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Andrea Wiegelmann Preface Elisabeth Boesch Foreword Aita Flury Inquisitive Openness
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Theory 19
Marco Pogacnik
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Research 75
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Christoph Wieser Pioneer and Projection: The Misappropriation of the Engineer in Modernist Architecture
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Yves Weinand New Structural Potential of Wood: the IBOIS Research Laboratory at EPF Lausanne
Christian Penzel The Culture of Construction: Examples from the Last Fifty Years of a Remarkable Development
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Jürg Conzett The Interplay of Technical and Architectural Aspects in the Palazzo della Regione in Trento by the Architect Adalberto Libera and the Engineer Sergio Musmeci
Technology as a Means of Expression in the Nineteenth Century – Architects and Engineers in Dialogue
103 Aita Flury and Jürg Conzett Tetto gigantesco – a diverse huge roof Foils of a Research
Christoph Baumberger Structural Concepts and Spatial Design: On the Relationship Between Architect and Engineer
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114 Model Photos
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Practice 133 Markus Peter
208 Meta-Dialogue
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Teaching 243 Joseph Schwartz Structural Theory and Structural Design
Deviations
139 Andreas Hagmann
249 Christoph Wieser Art and Science
Structure and Space
147 Mike Schlaich
257 Mario Monotti Constructing as a Science
Each His Own
153 Roger Boltshauser, Aita Flury and J체rg Conzett
263 Paul Kahlfeldt Construction Transforms Material into Space
A Process of Rapprochement
161 Stefan Pol처nyi
269 Roger Boltshauser, Aita Flury und J체rg Conzett Program and Structure
On Designing Structures
169 Renato Salvi The A16 Transjurane Highway: Architectural Acupuncture
175 Elisabeth und Martin Boesch, Carlo Galmarini, Urs B. Roth und Judit Solt
274 277 279 283 284
Authors and Interview Partners Literature Image Credits Acknowledgements Imprint
Rules to Play By and Play With
185 Adolf Krischanitz und Aita Flury Mutual Frankness and Self-Reassurance
193 Heinrich Schnetzer, Aurelio Muttoni, Joseph Schwartz und Aita Flury Strong Structures
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Inquisitive Openness Aita Flury
And on the sphere of the architect there appears a reflection of engineering: the reflection of the laws of physics. And on the sphere of the engineer there appears, from the other side, a reflection of architecture: the reflection of human problems. Le Corbusier Antagonism is the form of force. Nietzsche
In Andrew Saint’s book, Architect and Engineer. A Study in Sibling Rivalry 1 the author, after five hundred pages of meticulous historical research into the relationship between the architect and the engineer, constructs his conclusion around three issues. He affirms that the two disciplines were indistinguishable from one another from 1400 to 1750: in these years, the title of architect or engineer depended mainly on the type of project in question, as well as on its associated hierarchy and institutions (king, military, church, etc.). This distinction, however, reflected neither different construction techniques nor different design capabilities. The when and why of the professions’ subsequent separation is placed by Saint, as by others, in the period from 1750 to 1900: the continual demand for new types of building and construction during the nineteenth century; the emergence of new materials and a newly scientific basis for calculations inevitably led to the emergence of different sets of skills and thus to specialization. According to the author, this development should be dated earlier within the said period rather than later. He then identifies a reunification of the professions during the twentieth century, based on a need to counteract the spread of fragmentation within the professions and their consequent lack of unity and comprehensiveness—something for which the nineteenth century is often criticized. In the twentieth century, the engineer and the architect, equipped with different skills, worked together on the same projects. The most popular model to establish itself was a form of collaboration in which the consulting engineer answered the architect’s questions at a time chosen by the latter. Now, at the beginning of the twenty-first century, Saint argues, this thoroughly dialectical relationship hangs in the balance. He sees the engineer disappearing in a throng of equally important consultants, specialists, and subcontractors, and/ or—in a world dominated by art objects and medial symbolism—letting himself be dragged out of the temple of reason for exploitation by the architect in the service of a predetermined form. To put the conclusion of another publication at the beginning of this book may seem unusual, but that brief summary provides the ideal context for this collection
1 Andrew Saint, Architect and Engineer. A Study in Sibling Rivalry, New Haven and London: Yale University Press, 2007
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of material on the current state of collaboration between the engineer and the architect. In the last two hundred years of building, the many aspects of the relationship between the two professions and their mutual influence have always been the subject of lively debate. Today we seem to have reached the point at which the ‘informing idea’ has little to do with structure, with spaces being composed without any concern for the reality of the structure. As a result, the architect-as-artist often really sees the engineer as a pure service-provider who delivers the computational tools; as a means to an end who is able to implement an aesthetic concept, to render it buildable. In the face of this widespread view, the Zurich Architectural Forum launched the Constructors’ Dialogue exhibition in 2006, with the intention of showing that architects and engineers could easily take a more inspired approach to their roles. This hypothesis drew its conviction from a number of buildings that had been completed in Switzerland during the previous fifteen years—or were in the process of being built—and which seemed to draw their power precisely from the affirmation of a close design relationship between the architect and the engineer. Curating this exhibition was a leap into the dark for me, and my approach to the subject was rather intuitive and autobiographical—based less, at that time, on theoretical studies of the subject than on my own experience of the limitations and the potential of cooperation in practice, through my work as an architect. Influenced by years of ‘apprenticeship’ with some of the participants in the exhibition and collaborating with others, my view of the subject undoubtedly had its own particular focus. The exhibition seemed to me an opportunity to show, on the basis of several more-or-less well-known buildings, that the effort put into productive collaboration between architects and engineers often passes unnoticed and that intellectual recognition of their added value requires a kind of ‘second sight.’ These were projects whose authors (architects and engineers) discussed technology during the design process in a way different to that which they presented for public view. Their strategies were based on structural subtlety and saw no need to reveal everything at once—and for exactly this reason, they had a lasting effect on our ‘sensual intelligence.’ Emanating from these projects was the sense of a balance between the possibilities of structural discovery on one hand, and assured handling of space on the other. The resulting designs were the visible evidence of dialogical relationships between the two professions and of a new culture of constructing, based on impressive tenacity and skill in jointly developing ideas. It emerged that this depended greatly on the engineer and the architect interpreting the brief in terms of a jointly formulated understanding of the problem, as it were a voluntary commitment to accept common interfaces. This was most clearly evident in the case of shear wall/floor slab structures, because they define space more immediately than any other, i.e. the primary structure and the resulting space are inseparable. Back in the 1960s, German architect Fred Angerer had examined the structural nature of continuous solid surfaces in his remarkable publication Bauen mit tragenden Flächen [Surface Structures in Building. Structure and Form]. Angerer was convinced of the great creative possibilities of such surfaces
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as systems and he investigated the correct design of such buildings in its various aspects by analyzing the systems’ structural parameters. Using simple examples of the basic positioning of shear walls, he showed how they function structurally in combination—as long as they are touching—and then proceeded to address the resulting design issues: “The lack of sides to a space has serious architectural consequences. In place of a room enclosed on all sides there appears an intimation of space; rather than individual spaces being strictly delimited, they flow into each other. The sense of space changes.”2 This type of structure leads, then, to a new spatial distribution of ‘open’ and ‘closed,’ ‘heavy’ and ‘light’. Such systems become spatially and structurally interesting when they are applied over several stories: if developed as bridge-like structures (the upper floors spanning the ground floor, for instance, without intermediate columns) they can be suitable for large-span volumes combined with floors divided into small rooms above them. The structural behavior of the various elements remains open to interpretation and is not obvious at first glance, so that the systems acquire multiple layers of meaning. This apparent ambiguity oscillates between an engineering and an architectural character, as the ample amount of material to be found on both sides perfectly illustrates. Because this border area between architecture and structural theory perfectly illustrated ‘intimate’ collaboration on equal terms, it became an important starting point and cornerstone of the exhibition. The search for the conditions, possibilities, and limits of this dialogue naturally led to structures that are more resolved, i.e. more hybrid, and to relationships of cooperation that are more hierarchical: models in which the engineer affects the architectural idea by reinterpreting or transforming the architect’s original inspiration, or by ‘incorporating’ the structure into an architectural image. Overall, the exhibition was conceived as a platform for dialogue,
2 Fred Angerer, Bauen mit tragenden Flächen. Konstruktion und Gestaltung [Surface Structures in Building. Structure and Form], London: A. Tiranti, 1961], Munich: Georg D. W. Callwey, 1960, p. 61
Cover and page 57 from Fred Angerer, Bauen mit tragenden Flächen. Konstruktion und Gestaltung [Surface Structures in Building. Structure and Form], Munich: Georg D. W. Callwey, 1960
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3 Aita Flury, Dialog der Konstrukteure [Constructors’ Dialogue], Sulgen: Niggli Verlag, 2010
so that in describing different styles of dialogue, it included this possibility of continuing them. Dietmar Steiner, the director of the Architecture Center in Vienna, attested to “unfashionable tenacity” of this format in his speech at the exhibition opening. This turned out to be especially true in the sense that the display panels and models subsequently went on an exhaustive tour of Switzerland’s universities, in the course of which countless related events took place, including lectures and panel discussions involving members of both professions. The texts written for the exhibition were made available to the public in the publication Dialog der Konstrukteure,3 beginning a chain reaction of events. In the end, it was the Federation of Swiss Architects (BSA) that decided to provide long-term support for this move to foster public discussion between the two professions and to give it new impetus. Thanks to personal involvement by its vice president, Elisabeth Boesch, an expanded version of the “Constructors’ Dialogue” exhibition was shown at the German Center for Architecture (DAZ) in Berlin as the final event in the “Architecture in Dialogue” series during the spring of 2010. Two international symposia were organized to accompany it, to which a number of new essays and interviews were contributed; these contemporary position papers and general papers were compiled, to start with, in a self-published catalogue. These essays, lectures, and conversations, too, comprehensively covered the subject of practical cooperation, whether in competition entries or built projects. The range was extended by contributions that described educational concepts at various universities, and research topics. This publication is essentially based on the texts presented in Berlin, supplemented once more by several essays with historical and theoretical perspectives. These essays, which illuminate the relationship between the professions at specific times during the not-so-distant past, provide a historical context for reflection upon contemporary practice. All of the articles have been written by practitioners (architects and engineers), or teachers involved in both disciplines, with the exception of Christoph Baumberger, who is a philosopher. This compilation of material remains true to the initial idea of leaving the stage to the practitioners themselves, above all, and letting them talk about the subject in the light of their different experiences, in order to arrive at a stimulating blend of different perspectives. The circle of those involved has been widened by encounters with new people, and even more so by the participation of further associations and institutions, but the initial principle has nevertheless remained: that each text be written specifically in connection with the “Constructors’ Dialogue” with the aim of arriving at statements on cooperation between the professions. The compilation is not a reappraisal of the history of construction, but rather a reader that, by virtue of the material selected for it, aims to provide inspiration for productive collaboration and thereby have an effect that reaches further than a mere survey of the current situation could achieve. The exhibition had already shown that no one seriously calls the separation of the two professions into question. Accordingly, the premises of productive collaboration include no shifts of responsibility from one to the other, being based instead
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Le Corbusier’s sketch “Les Constructeurs,” which he explained as follows: “In the diagram, the domain of the engineer is shown as a hatched area, whereas the domain of the architect is dotted. Beneath this symbolic sign of synthesis are two hands interlocking ten fingers horizontally at the same level, fraternally, both working in solidarity on equipping the Machine Age. This is the sign of the constructors.” From: Science et Vie, 1960
on the notion of ‘close co-existence.’ Productive work in neighboring areas is, however, only possible if they share a common language, which in turn requires mutual interest (followed by knowledge) and empathy for the problems of others. Real curiosity about how things are made is lacking in many architects today. It may also be the case that familiarity with ‘making’ is not necessarily beneficial, given that a genius such as Le Corbusier, who vocally proclaimed and publicized the takeover of architecture by engineers, was ultimately more interested in engineering as an idea than in the reality of construction itself—because to follow the ‘path of technology’ could, if taken to the extreme, mean the loss of architectural freedom. For architects with an interest transcending their own borders, however, talking to an engineer with a sense for both structure and space can broaden their awareness of ideas and extend their patterns of thought. In doing so, each attains greater understanding of the other side’s position— for instance, of their respective enthusiasms, which may be imagined as follows: while the architect is interested, first and foremost, in the visible and directly experienced aspects of the finished work, the engineer is equally passionate about the hidden aspects, those that cannot be perceived directly. Engineers look forward to the finished building—to put it provocatively—no more than to the intelligent process of production and construction, to the acrobatic conditions of work on the site itself. They are inspired by organizing the construction schedule, by plotting out the phases of a building or edifice or, to phrase it poetically: the technical and structural narration of the construction process. 4 For them, it is therefore ultimately of secondary importance if the engineering input and the structural beauty remain concealed in the completed building, as the Reformed Church in Wädenswil (1764–1767), by the Grubenmann brothers, illustrates: outwardly the building is simple and unassuming; inside it is impres-
4 Bruno Reichlin, “Technisches Denken, Denktechniken” [Technical thinking, thinking techniques], in: Alexander von Vegesack (ed.), Jean Prouvé. Die Poetik des technischen Objekts [Jean Prouvé. The Poetics of the Technical Object, Weil am Rhein: Vitra Design Stiftung GmbH, 2006], Weil am Rhein: Vitra Design Stiftung GmbH, 2006, p. 32
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sive, using space to its full effect. A single, high hall of 20 m length x 38 m width is spanned without columns by a flat, white ceiling that is enlivened by applied stucco reliefs. Their patterns are abstract and atectonic. The ceiling as a whole gives no hint of the complex construction needed to support it, which develops for several levels above, out of sight. The audacity of that structure, based on the principles of bridge-building (of which the Grubenmann brothers were acknowledged masters), is completely hidden from church-goers—the engineer’s heaven-on-earth is to be found among the timbers of the roof! The fragmentation of experience, the disintegration of knowledge into many independent specialisms, each with its own language—specifically, in this context, the
Roof structure of the Reformed Church, Wädenswil . (1764–1767) by the Grubenmann brothers. Bold as a bridge, the roof trusses span an auditorium of 38 m x 20 m
Interior of the Reformed Church in Wädenswil. The structure through which they achieved this spatial effect is completely covered up
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separation of design from technically-driven structural planning—are now given facts that diminish our sense of the whole more and more. The promotion of active cooperation and teamwork, and the cultivation of a harmonious combination of various skills are therefore of the utmost importance. The prerequisite for this is an attentive, inquisitive almost Faustian readiness to cross borders: architects can find the key to a fruitful dialogue if they rediscover the master builder in themselves, the building designer with a keen understanding of structure. The engineers, on the other hand, would refresh their approach if they combined ‘sensibilità statica’ (Pier Luigi Nervi) with a spatial sensibility: this would allow them to approach the architects’ apparently subjective choices with self-confidence as engineers, and to question or even improve their proposals. The engineer would become an author, like the architect, which would shift the focus of attention and redefine their relationship.
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New Structural Potential of Wood: the IBOIS Research Laboratory at EPF Lausanne Yves Weinand
The IBOIS The predominance of steel and later reinforced concrete in practical applications and research within the fields of structural engineering and materials science over the last two centuries has created a huge gap of missing research on timber as an engineered structural material. The intuitive knowledge of carpenters and our professional predecessors has been lost since the eighteenth-century rise of the Ingénieur des Ponts et Chaussées (Engineer of Bridges and Roads), who does not take advantage of timber as a construction material, having a priori accorded it a lower level of importance than steel and concrete. My dual profile of architect and civil engineer allows me to focus on the interdisciplinary aspects of construction design in a synergistic way. Having conducted pioneering research work in both structural design and construction, my perspective on various phenomena differs significantly from that applied by most theoreticians or by practitioners specializing in only one of those specific areas. Uniquely positioned as an active practitioner, researcher, and teacher of both, my broad experience has established a balance in which the subjectivity and even aesthetic aspects required by architects is counterbalanced by a deep structural and technical understanding that reinforces rather than compromises these values. My research focuses on the technical, constructional, material, and structural aspects—which, with few exceptions since the time of Leonardo da Vinci, have been overly neglected or delegated away by architects driven by the search for aesthetic appeal. It takes account of myriad underlying links between art and science as well as the specific constraints of observed phenomena and their physical realization. Implications of the concept of scale are often simply ignored in the field of structural analysis for building construction. My approach perceives the mechanical requirements of form/structure as attributes that can only have full meaning and sense within the
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framework of the geometrically scaled phenomena upon which they depend. I see the rise of digital architectural representations as an invaluable tool, but as one that can only be exploited to strengthen the integration of structure, form, and material within our concept of design if the physical reality of every observed phenomenon is treated as a consideration of major importance, thus linking the production of form and space with that of structure. Research in Architecture and Structural Engineering Architectural research, composition, production, and even construction processes remain closely linked to the personal design processes of the individual architect, while the architect’s freedom of expression as an artist is, by definition, respected as being inherent to the creative process. This epistemological framework makes research in architecture different and also difficult to accept for disciplines primarily rooted in the cultures of either technology or the social sciences. In general, research in architecture is not primarily intended to give importance to the applied technique. Truly interdisciplinary research approaches that link architecture with civil and structural engineering remain uncommon. Technical considerations are very often considered as comprising an almost neutral set of knowledge that does not, or should not, affect the initial creative design process of a given architect in a determinate manner. Technique, construction methods, and ultimately considerations of structural design and engineering are seen as almost unwelcome factors in certain cases. More often than not, these supposedly neutral technical considerations are tacked on at a later stage in the design process, compromising the truly interdisciplinary and fundamental quality to which such research approaches could aspire. Even certain very celebrated iconic buildings—such as the Guggenheim Museum in Bilbao by Frank O. Gehry, or the Olympic Stadium in Beijing by Herzog & de Meuron— illustrate how formalism has pushed back the structural approach to the status of a secondary issue. First and foremost, engineered structures must adequately serve as robust systems—beams, columns, and construction elements that are constituent parts of larger integral units—in order to achieve their bearing quality. Our society does not presently associate major works of civil and structural engineering with expressions like ‘textile’ or ‘timber’. For most people, ‘textile’ has a connotation of softness that seems incompatible with the general context of engineering structures. Although the term ‘textile’ has a large range of applications and interpretations, to date there have been no attempts to employ its qualities and production technologies at the scale of timber construction. Yet the strategy of devising textile-like (woven) timber surfaces can exploit wood’s fibrous, inherently flexible nature and turn this feature of the raw material, which has been perceived over the last two centuries as a limitation, into a structural advantage. The invention of structural timber fabric embodies both a vision of the future and an understanding of the past. It is inspired by the vision of building as an integrated planning process, where aspects of craft, technique, aesthetics, and structural engineering converge as they did just before
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the revolutionary “Age of Enlightenment”—but this time using contemporary engineering methods and tools. The raw material resource in question has innate qualities (such as smoothness) that can also provide the aesthetic and conceptual qualities sought by architects. The emerging tools of digital architecture, design software, and the way digital drawing tools are now seen as instruments for conceiving architecture have opened the way for broader applications of digital technology, including those of a technical nature. Technical advances that now lie within reach render feasible the integration of textile principles, textile technologies, and fabrication systems in ways that were unthinkable only a few years ago. The environmental arguments in favor of increasing the possible uses of (renewable) timber resources are undeniable. Society’s burgeoning awareness of the urgent need to identify building materials that are sustainable has become an important influence in timber construction’s renewed economic importance in recent years. Environmental considerations are helping to restore or establish the legitimate use of timber in the built fabric of our cities on a scale unprecedented for many centuries. We are only now discovering that techniques ranging from friction-welding to knitting, weaving, and even origami can be applied to timber at the building scale. My own group’s work is already demonstrating that the application of such techniques can radically expand timber’s range of technical and aesthetic attributes. Such techniques allow us to invent timber products fit for novel purposes because society is both culturally and economically ready to accept timber as a construction material that is no longer marginalized. We foresee significant advantages to the application of such techniques because they should facilitate the creation of largescale, free-form structures from small repeating units—and this opens the way to expanded use of both timber off-cuts and post-consumer recycled wood products as high-quality construction materials. The gradual replacement of timber by steel and concrete over the last two hundred years has not helped to improve new and contemporary applications of timber construction from an architectural and engineering point of view. Only when examined at a closer perspective than the one traditionally associated with its present day uses in construction does timber reveal its surprisingly close connection to textiles and its vast potential for the application of textile techniques: timber can be classified as both a soft and a viscous material with smooth properties. It is subject to ‘creep,’ almost like a liquid material. All timber is basically composed of multitudinous cellulose fibers. These smooth fibers are flexible, allowing curvature. Such properties suggest that woven, flexible timber structures of a building scale should offer exceptional performance in resisting seismic instability as well as extreme wind or snow loads. To date, the potential that building-scale woven structures have for significantly reducing the risk of structural collapse in the face of such challenges has not been systematically explored. On a wider level, the investigations made by the IBOIS laboratory will contribute to a more profound understanding of spatial structures in general and set new prec-
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The development of woven structures is a field of research at IBOIS. Beginning with existing principles of weaving, a jump in scale is made to implement these same principles at the scale of buildings or load-bearing structures. For this purpose, the specification of global geometric patterns is necessary. Markus Hudert depicts such possible geometries using drawings The process of joining the textile module as depicted here creates a mechanically complex condition. The module possesses internal stresses that result from the juncture and are relieved in part by themselves (relaxation). The structural system reacts to the application of external loads through deformation, thereby functioning as an interactive system inasmuch as it adjusts its inherent stiffness in real time. The raw material, wood, appears particularly well-suited due to its deformability (we work with large deformations)
edents for cooperative interaction between the architects and engineers analyzing those structures. Case Study 1: Textile Module Applications The empirical models shown here have been developed by Markus Hudert at IBOIS. In this case, the initial drawings have given birth to an exciting structural module. Even though this first approach controls geometrical aspects, it revealed astonishing structural aspects in addition to its formal qualities. This structure gains static height when it is loaded. Thus it is a self-reacting structure and the very essential question becomes: Since we have observed that this specific structure gains static height when it is deformed under experimental conditions of increasing loads, can we assume that in the case of extreme loads—such as storms and earthquakes—it might also sufficiently adapt its disposition and strength to resist such extreme loads? In particular, research needs to be undertaken on initial stress analysis of large deformations and non-linear behavior. Case Study 2: Experimental Vault with Overlap Based on those geometries, a vault structure made of planar elements was defined digitally. This vault, initially composed of a wide range of elements of different sizes, was then redesigned in such a way that it now uses only two different overlapping basic elements. This work appears promising since it opens the way to approaching the following more detailed questions: How should the overlapping connections be built at a large scale? A deeper underlying question regarding this woven structure is: Since the global model depends directly on the local behavior and mechanical model of that connection, how should this structure be dimensioned? Ultimately it is the interaction between the global and the local that will lead (or not) to issues of feasibility for such large-scale structures and their potential application. It has also become clear that the relationship between the global and the local can only be successfully controlled through the design of the connection details. Thus the col-
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The textile module in this form was also developed by Markus Hudert, and poses a two-pronged question: What mechanical traits does this module have and what sculptural and space-defining qualities can it yield? The combination results in a fundamentally innovative, complex, and promising approach that can be studied from the viewpoints of both structural engineering and architecture
Repetition of the basic module creates arched or domed structures of a new character. From a mechanical viewpoint, what develop are hybrid structures that remain partly subjected to internal stresses. The study of these structures with regard to large deformations and non-linear systems is currently being pursued at the IBOIS laboratory
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The two elements along the weave’s primary axis are made from timber sheets of different lengths. The continuity of these sheets can be ensured in assembled systems. We are especially interested in the geometric condition at the points of overlap. At these junctures, there is also an opportunity to establish a third structural axis, which helps connect the panels to one another and also helps to achieve spatial rigidity
The proportions of the panels play a significant role in developing the textile module. A slender form is tested here in EPFL’s test facility. Numerical findings and test results are compared
The contact points and constraints of the structure need to be captured geometrically and mechanically. Differing support and connection conditions are designed and built for the individual prototypes. The construction details directly determine the internal stress condition, but also the manner in which the woven object can be extended
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laboration between architects and engineers discussed here also becomes crucial, as they must interact in defining the connection details. Case Study 3: Building Fabric Lookout Tower Steve Cherpillod has developed a tower made of a singular and highly specific timber module. His control of the general geometry and the global form of that tower enabled him to ‘reduce’ this complexity and define that basic module. Again, his initial input is a geometrical understanding of the interaction between stairs and towers, which is a very old and seductive theme. Having understood the spatial and functional requirements of a stair and successfully relating them to the structural requirements of a tower, the synthesis of those two main aspects of design that is shown here is achieved by controlling that basic module. Further structural analysis showed that this module will be the subject of intense discussions regarding its stability and further development of the tower as a whole. Conclusion This research is not subjected to the constraints of immediate practical applications. The IBOIS laboratory takes time and energy to explore unknown paths that do not directly confront the needs of application or efficiency, as do the engineering sciences. We do not expose our research to the real constraints or demands that a building must respond to. The research work shown here should be understood as potentially applicable for architecture and structural engineering.
The principle of weaving was applied to an arched bridge with a span of 85 m. Four arched sections made of laminated wood overlap and thus mutually support each other. The buckling length of each individual arch is thereby greatly reduced. This unusual geometric disposition defines a space on the bridge
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Taking into account the consequential high deformations, Masoud Sistaninia models the geometry with the aid of the finite element analysis program Abaqus. Since the deformed state differs geometrically to a significant degree from the non-deformed state, a fundamental condition of structural analysis is no longer respected
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Drawings—such as elevations, sections, and axonometric views—as well as digital and physical models are important in the development of the geometries
Model view of a parametric arched structure consisting of many facets. The insertion angle between one facet and the next can be adjusted as desired. This angle governs the global geometry, but also the way the local joint is formed. Bastien Thorel developed this structure as part of an exercise in the Weinand studio
Another version constructed as a cardboard model. The design process is guided iteratively
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All images on these pages: a 35 m high tower designed in the Weinand studio by Steve Cherpillod. The tower’s structure and the embedded stair construction constitute a single entity. The basic element was used approximately 300 times. Structural analysis of the tower revealed that the stair tread represents an important connection and bracing for this basic element. In further development of the tower, this element must be optimized
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0 .06
variation du module
développement du projet a tower for paléo festival
6.00 m 2.00 m
0.36 m
1.40 m
dimension du module
schéma assemblage
schéma assemblage
le projet
a tower for paléo festival
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Deviations Markus Peter
The dialogue between structural engineers and architects is based in no small part on mutually ascribed behavior and perception of roles. But it is not so much the dichotomy between aesthetics and engineered structures, as it was expressed in the debates at the end of the nineteenth century, nor the expulsion of engineers by the adherents of Neotectonic architecture, that is currently a cause for concern. Rather, concern lies increasingly in the knowledge that the pursuit of one’s own interests within the two disciplines does not necessarily coincide, and that an innovation in one medium does not inevitably and simultaneously reveal something in the other. The resulting call for dialogue, for a common education, criticizes the high degree of specialization. Indeed, it condemns the monological dimension of the engineering sciences. Yet since even the specialization of scientific thought necessarily builds upon a solid general academic education, which is contingent precisely upon specialization, it is surprising that scientific specialization is so readily, so persistently, condemned as a corruption of thought. Such judgments, whether they are expressed by a great thinker, like Goethe, or by lesser mortals, must at the very least astound us with their inefficacy. Science, to paraphrase Gaston Bachelard, goes its way unchallenged.1 1. In the works of the 1990s, our design strategy focused on establishing a relationship between structure and space. Grid, repetition, and order were less the goal than was the search for conveying tension from the load-bearing structure to the enveloping and pervasive space itself. Thus in Murau (Austria), for example, we treated the wood structure as a monolithic element—almost like a self-supporting car body—whose upper and lower chord bracing carry the roof and floor of the bridge. In close proximity to the structural design, the actual space of the bridge was created by manipulating the structural elements of the horizontal and vertical slabs. The structure is not located, as Hermann Czech describes it, 2 under or next to the circulation space that guides the user over the river, but actually in this space. The structural principle of the single-span Vierendeel truss, a structural frame without diagonals, enables both the horizontal opening in the middle as well as the staggered disposition of the planes at the sides. The truss itself is assembled from two vertical, plate-like box beams—the ‘shear walls’ made of three-ply plywood—and solid upper and lower chords made of laminated wood that are subsumed only by the overall form, such that the bridge constitutes a sculpturally formed, homogeneous and space-defining element of wood. This simple and experimental architectural scheme, however, can only be properly conceived in the
1 Gaston Bachelard, Epistemologie [Epistemology], Frankfurt am Main, 1993, p. 162
2 Hermann Czech, “Ungefähre Hauptrichtung,” in: Marcel Meili/Markus Peter 1987–2008, Zurich: Scheidegger & Spiess, 2009 p. 435
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Mursteg footbridge, Murau, 1993–95 Architect Meili Peter Architekten, Zurich Engineer Branger, Conzett & Partner, Chur
technical sense provided that it is in itself the product of a simplification process. In contrast to the Cartesian illusion of initially clear and distinctive ideas, the simple is necessarily the product of a purification process in the face of structural ambiguities. Only the simple and efficient connections made with ductile steel dowels and threaded rods, which transmit enormous shear forces between the chords and shear walls, permitted the conceptual supposition of a largely homogeneous transmission of force. Due to the rabbets along the chords, this simple connection technology resulted in a large bearing surface over the abutments, which proved helpful in stabilizing the single-span frame against overturning. On the other hand, the structural decision to use a single central girder required torsion-resistant chords, which inevitably turned out to be bulky. The beefy dimensions of the chords thus resulted from the shape of the bridge cross-section; of course it was now also capable, without additional measures, of absorbing considerable bending stresses in the longitudinal direction, enabling the central opening of the gigantic window. The staggered shear walls at the sides, due to their diagonal positioning, delimit the space together with the horizontal surfaces of the floor and ceiling slabs, and they evoke minimalist spatial experiments of the early Modern era. The experiments of that time, which took place predominantly in new areas of application and adapted material technologies, avoided using rodlike steel, which in no way defines space. The roofs over the platforms of Zurich’s main train station are constructed in this spirit: the delicate steel construction of the roof trusses is concealed from below by wooden latticework. Alone architecture and technology themselves are capable of drawing their own boundaries. For the field of engineering sciences, however, drawing a boundary already means crossing it. The scientific boundary is not so much a barrier as it is an area of particularly active thoughts, a zone of assimilation. 2. Our interest in the power of large forms and the inescapable ruthlessness of the programs changed our designs and shifted the experiments to areas of heterogeneous and also partly hybrid structural forms. The fact that the geometry of football stadiums is determined to a large extent by the logics of grandstand ge-
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ometry and roof structure effects the orderliness established by the multifunctional conglomerates, which is something characteristic of nearly all the new stadium projects in Switzerland. The dimension of the large-scale form, which emerged from the urban topography, no longer follows standard radial principles of ordinary stadium designs. The intended nakedness of the grandstand element is admittedly reminiscent of large stadiums in which the formal gesture presents itself as a direct indication of its contents, but its origin is a very different one. The form, with its enormous cantilevers, approaches that of an ideal pentagon. The bridge-like cantilevered beams of this grandstand are placed next to and within a conventional slab and column structure. They in fact come into contact with each other, even penetrate one another and transmit forces to one another, but remain autonomous in their composition and computational modeling. The actual structure of the Zurich stadium’s crown consists of individual beamcolumns, laid out in a rectilinear plan, that stand like balance beams on the crown’s piers, yet due to the differing lengths of their cantilevers, cannot be brought into balance on their own. Overturning of the truss elements is prevented by the loads of the adjoining ones, which push down on the short lever arms and thus establish a state of equilibrium. The crown rests secondarily on the inclined columns that constitute elements of the grandstand trusses. Due to their inclination, even though the bending moments of the vertical plane are greatly reduced, bending occurs in the horizontal plane of the crown. The hollow box construction, which permits the incorporation of a number of functions such as loges and sky boxes, can accommodate this flexure considerably more easily than it could cope with the solely vertical bending that would have occurred if the inclined columns had been omitted. The enormous torsional stiffness of this traversable box profile enables
Zurich stadium, unbuilt project, 2000–2009 Architect Meili Peter Architekten, Zurich Engineer Conzett Bronzini Gartmann, Chur/Basler & Hofmann AG, Basel
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What is meant is the computational effort for the hybrid structure, which was influenced by highly diverse forces and hence also by varied techniques for analyzing forces. This necessitated a huge effort in conducting CAD modeling. The consequences of even a very small change, such as the widening of a stair into a pier, were not foreseeable even by the engineers and involved week-long computerized calculations. Apart from that effort, the internal stability of the modeling system itself is also affected— it always had a somewhat precarious status, as opposed to a simple, or at least simpler, computer model of a Vierendeel truss.
supplemental restraint of the steel roof trusses, which counteract the moments that emerge due to the oblique columns and the corner bearing points. The immensely elaborate computational modeling for dimensioning this hybrid structure demanded maximum discipline with regard to changes and suppression of one’s own ‘original’ contributions: we were confronted with an engineering-oriented way of thinking that would not have easily found the stability and coherence of a secure existence.3 3. The design for a panorama restaurant on a site of spectacular beauty required an even more profound alteration of the epistemological field of engineering science. Far beyond the technological, such a mechanical complex is a significant step in the alteration of the mountains: it replaces the idea of the mountain lodge, which seeks to merge with the landscape, with a panorama-perception machine. We were fascinated by the sublime Villa Girasole by Angelo Invernizzi, in which the rotating, angular building cinematically orchestrates the view of the Veronese landscape and the guise of the building itself is animated within the landscape. Because the restaurant is supported off-center, the rotational movement projects the figure into the surrounding countryside to varying extremes. In the opposite direction, seen from the landscape, the mountain guesthouse is perceived as a mechanical sculpture that continually changes shape. Perhaps this project demonstrates one of the strengths of the much-criticized deductive theoretical construction in the engineering sciences—that all those technological objects whose physical behavior is primarily determined by the laws of
Revolving restaurant on the Hoher Kasten, Appenzell, 2004–2005 Architect Meili Peter Architekten, Zurich Engineer Conzett Bronzini Gartmann, Chur
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mechanics are fundamentally controllable with the system of theoretical mechanics that unfolded in the eighteenth century. The actual rotary mechanism was to be positioned inside, on top of the cylindrical tower housing the vertical circulation. It was imperative that the design of the structure assumed a stabilizing effect on the acting forces in order to impart a uniform capability for propulsion. In addition to the unequally distributed wind loads, live loads, and snow loads, the asymmetry—vis-à-vis the rotational axis—of the uppermost restaurant level also needed to be accommodated in establishing the equilibrium. For this reason, the rotating bearing seat has the largest possible diameter and is located as high as possible. Conversely, the center of gravity for the rotating mass needed to be situated as low as possible. Only after a prolonged study of variants did a solution appear for guaranteeing stabilization of the movable part by using the structure’s dead load, thus sparing costly efforts to safeguard the movable bearing against suction forces from wind. The boldly cantilevered roof, from which the restaurant floor is suspended, is supported by a host of radial, oblique wooden struts, which are held together at the periphery with a kind of tension ring. The roof itself is a thin, pretensioned concrete slab that absorbs the tensile forces as a membrane. The actual rotary mechanism is located on top of the concrete cylinder and as a result, only needed lateral guidance from rollers to maintain proper clearance at the sides. After initial attempts at constructing the rotating framework in the old tradition of the mechanics of railroad cars and other moving machinery like hoisting devices made from steel, a solution of different components assembled from various materials proved to be more efficient. To this end, the preconceived notion of fashioning the structure from a single material and, above all, of using lightweight construction, had to be overcome. In this case it turned out that, as Georges Canguilhem unremittingly emphasized, problems do not necessarily emerge on the terrain where they find their solution.
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Each His Own Mike Schlaich
The history of progress in construction is also the history of materials. Iron, steel, and reinforced concrete have each sparked revolutions with entirely new loadbearing structures. But inherent in this is also the history of the development of new technologies. For example, discovery of the principle of prestressing is what first made possible prestressed concrete, high-strength bolted connections, and complex cable and membrane structures. The same applies to the development of new joining techniques that led to the composite materials that are so widespread today. Ever since digital data processing entered the construction industry, the influence of new technologies has become perfectly obvious. Many load-bearing structures were not possible until this ‘watershed in construction’ was reached— these days we design, calculate, construct, manufacture, and install in a closed process chain with the aid of computers. Responsibility and Limitations To begin with, the structural engineer is solely responsible for built structures in which the load-bearing structure comprises a significant portion of the whole—typically bridges and long-span roofs. The profession of structural engineering is exceptional because, like few others, it closely combines technical and scientific skills with creative work, and because practically every design remains a prototype, much unlike other engineering disciplines. The structural engineer shoulders a great responsibility, because even a single oversight can have catastrophic implications. As a civil engineer, he is also responsible for the entire built infrastructure, the energy and water supply, and traffic on our roads, railways, and rivers, and along our tunnels, bridges, and canals. For ‘his’ projects, the structural engineer is of course responsible for the design. He who is most capable should lead the team. It is a gross misunderstanding to presume that the architect is always responsible for the form and the engineer is only responsible for the structure. Each is fully responsible within their field—also for the design. Structural engineers must therefore learn to recognize, expand, and transcend their limitations. When creative matters become too demanding, they must obtain support for the team in a timely manner. They must receive early training in conceptual design, not only in calculating and dimensioning. Otherwise, they won’t free themselves from the negative image—which, incidentally, is not so bad outside Germany—of being unimaginative structural analysts. In Spain, for instance, the ingeniero de canales y puertos is esteemed, much like doctors or lawyers in our country. But meanwhile, there is much also happening in Germany. From Stuttgart
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to Dortmund, and from Berlin to Hamburg, conceptual design is now taught to structural engineers. Creative minds—serious partners in the planning team—are being trained. We must also be aware that in addition to the architects, the building physicists and MEP engineers are becoming increasingly important in building construction. To achieve overall quality, they must also be integrated into the planning team from the beginning.
1 Compare Alfred Messel’s Wertheim department store in Berlin with the new shopping mall recently built on Alexanderplatz
Sunderland Strategic Transport Corridor, New Wear Bridge, 2003 Single-pylon, self-anchored suspension bridge with glass sculpture on the backstay cables Architect Gehry Partners LLP, Los Angeles Engineer Schlaich Bergermann & Partner, Stuttgart
Loss of Responsibility We engineers crave architects who share these goals. Unfortunately, however, one repeatedly encounters architects who, since they have ceded too many responsibilities, no longer have much in common with earlier, multifaceted master builders. That doesn’t imply a lack of understanding about just load-bearing structures and their construction: ‘acoustics, heat, and humidity’ are also delegated to building physics, the building services are handled by MEP engineers, the interiors are designed by a scenographer, there are project managers for administering design and construction schedules, and quantity surveyors prepare bills of quantities for invitations to bid. What remains, drifts helplessly in a cloud of 3D bubbles. The architect is at risk of degenerating into the maker of cute images for investors. Wertheim becomes Alexa.1 Fortunately that’s not the general rule, and working in a team, we occasionally get close to a synthesis of the arts. Whether the result is of lightweight or solid construction depends on the context, which itself depends on the local constraints, and of course also on the design wishes of the client and the planner. When acoustic insulation needs dominate, lightweight construction makes no sense, and for long spans, solid construction would be the wrong approach. The Search for the New In our engineering firm, we are always searching for something new. With each project, we try to take a small step forward, to develop things further. That way, the tasks remain interesting and we stay involved with
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progress being made in the building industry. We work on building design projects and bridges, on long-span roofs and facilities for producing solar energy. We try to be generalists. For instance, it could be that an engineer who has just finished working on a cable-stayed bridge is given a glass roof as the next assignment. That is admittedly demanding, because one needs to become acquainted with new subject matter, but on the other hand, there are no repetitive tasks to cause boredom or a lack of motivation. The loss in efficiency remains slight, because within the team there is always at least one person with the necessary experience. Our working method, which spans across building types and construction materials, liberates valuable synergies. Thus, for example, today we also regularly employ the collective experience in steel casting, which we originally gained in building construction, for bridge construction, in the same manner that we design cable-stayed roofs that support like bridges. Lightweight Construction—Active and Adaptable Even when the results of our design process are not always lightweight constructions, they’re still quite common in our work. This is not surprising, since we structural engineers fundamentally try to achieve maximum effect with a minimum of material, and because lightweight constructions are compellingly contemporary for aesthetic and ecological reasons: lightweight constructions manifest the load transfer in a natural way—we like things we understand. Lightness is associated with elegance, and the lighter and more transparent a structure is, the less it blocks the view—we don’t feel threatened. Light structures are labor-intensive and, by definition, resource-saving. Building with skilled labor and low material consumption facilitates sustainability. Lightweight construction is nothing new, and we ask ourselves: how and where will it progress? One direction is certainly that of active and adaptable structures, because other industries show that in this way, security, comfort, and energy consumption can be improved. New (micro-system) technologies, such as those already successfully introduced into the automotive industry, and bionic principles, like those
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Sunderland Strategic Transport Corridor, New Wear Bridge, 2003 View of the ‘loop cables’ and the glass sculpture Architect Gehry Partners LLP, Los Angeles Engineer Schlaich Bergermann & Partner, Stuttgart
we know from nanosurfaces, for instance, will certainly also generate advances in light construction and ensure that our structures become active, adaptable, smart, intelligent, autonomous, or adaptive. In this way, the demand for sustainability and a reduction in consumption in construction will hopefully also become less of an issue. Instead of thick-walled ‘boxes’ with windows the size of crenelated openings prescribed by building physics, new and interesting things can develop. Competitions offer a good opportunity for sounding out this potential for progress, and for collaborating in teams of architects and engineers. Examples include the currently ongoing competitions for IBA Hamburg on the topics of “smart material” and “smart houses,” in which the team is specifically called upon to deal with these questions of new materials and new technologies. Landmarks and Efficiency I also remember a bridge competition that we had the honor of doing in 2003–2004 with Frank O. Gehry as being very stimulating and instructive. We met for a two-day workshop in Gehry’s office in Santa Monica, California, to design the bridge in Sunderland in northern England. The clash of different worlds—we sketched and Gehry folded, we focused on an efficient structure for the bridge and Gehry thought about designing a landmark—led to an exceptionally fruitful dialogue and a result that, although it was never built, is quite impressive. A single-pylon, self-anchored suspension bridge spans approximately 300 meters over the River Wear. The loop cables are innovative: they are guided to the superstructure near the mast, consequently resulting in short hanger cables and an efficient load-bearing structure. The backstay cables that stabilize the mast landward simultaneously constitute the supporting structure for a glass sculpture approximately 100 meters high, which makes the river crossing recognizable from
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afar and is meant to be a symbol of the glass manufacturing tradition in Sunderland. For this competition, the constructors’ dialogue resulted in a formally and technologically ambitious design. We must cultivate the culture of dialogue—it is both sensible and promising when it is characterized by curiosity, respect, and a willingness for discussion.
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Rules to Play By and Play With Elisabeth and Martin Boesch, Carlo Galmarini, Urs B. Roth and Judit Solt
Judit Solt interviewed the architects Elisabeth and Martin Boesch, the structural engineer Carlo Galmarini, and the geometric engineer Urs B. Roth on May 13, 2011.
Judit Solt A team consisting of architects, a structural engineer, and a geometric engineer is unusual—simply because “geometric engineer” is not a common profession, but an activity that concentrates on solving mathematical and in particular geometric problems.1 You are now working in this constellation for the second time. How did this come about? Architects We got to know Carlo Galmarini when we were designing the “OUI!” pavilion at Expo.02. Urs Roth was not yet involved in the project, but we were already puzzling over the unusual geometry of one part of the building. There was a forest of columns, which supported a thin roof. The appearance of disorder was deceptive; in fact, the layout and color of the columns obeyed a system which, although it didn’t follow mathematical rules, was governed by a specific geometry. The columns were arranged according to spatial, empirically developed parameters. In the first section, they were quite openly spaced, after which they became ever denser, creating a visually impenetrable forest. There were probably many other positions that would have met our criteria equally well, but yet more that would not have met them. The engineer was not deterred by the lack of a grid. He acquainted himself with our seemingly random forest of columns, subjected it to his own criteria, informed us of his rules, and corrected us when a column needed to be positioned differently, or to be thicker, for structural reasons. This cooperation to ascertain the spatial and structural interaction was very productive. Afterwards, we were often asked whether we had designed the pavilion together with an artist.
1 Judit Solt: “Kein Mensch wartete auf mich!” [No one was waiting for me!], in: TEC21 – Zeitschrift für Architektur, Ingenieurwesen und Umwelt, 7/2010, Zurich, 2010, pp. 12–13
Structural Engineer “Form follows function”: we’ve all heard that thousands of times—but really to grasp one task means looking at it from all sides and understanding all of its functions, including the supporting function. In the Expo pavilion, nine-meter columns were supposed to support a roof that was as thin as possible, while the building on the shore of Lake Neuchâtel had to withstand strong winds from time to time. The load-bearing function, therefore, had a variety of implications. There was a relationship between the strength of the roof and the rhythm
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Expo.02, “OUI!” pavilion, 2002 Architect M. & E. Boesch Architekten, Zurich Engineer Walt+Galmarini Bauingenieure, Zurich
of the columns: the broader the clearings in the forest of supports became, the thicker the roof had to be. But there was also an interaction between the different thicknesses of the ‘tree trunks,’ because they had to withstand the sum of the wind stresses. The various columns performed different tasks: under wind stresses, the thick ones restrained the roof, whereas the thin ones were merely appended to it. The thick ones were like tree trunks, rooted only in the soil, the thin ones had to be stabilized at the top as well as the bottom. js You worked together for a second time on a competition entry for the extension of the Institute of Oriental Studies and the Department of Comparative Indo-European Linguistics (Indology) at the University of Zurich. Again, it was necessary to give an apparently chaotic form some structural and formal order—this time with the assistance of Urs B. Roth. Architects Besides minor works to strengthen the old building, a villa probably built by Leonard Zeugheer in 1863, an underground library was to be built. Contrary to the requirements in the competition brief, we located it under the drive on the side facing the mountain. This had the advantage of preserving the garden, while allowing the inner circulation to be resolved logically. It also meant, however, that the new building had to resist pressure from the weight of sloping ground, as well as avoiding the roots of two old trees. Our response to the conditions imposed by the terrain is reflected in the floor plan. The idea of giving the ceiling a relief pattern came to us early on, at the competition stage. We also wanted it to be omnidirectional, free of columns, and to float like the heavens above the room, with a form that referred to the Orient and Islam. Our vision of a geometric, three-dimensional treatment of the ceiling was inspired by a drawing by Sol LeWitt. Because the room was fairly large and located under the drive, which was used by trucks, the ceiling had to be prestressed. We decided to integrate the runs of the prestressing tendons, the cables, in the relief, with the proviso that its overall shape should be justified in structural terms. We didn’t want a random pattern, but a true geometry, in which all of our requirements—omnidirectionality, freedom from columns, topographical and formal references, statics—would merge as one.
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Continuous Forms and Color, 1988 Gouache on Paper, Sol LeWitt Conversion of a villa at 66, R채mistrasse, for the Institute of Islamic Studies, University of Zurich, Project 2004 Architect M. & E. Boesch Architekten, Zurich Engineer Walt+Galmarini Bauingenieure, Zurich Geometric Engineer Urs B. Roth, Zurich Ceiling relief in the underground library Axonometric Projection of the underground library Basement floor plan
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This brought us up against our limits and so we called in the geometric engineer. Geometric Engineer An incredibly beautiful task: a column-free, structured ceiling, under which historical Islamic manuscripts are stored! Anyone who has an interest in geometry knows the refinement of Oriental patterns. It was, however, out of the question for me to borrow from this cultural sphere for the relief. I rather wanted, as a western European who works with geometry, to create something new that would reflect the Oriental canopy in spirit. When the architects showed me the floor plan, my first question was: “Does it have to have exactly this shape?” I knew that the outer wall had to run around the tree roots, I just wanted some leeway to develop the pattern so that it rises at the edges. The architects agreed on the condition that the deviation remained small. My first suggestion, which I called “mountain and valley,” was made up of shallow, concealed pyramids, overlapping one another, with deep valleys in-between. The structural engineer took one look and immediately said no. The prestressing cables would have had to zigzag, which is not possible. Architects
Prestressing cables are usually straight ...
Structural Engineer vertical plane.
... to put it more precisely, they are usually bent only in the
Geometric Engineer But a pattern that adopted the straight lines of the prestressing cables would have been directional. The engineer proposed a solution in which the prestressing cables were bent slightly in the horizontal plane, like a flat S. A very small degree of bending seems to be possible, but without sharp kinks, and especially not in the middle of the room, where the prestressing cables hang the lowest. Then I realized that I needed to consider the problem from the other end, and start with the flat S of the prestressing cable in order to find the pattern for the relief. The architects didn’t want people to see masses of wavy lines when they look at it, and so I came up with the polyhedron pattern. It still contains the snaking lines, but the trick is that you don’t really notice them. The eye is distracted, it focuses on the fields instead of on the edges. To check whether the ridges were thick enough to take the prestressing cables, I drew a horizontal section through the formwork. The image is reminiscent of a river bed, from which large stones protrude, with water flowing between them—the spaces would indeed have been large enough to accommodate the prestressing cables. Structural Engineer The geometric engineer understood that it makes sense for a long-span roof that has to carry high loads to be resolved into components. For a rectangular floor plan, a hollow block or concrete beam construction would have been chosen. In this case, the shape of the room means that the forces flow more dynamically. In order to achieve a really good solution, the structural functions
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had to be clear. The architects and geometry specialist wanted to understand the details of the load-bearing function. Ultimately, the form followed the load-bearing function: it makes sense to thin out the weight between the ribs of the ceiling— only these are no ordinary ribs ... Architects The pattern created by the polyhedra does have an approximate orientation, but it contains no straight lines or beams. The ridges, where most of the mass is concentrated, contain the prestressing cables. In addition to these, the rest of the reinforcement had to be accommodated. The idea that someone should have to prepare a reinforcement drawing for this complicated form and lay the rebars accordingly on site, seemed rather awkward to us. Many things are possible, but was that really necessary? Then the structural engineer proposed using steel-fiber reinforced concrete, completing a solution that would have been very elegant, right through from the drawing board to the building site. js You are now working as a team again, on new stairs for the freshly renovated Hardbrücke viaduct in Zurich. This project brings together two very different geometric systems and some very special structural requirements ... Architects We imagined elegantly styled flights of concrete stairs, which would descend from the tower in a dynamic curve. They were not supposed to be spiral staircases, on which people move in circles: at the base, they open out invitingly into the city, while as they rise towards the bridge, their radius narrows and they cling to the elevator tower. To start with, the structural engineers working with us at the time claimed that it was impossible to build the design in that form. It seemed inevitable that columns would be needed under the stairs, or suspended beams to absorb the movements of the bridge. Then another structural engineer joined the project, and he suggested constructing the stairs as cantilevers. So the structural principle was decided. Now we had to sort out the form—a kind of spiral that also developed along the axis in the third dimension, as it were. The traffic engineers mentioned clothoid curves to us. We had never even heard of them ... There were two main difficulties. Firstly, the staircase stood in public space, so it had to meet high standards of design, in addition to all the safety requirements. Because it had no landings, it had to be as comfortable to use as the main staircase of a palace; not to mention being fun, robust, and durable. Nothing less than the perfect staircase! Secondly, how does one describe these clothoids, and how do you build them? Geometric Engineer A clothoid is a curve whose radius increases and decreases linearly. It is often used in road construction, but for a stairway there is something better. The logarithmic spiral, which occurs naturally—in nautilus shells, for example—has all the necessary characteristics. Not only does its radius change constantly, it also has an inner logic that permits a nice solution to the problem of the
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stairs. Each radial that you draw from the center of a logarithmic spiral intersects the curve at the same angle. This constant angle determines the form of the spiral, while the spiral itself always grows by the same factor, according to a geometric progression. I chose a very special one, a self-generating logarithmic spiral. It is the one logarithmic spiral whose tangent intersects the next turn of the spiral orthogonally. The radials dictate the direction of formwork on the underside of the stair. This basic geometry had to have a second geometry superimposed on it. The pitch of the stair necessarily requires regularity, not a progression. This combination led to an antilogarithmic, linear division of the curve. Architects Lots of identical, narrow boards were used as shuttering for the underside, so as to illustrate how the stair is built up from layer upon layer. The formwork contractor would certainly have been able to produce a smooth, continuous surface, but we wanted the material to express the geometry behind it. Geometric Engineer The superposition of two sets of directions for the top side and the underside of the stairs has a further consequence: in section it produces a taper towards the outer edge. That makes sense structurally, because the steps are cantilevers and so the greatest torques are on the inside. And it makes sense aesthetically, too, because the stairs should appear as lightweight as possible. The logic underlying the chosen geometry is consistent with that of the staircase. Structural Engineer From the architects’ design sketches it was clear that the stairs should bear like a spring and would require torsional rigidity. The steps form projecting angles and are therefore strongest at the inner stringer. The architectural idea, the structural function, and the mathematical form are congruent. js You have the objective of dovetailing the various aspects of a project in such a way that they are inconceivable without each other. This correspondence is recognizable in both the library and the staircase. Nevertheless, you avoid making any kind of didactic gesture. For example, visitors can follow the distribution of forces in the library ceiling, if they so wish, but the knowledge is not imposed on them. And as for the nautilus shell ... Architects We are not interested in obvious representations; relationships should be evident in a subtle way. After all, buildings have to communicate without being explained by their authors—subcutaneously, as it were—and to reveal their secrets by themselves to anyone who takes a close look. Geometric Engineer Some things naturally remain invisible. The prestressing cables in the library ceiling are not visible in the finished building; you only see where they ought logically to run. The mathematical laws of the ceiling relief are of no interest to the majority of visitors, but a mathematician can reconstruct them,
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Hardbrücke stairs, Zurich Plan view with steps and underside board pattern overlaid Each radial drawn from the center of a logarithmic spiral intersects the curve at the same angle. In the selfgenerating logarithmic spiral, this angle is orthogonal
Example of a natural logarithmic spiral: a nautilus shell Logarithmic spiral k = 4,78936902918 × 10-3 Antilogarithmic division 17 / 26 / 40 Good approximation to a = 1,53886204679
Hardbrücke stairs, Zurich 2011 Architect M. & E. Boesch Architekten, Zurich Engineer Walt+Galmarini Bauingenieure, Zurich Geometric Engineer Urs B. Roth, Zurich
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Hardbrücke stairs, Zurich Cross-section
including the system of proportion, from the evidence available. js In hindsight, it all sounds very natural. That the library responds to the pressure of sloping ground and the trees in the park; that the construction of the ceiling obeys structural laws; that the pattern has to do with the contents of the library; and that the ridges match the lines of the prestressing cables—of course. That a flight of stairs in public space is inviting, safe and comfortable; that the production of the shuttering and the arrangement of the steps obey the same geometric principle—how could it be otherwise? But a great deal of intellectual effort has gone into achieving this simplicity. The projects are incredibly concentrated; every single particular is filled with multiple significance and functions. Architects The word ‘concentration’ is apt. What we are looking for together is the “solution élégante.” Or as Le Corbusier put it: “très difficile, mais satisfaction de l’esprit.” That makes us happy; the difficulty must not be visible in the end. Geometric Engineer The stairs’ two overlapping geometric systems cost us a substantial amount of work. How many passers-by notice them? If the result seems so much a matter of course, that’s perfect. We know the secret, we don’t have to broadcast it ... Structural Engineer Beautiful projects always come about in the same way: you try to comprehend a brief with all its functions and to develop rules that perform as many of these functions at once. js This concentration requires collaboration between architects and engineers as equal partners. You look for “judicious intervention” as you call it, in your respective areas of expertise. How would you describe your collaboration? Is it as free of conflict as the result? Architects
Working in this constellation is inspiring. Although the responsibility
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Rules to Play By and Play With
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lies with us as architects, we are open to any clever input. And if one of us explains why something will not work, then we won’t attempt to enforce the impossible. Stubbornness blocks. Geometric Engineer It is important that everyone has their own area of responsibility. We complement each other well. Structural Engineer Freedom from conflict is important. When working in a team is enjoyable, people’s interaction functions and everyone responds to each other. Then it doesn’t matter who put forward which argument—usually no one has the final idea at an early stage, anyway. Sometimes this joint work produces a feeling of conspiratorial fun. In the Hardbrücke stairs, for example, the walkway leading from the stairs to the bridge cantilevers out seven meters, like a diving board. It must be elastic enough to adapt to the not-inconsiderable movements of the bridge. We find it particularly nice that our walkway, our thin little cantilever, also makes a tiny contribution toward stabilizing the bridge itself: if the bridge settles, the walkway pulls it up a little bit; if the bridge rises, the walkway pushes it down a little bit. Architects One has to be careful with idealizations, but it’s an extremely satisfying and efficient way of working!
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