Innovative Surface Structures, Technologies and Applications A Review of Martin Bechthold’s Book Marine Bagnéris* Laboratoire de Mécanique et Génie Civil Université Montpellier II, France

While he was writing this book, Martin Bechthold was Associate Professor of Architecture. He recently became Professor of Architectural Technology at the department of Architecture, Harvard University Graduate School of Design. He currently teaches and investigates about the main topics dealt in Innovative Surface Structures. This book provides the designer with the necessary overview to make an enlighten decision about structural approaches that include tensile membranes, shells and folded plates. Throughout the history of structural surfaces, the author focuses on their development that has largely been triggered by technological advancements generally coupled with a search for new calculation tools, better design methods, higher performing materials and tighter

construction tolerances. The designer is reminded of the awareness that such structural systems require these considerations and their dependencies early in the design process. Enthusiastic encouragements are constantly given through case studies to rise to the challenge toward creative exploration and innovation in building technology. Four parts structure the discourse and we follow this organisation to discuss about it. The first part introduces a surface classification that organises what is discussed deeper in the next sections. This classification relies on two main types of surfaces arbitrary called rigid and non-rigid. On a pure mechanical point of view, this organisation differs from the classical refinement done on behaviour hypothesis between shells whose bending moments can’t be ignored and thin shells only subjected to shear and membrane strains. This choice may firstly appear more intuitive to familiarize the reader with the topic but it could introduce misunderstanding between structural principles and material behaviours. Then, an historical description reviews the pioneer realisations, listing the different materials used and their technological requirements. The novice reader could regret that most of the time, the legends of the pictures don’t notify the date of the realisations which disturbs a chronological perception of this architectural movement. The well-advised reader would probably recognize an iconography largely published in other references while other less known realisations would have required some descriptive schemas. The second part covers an introduction to tensile membranes. The concepts of curvature and shape are closely linked to the notions of stiffness and

*Corresponding

author email: [email protected] Martin Bechthold, Innovative Surface Structures, technologies and applications, Taylor & Francis Ltd, 2008, 232 pp.

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Innovative Surface Structures, Technologies and Applications

Categories of surface structures in the context of related systems, p. 4.

Examples of possible arrangements of point supported membranes. The edges can be cables or rigid members, p. 55.

Concrete shell for a department store by architects Ingenhoven Architekten and structural engineer Werner Sobek Ingenieure in Lübeck, Germany, p. 109.

equilibrium. Those fundamental principles are described according to both types of anticlastic and synclastic membranes, respectively named as mechanically or pneumatically prestressed shapes. Following the different stages of the design process, the next chapters deal with form-finding and analysis methods, materials and fabrication techniques. Surprisingly, no references are given to previous and respectful works such as “Tensioned fabric structures, a practical introduction” published by the American Society of Civil Engineers or “Pneumatic Structures, a handbook for the Architect and Engineer”, written by

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T. Herzog. This lack of references becomes embarrassing as soon as the few mechanical relations given in the case of air-inflated spherical systems are false probably due to misprints. The first chapter of the third part claims to explain how to model the load-carrying mechanisms of structural systems like folded plates and shells. The reader without previous mechanical skills is supposed to admit analytical results on simple shapes without any demonstrations. This approach can not be admitted by more experienced practitioners since basic equilibrium equations concerning the spherical shell

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Marine Bagnéris

under snow loading are totally wrong by reference to equations provided by Larger [1] Then, following the same outline of the previous part, the related design methods, materials and construction techniques are well documented. At this stage of the reading, one should assume that the author is clearly better experienced in form-finding and technical aspects than structural ones. At last, the fourth part speculates on emerging technologies like self-healing materials, structuralhealth-monitoring technologies, adaptability or thermally active materials that could be applied on such structural systems in order to provide better sustainability and energy consumption. All these actual developments could be interestingly coupled with the advantages of structural surfaces in term of material efficiency in a coherent way. If this architectural expression has been partly exhausted, new paradigms

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in the design process argue for an optimistic future of structural surfaces and a potential rebirth. According this favourable context, the author regrets the lack of teaching about their fundamental principles. This book can be considered as a practical guide for the designer who would like to cover an historical summary and a detailed description on materials and construction techniques used for fabric membranes and thin shells. However, the publication of a list of errata should be encouraged in order to revise some basic equations and thus clear up a feeling of mechanical confusion appearing in this first edition. [1] J.C. Larger, Introduction au calcul des structures en résilles, partie 1: Théorie des coques, application au calcul des résilles, chambre syndicale des fabricants de tubes d’acier, Ed. Brémo 81, 1978.

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