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Homage - Source of inspiration

© HG Esch
Baukultur 10.11.2016Homage

Prof. Dr. sc.techn. Mike Schlaich

Introduction

Sometimes we are asked what characterizes our work, if there is a style or even a design philosophy. Do our structures differ from others? It is the author’s intent to answer these questions.

 

We are structural engineers and collaborate with architects, with landscape architects, with artists and sometimes - mostly when bridges are concerned - work alone, thus reducing the collaborative work, compared to that between the members of our design team in other projects.

 

Ideally, our work is the result of a conscious iterative design process that almost always stems from the local boundary conditions, the context. We aim for Gesamtkunstwerk, which in the case of collaborating with architects means that we strive for the overall quality, good form and good function. A building is really good only if all of its components are done well, those of the architect and those of the engineers. Then, often the individual contributions can hardly be distinguished anymore.

 

Conscious means that the members of the design constantly challenge each other, and also that the intent is made to follow some general principles, not only the codes. 

 

The word cloud, shown below, gathers the principles for good building as defined by Vitruvius, Jörg Schlaich, Volkwin Marg and David Billington. The first author set the bar some 2000 years ago and the other three authors are the ones from whom the author has drawn valuable insights along the years.

Fig. 1: General Principles for good building

Even though lightweight structures are not necessary, and only under certain conditions the outcome of the design process, at schlaich bergermann partner they are rather fre-quent. This is not surprising. According to Jörg Schlaich, lightweight structures convince for several reasons:

 

  • cultural: light structures are transparent and show the flow of forces in a natural way. We like what we understand. We also like lightness because we associate it with elegance and because the lighter a structure is, the less it obstructs our view and the less we feel threatened.
  • ecological: light structures generally require minimum material quantities. They save resources and are therefore sustainable.
  • social: the complexity of lightweight structures requires qualified designers and builders. The outcome not only enriches our culture and but also creates employment. 

 

For the design of a lightweight structure several structural principles can be followed:

 

  • scale and appropriate spans: as bending moments increase with the square of the span, only short spans yield slender girders. If bending cannot be avoided, work "werkstoffgerecht", e.g. with concrete where the section works in compression and steel where tension governs.
  • no bending: sections are optimally used if they work only in tension and compression as long as stability can be guaranteed. Therefore, trusses are much lighter than beams in bending.
  • materials with long breaking lengths: a very efficient way to achieve lightness is to use materials of high strength and low weight. In this respect a very promising building material is carbon fibres. 
  • pre- or post-tensioning: permits to transform unfavourable compression into favourable tension. It adds stiffness to the structure and reduces deflections.
  • double curvature: lightweight spatial structures can carry loads with pure axial forces, i.e. membrane stresses. Such structures are not only extremely light, but they also open up a whole new world in architecture, an unsurpassable variety of forms which is not yet fully exploited.

 

Over the years, whenever reasonable, we have applied the principles of lightweight design to all types of structures, including bridges, towers and roofs, with concrete shells, cable-nets, membranes, and glass.

Fig. 2: Application of Structural Principles for lightweight building

In this process following simple structural concepts such as the spokes wheel, the tennis racket, the salad sieve or just a ring has stimulated us for numerous variations.

  • Fig. 3 a: Glass roof Paunsdorf Center: kitchen sieve
  • © Manfred Storck
    Fig. 3 b: Roof of Mercedes-Benz Arena in Stuttgart: spoked wheel
  • © Fa. Roschmann
    Fig. 3 c: Facade Airport Málaga: tennis racket
  • © Wilfried Dechau
    Fig. 3 d: Footbridge in Sassnitz: circular ring girder

Sometimes, consciously or unconsciously, we have drawn from the works that great engineers have done before us. This aspect of our work shall be illustrated in the next section.

Homage

"The term is often used in the arts for where one author or artist shows respect to another by allusion or imitation". So it is more than just copying! In the authors opinion it is perfectly alright to study the great work earlier engineers have done, and then to use their ideas to further elaborate, to update it, to express with modern means or to just vary and play. As a matter of fact, it is very important that we know our roots, that we know what was done before. The wheel cannot always be reinvented; often we can only progress when we start starting from the achievements of others.

 

When going through the projects of schlaich bergermann partner it becomes obvious that "homage" is a tool that is used rather purposely. Naturally, just copy-and-paste is not what is meant here, rather it is the application of our principles and concepts to existing great ideas. Compare it to the "cover-song" in popular music. If the translation of an "old" idea to other boundary conditions, or to a new context, perhaps with new materials or with other uses, if it is successful, surprisingly "new" structures appear.

 

This shall be illustrated with examples:

  • Fig. 4 a: Candela: Xochimilco
  • Fig. 4 b: Stuttgart

In 1974 Jörg Schlaich was inspired by Félix Candela´s famous Xochimilco shell for a temporary shell, which contrary to the original, is made of glass fibre reinforced concrete of only 1.5 cm thickness. Candela came to visit the shell and was happy that his work had influenced German engineers.

  • Fig. 5 a: Candela again: Playa Azul
  • Fig. 5 b: Hamburg Sechslingspforte

Much before that in 1967, Jörg Schlaich, at that time working at Leonhardt Andrä und Partner, designed one of the longest span hyperbolic Paraboloids the 96 m span roof above a Hamburg swimming pool which bears a striking resemblance with the much smaller playa Azul beach bar roof by Félix Candela. (Architect: Niessen und Strömer, Hamburg)

  • © FBM studio Ltd.
    Fig. 6 a: Maillart: Schwandbachbrücke
  • © Gerd Elsner
    Fig. 6 b: Auerbachbrücke

The Auerbach Bridge in Stuttgart, Germany is an all integral concrete arch bridge, which very much like the Schwandbach Bridge by Robert Maillart, carries a curved deck with a straight arch.

  • Fig. 7 a: Zollinger: roof truss from the twenties
  • © Heiner Leiska
    Fig. 7 b: Warnow exhibition hall Rostock

The timber roof for the Warnow exhibition hall in Rostock, in Germany proves that with modern means of connecting laminated timber, even large span roofs can be built following the system introduced by Friedrich Zollinger in the 1920s for small roofs. (Architect: Architekten von Gerkan, Marg und Partner)

  • © HG Esch
    Fig. 8: Buckminster Fuller: Tensegrity and the Rostock tower

This landmark for the Rostock fair shows that Tensegrity towers can actually be built to heights above 50 m. It also showed, however, that Tensegrity structures of this type are so flexible that on top of wind loads they cannot carry much more than their own weight. (Architect: Architekten von Gerkan, Marg und Partner)

  • Fig. 9 a: Fink: railroad bridge
  • © Michael Zimmermann
    Fig. 9 b: Passerelle La Défense, Paris

Inverting the Fink Truss, an idea of the German engineer Albert Fink, who has lent his name to numerous railway bridges in the 19th century, leads to the pedestrian bridge at La Défense in Paris. (Architect: Dietmar Feichtinger Architectes)

  • Fig. 10 a: Suchov: Television tower
  • Fig. 10 b: Cooling tower Schmehausen

Again it is inversion which leads from Vladimir Suchov´s slender towers, which work as rotational hyperboloids in compression to similarly shaped cable net towers, which are tensioned by a central mast.

  • Fig. 11 a: Nowicki: Dorton Arena
  • © Tobias Hein
    Fig. 11 b: Canopy for exit of customer center of Autostadt in Wolfsburg

Nowicki´s and Severud´s concrete covered cable-net roof was made known in Germany by Frei Otto. The canopy roof in Wolfsburg proves that such double curved surface also works without supports along the edge girder (Architect: GRAFT Architekten). 

 

Finally, it must be mentioned that the written work of Frei Otto, from his famous book "Das hängende Dach" to the more than 40 books published by the Institute Il at the Stuttgart University, then led by him, has had an enormous influence on many of today’s engineers. As a matter of fact, in lightweight engineering it is difficult to come up with a new structure that has not yet been conceived or sketched by Frei Otto before. Many of the movable structures designed by schlaich bergermann partner draw from his abun-dant ideas.

  • Fig. 12: Ideas for movable structures by Frei Otto

Today, after more than 35 years of schlaich bergermann partner, Jörg Schlaich´s early work has already become a rich source to pay homage to. We try to face today´s challenges by combining innovation with our evolving professional past.  

Summary

The contribution of the engineer to a high quality design outcome can be manifold. We try to be constructive members of the design team, we consciously play this role and de-rive our structural solutions from experience and local context, we follow general princi-ples and structural principles that have been proved helpful, we apply and vary structural concepts and we study our professional history, because it allows us to also progress through paying tribute to good work done by others before us.

 

NOTE

This article was published as a paper on the ICSA conference in Guimaraes Portugal. All references can be found in the official paper: Link 

Prof. Dr. sc.techn. Mike Schlaich

Schwabstraße 43
70197 Stuttgart

+49 711 648 71-0
info@sbp.de