Visionaries and Unsung Heroes

Visionaries and Engineers Unsung Heroes Design Tomorrow

6 Engineers in the Building Sector Werner Lang, Cornelia Hellstern 9 Designing Life Wilhelm Vossenkuhl

On Inventors, Entrepreneurs, ­Problem-Solvers and Designers 14 Civil and Building Engineers – the Emergence of the ­Professions Bill Addis 20 Networks of Engineering Expertise Dirk Bühler 26 Women Pioneers of the Big Modern Building Sites – How They Became Who They Are Margot Fuchs 30 On the Education of Engineers Gerhard Müller 36 Engineering Aesthetics Nina Rappaport

Tensile Structures 65 Wide and Light 66 Lightweight Textile Construction – Development of Simulation Methods from the 1970s to the Present Kai-Uwe Bletzinger 71 The Spoked Wheel for Ring Cable Roofs in Lightweight ­Construction Knut Göppert 75 Lightweight Construction in Motion

Building Construction – Focus on Timber 77 Exploring New Dimensions with Timber 82 Material and Design – Is Hybrid the Future?

Stefan Winter

Towers and High-Rises 87 Aiming High 89 Pushing the Limits Annette Bögle, Christian Hartz, Bill Baker 94 The Buttressed Core

WATER + ENERGY

ENCLOSURE + SPACE Arch and Shell Structures 43 Creating Spaces: Linking Aesthetics and Structure 44 On the Development of the Zeiss-Dywidag Shell Construction System Cengiz Dicleli 47 Form Finding – Graphical Tools, Experiments and Models, ­Numerical Methods 51 Computer-Based Processes for Biomimetic Structures Jan Knippers, Achim Menges 58 Structural Design and Form Finding Processes Christoph Gengnagel

Water Supply and Wastewater Disposal 99 Water in Cities 100 Water Transitions in Cities of the Future Jörg E. Drewes 105 Sewage Becomes Heat Energy 106 Emscher Conversion: Ecological Restructuring of a Wastewater System

Functional and Protective Structures 109 Protection and Safety, Water and Energy Supply 110 Protection from the Forces of Nature 114 Reinforcing Reservoir Dams: the Sylvenstein Dam Pilot Project Peter Rutschmann 116 Challenges in the Discourse Between Technology and Society Peter Rutschmann

Table of Contents

119 Engineers as Entrepreneurs – Influences on the Development of Civil Engineering and Society Roland Pawlitschko 124 The TUM Hydro Shaft Power Plant Innovation

Peter Rutschmann

Offshore Wind Turbines 127 Wind Becomes Energy 128 Electricity from the Sea 130 The Energy Transition as an Assignment for Civil Engineers Christian Dehlinger 133 Floating Wind Farm – Hywind Scotland 134 Floating and Self-Erecting: TELWIND 135 Flexible Membrane Wings for Wind Turbines 136 The Role of Environmental Engineers in Limiting the Side Effects of Modern Technology Joachim Scheuren, Carl-Christian Hantschk

MOBILITY + TRANSPORTATION

162 The Development of Tunnel Construction and Tunnelling Machines Roberto Cudmani 166 Traversing Mountain Ranges 168 Geodesy – a Breakthrough Success Thomas Wunderlich 171 Using Tunnels for the Extraction of Geothermal Energy Roberto Cudmani

Cable and Suspension Bridges 175 Overcoming Distances 176 Linking Continents 178 Spanning Farther 180 Shortening Journeys

Traffic Technology 183 New Mobility 184 Mobility and Traffic as Dynamic Fields for Engineers Fritz Busch 188 Diagonal Crossings: Oxford Circus 189 Cooperative Systems

Construction of Roads and Railways 141 Gaining Access 145 Record Heights: the Zugspitze Cable Car 147 Slab Tracks for Rail Traffic Stephan Freudenstein

Outlook 192 Future Challenges for Civil Engineers Werner Lang

Beam Bridges 151 Bridges into the Future 152 Integral and Semi-Integral Bridges 154 Ulrich Finsterwalder and the Development of Cantilever Construction

Cengiz Dicleli 157 Improving Quality and Efficiency through Procurement ­Procedures Involving Supplemental Offers and Alternative ­Proposals Roland Pawlitschko

Appendix

Tunnel Construction

Introductory texts and project descriptions are written by the curators of the exhibition.

161 Below the Water and Through the Mountain

198 Biographical Listing of Engineers 209 Index of Names 209 Project Index 210 Subject Index 211 Picture Credits 212 References 213 Authors, Panel of Experts and Specialist Advisors 216 Imprint

Engineers in the Building Sector

“The innovative power of engineers ensures the viability of our highly developed national economy and an appropriate standard of living. It is therefore imperative for both our self-preservation and for the successful advancement of society to value and esteem engineers and their achievements. Engineers in the building sector must position themselves in the public sphere in a manner that is commensurate with their importance and their responsibility.”1 With its mission statement, the Bayerische Ingenieurekammer – Bau (Bavarian Chamber of Civil Engineers) expresses the relevance and the duty of this branch of the engineering profession.

Innovative power, entrepreneurship as well as design and practical abilities are essential characteristics of engineers in the building sector.2 Their services, such as the provision of needs for safety and security, water supply and wastewater removal, energy transformation and distribution as well as mobility, prove that life as we know it today would not be as fulfilling – or indeed possible – without them.

But despite the key role they play in satisfying the fundamental requirements of our civil society, and specifically of a good communal coexistence, our knowledge of the tasks and accomplishments of engineers in the building sector is relatively limited. Even the great economic importance of the building industry, which in Germany has a total annual revenue of about €340 billion and employs more than 2.7 million people (2015) 3, does little to improve this state of affairs.

According to the authors of “Zwischenruf”4 (“Interjection”), published in 2006, the serious consequences of undervaluing the importance of engineers in building include not only a shortage of skilled workers and a lack of consideration in the allocation of research

Preface

funds, but also the resulting loss in the quality of our infrastructure and thus in the material and cultural foundations of our lives.

The duties of engineers in the building sector encompass a wide spectrum of activities that are relevant to our everyday existence. Aside from the design and construction of civil engineering structures and other individual built works, these also include facilities for gas and water supply, for hydraulic structures and for the removal of gasses, substances (including liquids that can endanger the water supply) and waste. Without structural engineers, surveyors and geotechnical engineers, the design and implementation of these types of buildings and installations would be impossible.5 Many of these spheres of activity occupy intersections with other disciplines and require different modes of thinking. An example of such a field is traffic planning, in which the goal is an integrated development of settlements and transportation systems with an eye to the interactions between space and traffic at an urban and regional level. In addition to the interdisciplinary angle, a visionary thought process is also important. To develop concepts for the immediate future, one must be able to consider a change in mobility behaviour just as one must be capable of imagining the coming effects of digitisation and technological advances on our society. Beyond the spheres of activity mentioned, engineers in the building sector also cover a wide range of consulting work that is important for our society. Work in this category is drawn, for example, from fields in building physics such as thermal insulation, energy balancing, building acoustics and noise abatement as well as spatial acoustics.

6

1 Mission statement of the Bayerische Ingenieurekammer – Bau, http://www. bayika.de/de/kammer/index.php?navanchor=2110000 (7 August 2017).

2 Similarly to the mission statement quoted in the opening lines, the 2006 ­article “Zwischenruf: Verantwortung und Ansehen der Bauingenieure – ein Aufruf” draws attention to the central role of the profession in the design, construction and preservation of the infrastructure that shapes our lives. In: Bautechnik 10 / 2006, p. 737ff.

3 https://www.bundesstiftung-baukultur. de/sites/default/files/medien/78/downloads/bbk_bkb-2016_17_low_1.pdf (7 August 2017).

4 see note 2.

5 see HOAI Paragraph 41, http://www. hoai.de.

6 see note 2.

Opposite Drawing of the triangulation net for the “Determination of the St. Gotthard Tunnel Axis” taken from the report of the same name by the civil engineer Otto Gelpke in Der Civilingenieur 16/1870

In order to act sustainably in the fulfilment of a social mandate – against the backdrop of global challenges such as climate change, environmental destruction, competition for ­resources and demographic change – it is more important now than ever to redefine the building-related responsibilities and tasks that arise from these challenges.

One aspect of this approach is to consider the interactions of buildings and other infrastructure systems with the environment from the initial planning stages, with particular atten-

tion to resource consumption, emissions and their associated economic and sociocultural concerns. Analogue and, increasingly, digital methods and tools used in analysis, modelling and synthesis support design and construction processes and enable engineers in the building industry to confront and successfully address continually changing and more complex challenges in the service of society.

To ensure that this ability remains secure in future, engineers in the building sector must “fight for improvements in their professional standing in order to be able to continue living up to their civilisational and cultural responsibilities. In pursuit of these aims, they must consistently adapt the quality of their work in research, education and practice to the people’s needs, and they must campaign for social recognition by making it clear that in engineering, too, quality has its price.”6 The promotion of these goals was the primary motivation for the exhibition Visionäre und All­tagshelden. Ingenieure – Bauen – Zukunft ­(Visionaries and Unsung Heroes. Engineers – Design – Tomorrow) as well as this accompanying publication.

The exhibition was conceived by the Oskar von Miller Forum in collaboration with the Museum für Architektur und Ingenieurkunst Nord­rheinWestfalen e.V. (M:AI). Its goal is to represent the work of all engineers in the building sector as it really is: of central, civilisational importance, as well as being multi-faceted, exciting, fascinating and innovative from both a cultural and technological perspective. This recognition is important for society and its comprehension of and regard for the profession, but also for the education of engineers in the building field.

The exhibition is therefore designed specifi­

7

Enginieers in the Building Sector

cally to address students and the new generation of engineers.

The significance, range and depth of the creations and work of selected outstanding engineers are illustrated. Taken from historical to contemporary times, projects are used to show the conditions under which the engineers were or are active and how their work must be evaluated in its societal, political and economic context. The focus lies not on projects that are impressive by virtue of their superlative qualities, but rather on those that have provided or are providing a significant stimulus and have paved the way for future building trends.

Following an introduction by philosopher ­Wilhelm Vossenkuhl, this publication is separated into four basic sections.

The first section deals with the development of the engineering professions, starting in the mid-17th century when the first textbooks on the subjects of hydraulic and bridge construction were published. Soon after, the first networks and alliances were formed, which played an important role in the exchange and communication of knowledge and experience and thus contributed to the spread of civil engineering. Female pioneers in the civil engineering branch – representative of the developing role of women in engineering in general – are portrayed. An overview of the education of engineers in the building sector, presenting the changes this training has undergone over the centuries, and a contribution outlining the importance of aesthetics in engineering culture round out the section.

Proceeding just as in the exhibition, the three following sections address the fundamental needs of society and the challenges for building engineers that arise from these needs.

The basic human need for shelter and security is explored in the section “Enclosure + Space”. This section includes contributions on contemporary developments in materials, in computation, simulation and construction methods as well as in building technologies.

“Water + Energy” deals with the need for a sustainable and reliable supply and with the scope of tasks associated with this need. Urban water supply, defences against the forces of nature and the provision of energy are presented in this section, along with the interrelationships between technology, society and entrepreneurship. These are contextualised by the energy transition, which represents an important opportunity for building engineering.

The necessity of the transportation of goods and the human need for connecting and net-

Preface

working are covered in the section “Mobility + Transportation”, which highlights the many options that exist for making spaces accessible, be they on land, underground, on water or in the air. The section also explores themes such as improvements in quality and efficiency and ground-breaking developments in geodesy and construction methods. A discussion of new, sustainable mobility concepts concludes the chapter.

The section “Outlook” appended to the main body of the book describes trends that are already evident, and the challenges for building engineers that arise from these trends. Engineers’ relevance in future advances in technology and research, considered within the context of rapidly changing societal expectations, shows that they will continue to be in urgent demand as their critically important services to society secure a pathway for future sustain­ able development.

This publication would not have been possible without the contributions from specialists who adopted the idea for the book with great enthusiasm and supported it with their substantial efforts. The same can be said of the advisory board for the exhibition and the other experts who acted as consultants. We would like to extend our special thanks to all of them.

We would also like to thank the institutions that were closely involved with the content and the creation of the exhibition, such as the Oskar von Miller Forum – an educational initiative of the Bavarian construction industry – and the Museum für Architektur und Ingenieurkunst NRW e.V. (M:AI), as well as their employees.

We hope that this publication contributes to a general understanding of how engineers in the building sector have always managed, even under difficult circumstances, to respond to the needs and challenges of society in a solution-oriented, economical, responsible and innovative way. They possess the critical ability to recognise and proactively address the questions and tasks of the future. This ‘inventive response’7 is one of the essential characteristics of constructive engineers and will continue to distinguish them as the inventors, designers, entrepreneurs and service providers of our society for many years to come.

Werner Lang, Cornelia Hellstern Editors

8

7

Peter Rice states the following as a ­­ relevant guiding principle for engineers: “I would distinguish the difference between the engineer and the architect by saying the architect’s response is ­primarily creative, whereas the engineer’s is essentially inventive.” See ­Martin Trautz: “Baugeschichte oder Bautechnikgeschichte?” Views on the topic “Was ist Bautechnikgeschichte?” in the context of the 1st International Congress on Construction History, ­Madrid 2003. https://gesellschaft.bautechnik­ geschichte.org/was-ist-bautechnik­ geschichte (7 August 2017).

Wilhelm Vossenkuhl

Designing Life

There is probably no greater praise than being singled out as someone who sets new standards. Achievements that merit this distinction are usually conspicuous, instantly recognisable, often spectacular. But there are standards we have become so accustomed to that we do not notice them anymore. They are part of our everyday existence, shaping our lives in ways that we no longer consciously perceive. Though they are unspectacular, they are inextricably integrated into our existence as a part of what the French sociologist Pierre Bourdieu called “symbolic order”. Engineers in the building sector have set many standards that people eventually came to see as commonplace. But they have also set standards that remain spectacular. In many of these works, entire buildings or even just roofs appear to float weightlessly above the ground, seeming to defy gravity. We are impressed by these sights and marvel at them, yet over time, like all magnificent things, they take on a museum-like quality, becoming objects of memory and threatening to fade into obscurity entirely. The everyday, on the other hand, is a lasting part of life precisely because we don’t have to think about it – or because we only notice it when it is no longer available. The standards that are part of our existence shape our perception, even if they themselves fade from notice. Like our native language or our dialect, they are part of who we are.

We often pay attention to the bridges we cross – to name but one example – only when buffeted by wind gusts. We do not see their structures, the safety and elegance of their design, the refinement in the connections among elements, the interplay of building materials with mathematics and physics. It is a matter of course, below our level of aware-

9

ness, that the extraordinary achievements of engineers characterise our everyday lives.

We do not doubt their quality or reliability. It is, after all, exactly what we expect and take for granted. But that which guarantees our normality is intricate – extremely exacting and complex, and replete with conditions and constraints that are all unique. And this is not only the case for tunnels being excavated for underground rail lines, as is happening right now in the centre of Stuttgart.

The Swiss art historian Jacob Burckhardt postulated that art creates a “total picture of mankind”. In doing this, art hews to a comprehensive, all-encompassing standard. This is keenly observed, since art concerns the whole of life.

When we look for a label to describe all the many standards to which building engineers must conform, we should likewise speak of a comprehensive, all-­encompassing standard.

Included within it are material sciences, structural and building physics, ecology, design and – more recently – ethics. What important standards for the shaping of our existence could there be beyond these?

The expression ‘total picture of mankind’ is a bit pompous and can stay in the art world.

For the art of building engineers, it is enough to speak of the ‘full picture of life’, which they design or at least have a main role in designing. We want to drink clean water, drive on safe bridges, live in good, earthquake-proof and attractive houses and enjoy the appearance of the cities in which we reside. Engineers in the building sector play no small part in our health and well-being, in our joie de vivre, maybe even in our happiness; and most certainly in environmental conservation and in energy production, both the clean and the not-so-clean kinds. Similar claims can also be made generally for many other scientists.

Designing Life

On Inventors, Entrepreneurs, Problem-Solvers and Designers

Civil and Building Engineers – the Emergence of the ­Professions

The engineering specialisations known by the modern terms civil and building engineering can trace their roots back to the very beginnings of civilisation and were already very ­sophisticated during Roman times. Hy­draulic engineers focused on managing water for the benefit of humankind: they redirected natural water sources for use in irrigation, provided potable water and removed and treated wastewater, drained land and managed floods, and created waterways to facilitate navigation. Such projects demanded moving large amounts of earth and building masonry structures for channels and dams. Bridge engineers built structures for crossing ­rivers, and aqueducts for the transport of fresh w ­ ater. All this construction required accurate surveying and land measurement methods. Military and civilian construction projects both required the same engineering skills and, in fact, usually employed the same people. Only once these fundamental requirements of civilisation had been provided, and relative peace reigned, were e ­ ngineers able to devote their efforts to non-military projects such as the religious, commercial and civic buildings of ancient Greece and Rome, Renaissance Italy and the European Enlightenment of the 18th century.

In modern times, researchers studying the careers of the great historical figures involved in construction have succumbed to the somewhat romantic tendency of labelling them as ‘architects’ to distance them from the bloody world of war. However, Vitruvius was trained as a military engineer to build defensive earthworks and fortifications as well as bridges and large weapons of war. After his military service he was commissioned to manage the ­water supply (presumably of Rome) in addition to various civil construction projects. Filippo Brunelleschi worked for many years on the

fortifications of Florence; Michele S ­ anmicheli, the large Sangallo family, F ­ rancesco di ­Giorgio ­M artini – who among other things was responsible for Siena’s water supply – and even ­Leonardo da Vinci were also all military engineers. During the Renaissance it was still common for the same civil and building engineers to work on military and non-military projects alike.1

Civil engineering in the Age of Enlightenment and in the Industrial Revolution Civil engineering in the 17th and 18th century focused on water management – land drainage, water supply and navigation – and on building roads and bridges. In France, especially, civil engineering works were considered to be of national importance for economic and commercial as well as for military purposes. Between 1662 and 1671, the Minister of ­Finance Jean-Baptiste Colbert increased the state expenditures on roads and b ­ ridges from 22,000 to 623,000 pounds (livres). In 1666 he also commissioned the civil engineer PierrePaul Riquet to build the 240-­k ilometre-long Canal du Midi linking the Mediterranean with the Atlantic Ocean. In 1669, Colbert ­created a Corps des commissaires des ponts et chaussées (Corps of Commissaries of ­Bridges and Roads) which, in 1716, became the Corps des ingénieurs des ponts et chaussées (Corps of Engineers). The first technical institute in France dedicated to military and civil engineering and building construction was the Académie royale d’architecture (Royal Academy of Architecture), founded in 1671 under the directorship of François Blondel, who was himself a military engineer and architect for Louis XIV as well as architect of the City of Paris. To attract more recruits and to raise

On Inventors, Entrepreneurs, Problem-Solvers and Designers

14

Bill Addis

1

For further discussion on the growth of civil engineering during the Renaissance, see William Barclay Parsons: Engineers and Engineering in the Renaissance. ­Baltimore 1939, reprinted Cambridge, MA 1968.

2 The role of the École nationale des ponts et chaussées in the development of modern civil engineering is described in: Antoine Picon: L’invention de l’ingénieur modern: L’École des Ponts et Chaussées 1747–1851. Paris 1992.

Below Locks at Fonceranne on the Canal du Midi (FR) 1670s, engineer: Pierre-Paul Riquet

the quality of entrants into the Corps des ingénieurs des ponts et chaussées, the École des ponts et chaussées (School of Bridges and Roads) was founded in 1747. By the end of the century, the Corps was responsible for virtually all French public works in all branches of civil engineering. The importance of these two institutions cannot be overstated. They defined the modern civil engineer and developed the model for training engineers which is now used throughout the world. The first important textbooks on civil engineering (which included military applications) were published around this time – among them La science des ingénieurs dans la conduite des travaux de ­fortification et d’architecture civile (1729) and L’Architecture hydraulique (1737–1753) by Bernard Forest de Bélidor.2 In the late Middle Ages, German engineers were world leaders in military e ­ ngineering as well as in metallurgy and mining-related civil engineering, as demonstrated in the great books Bellifortis (c.1405) by Konrad Kyeser (1366–1405) and De re ­metallica (1556) by Georgius Agricola. However, from that time to the end of the 19th century, civil engineering in German-speaking countries did not achieve the same international impact as that of Britain and France. Nevertheless, there were many great German civil engineers in the 18th century who worked mainly on hydraulic engineering and bridge building and on developing a national infrastructure, chiefly for commercial purposes. Caspar Walter was a ­hydraulic engineer and bridge builder from Augsburg and is well-known today for his books Architectura hydraulica (1754), Brücken-­ Bau (1766) and ­Zimmerkunst (1769).

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During this era of emerging globalisation, civil engineering made possible the development and construction of the infrastructure needed to support maritime trade – docks and harbours, canals, wharves and warehouses – for the importation, storage and distribution of high-value commodities and raw materials not available in Europe, such as spices, cotton and silk. Alone among European countries, Britain developed the industries that converted these imported raw materials (mainly cotton and silk) into products (textiles) that could themselves be exported, generating vast profits. From the 1750s, this enormous trade led to an even greater demand for civil engineering works in harbours, as well as to a boom in the construction of multistorey textile factories and the manufacture of textile machinery. While early factories had been powered by water wheels, the second half of the 18th century saw water power replaced by steam engines. Since the textile factories were all located inland, a huge network of canals was constructed to connect them to the major ports. Demand for bridges and a larger system of roads grew as well. Starting in the mid-1830s, a new railway network for goods – and later for passengers – revolutionised transportation throughout the world. By the 1870s, British railway contractors had constructed not only the British rail network, but also thousands of kilometres of railway lines throughout Europe and in North and South America.

The most remarkable difference between developments in Britain and in continental ­Europe was that all the commercial and construction activity in Britain – specifically, the

Civil and Building Engineers – the Emergence of the Professions

Networks know no boundaries The Pauli truss employed by BRUNEL achieved technical maturity within another network, this one located in Bavaria. Together with the Glass Palace in Munich, built 1853–1854, the Großhesseloher Bridge (which was finished in 1857 and replaced with a new construction in 1985) was the kingdom’s most prominent civil engineering structure of the 19th century, and its effects spread far beyond its borders. The 259-metre long bridge was part of the Bavarian Maximilian Railway linking Munich and Trieste, and it crossed the valley of the Isar River at a height of 31 metres. The length of each of its two central Pauli trusses spanned 56 metres, while those at the ends were 30 metres long.

FRIEDRICH AUGUST VON PAULI, from whom the truss takes its name, came to the Supreme Building Authority of Bavaria as a senior engineer, and was appointed a professor at the University of Munich and director of the ­Polytechnic. He travelled to Great Britain in 1843 and 1844. From 1841 on he had already been working on the Ludwig South-North Railway and is therefore considered one of the progenitors of the Bavarian State Railways.

His first constructions were timber bridges with Howe trusses and, less frequently, Town trusses. One of the first innovations of his professional life was an iron bridge spanning the Günz River near Günzburg; the bridge’s truss, for which he improved the calculation methodology, is considered the forerunner of

the Pauli truss. PAULI worked closely with the Nuremberg-­based iron construction company Klett & Co., which had gained recognition with the construction of the Glass Palace in Munich and in the following years built many bridges with Pauli trusses. By 1870, five large bridges, including the Großhesseloher, and innumerable smaller bridges had been created. But when PAULI retired at the age of 68, the use of the Pauli system in Bavarian bridge construction essentially came to a halt.

At PAULI’S special instigation, his colleague KARL CULMANN visited Great Britain and the United States in 1849 –1850 in order to study the many types of truss systems in use there.

His publications describing the freer and more innovatively designed timber and iron trusses he saw overseas caused a sensation at home. In 1855, he became a professor at the Techni­sche Hochschule in Zurich. His book, Die ­graphische Statik (Graphic Statics) paved the way for a new theory of frameworks. His students included famous engineers such as MAURICE KOECHLIN. The framework system of the lenticular truss was thereafter improved by PAULI’S student HEINRICH GOTTFRIED GERBER and Karl von ­Bauernfeind. PAULI himself, whose achievements lay more in the realm of organisation, had never written anything about the lenticular truss; it was GERBER who first published an essay in 1865 about what he called the “Pauli” truss. Since the continuous beams that had been used thus far made calculations difficult,

On Inventors, Entrepreneurs, Problem-Solvers and Designers

24

Above The Royal Albert Bridge over the River Tamar was built under the direction of Isambard Kingdom Brunel from 1854 to 1859. It boasts two 139-metre Pauli trusses, the longest ever built. The force distribution in both of these trusses is readily observed: the upper chord is formed by a tube under compression, the lower by a chain under t­ ension.

Opposite, left The Walchensee Power Plant in Kochel am See is a high-­ pressure storage power station that was commissioned in 1924. It had been designed and built by entrepreneur and civil engineer Oskar von Miller starting in 1918. Its power output of 124 megawatts makes it one of the largest plants of its kind in Germany to this day. The Pelton turbines are coupled with single-phase generators (installed on 30 October 1924), which are designed to generate electricity for the ­railway.

Opposite, bottom The foundation and construction of the Deutsches Museum became a milestone in the history of ­civil engineering, a development for which we once again have Oskar von Miller to thank. The illustration depicts the state of construction in 1914: at the beginning of World War I, the finished copper roofing had to be taken off again and donated to the state. The museum building, located on an island in the Isar River, was not inaugurated until 1925.

a cantilevered hinged girder represented a practicable alternative. GERBER, who eventually worked at Klett in Nuremberg as a contractor and engineer and later at the Gustavsburg Works of the Augsburg-Nuremberg Machine Factory Corporation (MAN) (see “Engineers as Entrepreneurs”, p. 119) was granted a patent in 1866 for a hinged girder that bears his name. This system was used by BENJAMIN BAKER and JOHN FOWLER in their design for the Firth of Forth Bridge at Queensferry in Scotland, which was built from 1882 –1890 and spans 521 metres.

The civil engineer OSKAR VON MILLER and his network, which extended to the United States and Japan, exemplify the state of affairs in the early 20th century. VON MILLER was determined to electrify the Bavarian railways and built storage and hydraulic power stations to supply the necessary electricity. In his first sensational attempt he transformed the hydraulic power of the Neckar River into electrical current and demonstrated that alternating current could be successfully relayed over long distances. In 1891, as the director of the International Electrotechnical Exhibition in Frankfurt am Main, he organised a 20,000-Volt power transfer between Lauffen and F ­ rankfurt, marking an important breakthrough in the transmission of alternating currents. The American electrical engineer Nikola Tesla and the engineer and entrepreneur George Westinghouse made use of the German engineer and researcher’s findings when they installed alternating current generators in the Niagara Falls Power Plant, which was completed in 1895 and whose 78.3 megawatts made it the most powerful station of its day. From 1918 until 1924, VON MILLER was the project manag-

25

er of the Walchensee Power Plant, which at the time was the largest hydroelectric power plant in the world and boasted an output of 124 megawatts (see “Engineers as Entrepreneurs”, p. 119). VON MILLER’S enthusiasm for technology caused him to draw on his network of contacts in order to found the Deutsches Museum in Munich as a beacon of technology.

During the construction of a concrete dome for the Zeiss Planetarium in Jena, he became the nexus of a subsequent network of civil engineers including WALTHER BAUERSFELD, ULRICH ­FINSTERWALDER and FRANZ DISCHINGER (see “On the Development of the Zeiss-Dywidag Shell Construction System”, p. 44).

There can be no doubt that the networks of shared information among civil engineers are essential for optimal design and building solutions. By facilitating the exchange of knowledge and expertise, networks contribute to a continual improvement in technological opportunities and increase their potential uses. With their individual abilities and their particular life aspirations, building protagonists do their part by creating masterworks that project their effects far beyond their own times.

Especially since the years after World War II, increasingly denser and more effective networks have sprung up, and not just of engineering knowledge. The development of new and ever faster methods of communication, digitisation and specialised publications, ­disseminated also via new media, as well as the merging of different fields of expertise in project-specific collaborations, have all smoothed the way for the largely globalised network of the present day that we all use on a daily basis and as a matter of course.

Networks of Engineering Expertise

Women Pioneers of the Big Modern Building Sites – How They Became Who They Are

Female civil engineers are rare – and brave.

Though today they are in demand by industry and universities alike, there are still many fewer women than men involved in building. Female role models can be found only through painstaking research, but they exist: the women pioneers of the great building sites of the Modern Age. Researchers into the history of civil engineering who are looking for its female contributors quickly learn that it was no small matter for them to gain a foothold in the civil engineering profession. In the United States, women were generally granted access to a secondary education at women-only colleges and at some state universities beginning in the 1840s. In Britain, Oxford accepted women in 1919, ­Cambridge not until 1948. Princeton and ­Harvard, as well as the French Grandes Écoles, on the other hand, refused to admit women into a technical course of study until the 1970s.

In Western Europe, women were occasion-

ally accepted starting in 1871, while the first woman to graduate from the Swiss Federal Institute of Technology in Zurich did so in 1877.

Here, women had been admitted as students since 1855, but it was not until 1918 that the first female civil engineer, Elsa Diamant from ­Hungary, earned her degree.

In the German Empire, technical universities opened their doors to women between 1905 (Bavaria)1 and 1908 (Prussia), but in Austria it took until 1919, and only on the condition that their fellow (male) students were not to be disturbed.

Only a few spirited women enrolled. Depending on their bearing, they either tolerated or self-­ confidently ignored the overt and covert discrimination to which they were subjected. What they all had in common was their indisputable courage: the women civil engineers of the Industrial Age, who found access to and used technology, and the women of the early Modern Age, who went even further to build their careers on it.

Margot Fuchs

1

Starting in 1899, women were accepted as auditors to what is now the Technical University of Munich, but they could not matriculate until 1905.

2 Madge Dresser: “Sarah Guppy”. In: ­Oxford Dictionary of National Biography, Oxford 2016. Online: www.oxforddnb. com/index/109/101109112.

3 Unknown writer in the Bristol Mercury, 14 December 1939. See also: www.cliftonbridge.org.uk/did-­sarah-guppy-designclifton-suspension-bridge (30 June 2017).

4 Richard G. Weingardt: “Emily Warren Roebling”. In: Engineering Legends.

Great American Civil Engineers. 32 Profiles of Inspiration and Achievement.

Reston, VA 2005, p. 55 ff.

5 ibid., p. 58.

Left Patents by Sarah and Samuel ­Guppy in Bennet Woodcroft’s Alphabetical index of patentees of inventions Above Emily Warren Roebling, in a photograph taken between 1860 and 1880 Opposite Brooklyn Bridge, documentary photograph of opening day on 24 May 1883

On Inventors, Entrepreneurs, Problem-Solvers and Designers

26

cured the family business a lucrative contract.

The Guppys kept company with I­SAMBARD ­KINGDOM BRUNEL and THOMAS TELFORD, the most respected engineers of the time; their son Thomas Guppy was BRUNEL’S assistant.

The press, meanwhile, whispered that TELFORD and BRUNEL were using Sarah’s ideas, passing her over as the actual inventor.3 But it was not only as an innovator that SARAH GUPPY made a name for herself. As a businesswoman she invested in suspension bridge projects, was the part-owner of a railway company and contributed to the funding of the Bristol Institute for the Advancement of Science. As an author and reformer she not only participated in discourses on construction engineering, but also drew public attention to societal problems in her surroundings and campaigned for change.

Hands-on and on-site – self-taught doers In the early 19th century, there were families of affluent entrepreneurs in England and the United States in which women had significant standing without being relegated to the roles of housewife and mother, as the societal norms of later years dictated. These were the circles in which SARAH GUPPY moved. She came from a family of metalworkers and sugar traders. In 1795, SARAH married Samuel Guppy, a smelter, manufacturer of agricultural machines and merchant from Bristol. 2 She gained her technical training ‘on the job’ in the informal educational environment of the family business. She developed drawing skills, built a model of a suspension bridge and kept written records of all her technical knowledge. Ten patents were issued to her, ranging from the protection of railway embankments from erosion and landslides by the planting of poplars and willows (1811) to a method for caulking the hulls of ships (1844). While negotiating with the Admiralty one day, she cannily mentioned a patent for an antifouling paint, which se-

27

In the second half of the 19th century, in the United States, EMILY WARREN ROEBLING occupied a similar place in society.4 She married the engineer WASHINGTON ROEBLING, the eldest son of the German immigrant JOHN ROEBLING, who was a cable manufacturer, architect and bridge-builder. Together, father and son planned the construction of a suspension bridge over the East River in New York. After the death of JOHN in 1869, WASHINGTON took over as chief engineer of what later became known as the Brooklyn Bridge. When he himself fell ill and was unable to work for extended periods, EMILY kept the construction work on track, since the family business depended heavily on the success of this project. Through self-study she acquired specialist knowledge in mathematics, the strength of materials, catenaries of chains, and in cable and bridge construction. In her daily inspections of the building site she learned the engineers’ language, handled the technical correspondence, and negotiated with subcontractors, materials suppliers, the authorities and public building clients – in constant consultation with her husband and in line with his ideas. From 1872 until the bridge was opened in 1883, EMILY ROEBLING was the public face of the Roebling engineering firm.5 After the bridge was completed, she went on to study mathematics and law in New York, graduating with a law degree in 1899.

Women civil engineers of the Modern Age: elite education and practical experience The engineering elites that came into being in industrialised societies up through the early 20th century believed that a formal scientific education at a university and hands-on experience obtained by working at a public or private

Women Pioneers of the Big Modern Building Sites – How They Became Who They Are

Engineering Aesthetics

Structural engineering combines apparent contradictions – science and art, intuition and empiricism – but its full creative potential is often underestimated. Creativity in engineering goes far beyond the usual intuitive interpretations of the basic principles of physics and geometry and of the building code to establish new, non-standard techniques. A structure is often discussed merely in terms of economy and efficiency, but it also incorporates aesthetic factors. The combination of both aspects is crucial, as the Spanish engineer EDUARDO TORROJA has observed: “The functional purpose and the artistic and structural requirements must be considered integrally from the initial conception of the project. The artist should not be required at the last moment to give artistic appearance to what is already completed, and the technician’s task should not be limited to only devising means of keeping the structure up. Both should work together to form an integrated whole.”1 The engineering discipline, at its very best, forms a complex synergy that OVE ARUP called “total design” or “total architecture”, wherein building design, structure, and construction are integrated to form a coherent, intertwined process and project.

to be found imagination, intuition, and experience, and which demands a certain freedom in the creative agent. It adheres, in short, to the same laws as those of artistic creation. Thus it presents to some minds an inconvenience, in that such laws cannot be included in any chapter of the Building Regulations.”2 However, throughout history engineers have not always received the recognition that they deserve as both designers and problem-­ solvers. What is design to an engineer, where do the focal points of innovation lie and what does the creative process of problem-solving look like? What appears in their mind’s eye as they design and what do they want to render visible?3 How do they influence the design of not just the technical elements but of the formal aspects of architecture as well?

In engineering culture there has been a shift in the understanding of structure’s influence on the shaping of form and space, of its relationship to aesthetics and its impact on pragmatic and theoretical concerns. Structures are often presented poetically as an engineering accomplishment, because they both combine and arise from creative and technical thinking. FÉLIX CANDELA, in emphasising efficiency, economy and elegance, noted that “design and structural design, of course, is an intellectual process of synthetic nature in which is

On Inventors, Entrepreneurs, Problem-Solvers and Designers

36

Nina Rappaport

1 Eduardo

Torroja: Philosophy of ­Structures. Berkeley 1958.

2 Felix Candela: Toward a New Philosophy of Structure. Student publication, School of Design, NCSU, 5, No 3, 1956.

3 See Eugene S. Ferguson: Engineering in the Mind’s Eye, Cambridge, MA, 1992.

4 Sylvie Deswart, Bertrand Lemoine: L’Architecture et les Ingenieurs. Paris 1979.

Below The Penguin Pool at the London Zoo (GB) 1935, Ove Arup Opposite, top Boots Pure Drug Company, Beeston (GB) 1933, E. Owen Williams Opposite, centre Raleigh Arena, North Carolina (US) 1953, Matthew Nowicki / Fred Severud Opposite, bottom Spiral ramp inside the Fiat factory at Lingotto, Turin (IT) 1926, Giacomo Mattè-Trucco

Ingenuity A straightforward analysis of etymology yields an interesting fact: The English word ‘engineer’, or in French and German ingenieur, has the same root as the word ‘ingenious’, defined as that which is imaginative and ­creative. The engineer’s work is closely related to creative design, since it involves solving problems in many different fields. Yet engineering is often seen as largely mathematical and empirical rather than aesthetic and intuitive. But the work of the engineer goes far beyond mathematical equations; it is conceptual, drawing on the formal as well as the rational. On the other hand, engineering is not a science, because it is subjective; when two engineers are presented with the same problem, they will provide different solutions. However, the structural feasibility of both approaches can be tested, and in this way the work is sci­ entific. Some engineers always work with the proven systems known as structural building codes, which are tied to strict parameters, while others use rules of thumb. Some use these rules as a baseline and manipulate them from concept through to implementation with a combination of analysis and intuition. Creativity enters the picture when the manipulation of structure exceeds established norms.

that proved to be more innovative. They experimented with newly available technologies and materials such as iron, steel, and glass.4 This development is evidenced by the introduction of professional engineering courses in architecture schools, but also in the work of early British and French engineers such as Thomas Pritchard, whose Iron Bridge (1779) near Coalbrookdale in England was the first iron bridge ever designed, or in the prefabricated steel bridges and the Eiffel Tower (1889)

by GUSTAVE EIFFEL. Structures of glass and steel became a manifestation of a new industrial and technology-based culture. This is especially apparent in the works of JOSEPH PAXTON, who drew inspiration from the giant water lily Victoria amazonica to develop the steel beam structure for the Great Conservatory at C ­ hatsworth (1840) and for the Crystal Palace (1851) in ­London. With these accomplishments he shaped the new aesthetics of his time.

In the early modern era, engineers experimented with new reinforced concrete systems to develop longer spans and parabolic shells. Examples of this are the works of the Frenchmen FRANÇOIS HENNEBIQUE and ­EUGÈNE FREYSSINET or that of Swiss engineer ROBERT MAILLART, who designed elegant concrete bridge structures. Experimentation in concrete was also critical for large spans in industrial structures, as seen in the buildings

by British engineer OWEN WILLIAMS. Italian engineer ­Giacomo Mattè-Trucco was impressed by the designs of American engineers and experimented with function and spatial structure at the Fiat factory in Lingotto (1926) by building an automobile test track on the roof. PIER LUIGI

Historical context Over the years, there have been critical moments of transformative change in engineering, ushered in by novel materials, new technologies or ingenuity. Especially in Europe during the late 19th century, engineering was considered distinct from architecture both academically and culturally. But by the end of the century, it was often the architectural projects and prototypes designed by engineers

37

Engineering Aesthetics

Creating Spaces: Linking ­Aesthetics and Structure

The need for protection and security has always been a motivation for the creation of spaces. The cultural and communal goals of different societies are reflected in the way their private and public spaces are designed.

At the same time, the designs are often also a demonstration of what is technologically possible. About 200 years ago, exhibition halls and event venues, and later on also aircraft hangars and the enormous spans in railway stations and market halls, represented the vanguard of experimental approaches that led to new geometric forms and innovative uses of materials. Nowadays it is often the smaller projects that lie at the cutting edge.

The development of different types of support structure and constructional form is often linked to the use of newly developed materials.

Domes and vaults based on the shapes of tents and huts long dominated structural engineering, until industrialisation and the new material iron allowed the introduction of framework and skeleton structures, which became a new building type and ushered in the era of prefabrication. Though these structures were defined along largely geometric lines, force flows would soon inspire the design of corresponding constructions such as shells (later also ­network and grid shells), folded plate as well as tensile structures (see “Wide and Light”, p. 64).1 In these designs, form finding occurred (and still occurs today) in a number of different ways: through models, simulations, experiments, analytical and mathematical methods or through inspiration drawn from systems and structures of the world’s flora and fauna.

1 Rainer Barthel distinguishes between three categories: geometrically defined structures (orthogonal structures), structures generated from the laws of statics, and free-form structures. See Rainer Barthel: “Form der Konstruktion – Konstruktion der Form.” In: Exemplarisch.

Konstruktion und Raum in der Architektur des 20. Jahrhunderts. Munich 2002, pp. 15 – 26

Facing page ICD / ITKE Research Pavilion 2013 / 14, Stuttgart (DE) Jan Knippers, Achim Menges Left Centennial Hall, Wrocław (PL) 1913, Günther Trauer, Willy Gehler; architect: Max Berg

43

Creating Spaces: Linking Aesthetics and Structure

usual computer-controlled fabrication methods do. Thanks to the completely computer-based design and prefabrication techniques, the entire building was manufactured and assembled in just four weeks.

Innovations in building materials: fibre composites A careful analysis of biological structures reveals that these are very frequently not isotropic but composed of fibres, such as the cellulose in plants, chitin in insect carapaces, collagen in bone or spider silk. A combination of different alignment directions and packing densities allow them to achieve very finely tuned structural ­characteristics. In addition, ­fibre bundles facilitate a multitude of other functions: they transport nutrients, catalyse chemical reactions, recognise signalling substances and act as ­passive actuators (in pine cones, for e ­ xample, drying out or moistening the fibre layers oriented along different directions causes them to open and close in response).

Many modern high-performance materials rely on the principle of anisotropic fibre reinforcement but, in comparison to natural structures, make very limited use of the potential for structural and functional differentiation. In general, mats with orthogonally arranged strengthening fibres of glass or carbon are placed in a mould and impregnated with polyester or

ENCLOSURE + SPACE | Arch and Shell Structures

epoxy resin. These fibre composites are used today in all sorts of technological applications in which form or weight are of critical importance, such as in wind energy facilities, in the aerospace industry, on sailing boats and, increasingly, in automobile manufacture.

Only in the building sector has their use remained limited to specialised niches, even though they are by no means new to the field.

The Monsanto House in California, built in 1957, was the first prototype of a house built from prefabricated sandwich elements with a polyurethane foam core and a facing layer of glassfibre-reinforced plastic. Despite enormous public interest and a series of ­follow-up projects, this “house of the future” never achieved lasting success. In the mid-1970s, the experimentation with synthetic structures ended as quickly as it had begun. A lack of design experience and flaws in implementation had caused structural damage that gave fibre-reinforced plastics a reputation for being inferior materials. But a more salient reason for their decline is probably the fact that an ever more individualistic society found the concept of a serially prefabricated living unit increasingly unattractive.7 Still missing today are approaches for the manufacture and assembly of fibre composites that are adapted to the specific demands of the building industry. In contrast to aeroplane or automobile production, the focus in

54

Above Comparison of the wing cases (elytra) of flying (left) and flightless ­beetles (right) Below Frames that can be adapted to given module dimensions are mounted onto two industrial robots with coupled steering. The stationary fibre spool is placed between the robots. The inexpensive glass fibres are drawn through an epoxy resin bath and wound to form ­hyperbolic surfaces. The high-strength carbon fibres are deposited wet on top of this form, following the path of the primary loads. As soon as the resin has cured, the elements can be removed from the frames.

7

Jan Knippers et al.: Atlas Kunststoffe und Membranen. Munich 2010, p. 12ff.

8 Stefana Parascho et al.: “Modular ­Fibrous Morphologies. Computational Design, Simulation and Fabrication of Differentiated Fibre Composite Building Components”. In: Philippe Block et al. (eds.): Advances in Architectural Geometry 2014. Zurich 2015, pp. 29 – 46.

Top and bottom ICD / ITKE Research ­Pavilion 2013 –14. Finite element analysis of the stress curves and implementation into a production-ready force-flow arrangement of the carbon fibre reinforcement (below)

construction is predominantly on the manufacture of custom-made large-scale pieces whose geometry is individually determined.

For these, the creation of the usual polyurethane foam moulds is not only very expensive, but also produces a lot of residual waste. In construction, furthermore, criteria such as durability play a major role during both the manufacture and usage phases of the building, while other aspects, like meeting high standards in production tolerances or in mechanical efficiency, are of secondary importance.

For the design of the ICD / ITKE Research Pavilion 2013-14, a process was developed specifically for architectural applications that minimises the cost of producing formwork moulds. In a technique known as coreless

winding, robots deposit resin-saturated fibres onto a rotating steel frame.8 The frame is later removed, yielding a rigid and load-bearing fibre structure whose metal content is limited to screws and screw sleeves.

The natural inspiration for this was supplied by the wing cases (elytra) of beetles, which protect the hind or flight wings from mechanical damage. The elytra consist of two layers, combined via a special orientation of the chitin fibres into a very light-weight yet robust structure. This concept was transferred to the pavilion in the form of its modular, double-­layered structure of glass- and carbon-­reinforced ­fibres. The 36 geometrically different modules are so light that a single person can carry them. The goal of the research project was primarily to explore the fabrication process

55

Computer-Based Processes for Biomimetic Structures

nates of the design model control nodes such as the FEM nodes, or the positions of the Non-Uniform Rational Basis Spline (NURBS) control nodes in the IGA. All the outputs of a structural analysis – for example, displacements, stresses or resonance frequencies – are suitable candidates for target functions and boundary conditions. If the goal of optimisation is given as the minimisation of strain energy for a predefined structural mass, the inefficient bending states are removed during the optimisation process in favour of load transfers via membrane stress states, resulting in a structural geometry of maximum stiffness and minimal bending that is comparable to that of a hanging model.14 The form finding process for elastic (prestressed) grid shells differs from traditional form finding for shell or membrane surfaces in that a target geometry

ENCLOSURE + SPACE | Arch and Shell Structures

is specified. This can be defined geometrically or determined via a balance of forces in a hanging model. The final generated form of the elastic grid shell reflects an approximation of this “ideal” geometry that takes into ­account the bending and axial stiffness of both the rods and the grid topology.15

A new numerical tool for form optimisation: IGA The shift in timing between the development of computer-assisted imaging and numerical structural analysis has led to the evolution of independent and mathematically divergent descriptions of geometric objects in these fields.

The separately performed discretisation of design geometries generally required for computer-aided analysis (“meshing”) is a computation-

62

14

see note 4.

Christoph Gengnagel, Gregory Quinn: “Große Verformungen. Über das Entwerfen von vorbeanspruchten Gitterschalen”.

In: GAM 12. Structural Affairs. Potenziale und Perspektiven der Zusammenarbeit in Planung, Entwurf und Konstruktion. Basel 2016, pp. 169 –189.

16 Michael Breitenberger et al.: “Analysis in Computer Aided Design. Nonlinear Isogeometric B-Rep Analysis of Shell Structures”. In: Computer Methods in Applied Mechanics and Engineering, Vol. 284, 2015, pp. 401– 457.

17 Benedikt Philipp et al.: “Integrated ­Design and Analysis of Structural Membranes Using the Isogeometric B-Rep Analysis”. In: Computer Methods in ­Applied Mechanics and Engineering, Vol. 303, 2016, pp. 312– 340.

15

Opposite, top Interior vertical view of ­Hybrid Tower One, showing the internal radial restraining system Opposite, below Hybrid Towers One and Two; far left Tower One prototype of an 8-metre high tower of bending-active glass-fibre reinforced plastic (GRP) rods and knitted membrane in Copenhagen (DK) 2015. Centre for Information Technology and Architecture (CITA) at the Royal Danish Academy of Fine Arts, ­Department of Structural Design and Technology (KET) at the Berlin Univer­ sity of the Arts; centre Tower Two simulation of form finding with the FEM for the hybrid system and analysis of the stresses under prestressing and wind loads. KET, 2016; far right Tower One prototype of an 8.30-metre high tower of bending-active glass-fibre reinforced plastic (GRP) rods and knitted membrane in Guimarães (PT) 2016. CITA, KET, Universidade do Minho, AFF – A. Ferreira & Filhos Above Simulation of the erection, i.e. shaping, process of the elastic grid shell, KET Below Prototype of the elastic grid shell: span 10 m, GRP rod diameter 20 mm, wall thickness 3 mm, Berlin (DE) 2013, KET

ally intensive part of the analysis process, and accounts for significant time delays between the generation of geometric design iterations and the assessment of their physical performance capabilities. A typical mathematical description of free forms in CAD systems is implemented via streamlined assembled NURBS (Non-Uniform Rational B-Splines) patches for the surfaces. Using these NURBS surfaces as a common basis for both geometrical description and structural computations makes it possible to integrate the geometrical design and analysis processes.16 It also allows for an avoidance of unwanted geometric differences between the design model and the numerical structure analysis model that arise from approximations based on the discretisation of low-order polynomials. The critical advantage of the Isogeometric Analysis process, apart from the removal of the geometrical conversion step, lies in the possibilities for refining the discretisation of the structural geometry without changing geometric or mechanical parameters.

The greater precision of the NURBS initial functions results in better convergence characteristics than those for the polynomials that have been used in Finite Element Analysis to date.17

63

Form finding processes are part of structural design. The classical approaches to form finding, such as hanging models and soap film analogies, now play a much diminished role due to their inherent design limitations. The many opportunities for digital experimentation in the context of structural optimisation create new design options for generating forms using a multitude of different parameters. Not only is it thus possible to fully depict the mechanical properties of a structure in a continuum-­ mechanical model; simplified modelling strategies can now be employed that take into account only the most important characteristics of a structure, and allow, for example, kinematic states to direct an iterative approach to a solution. In this way, form ­finding is transformed into a highly complex process characterised by freely chosen parameters and design choices.

Structural Design and Form Finding Processes

7

method is implemented in different ways. A survey of current software products regarding this issue revealed an astonishing degree of scatter in the results.7 This is of little concern in practice, since the stress states found in all the identified forms may be different, but are all valid.

Pattern cutting methods and special material formulations are available only in very specialised software or as a service. In practice, the broad spread in material parameters usually requires extensive experience with compensation techniques. New pattern cutting methods yield high-quality cuts even for strongly curved surfaces and for extremely stretchable materials like knitted fabrics. Material models geared specifically toward cutting applications have been developed based on the Adaptive Response Surface Method, and can be adapted using standardised measurement data for a large number of different materials.8 Developments in the fields of coupled multiphysical analyses, Computational Wind Engineering or adaptive structures place significant demands on software and hardware. They also require the users of the computational tools to have extensive experience and indepth knowledge of their physical and methodological foundations. The use of commercial software therefore makes sense only in the case of specific installations. The numerical wind tunnel, for example, is used to deter-

mine the correlations between the deformations of lightweight tensile structures and the wind flowing around them (known as the Fluid-Structure Interaction or FSI).9 Since these fields promise to be rich in synergistic effects across the board, they are at present a very active and innovative area for basic research.10 The integration of CAD and FEM is being approached by way of Isogeometric Analysis (IGA). Program upgrades for use with original CAD models are available to practicing engineers, as are special applications for shells and membranes and even plug-ins for individual programs.

The history and development of lightweight tensile structures is an ideal example of the way in which innovative building techniques and computation methods serve as mutual inspiration for one another and open up new, fertile fields of research with great potential for the future – fields whose results have effects far beyond their originally targeted aims.

The special expertise in lightweight structures developed in civil engineering, for example, is highly sought after for applications in other areas of structural engineering, such as in the construction of high-altitude weather balloons.11 Though it is a fair bet that FREI OTTO never thought of computer-aided simulation methods, his visionary power still affects us here and now.

Numerical wind field

Wind

ENCLOSURE + SPACE | Tensile Structures

70

cf. P. D. Gosling, B. N. Bridgens, A. ­ lbrecht et al.: “Analysis and design A of membrane structures: Results of a round robin exercise”. In: Engineering Structures 48/2013, pp. 313 – 328.

8 cf. B. N. Bridgens, P. D. Gosling: ­“Direct stress-strain representation for coated woven fabrics”. In: Computers and Structures 82/2004, pp. 1913 –1927; F. Dieringer, R. Wüchner, K.-U. Bletzinger: “Practical advances in numerical form finding and cutting pattern generation for membrane structures”. In: Journal of the International Association for Shell and Spatial Structures 53/2012, pp. 147 –156.

9 cf. A. Michalski, E. Haug, R. Wüchner, K.-U. Bletzinger: “Validierung eines ­numerischen Simulationskonzepts zur Strukturanalyse windbelasteter Membrantragwerke”. In: Bauingenieur 86/2011, p. 129.

10 cf. M. Andre, K.-U. Bletzinger, R. Wüchner: “A complementary study of analytical and computational fluid-structure interaction”. In: Computational ­Mechanics 55/2015, pp. 345 – 357.

11 cf. A. Bown, D. Wakefield: “Inflatable membrane structures in architecture and aerospace: Some recent projects”. In: Journal of the International Association for Shell and Spatial Structures 56/2015, pp. 5 –16.

Top left Soap film model of a four-point sail Top right Streamlines around a fourpoint sail Bottom left Numerical wind field above a stadium roof Bottom centre Schematic sketch of a ­numerical wind tunnel Bottom right Simulation of the wind pressure distribution on a large sunshade

Knut Göppert

Right Spoked wheel principle

The Spoked Wheel for Ring Cable Roofs in Lightweight Construction

The spoked wheel, which everyone is familiar with from the bicycle, is an extremely material-­ conserving and clever structure. In the bicycle, tension members known as the spokes transfer the loads between the ground and the axle. To ensure the necessary lateral stability, the spokes are spread apart slightly toward the hub, which allows loads perpendicular to the plane of the wheel to be redistributed as well. These are the properties that are put to use by orienting a wheel horizontally, so that wind and snow loads are transferred out through the flared spokes.

But how is it possible for such a delicate structure to withstand such high loads? The answer to the riddle is pretensioning: the many spokes of the wheel are pretensioned between the compression ring (the rim) and the hub. Though exterior loads will change the forces within the spokes, the spokes will always remain under tension. They stabilise the rim, so the support structure can remain slender even though it is under compression.

A system tensioned in this way, in which the hub can be replaced as needed with a tension ring, can be used for many building tasks and is especially suited for large-span roof structures. Using a few tricks and keeping in mind the appropriate equilibrium conditions, it is even possible to evolve the form from the circular bike wheel to a curved rectangle. Roofs like this are known as ring cable roofs. There are four main reasons that favour the ring ­cable roof principle: Economy – All interior forces are s ­ hort-­circuited.

This represents an elegant solution to a p ­ roblem that commonly arises in lightweight construction: the large cost of the foundations. The building components are defined as purely tensile or compressed structural elements, v­ irtually free of bending moments, so that they can be

71

Horizontal spoked wheel

The spreading of the spokes radially outward; two compression rings, one central point

Expansion of the central point to a circular tension ring

The Spoked Wheel for Ring Cable Roofs in Lightweight Construction

Water in Cities

In Germany, the average daily consumption of water is approximately 125 litres per person, of which only about 1.3 litres are used for drinking. In all, 85 per cent of water consumption in Germany is attributed to commercial uses in industry and agriculture.

Every day, enormous quantities of high-quality water must be supplied, and the wastewater must be collected, treated and recycled. The supply and drainage of water from districts and cities are of fundamental importance for public and environmental health, and present a challenging task for civil and environmental engineers.

The processing, purification and collection of water are just three of the functions of modern water networks. The conversion of old sewage canals, as for example in Emscher Park, ­creates new landscapes that very often result in an overall improvement in the quality of the

living environment. Open waterways that constitute part of the drainage system are now perceived as attractive green spaces that provide opportunities for local recreation, energy production and climate regulation. As a consequence, they have become a core component of urban development projects, necessitating a multitude of design and construction processes.

While the primary challenge about 150 years ago was to improve the sanitary conditions for the population at large, today’s designers are faced with a much more complex set of requirements. Increasingly scarce resources and a rise in the incidence of extreme rain events, together with demographic changes and urbanisation, demand focused attention. The solution lies in flexible modular systems that address technical concerns while simultaneously providing sustainable approaches to confront and facilitate the water and energy transition.

Facing page Groundwater well, Frastanzer Ried, Feldkirch (AT) 1980 Left Sewer system for Hamburg (DE) from 1856, William Lindley. After a great fire that destroyed almost a third of the Hanseatic city in 1842, the city council voted in favour of implementing a design submitted by canal construction engineer Lindley shortly after the disaster.

The plan for the reconstruction of the city and its sewage system also included a public water supply as well as washand bathhouses. In the following years, the first network of sewers on the ­European continent was established, which Hamburg residents call the ­Sielnetz.

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Water in Cities

Floating and Self-Erecting: TELWIND

Telescoping, self-erecting wind turbines would represent a significant simplification in offshore construction projects. The European Commission’s TELWIND research programme is currently studying how such floating turbines could be built.

The substructure consists of a buoyant hollow tank, attached with underwater cables to a heavy ballast tank that stabilises the entire structure. Assembled like a telescope, the tower is made up of tube-like segments of either prefabricated concrete or steel elements. An integrated self-lift allows the tower to be telescoped out from its mounting platform into its final position.

Above Schematic representation of a wind turbine Far left (top to bottom) Erection ­sequence: Positioning the tanks and mooring the tower – Ballasting the tanks – Jacking up the tower Left Rendering of the wind turbine

WATER + ENERGY | Offshore Wind Turbines

134

Flexible Membrane Wings for Wind Turbines

Right The equilibrium form identified by the form-finding process is the ­starting configuration for the numerical simulation.

Below Cross section of a membrane-­ covered wind turbine blade on a rotor.

This numerical simulation was used to calculate the airflow field.

Below, far right The Wright Brothers‘ glider, Kitty Hawk (US) 1901

To optimise the energy yield of wind turbines, the size of their rotor blades is constantly being increased. The loads generated by the extreme forces acting on the wings require commensurate adjustments to the support structure.

Membrane-covered wind turbine blades show great potential for reducing these loads. The flexibility and the modest self-weight of a membrane wing allow it to adapt to wind flows.

Engineers draw inspiration from many sources: the idea for this construction came from the design principles of the early days of manmade flying machines, e.g. the famous bi-plane gliders of the Wright Brothers, who tested their first aeroplanes in October 1900.

The membrane blades and their aeroelastic properties are developed in an iterative process involving a combination of simulation and form optimisation. The first step uses form-finding analysis to calculate the equilibrium geometry of the pretensioned membrane structure. Then the coupled interaction between the membrane wing and wind flow is determined via numerical simulation, which

135

evaluates the performance of the wing. Finally, the pretensioning condition of the wing is updated and the design cycle is repeated in order to optimise the wing configuration.

The numerical simulations are confirmed through wind tunnel experiments on a scaleddown prototype. For greater pitch angles, the membrane blades demonstrate increased lift properties as compared to their hard-blade counterparts.

TELWIND | Flexible Membrane Wings for Wind Turbines

Gaining Access

Facing page Construction site of the Zugspitze Cable Car, Garmisch-­ Partenkirchen, (DE) 2017.

Arge BauCon-­Hasenauer-AIS Below Today, 35 million kilometres of road are spread out over all the continents of the globe, partitioning the world into 600,000 sectors.

A functioning transportation infrastructure provides the foundation for our mobile society.

The demand for physical connectivity and for its associated networks is becoming increasingly complex. Pollution concerns, the maintenance of transportation routes and the safety of roads in topographically and climatically demanding regions all pose additional challenges.

The intricacy of this remit is expanded by the multitude of different modes of transit alone, which range from the car to the railway to various cable cars, maglev trains and funiculars, etc. and further to ships and aeroplanes.

Underlying it all is the basic question: who or what is being transported: goods or passengers? What does a given situation require, private transport or a public transportation system? Specialised constructions such as locks, ship lifts and canal bridges that arise in

the context of waterways are only some of the transportation structures that must be built, in addition to railway lines, canals, airports and countless others.

The extremely rapid development of transport infrastructure is inextricably entwined with industrialisation. From the beginning, the shipment of raw materials and goods put a higher burden on roads. The aim became to cover distances in as little time as possible and to achieve an effective linkage between different infrastructures to achieve this end. Approaches to the goal varied: in the UK, exceptionally talented individuals used experimentation to search for answers to the societal needs that intrigued them. In France, the method was more theoretical, entailing the foundation of academies.

No data Areas with high road density (interval between roads below 1 km) Roadless area patch size in km2 0 2,200 25,000 4,800,000

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Gaining Access

of view was the slab track using prefabricated slabs. Already in 1977, on a railway line segment linking Dachau and Munich-Karlsfeld in Bavaria, the first test track was laid in which prefabricated slabs were used as the load-bearing element on which the rails were fixed.

During the early years of the new millennium, the prefabricated-slab approach and the improved versions of the original slab track system, dubbed Rheda 2000, were the preferred solutions in the transfer of railway track technology expertise to Asia. Routes in Korea

and Taiwan were initially built on the basis of the Rheda variant. Since 2005, China has constructed more than 26,000 kilometres of ballastless high-speed rail line (with design speeds of up to 350 kilometres per hour) that can be traced back to German development work and to work done at the Chair of Road, Railway and Airfield Construction at the Technical University of Munich.

The slab track is the preferred standard for high-speed rail superstructure not only in Asia,

Left and below Newly constructed ­Berlin – M ­ unich ICE rail line segment between Ebensfeld and Erfurt (DE) 2017.

As part of the German Unity Transport Project, the Deutsche Bahn plans to use high-speed trains to provide an environmentally friendly alternative to travel by car and aeroplane. On the new 107-kilometre long stretch between Ebensfeld and Erfurt, passenger trains traverse the Thuringian Forest at 300 km/h, negotiating 22 tunnels and 29 bridges along the way. The Ebensfeld – Erfurt segment is the final step in the connection between Munich and Berlin. Parts of the line have four tracks to accommodate the different routing demands of passenger and cargo trains: the fast trains need relatively curve-free stretches of rail, whereas the slower and more heavily loaded trains require small gradients. Stations along the route that allow for passing ensure smooth traffic flow. Visual signals have been eliminated, since the important data is relayed by radio between trains, line control centres and transponders in the rail. This new train control and communication system will be used throughout Europe in the future.

Opposite The trains on the newly constructed Ebensfeld – Erfurt railway line will proceed on a ballastless track. The track slabs were positioned one after the other, even on bridges and in tunnels. The prefabricated elements allowed track construction to proceed much more rapidly than in the conventional ballasted system.

Grubental Bridge

Gümpental Bridge Viaduct at Weißenbrunn am Forst Mühlbach Bridge at Untersiemau Flutmulden Bridge at Wiesen

Füllbachtal Bridge

Kiengrund Bridge

Fornbach Bridge

Viaduct at Pöpelholz

Goldberg Tunnel

Itztal Bridge

Bridge over the Main at Wiesen

Kulch Tunnel

Truckenthal Bridge

Viaduct at Frosch­grundsee

Stadelbach Bridge

Eierberge Tunnel

Rennberg Tunnel

Lichtenholz Tunnel

Dunkeltal Bridge

Füllbach Tunnel

Müß Tunnel

Reitersberg Tunnel

Feuerfelsen Tunnel

Höhnberg Tunnel

MOBILITY + TRANSPORTATION | Construction of Roads and Railways

148

Baumleite Tunnel

Bleßberg Tunnel

Rehberg Tunnel

but in many other countries throughout the world. In Europe, significant lengths of railway line in the Netherlands, Spain and Italy were built using this system. In Germany, slab tracks are in use on the high-speed sections of the rail route between Hanover and Berlin (chiefly east of the Elbe), as well as for the Frankfurt – Cologne and Nuremberg – Ingolstadt lines.

On the latter two track segments, trains regularly reach speeds of up to 300 kilometres per hour. At the end of 2017, the railway line from Nuremberg to Leipzig via Erfurt was opened to high-speed traffic. Here, too, extended portions of the new track were laid using the slab track system. Ballastless track will be deployed on the Ulm – Wendlingen line as part of the Stuttgart 21 railway development programme and of the Trans-European Rail Network. When that is completed, all of the important newly

Rehtal Bridge

built rail routes in Germany will have been constructed using the ballastless track system.

Ballastless tracks in tunnels Ballastless tracks have many significant advantages for the sections of modern railway lines that traverse tunnels. Both the Channel Tunnel between France and the UK and the world’s longest railway tunnel, the Gotthard Base Tunnel in Switzerland, were completed using the ballastless track system. Its advantage in tunnels lies in the fact that no ballast needs be laid on the existing hard tunnel floor, as the elasticity can be provided either via the rail fasteners or underneath concrete blocks. This results in a significant reduction in wear. In addition, when slab tracks are employed, the vibrations in nearby built-up areas due to rail traffic, or the secondary airborne noise resulting from the transmission of those vibrations, are fairly easily minimised through mass-spring systems. Austria, for example, specifically installed a heavy mass-spring system in the slab track on the approaches to the Brenner Base Tunnel; the natural frequency of this system lies below 6 hertz, giving it a strong damping effect even for nearby buildings.

The slab track system is a good example for how decades of basic research at universities, performed in collaboration with industrial partners, can lead to new developments. If these can prove their worth in a successful transition into practical applications, they often find worldwide acceptance.

Oetztal Bridge

Massetal Bridge

Wohlrosetal Bridge

Schobsetal Bridge

Ilmtal Bridge

Wümbachtal Bridge

Röstal Bridge

Humbachtal Bridge

Wipfratal Bridge

Silberberg Tunnel Masserberg Tunnel Fleckberg Tunnel

Geratal Bridge at Ichtershausen

Brandkopf Tunnel Lohmeberg Tunnel

Tragberg Tunnel

Sandberg Tunnel

Apfelstädttal Bridge

Geratal Bridge at Bischleb

Behringen Tunnel

Augustaburg Tunnel

149

Slab Tracks for Rail Traffic

like bridges are beset even in the preliminary phases with the needs of many different interest groups: design advisory committees, residents, nature conservationists, etc. In an effort, in part, to retain some sort of control over all these demands, and to make it possible to implement design plans once the complicated negotiations with stakeholders have yielded some sort of agreement, building authorities have taken to considering supplemental and alternative proposals only in exceptional cases.

As long as the call for tenders is well thoughtout and all the construction constraints (building phases, buildability, required tolerances, etc.) have been considered, this approach certainly has its advantages from the perspective of the building clients. For example, the contract can be awarded more quickly at a lower administrative cost and with greater legal protection, since excluding alternative proposals from the tender process makes the project as a whole less vulnerable to attack (occasionally, procurement participants will feel unfairly treated and initiate legal proceedings against the awarding authorities). Sometimes even the alternative proposals by competitors are the subject of lawsuits, especially if they have not been explicitly requested.

Public building clients often exclude supplemental offers and alternative proposals because, to save time, the technical development or other subservices have already been awarded before the conclusion of the procurement process, which makes changes in the design or in the construction sequence difficult to accommodate. Frequently, they simply have too few staff or too little technical expertise to be able to evaluate alternative solutions.

In parallel, construction companies withdraw from consideration because, given this state of affairs, they see little point in submitting supplemental proposals and are therefore unwilling to incur the costs. To submit such tenders, companies have to go through considerable effort and expense during the preparatory phase to prove that the proposed alternatives are at the very least equivalent to the originally conceived project – and they still run the risk that their proposal will not even be considered.

Conversations that used to take place to clarify or discuss a proposed solution have been dispensed with for legal reasons, as the contents of an invitation to tender cannot be supplemented or changed after it has been issued.

What all these considerations fail to recognise is that it is critical to allow the operational know-how of an experienced company to influence the development of a technological solution early on, especially and specifically in the conceptualisation of technically difficult or

MOBILITY + TRANSPORTATION | Beam Bridges

complex construction tasks – which is what occurs as a matter of course in the development of alternative proposals. If such expertise is not available at the outset, the risks are, one, that the design contains weaknesses that impact its implementability; or two, that after having been awarded the commission, the contracted company attempts, with or without justification, to prove that the original conceptual design put out to tender cannot be realised.

Initiatives to foster a new spirit of ­enthusiasm and competition The consequence of recent developments has been the paradoxical situation in which supplemental offers and alternative proposals are seen as a complication rather than as a proven method for the overall optimisation of a project. With the goal of bucking this trend, lobbyists for the building industry have been approaching important public clients who are responsible for setting agency and community guidelines. At the German federal state level, some successes in this context have already been achieved. In Bavaria, for example, supplemental offers and alternative proposals will once again be admissible.1 This important first step must, of course, be followed up by many more. There is an urgent need for initiatives2 to infuse young civil engineering students with the same creative excitement and enthusiasm that were the hallmark of the profession during the Industrial Revolution. Another desirable step would be an increase in the personnel of government building authorities or more frequent consul-

158

1 On the premise that it was intolerable to subordinate engineering to bureaucratic, legal or procurement concerns, the Bavarian Building Industry Association (Bauindustrieverband) approached the Supreme Building Authority and succeeded, according to association president Josef Geiger, in convincing it in numerous discussions to accede to this important step.

2 e.g. www.ingenieur-talente.de

Opposite, top The Eschachtal Bridge near Rottweil (DE) 1977. On the basis of a supplemental proposal, this bridge was built in prestressed concrete instead of the steel specified in the original call to tender ­(opposite, centre). In order to design the dimensions of the necessary cross sections economically, a box girder with short cantilever slabs was first built by cantilever construction. After the force flows of the cross sections were established, the surface road was completed over the whole width with rear carriages.

Because of the innovative use of diagonal concrete braces, as well as for the construction method itself, this 443-metre long prestressed concrete bridge became the model for the more than 1-kilometre long Kocher Viaduct near Geislingen (DE) in 1979, which was successfully upgraded using an innovative concept in 2015.

Below Construction of the Lahntal ­Viaduct, Limburg (DE) 2017Max Bögl Stiftung and Büchting+Streit won the contract for its supplemental proposal.

This differed from the original specification in calling for more economical and environmentally friendly, but technically difficult, cantilever construction to be used along with cantilever formwork ­carriages.

tations with external engineering practices, in order to ensure that submissions to a call for ­tender can be evaluated by experts. Though such measures incur costs, these can be recouped in other ways. After all, alternative proposals are usually only accepted if they offer significant financial and technological advantages, such as extended lifetimes, easy maintenance or reduced construction times.

In addition to the urgently needed measures to raise general awareness of this issue, completely new contract models must be implemented that ensure a legally stable framework during the bidding process. This must stipulate, for example, that supplemental offers or alternative proposals should not require a re-evaluation of environmental compatibility tests, land use planning procedures or planning approval processes or lead to lawsuits against rival competitors. The goal must be to foster competitive spirit and ambition, to make participants aware that the contract will be awarded not for the least expensive proposal but for the best idea – that it is a competition of innovation and quality rather than a mere price war. A model that reflects these priorities is the ‘best bidder’ principle that was introduced by the corporation for the financing of the A ­ ustrian autobahn and highway network, the Autobahnen- und Schnellstraßen-Finan­z ierungsAktiengesellschaft (ASFiNAG). In its process, cost is only one of a series of criteria to be evaluated, which also includes such considerations as the quality of the workforce, the ­technical proposals or the construction time. Similar procedures have already been the standard in Anglo-American countries and also in Scandi-

159

navia for many years. These quality-­oriented approaches enable public building clients to seek out ideas and proposals that are advantageous for the process, the environment, the timing and the budget in equal measure.

New contract models support creative, holistic thinking In partnership agreements, the sponsor of the procurement process establishes clear criteria well in advance, which are then used in conjunction with a prearranged point-awarding system to evaluate the submissions. The bidder with the most points is awarded the contract. Afterwards, all join in identifying possible improvements, and any financial savings this results in are distributed among the participants. In the private sector this approach is already widespread, in the form of the ‘Guaranteed Maximum Price’ (GMP) construction contract model. In this model, the general contractor performs open-book calculations and guarantees project completion for a specified maximum amount. Any cost savings at the end are shared according to an agreed-upon key.

For complex undertakings, the German construction contract procedure (VOB) allows for a ‘competitive dialogue’, in which the operational expertise of general contracting firms can inform the development of a technical solution at an early stage of the proceedings.

The prerequisites for contract types in which quality is valued over price are a relationship built on trust, timely cooperation and single-­source planning whenever possible. In Germany, the still-prevalent separation of design and construction, combined with the segmentation of building processes, hampers progress. When competition planning, calculations, work preparation, execution planning and construction management are all performed by different practices, it is common for the parties to concentrate so much on their own assignments that they lose sight of the big picture. On the other hand, operating companies who bear more overall responsibility are eager to prevent operational problems that can negatively impact their own performance, rather than passing them along to their project successors.

The joy and fascination inherent in structural engineering should become the common denominator for engineers, construction companies and public clients. This will require initiatives that foster integrated knowledge and collaborative work to achieve common goals – not only to enrich the built environment, but also to allow engineers and building firms to thrive in an internationally competitive field.

Improving Quality and Efficiency through Expanded Procurement Procedures

refraction, a light-refracting effect that bends the supposedly straight-line aiming beam and therefore causes the calculated path from poly­gonal point to polygonal point to diverge from the true path. In the case of the C ­ hannel Tunnel on the British side, this resulted in a whole metre’s worth of deviation after little more than one kilometre of advance. The bending of the beam is caused by horizontal temperature gradients that develop due to the temperature difference between the rock and the tunnel atmosphere, and can be neither perceived nor avoided. The only available counter-strategy for the geodesist lies in determining the refraction angle of the beam by gyroscope measurements and by using the compass rule from opposing ends of a polygon side. The instruments necessary for this tap one component of the earth’s rotational moment to establish an absolute reference to true north. Given the refraction angle, if one also assumes that the beam follows a geometric circular arc, the refraction can be eliminated.

Within the last 100 metres of the work face in standard mining practice, the tunnel profile for the next drilling round must be set out, or, in the case of machine boring, the drive heading must be determined. In the latter case, careful advance planning is required, since the location of the narrow sighting window for the necessary measurements must be definitively established right up to the cutter head while the expensive tunnel boring machine is being built.

These minimum requirements come into play when the tunnel is driven just from the two portals. In order to accelerate the construction process, as is absolutely necessary in traffic tunnels several tens of kilometres in length, additional intermediate openings must be created. Usually these are lateral access tunnels that are driven to the main tunnel ­axis, where caverns are blasted from which the main tunnel can again be driven from both sides. Vertical intermediate shafts, such as the 800-metre one leading into the Gotthard Base Tunnel or the 400-metre one into the Semmering Base Tunnel, also require precise vertical alignment and transmission of the heading, the verification of which is absolutely critical. It is g ­ eodesy’s job, under the most challenging of conditions, to ensure that there is no more than a centimetre’s worth of lateral deviation for every kilometre of tunnel advance. The degree of difficulty here is only comparable to making a hole-in-one for every swing in a round of golf.

The question asked of tunnel surveyors at the beginning of this chapter is almost always followed up with: “And why is it important for it to be so exact – isn’t it enough if the two tun-

MOBILITY + TRANSPORTION | Tunnel Construction

nels meet at all?” The answer is no – particularly for the high-speed railway tunnels, it would most certainly not suffice. For high-speed transit through tunnels, it is critical for the tunnel axis to conform to a particular minimum radius of curvature. If breakthrough is not achieved with the stipulated precision, the segment in question must be rerouted with smaller minimum radii and a commensurate reduction in the maximum allowable train speeds, which in turn would impact the planned use of the tunnel and cause economic losses over the course of the next few decades.

The other possible outcome is parodied in the third verse of the Viennese Surveyor’s Song (Wiener Vermesserlied)1 (1985 –1997) by Thomas Wunderlich, sung to the well-known (in ­Austria) tune of the Fiakerlied by Gustav Pick.

A rough translation follows: “No Qxx, no gyro, to point the tunnel straight, We’re waiting at the pub to see if the heading’s right right right, And if by chance we miss our goal and just keep digging on, Well, there’s no tunnel anymore – there’s two of ‘em, by gum!”

170

1

Wiener Vermesserlied. See Thomas Wunderlich: “Grazer Spuren in der Wienerstadt und in Wiener Herzen: Gerhard Brandstätter”. In: Festschrift Univer­ salgeodäsie in Graz, TU Graz, 2008, pp. 174 –177. ‘Qxx’ is a parameter computed in the course of net adjustment that determines precision.

2 Theresa Neuhierl: Eine neue Methode zur Richtungsübertragung durch Koppe­ lung von Inertialmesstechnik und Auto­ kollimation. Dissertation, TU Munich, ­Department of Geodesy, 2005.

Above Gotthard Base Tunnel (CH) 2016, Giovanni Lombardi. For the approximately 800-metre deep intermediate access shaft at Sedrun, a new procedure had to be developed for underground orientation, as the locally prevalent high rock temperatures limit the precision of commonly used measuring devices (north-­ seeking compasses). The solution was found in the vertical transmission of the heading through the shaft by means of an inertial measurement unit (IMU) and autocollimation. Attached to a mounting plate and equipped with plane mirrors, the unit conveyed the heading with very high precision.2

Roberto Cudmani

1

Bayerisches Staatsministerium für ­Umwelt, Gesundheit und Verbraucher­ schutz (eds.): Oberflächennahe Geother­ mie. Heizen und Kühlen mit Energie aus dem Untergrund. Munich 2005; Baye­ risches Landesamt für Umwelt (eds.): Erdwärme – die Energiequelle aus der Tiefe. UmweltWissen – Klima + Energie.

Augsburg 2016.

2 Klaus Dorsch: 10 Jahre geothermische Exploration im süddeutschen Molasse­ becken – Ein Fazit. Munich 2012.

3 Bayerisches Landesamt für Umwelt (eds.): Oberflächennahe Geothermie.

UmweltWissen – Klima + Energie. Augsburg 2013.

4 Bayerisches Landesamt für Umwelt (eds.): see notes 1 and 3.

5 see note 3.

Using Tunnels for the E ­ xtraction of ­Geothermal Energy

Geothermal energy is energy that is stored as heat in the technologically accessible portion of the Earth’s crust. Geothermal heat comes from the particle collisions that took place ­during the formation of our planets, the decay of radioactive isotopes, tidal forces and solar radiation. The worldwide geothermal energy reserves that are accessible through current deep-drilling technology are estimated to exceed all available fossil fuel energy reserves (coal, oil and natural gas) by a factor of about 30.

In geothermal energy utilisation schemes, a distinction is drawn between deep and near-­ surface geothermal energy. The geothermal temperature level in near-surface applications is limited to well under 100 °C, and often lies between 10 and 20 °C. Near-surface systems are thus used mainly in conjunction with heat pumps for heating and cooling. In deep geothermal energy systems, which access and use heat at depths of more than 400 metres,1 temperatures in excess of 100 °C make the use of heat pumps unnecessary. Here, the energy extracted from the ground can be used for heating directly.2 In regions outside the areas that are geothermally anomalous due to tectonics (for example, regions with increased volcanic activity), the heat of the upper ground layers down to a depth of about 100 metres is a combination of stored energy due to solar radiation and energy from the Earth’s interior. The temperature levels within 10 metres of the surface are characterised largely by seasonal temperature variations.3 Below this zone, temperatures are almost constant year-round, and because of the upward-trending heat flow from the Earth’s interior they rise by an average of about 3 °C for every 100 metres of depth. In Central ­Europe, the mean temperatures of 8 to 12 °C

in the near-surface regions are too low to allow for direct heating, so the geothermal heat is brought up to the required temperature, generally between 35 and 55 °C, by means of ground-coupled heat pumps.4 Heating and cooling are the main reasons for harvesting geo­thermal energy – an immense resource owing to the enormous storage volume and the year-round even underground temperature – using geothermal collectors, geothermal probes, groundwater wells or concrete building parts in contact with the ground.5 Because of their large contact surfaces, tunnels are among the geotechnical structures with the greatest potential for the extraction of geothermal energy. The fact that most tunnels pass below residential and commercial areas is especially advantageous, since this makes it possible to supply consumers efficiently with the geothermal energy they need to heat and cool their homes, offices and businesses.

171

Using Tunnels for the Extraction of Geothermal Energy

Two processes currently exist to make use of tunnels in the harvesting of geothermal energy: the hydro-geothermal process and socalled absorber technologies.

In the hydro-geothermal process, the groundwater flowing in tunnels is collected in drainage ditches, diverted to the tunnel portals and used there as a heat source. The energy generated by this hydro-geothermal means is basically a by-product from tunnel drainage, a process that is necessary from a statics viewpoint to reduce the water pressure exerted on the tunnel lining. Hydro-geothermal plants are usually connected to deep tunnels – in ­Alpine regions, for example – rather than to the more near-surface tunnels that are used in the context of urban infrastructure. The immense mass of the overburden as well as the thermal

Future Challenges for Civil Engineers

“The future is […] the consequence of the ­decisions we make today.” (Franz Alt) There is no way to make a detailed long-term prediction of what the future role of engineers in the building industry will be. Current challenges and trends, however, already reveal the emergence of issues that will come to define the scope of engineering responsibilities for the future. These include, for example, the ‘15 Global Challenges’ described by the panel of experts of the Millennium Project,1 as well as the ‘17 Sustainable Development Goals’ defined by the United Nations.2 One of the challenges addressed in these forums is the growing world population and the related question: how can sustainable development be achieved while the consumption of resources rises sharply with the number of consumers?

The first three goals, founded on the most basic human needs, are defined as the fight against poverty and hunger and the establishment of a healthy existence for all people of all ages. The fulfilment of these demands is i­nextricably entwined with the availability of energy, water, safety and security – all of which are provided through buildings and their associated infrastructure. The latter represent the central areas of responsibility directly linked to the knowledge and skills of engineers in the building industry.

With a designation derived from the Latin word ingenium, engineers are furnished with a creative talent and gift for invention that – combined with technical knowledge and practical experience – positions them perfectly to develop and implement approaches to solving tasks of global importance. Because of ­societal and political changes, they are forced to involve themselves to a much greater extent

Outlook

Werner Lang

than previously in the decision-making process governing the implementation of relevant measures.

1

Founded in 1996 by the United Nations Univer­sity (UNU), the Smithsonian Institution, ­Futures Group International and the American Council for the UNU. It is an ­independent, not-for-profit think tank that includes futurists, scientists, economic experts and political decision-­ makers who work for international ­organisations, governments, corporations, non-governmental organisations and universities. www.millennium-­ project.org (1 August 2017).

2 www.un.org/sustainabledevelopment (30 July 2017).

In the spirit of the term ‘civil engineer’ introduced by JOHN SMEATON in 1750, it is the civil engineers in the building sector that must ­develop and implement enduring solutions – based on sustainable, ecologically oriented actions – that will ensure our well-being and our common future.

The provision of adequate amounts of clean, hygienic, safe drinking water, and of the as-

Sustainable ­Development and Climate Change Global Ethics

Clean Water Population and Resources

Science and Technology

Democratisation

Energy Demand

Transnational Organised Crime

Global Forecast and Decision-Making

Global Convergence of IT

Women’s Rights

Economic Inequality

Peace and Conflict Education and Learning

Health Problems

192

Asia 60.4 %

2010

Africa 14.8 %

Latin America 6.8 % Europe 6.7 % North America 5.2 % Pacific 0.7 %

In billions 10 9 8 7 6 ion ers alV on ati uc Ed GS

ion ers alV on ati uc Ed GS

Pacific 0.5 % North America 5.0 %

Europe 10.7 %

Latin America 8.6 %

5

Africa 35.3 %

4

2100 Asia 45.4 %

3 2 1 0 1750 1800 1850 1900 1950 2000 2050 2100

3

www.bmwi-energiewende.de/EWD/ Redaktion/Newsletter / 2014 / 22/ Meldung/ hoher-energieverbrauch-des-gebaeude­ sektor.html (31 July 2017).

4 www.eia.gov/outlooks/ieo/buildings. php (31 July 2017).

5 International Energy Agency (ed.): World Energy Outlook 2009. Paris 2009.

6 Diána Ürge-Vorsatz et al.: “Mitigating CO2 Emissions from Energy Use in the World’s Buildings”. In: Building Research & Information. Special Issue: Climate Change – National Building Stocks, 04 / 2007, pp. 379 – 398.

7 Directive 2012/27/EU of the European Parliament and of the Council of 25 ­October 2012, European Commission, ­Brussels 2016. http://eur-lex.europa.eu/ resource.html?uri=cellar:fa6ea15b-­b7b011e6-9e3c-01aa75ed71a1.0003.02/ DOC_1&format=PDF (1 August 2017).

8 www.unep.org/greeneconomy/Portals/ 88/documents/ger/9.0_Buildings.pdf (9 June 2014).

9 Heinrich Matthias: “Material Flows of the German Building Sector”. In: Francesco Di Maio et al. (eds.): HISER ­International Conference. Advances in Recycling and Management of Construction and Demolition Waste. Delft 2017, pp. 302 – 305.

10 www.bmub.bund.de/themen/nach­ haltigkeit-internationales/nachhaltige-­ entwicklung/strategie-und-umsetzung/­ reduzierung-des-flaechenverbrauchs/ (01 August 2017).

11 see also: www.footprintnetwork.org.

Opposite The 15 global challenges offer a framework for the evaluation of global and local perspectives for all humankind.

Top left Comparative distribution of the world’s population Top right Population trend from the ­beginning of industrialisation to 2100 (estimates)

sociated sanitary living conditions that aid in combating both recurring and new diseases, has been one of the greatest global challenges since the mid-19th century. From the beginning, engineers have taken a leading role in the area of water supply and wastewater removal, without which a healthy existence would not be possible anywhere in the world.

The subjects that are most closely linked to civil engineering, specifically in Germany, are energy demand and the consumption of resources – sustainable consumption and sustainable production measures included. In Germany, for example, the present-day portion of final energy used in buildings lies at 40 per cent.3 The global value of about 20 per cent4 may be significantly lower than this at present, but the current annual growth of 1.5 per cent coupled with a continually increasing world population presage a drastic surge in building-related energy demand. The building-­ related percentages of resource consumption are even higher in the electricity sector. About 60 per cent of global energy demand is from the built environment.5 These numbers alone illustrate the degree to which civil engineering plays a key role in finding solutions for the worldwide resource and energy problem. The same can be said for the closely related problem posed by rapidly increasing emissions of climate-damaging greenhouse gases. Roughly one third of global CO2 emissions are attributable to the buildings sector.6 Civil engineers are already being called upon to come up with and implement solutions that feature appreciable improvements in energy efficiency. These improvements are needed in order to achieve the ‘nearly zero-­ energy’ standards7 required by the European

193

Commission by 2020, and to cover the remaining demand through the almost exclusive use of renewable energies such as geothermal, wind and solar energy.

Given its share of approximately 40 per cent of global waste production, the building sector is especially responsible for actively promoting solutions to these challenges, solutions such as completely closed-loop material cycles and the use of renewable materials in construction. 8 In Germany alone, about 450 million tonnes (approximately 5.6 tonnes per person) in mineral raw materials – gravel, sand, etc.

– and more than 15.5 million tonnes (194 kilogrammes per person) of metal – steel, aluminium, copper, etc. – are used for the repair and new construction of buildings every year.9 These figures serve to illustrate the enormity of the task set before us in complying with the demand for sustainable consumption and production processes in the building industry in the near future.

In addition to all this, every day about 66 hectares of German land are newly designated as development or transportation space,10 making them unavailable for other uses such as food production, provision for ecological compensation areas, recreational spaces or water storage. An analysis of current resource consumption shows that the globally available land and water surfaces necessary to ensure long-­ lasting maintenance of the typical present-­day living standards of industrial nations are not sufficient to supply the basic food, water, energy, clothing and other consumer goods needs of all people on earth. The average ecological footprint11 in Germany of about 5.5 global hectares per inhabitant exceeds the biological capacity of 2.3 global hectares per inhabitant

Future Challenges for Civil Engineers

Biographical Listing of Engineers

The selection of (no longer professionally ­active) engineers and other individuals listed here corresponds to the development of the profession as presented at the exhibition ­Visionäre und Alltagshelden (Visionaries and Unsung Heroes). The country given is not the country of birth, but the country in which they practiced.

Othmar Ammann 1879 – 1965, USA

After completing his studies, the Swiss native OTHMAR AMMANN travelled to the United States to continue his ­education. There, he became one of the foremost bridge builders. From 1912 on, he worked with the influential bridge specialist GUSTAV LINDENTHAL. In 1925, AMMANN was appointed bridge engineer to the New York Port Authority. His final breakthrough came with the George Washington Bridge.

AMMANN heavily influenced the current appearance of New York, but his impact extended far beyond the city, as he ­consulted e.g. on the construction of the Golden Gate Bridge in San Francisco. ­After he had r­ etired, he founded a new engineering practice with Charles Whitney. Shortly before his death he ­created the ultimate memorial for ­himself in the form of the Verrazano-­ Narrows Bridge.

Ove Nyquist Arup 1895 – 1988, United Kingdom

OVE ARUP had a discerning mind and fought for an open dialogue between ­architecture and engineering. He grew up in Germany and studied philosophy and civil engineering in Denmark. In 1923 he moved to London. He created

Appendix

joint projects with Berthold Lubetkin and advocated strongly for the use of ­reinforced concrete. Prior to World War II he had already been engaged in building defensive structures and ­prefabricated housing for the British government. In 1946, ARUP founded his engineering practice, which became an internationally active company during his lifetime. He achieved worldwide fame through his involvement with the Sydney Opera House, the Centre Pompidou and the Hong Kong and Shanghai Bank Building.

Benjamin Baker 1840 – 1900, United Kingdom

BAKER gained his first practical experience in an ironworks, after which JOHN FOWLER took him on as his assistant in London. The two worked closely together and built the first underground railway in London. BAKER was also involved in the transport by sea of the 180-tonne obelisk known as Cleopatra’s Needle from Egypt to the UK. Beginning in 1867, BAKER was active in the construction of long-span bridges and published several papers on the subject. He improved on the principle of the cantilever bridge, which became the foundation for his joint masterwork with FOWLER, the Firth of Forth Bridge in Scotland.

This structure also marked the transition from wrought iron to steel bridges.

Walther Bauersfeld 1879 – 1959, Germany

BAUERSFELD was an outstanding scientist who influenced many branches of technology. He studied mechanical

engineering and took over a managing position at Carl Zeiss Jena in 1905.

More than 100 patents in the areas of microscopy, cinema and lighting ­technology are associated with his name. The high point of his career was the ­invention of the projection ­planetarium initiated by OSKAR VON ­MILLER. For the construction of the dome he worked closely with FRANZ ­DISCHINGER of Dyckerhoff & ­Widmann.

The joint ­project led to the development of the ­internationally successful Zeiss-Dywidag shell construction ­method. BAUERSFELD taught in ­Jena and Stuttgart and remained a member of the executive board of Carl Zeiss ­Jena until his death.

Hermann Bay 1901– 1985, Germany

HERMANN BAY studied civil engineering in Stuttgart. His meeting and collaboration with EMIL MÖRSCH shaped his career. Like his role model and mentor he worked and performed research in the field of reinforced-concrete construction. After he graduated, BAY joined Wayss & Freytag where he spent the next 54 years of his professional life. He built power plant structures and bridges such as the first prestressed concrete bridge at Ölde and the Limburg Viaduct.

He is credited with maritime and port structures as well as large administrative buildings for BASF and Bayer Lever­ kusen. In addition to his entrepreneurial activities, BAY published numerous ­scientific papers. His name is closely ­associated with the shear theory in concrete construction.

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Joseph William Bazalgette 1819 – 1891, United Kingdom

With his innovative sewer system, BAZALGETTE made a unique contribution to London and the health of its population. As a railway engineer he had gained experience in the drainage and reclamation of land. Starting in 1849, he worked for 40 years on London’s municipal infrastructure. BAZALGETTE built more than 80 miles of masonry sewers under the city, at least 1,000 miles of street sewers as well as four pump stations. Parts of his foresighted system are still in use today. BAZALGETTE also left his visual mark on London with the Thames Embankment. He served as an expert consultant in many other cities and educated influential engineers in public health.

Helmut Bomhard *1930, Germany

During his 40-year career at Dyckerhoff & Widmann, BOMHARD shaped the field of concrete construction. He joined the company in 1955 and worked closely with ULRICH FINSTERWALDER for many years. He was appointed director of the company in 1973, when ­FINSTERWALDER retired. BOMHARD is credited with well-known buildings throughout Germany. He was involved in the construction of the Munich Parcel Post Hall and directed the 1986 – 97 ­refurbishment of the Berlin Congress Hall. In the 1970s, together with Karl Schwanzer, he developed a novel, hanging prestressed concrete construction for the spec­tacular BMW headquarters building in Munich. After his retirement from practice, BOMHARD remained active as a c ­ onsulting engineer and honorary professor in Dresden.

Thomas Brassey 1805 – 1870, United Kingdom

BRASSEY began a surveying apprenticeship at the age of 16. His employment at THOMAS TELFORD’s practice put him in contact with the railway pioneer GEORGE STEPHENSON. Through STEPHENSON’s intercession, in 1835 BRASSEY was commissioned to build a viaduct, and thereafter was active as a railway contractor.

With great success he took part in the construction of numerous railway lines, first in the UK but later also on the Continent. Another of his extensive projects was the routing of a railway line more

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than 1,000 miles in length in Canada.

BRASSEY always supported the innovative ideas of up-and-coming engineers.

One of the engineers he sponsored was ISAMBARD KINGDOM BRUNEL.

James Brindley 1716 – 1772, United Kingdom

JAMES BRINDLEY is considered the father of the British canal network. Together with his employee JOHN SMEATON, he built the first man-made canals for inland shipping in the 18th century, allowing for the efficient transport of goods in the United Kingdom. With this accomplishment he was involved, much like the road building engineer JOHN LOUDON MCADAM, in providing the essential ­requirements for the Industrial Revolution. As a trained millwright, BRINDLEY had little formal education. He gained his technical and mechanical knowledge on the job. This was a characteristic ­feature of British e ­ ngineering at this time, which had pronounced practical leanings and traced its roots back to skilled manual crafts.

Samuel Brown 1776 – 1852, United Kingdom

The naval captain and engineer SAMUEL BROWN was a pioneer of suspension bridge construction in the UK. He built a series of chain bridges, for which he submitted a patent in 1817. The precursors of his constructions are considered to be the first modern suspension ­bridges by JAMES FINLEY in North ­Amer­ica. BROWN’s most well-known bridge is the Union Bridge, built 1819 – 1820, which has a span of 135 metres.

This project initiated an active correspondence between the leading bridge builder BROWN and the much-­respected engineer THOMAS TELFORD. The latter analysed BROWN’s structure and utilised his findings in the construction of his own bridge over the Menai Strait.

Marc Isambard Brunel 1769 – 1849, USA / United Kingdom

MARC ISAMBARD BRUNEL was an architect, civil engineer and inventor. He was born in Normandy, but fled to the United States during the French Revolution.

There he became chief architect of New York. In 1799, he settled in the UK and gained recognition for the mass production of pulley blocks for the Royal Navy.

But his most important project was the

construction of the first tunnel under the Thames, which opened in 1843. For this undertaking, together with THOMAS COCHRANE, BRUNEL developed a novel tunnel-boring shield – an innovation that was to have a decisive and lasting impact on underground e ­ ngineering. His comprehensive knowledge also benefited his famous son I­SAMBARD KINGDOM BRUNEL.

Isambard Kingdom Brunel 1806 – 1859, United Kingdom

The broadly talented BRUNEL was driven by a technical spirit of enterprise. The foundations of this were laid by his ­father, MARC ISAMBARD BRUNEL, who taught his son technology and mathematics from an early age. Already in 1829, the young BRUNEL submitted the design of the famous Clifton Suspension Bridge in a competition, though the construction of the bridge was completed only after his death. As the chief engineer of the Great Western Railway he became a pioneer of the modern railway system. BRUNEL built more than 1,500 kilometres of railway line in the UK, in addition to viaducts, railway ­stations and tunnels, and succeeded in ­introducing a wider track gauge. He also designed three visionary ocean-going steamships, thereby cementing his reputation as an ingenious designer.

Félix Candela 1910 – 1997, Spain / Mexico

CANDELA graduated with degrees in ­architecture and engineering and had a great passion for mathematics. Born in Madrid, CANDELA went into exile in Mexico in 1939, after the Spanish Civil War. There he became a specialist in concrete shell construction. He questioned the prevailing rules and used new calculation methods to determine the optimal relationship between weight and rigidity. About 900 buildings can be traced back to him, among them timeless creations like the ‘Los ­Manantiales’ restaurant in Mexico City.

In 1971 CANDELA moved to Chicago for a seven-year stint as a professor ­before returning to Madrid. His last ­creative period was characterised mainly by building projects abroad.

Joseph Chaley 1795 – 1861, France

In the 19th century, JOSEPH CHALEY was one of the most respected bridge

Biographical Listing of Engineers

Recognition

This publication was written to accompany the exhibition Visionäre und Alltagshelden.

Ingenieure – Bauen – Zukunft (Visionaries and Unsung Heroes. Engineers – Design – Tomorrow) at the Oskar von Miller Forum in Munich.

The exhibition was made possible through collaboration with the M:AI, Museum für ­Architektur und Ingenieurkunst (Museum of Architecture and Engineering) in North ­Rhine-Westphalia and through the support of the Bavarian construction industry.

Educational initiative of the Bavarian construction industry

Editors Werner Lang, Cornelia Hellstern With contributions by Bill Addis, Bill Baker, Kai-Uwe Bletzinger, Annette Bögle, Dirk ­Bühler, Fritz Busch, Roberto Cudmani, ­Christian Dehlinger, Cengiz Dicleli, Jörg E. Drewes, Stephan Freudenstein, Margot Fuchs, Christoph Gengnagel, Knut Göppert, Carl-Christian Hantschk, Jan Knippers, Achim Menges, Gerhard Müller, Roland ­Pawlitschko, Nina Rappaport, Peter ­Rutschmann, Joachim Scheuren, Wilhelm Vossenkuhl, Stefan Winter, Thomas ­Wunderlich Introductory texts / project descriptions Werner Lang, Cornelia Hellstern, Ursula ­Kleefisch-Jobst, Peter Köddermann Biographical listing of engineers Claudia ­Gabriel Editorial team Johanna Christiansen, Isabelle Krier-Michaeli (exhibition project ­management), Sandra Leitte, Natalie Muhr, Jana Rackwitz

Translation into English Susanne Hauger, New York Copy-editing Stefan Widdess, Berlin Proofreading Meriel C ­ lemett, Bromborough

For their generous support in the publication of the English edition, the editors would like to thank

Graphic design Cornelia Hellstern Drawings Theresa Tölle Publishing house coordination Steffi Lenzen Production / DTP Roswitha Siegler Reproduction Ludwig:media, Zell am See Printing and binding Druckerei Mayer & ­Söhne, Aichach © 2019, first edition, DETAIL Business Information GmbH, Munich. www.detail.de ISBN 978-3-95553-460-8 (Print) ISBN 978-3-95553-461-5 (E-Book) The Essay “Lightweight Textile Construction – Development of Simulation Methods from the 1970s to the Present” (Kai-Uwe Bletzinger, pp. 66 – 70) is based on: Kai-Uwe Bletzinger: “Simulationsmethoden im textilen Leichtbau – Die Entwicklung seit 1972 und aktueller Stand”. Bautechnik 92, Issue 11, 2015, pp. 800 – 805. Copyright Wilhelm Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG. Reproduced with permission.

This work is subject to copyright. All rights ­reserved. Reproduction of this work in whole or in part even in individual cases is ­only p ­ ermitted within the limits specified in the provisions of the applicable copyright law. A charge will be levied. Infringements will be subject to the penalty clauses of copyright law.

Bibliographical information published by the German National Library. The German ­National Library lists this publication in the Deutsche Nationalbibliografie; detailed ­bibliographical data are available on the ­Internet at: http://dnb.d-nb.de.

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