create a small factory at Saxonburg, producing cables from iron wires to ease handling ships and wagons. In 1848 the success is so large that he moves his factory to Trenton, New Jersey. His engineering activity begins in 1844, when he designs a suspension bridge to carry the Allegheny river above the Pennsylvania canal. The structure is made of timber, and the suspension cables of high strength parallel wires; his technology is fixed already in this first application, with a wire wrapped around the circular section for corrosion protection. Several other bridges follow, the most important ones being the Niagara bridge (figure 18) – the single suspension bridge to carry a railway line at the time – and the Cincinnati bridge over

the river Ohio. In 1857-1860 he builds a new bridge in Pittsburgh across the Allegheny river, associating for the first time his son Washington to his work.

Figure 18 : The Niagara bridge (from 13).

Figure 19 : The Brooklyn bridge (from 29). But of course he is mainly famous for his design of the Brooklyn bridge (figure 19). Unfortunately his leg is pounded in an accident during preliminary works, and he dies from tetanus in 1869 before the real beginning of the bridge erection. Logically, his son Washington is named chief engineer to follow him. But he had to suffer from two severe accidents: in December, 1870, fire started in the Brooklyn pneumatic caisson and after a hard night to fight fire, he collapsed and had to be taken home; in May, 1871, he collapsed again, in the New York pneumatic caisson, this time after a series of accidents which produced the death of several workers. This second accident was more serious, and he has lain near death for days; he returned to work for a time but never recovered and had to take a leave of absence in December, 1872. He travelled to Germany for six months, then directed construction from his Trenton house, and from 1876 watched erection form the window of his house on Columbia Heights; but during all these years until the inauguration, on 24 May, 1883, he has been strongly supported by his wife, Emily, who received no engineering education but revealed able to grasp her husband's ideas and instructions to his assistants, and visited the site twice or three times a day to check details. An editorial of a New York journal called her the “Chief engineer of the work”, and she has been admired and respected by anyone, including assistant engineers, bridge trustees and local politicians, a very unique example in the construction history. Othmar H. Ammann (1879-1965) Othmar H. Ammann is the successor of Roebling in the great history of suspension bridges (figure 20). Born in Schaffhouse, in Switzerland, he is graduated in 1908 at the Swiss Federal Polytechnic Institute in Zurich; after a short stay in Germany, he settles in the United States in 1904 and becomes an American citizen in 1924. From 1904 to 1914, he works with several famous American designers – Mayer, Modjeski, Kunz and Lindenthal (figure 21) – before joining the Swiss army when it was feared that Germany pass the border, leaving to David Steinman his place of chief assistant to Lindenthal. But three months later, as war did not erupt on the Swiss border, he came back and Lidenthal immediately reinstalled him, creating the bitter rivalry between Ammann and Steinman which lasted during all their lives.

Figure 20 : Othmar Ammann (from 29).

Figure 21 : The Lidenthal team in front of the Hell gate Bridge, with Ammann and Steinman (from 29).

Ammann was deeply associated in the erection of the Hell Gate bridge (1917) designed by Lidenthal, and after some time spent outside the office worked on the later’s project to cross the Hudson river. But this project was too ambitious with 12 railway lines and 16 road lanes; convinced that it was hopeless, Ammann decided to develop his own project and settles as independent designer in 1923. His project was unveiled in 1924 and immediately received strong supports, including the support of the governor George Silzer. The project was finally accepted and was about to be built by the Port of New York Authority, leaving Ammann jobless. Silzer remedied the situation by encouraging the Authority to establish a position of bridge engineer and to name Ammann at the post, so that Ammann has been civil servant during 15 years, from 1925 to 1939. Everybody knows the story. He built his Hudson bridge, the George Washington Bridge (1931), the first modern suspension bridge with a main span 1000 metres long, doubling the previous record (figure 22). Then he multiplies his achievements with the Bayonne bridge to cross the Kill van Kull (1931), the famous arch bridge competing with the Sydney Harbour bridge for the world record (504 metres) which he brought back to the USA (figure 23); with the Lincoln tunnel, but also with a series of suspension bridges: the Triborough bridge and the Bronx Whitestone bridge (1939).

Figure 22 : The George Washington Bridge with the initial deck (from 29).

Figure 23 : The Bayonne Bridge (from 29).

Ammann then leaves the civil service and settles a new design office in 1946 with Charles Whitney, Ammann and Whitney. This is within his office that he builds the Verrazano bridge (1963), regaining his world record (1298 metres) taken by Joseph Strauss in 1937 with the erection of the famous Golden Gate bridge (1281 metres).

From this rapid evocation it is clear that Ammann gave us a fantastic example of creativity and innovation, but also of persistency and of political perspicacity. I have been specially interested, when reading his history, by the fact that he never worked according to his positions, but selected his positions to the works he desired to perform. It is also interesting to note the connections which existed between the engineers of the American school of the time: Modjeski, Lindenthal, Ammann, Steinman, Strauss – who began with Modjeski – and Moisseiff, the unfortunate designer of the Tacoma bridge. It would be worth spending some time on the development of knowledge and theories on aerodynamic stability, as well as it would be worth to evoke in more details Strauss and Steinman, the first engineer to design a suspension bridge – over the Mackinac straights – after the collapse of the Tacoma bridge. Robert Maillart (1872-1940) But we have to pass from steel to concrete, and back to Europe. It would have been better to begin with the French engineers who developed concrete constructions – mainly Monier and Hennebique –, but due to the limited size of the paper we shall first evoke one of the most famous of engineers, Robert Maillart (figure 24). When the journal Bridge made an enquiry among engineers and architects to know which is the most famous bridge of the 20th century, a majority selected the Salgina bridge in the Swiss Alps (figure 25). Maillart’s father was Belgian, but his mother Swiss. He has been graduated at the Swiss Federal Polytechnic Institute in 1894. He began his career in a contracting company, built a bridge in Zurich and then worked with a designer to erect the Zug bridge, the first concrete box-girder. In 1902 Maillart settles his company to design and built concrete structures and is immediately successful.

Figure 24 : Robert Maillart in 1901 (from 6).

Figure 25 : The result of the enquiry on the most famous bridge of the 20th century

(from 27). In 1902 he builds the largest concrete water tank in the world, in 1905 an arch bridge with a box-girder structure, and the first slab structures which he patents in 1909 (figure 26) . In 1912 he wins several design competitions and becomes very famous, extending his activities to Spain and Russia. In 1914 he travels to Russia for Summer vacation and is trapped there by the war and the revolution. He can escape only at the end of 1918, and when he comes back to Switzerland he is ruined.

Figure 26 : A mushroom slab, the Giesshübel Warehouse in Zurich, 1910

(from 6).

Figure 27 : The Valtschielbach bridge, 1925 (from 6).

He then writes many technical papers and progressively recovers his reputation and success. In 1924 he erects the first arch bridge in which the arch is stiffened by the deck, the Valtschielbach bridge (figure 27). In 1928 he wins the competition for the Salgina bridge which is completed in 1931. Then bridges are built one after another, all with an extreme structural efficiency and a great elegance. At the end of his life, he builds a concrete roof, a very thin shell for the national exhibition in Zurich (1939). During his last years he publishes many papers on “structural architecture”. Due to his constructions and his papers, he is considered as much as an artist as an engineer, and famous authors devoted papers and books to his works such as Siegfried Giedion, Max Bill and David Billington. Albert Caquot (1881-1976) Concrete has been very successful in France where some major progress took place, and of course everybody knows Eugène Freyssinet who developed the concept and the technology of prestressing. His life and his strong character are so well known that I prefer concentrating on another engineer, Albert Caquot, who also had a fantastic career; Graduated the same year as Freyssinet at the Ecole des Ponts et Chaussées, he is nominated at Troyes, a very unhealthy city at the time. He strongly encourages the construction of sewers and drains which rapidly improve the situation and help limiting the effects of the large flood in 1910. But he loses interest in administrative work and joins Armand Considère – a pioneer of reinforced concrete – to settle a design office, in association with Considère’s son-in-law after Considère’s death in 1914. They design concrete dams, tied-arches and other structures. During the first World War he designs observation balloons which are extremely stable, even under rather high winds, taking a major part in the supremacy of the allied artillery (figure 28). After the war, he designs and erects many structures, like the les Usses arch bridge (figure 29) or the Saint-Nazaire dry dock, and develops some erection techniques. In the same time he is named general director of the new Aviation Ministry and he tries to develop a modern aviation. Disappointed by the lack of funds he resigns in 1933, and is nominated again in 1938 without more success.

Figure 28 : A Caquot balloon on observation above a British warship during the war (from 4).

Figure 29 : Les Usses arch bridge (from 4).

After the second World War he comes back to structural engineering, erects the la Girotte dam and the Donzère-canal cable-stayed bridge (1952), a pioneer concrete cable-stayed bridge which is often forgotten in the construction history (figure 30).

He received almost all possible honours: the highest level of the French Legion d’honneur – the Great Cross – as well as many decorations from the allied countries during the first World War ; he has been member of the French Academy of Sciences, even becoming its president in 1952. Figure 30 : The Donzère canal bridge (from 4).

Caquot has certainly not paid as much attention to aesthetics as Maillart did for example, but the diversity of his career is very unique in the modern times. He has also associated very closely theory and practical applications in structures as well as in soil mechanics, evidencing a very universal spirit. Riccardo Morandi (1902-1989) I have a very special appreciation of Riccardo Morandi who developed his own structural philosophy without any relation with the international trends (figure 31). His most famous construction is the Maracaibo bridge in Venezuela (1962) which I consider as one of the major ones in the world, together with the Brooklyn Bridge, the bridge across the Firth of Forth, the Washington bridge and the Golden Gate bridge (figure 32). This is one of the largest constructions of the time, one of the first large concrete constructions built with heavy equipment. It is remarkable that, like the bridge above the Firth of Forth, this is a hopeless solution : the gigantic truss of the Firth of Forth was overpassed by suspension bridges, lighter and much cheaper to erect, more elegant also; and the Morandi’s system for cable-stayed bridges was overpassed by the design of the German cable-stayed bridges, with flexible pylons and deck; lighter, at much lower cost and finally more elegant. But what a strength in these two designs, the Firth of Forth and Maracaibo ! How evident is the flow of forces, even if not the most logical ! This is not a surprise if these two bridges, two deadlocks,

are highly appreciated by architects and the public ; they express their strength and their behaviour.

Figure 31 : Ricardo Morandi (from 19).

Figure 32 : The lake Maracaibo bridge (from 12)..

Morandi kept the same line during all his career, mainly inspired by the architecture and the art of the twenties and thirties ; priviledging assemblies of beams and slabs. He graduated in 1927 at the Scuola di Applicazione per Ingegneri and begins his career in Calabria to rebuilt in reinforced concrete churches destroyed after an earthquake. In 1931 he settles the Studio Morandi, mainly to work with a contracting company. He builds habitation buildings in reinforced concrete, large cinemas in Rome (figure 33), churches, factories, schools; all with his specific style. He develops his prestressing systems (1949) and a new technique to erect arches : each half-arch is built almost vertical inside a scaffolding, and then rotated with the help of maintaining cables to take its final position ; the Lussia pedestrian bridge (1954) and the Storms river bridge in South Africa (1954) are built that way (figure 34). And then he begins building his cable-stayed bridges : the Maracaibo bridge (1962), the Polcevera viaduct in Genoa (1964) and the Wadi-kuff bridge in Lybia (1971) with the same design (figure 35); and some more recent with amended solutions, tending to the international way. But he also builds cable-supported roofs for Alitalia in the Fiumicino airport (figure 36) and a very large arch bridge, the Fiumarella bridge with the same design philosophy.

Figure 33 : A cinema in Rome (from 19).

Figure 34 : The Storms river bridge during erection (from 19).

Figure 35 : The Polcevera viaduct in Genoa (from 19).

Figure 36 : The Alitalia hangar at the Fiumicino Airport (from 19).

A rather rare example of a man who followed his own way with no relation with the international trends and fashion. Fritz Leonhardt (1909-1999) If it had been possible, I should have evoked Nicolas Esquillan, one of the greatest French engineers of the 20th century, respected worldwide including by Fritz Leonhardt who admired him for his works and also for his modesty and personal character. But it is better to concentrate on Leonhardt himself who can be considered as the master of the second half of the century (figure 37).

Figure 37 : Fritz Leonhardt in 1999 (from 30).

Graduated at the Stuttgart University in 1931 he travels to the United States in 1932-1933 on occasion of a students programme. In 1934 he has a technical position in the administration in charge of the motorway development, and he works there in close cooperation with two architects, Paul Bonatz and Friedrich Tamms; this has been for him a very important experience which explains his dedication to structural elegance. Between 1938 and 1941, he designs and builds the Kölhn-Rodenkirschen suspension bridge which is – with its main span of 378 metres – the longest in Europe at the time, far behind the American bridges (figure 38).

Figure 38 : The Köhln-Rodenkirchen bridge built in 1941 (from 30).

Figure 39 : The Emmerich bridge project in 1961 (from 30).

After the war he takes a decisive part in reconstruction, developing new systems for buildings and improving bridge construction techniques. His major achievements are the Köhln-Deutz bridge (1948), a light and elegant composite bridge, the three famous cable-stayed bridges over the river Rhine in Kölhn, with Tamms, and the Kochertal bridge; he developed the concept of a suspension with a unique axial cable, patented in 1953, with unsuccessful projects proposed in 1955 for the Tancarville bridge and 1961 for the first Tagus bridge in Lisbon and the Emmerich bridge over the Rhine (figure 39). Leonhardt has also built many towers such as the pioneer one, the Stuttgart television tower in 1955 (figure 40), with a concrete core supporting the floors, a model which has been reproduced many times later. He also built shells, cable-supported roofs such as for the Munich Olympic stadium (figure 41).

Figure 41 : The Munich Olympic Stadium built in 1972 (from 30).

In addition to this important activity of designer – through his office, Leonhardt and Andrä – Leonhardt has been professor during twenty years at the Stuttgart University (1953-1973). As such he publishes his famous red books which have long been the bible for reinforced and prestressed concrete structures, and he wrote many technical papers, for an example on cable-stayed bridges. But his major influence, world wide, came with his two books, Bridges and Towers, in which in addition to historical and technical information he gave his views on structural architecture, on aesthetics and beauty. Honoured by almost all international awards in structural engineering, he had a direct or indirect influence on all living designers. René Greisch (1929-2000) René Greisch is not so famous as Leonhardt, and had not the same influence worldwide; on the contrary he modestly followed his own way in Belgium, and only after a long time his works have been really discovered (figure 42).

Figure 42 : René Greisch (photo BEG).

Figure 40 : The Stuttgart

television tower (from 30).

René Greisch was graduated as civil engineer (1951) and as architect (1955) at the Liège University. In between, during four years, he works at the European Convention for Steel Construction with Professors Louis and Massonet. In 1959 he settles an office as consulting engineer and independent architect. He takes part, as such, in the design of the new buildings for the Liège University, works for the Louvain-la-Neuve campus and the Notre Dame de la Paix University at Namur as well as for some bridges. In 1973 Jean-Marie Cremer joined the office, and since this time they worked in close collaboration mainly to design elegant bridges, René Greisch more attached to the architectural aspects and Jean-Marie Cremer to the structural design and erection techniques. Their first achievements are the tied arches over the river Meuse (the Albert Canal), at Haccourt (1979) and Hermalle (1980); some other tied arches were built later : Maresche (1983), Milsancy (1987), Landegen (1986). Almost in the same time they begin designing cable-stayed bridges, in a very classical way for beginning with the Lixhe (1979) and Lanaye (1980) bridges (figure 43), also on the rive Meuse, but soon after with more original designs. The most famous are on the river Meuse once more, the Ben Ahin bridge in 1988 (figure 44) and the Wandre bridge in 1989 which is now a Historical Monument of the Wallon Region (figure 45).

Figure 43 : The Lanaye bridge over the river Meuse, also called Albert Canal (photo BEG).

Figure 44 : The rotation of the Ben Ahin cable-stayed cantilever (photo BEG).

For this bridge René Greisch received in 1989 the Gustave Maguel Gold Medal given by the gent University, probably the most important international award for concrete constructions.

Figure 45 : The Wandre bridge over the river Meuse (photo BEG)..

Figure 46 : The Greisch office at Angleur, near Liège (photo BEG)..

But René Greisch also built some television towers, in concrete or steel, and one of his last achievements is the design and construction of his office. This building is a good image of his personality : it is simple, even with some austerity, but in the same time perfect (figure 46). Simplicity and perfection are certainly the main words to qualify his works, and despite the quality of his constructions he was always anxious of the last detail and in the same time of others judgment.

Christian Menn (born 1927) Christian Menn is certainly another great engineer. Perhaps some will be surprised that I present living engineers, two in fact. But as my goal is to evidence the continuity in engineering and the influence of great engineers on our profession, it would be counterproductive to stop my list here and to leave the impression that there are no more great engineers today. At least there is a strong criterion : a book has been already published on the works of Christian Menn and of Jörg Schlaich. Christian Menn has been graduated at the Zurich ETH in 1950, and in 1953 he became assistant to professor Lardy to receive his PhD in 1956. Working with Dumez in Paris he takes part in the erection of the Unesco building designed by Pier Luigi Nervi, and in 1957 he opens his own office in Switzerland. His first constructions are very much inspired from Maillart, and he developed Maillart’s concepts to the extreme, designing very light arches with light decks : the Crestawald bridge in 1958 (figure 47), the Averserrhein bridge at Cröt (1959), the Grüne bridge (1961), the Valserrhein bridge (1962), the Rhine bridge at Reichenau in 1964 (figure 48) and the two bridges at the San Bernardino pass (1967) – the Nanin and Cascella bridges – are among the most elegant arches built in the world (figure 49).

Figure 47 : The Crestawald bridge (from 24).

Figure 48 : The Rhine bridge at Tamins, near Reichenau (from 24).

Menn has also built more classical bridges – for modern times, since no other structure can be as classical as an arch –, but with extremely elegant shapes. The Felsenau bridge (1975) is one of these examples. But Menn proved his originality when he designed the Ganter bridge, with a structure which can be compared to no other one at the time (figure 50) : the box-girder deck is supported not by cable-stays, but by prestressed concrete walls. This design has been reproduced by some other designers – in Mexico with the Papagayo bridge, in the USA with the Barton Creek bridge, in Portugal with the Socoridos bridge and in Bahrain –, and inspired what is now called extradossed bridges following the name given by Jacques Mathivat when he developed an unsuccessful design for the Arrêt Darré viaduct. These extradossed bridges received many applications in Japan – some very elegant like the Odawara Blue Bridge –, but the most elegant has been recently designed and built by Christian Menn himself, the Sunniberg bridge.

Figure 49 : The Nanin and Cascella bridges

on the San Bernardino Pass (from 24).

Figure 50 : The Ganter bridge (from 12). Christian Menn followed his own way, his own philosophy. To evidence his strong character I just evoke his accident: when skiing alone he broke his leg ; as no help could come, he crawled on the snow on a long distance with his broken leg to be rescued. In parallel with his professional activity, following the German and Swiss tradition he has been professor at the Zurich ETH from 1971 to 1992, influencing generations of Swiss engineers; but also engineers all over the world who have been impressed by the elegance of his constructions. Jörg Schlaich (born 1934) I conclude this presentation with Jörg Schlaich (figure 51). He studied in Stuttgart, Berlin and Cleveland at the Case institute (1960). He enters Leonhardt's office of which he becomes an associate in 1974. There he takes part in many major projects, mainly for light structures: concrete television towers, the suspended roof of the Munich Stadium for the Olympic Games, the Munich

Figure 51 : Jorg Schlaich with a young engineer (photo Nicolas Mouzakis).

ice-stadium and the cooling tower of the Schmehausen nuclear plant (1974). He progressively develops from Otto Frei's theories a concept of light roofs, a cable net supporting glass or plastic membranes. In 1972 he becomes the successor of Leonhardt at the Stuttgart University, as professor of concrete structures : but in 1980 he leaves Leonhardt's office to create his own, Schlaich-Bergermann and Partners. From his own office he develops his activities in light structures, such as for the fixed or mobile roofs of the Hamburg History Museum, the stadiums in Saragossa, Stuttgart, Hamburg and Oldenburg, for the Nimes roman arena or the Montreal stadium for which the roof could not have been installed in 1972 (figures 52 and 53).

Figure 52 : The glass roof of the Zublin building (from 25).

Figure 53 : The Stuttgart Stadium (from 25). He also designs bridges; some more or less classical, like the Hooghly bridge in Calcutta, a composite structure which would have taken the world record if construction had not been so slow (1978-1993), and more original ones, like the Evripos cable-stayed bridge in Greece, a simple prestressed concrete slab with a span of 210 metres inspired from the ideas of Ulrich Finsterwalder and René Walther, who pioneered the domain and had also passed in Leonhardt's office. But from his experience in light roofs, Schlaich developed a very personal design of suspended and cable-stayed pedestrian bridges, extremely light and elegant; structures with very simple elements associated to produce an extremely efficient structure. More recently, he designed structures made form steel tubes, pedestrian bridges – arches for example, with a very light upper slab – and road bridges, mainly in Stuttgart area (figure 54).

Figure 54 : A pedestrian bridge in Stuttgart (from 25).

Figure 55 : The Kelheim pedestrian bridge (from 25).

His structural capacities made possible the development of light bridges in any condition, like for a semi-circular pedestrian bridge in Kelheim where he took advantage of the curvature itself in the design (figure 55). He also developed new ideas for mobile bridges, sometimes having a hard time to make them work. He is an unpredictable designer, because each time he looks for a new idea, a new solution; this is also why I don't like all his structures, but I am always astonished by his creativity. Being strongly engaged in sustainable development, he worked on the structural aspects of renewable energies, like for dish concentrators of solar receivers, or solar chimneys to create energy from the induced updraugth wind (figure 56). Figure 56 : The experimental solar chimney in

Spain (from 25).

As a conclusion he is a fantastic example of creativity and imagination, and as many of his predecessors, other great engineers, he has a very universal activity. Among many deserved honours he received two exceptional ones: an excellent book by Alan Holgate recognizing his career, and having been black-listed by the German administration for his strong – and justified – positions against an official recommendation about internal and external prestressing. 4. CONCLUSION I regret that I could not evoke many other names of great engineers, like Paul Séjourné, Franz Dischinger, Ulrich Finsterwalder, Carlos Fernandez Casado, or more recently Hans Wittfoht, Javier Manterola, Armando Rito, Jean Muller, Jiri Strasky as well as those who inspired me more directly like Jacques Mathivat and René Walther. There cannot be any conclusion after my presentation. I just hope that I could show the importance of great engineers in the development of modern civil engineering, and of the example given by their careers. Ours associations, fib and IABSE, certainly have to make some efforts to have them more recognized in the society. I am more optimistic than I was some years ago : even if the title of the series might be considered as a problem, if taken in the wrong direction – the engineer's contribution to contemporary architecture –, it is a good sign that Thomas Telford issues a series of books on great engineers like Peter Rice and Heinz Isler [28]. As well as we all appreciate that the journal Bridge published a series of papers on engineers in activity: Fritz Leonhardt just before his death, T.Y. Lin, Jörg Schlaich and many others [26]. But we have to do more to have them recognized outside the small professional circle of engineers, through specific actions like biographies, exhibitions and a greater attention to our image in the society. AKNOWLEDGMENTS It is impossible, when preparing a non-commercial paper of this type, to obtain on-time an official permission to reproduce the necessary drawings from existing publications. They have been all cited, recognizing their high quality and interest; these books have to be in the personal library of all structural designers.

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