Agustí Obiol
Professor and Member of the BIArch Academic Board
Structural Types: Geometry and Material
Building Technologies
03/12/2010In a speech delivered in April 1950, Mies praised technology, saying that its fulfilment transformed it into architecture and voicing the hope that, one day, one would be an expression of the other. Regrettably, rarely has this wish been realized. There is a far greater tendency for architects and engineers to dissociate than to associate.
Manifestly across-the-board views, such as Eduardo Torroja’s Philosophy of Structures [University of California Press, Berkeley, 1958], have tended to be the exception rather than the rule. The approach to technology that forgets its origins rooted in scientific principles is unlikely to reach its full potential.
The dizzying development undergone in recent decades by the technologies of materials and analytical methods has tended to exacerbate this problem in the field of structural design. In some cases, in the framework of a markedly expansive economic context, this has prompted rather arrogant attitudes that seek only to produce iconic images and disregard efficiency and optimization of resources.
In others, conversely, pure calculus has simply gradually taken over from design. The optimized response of the structural framework has always been strongly conditioned by the geometry of the framework in question. But in turn, inevitably, this geometry is the product of the morphology of construction.
Le Messurier saw the structure as the result of a quasi-sculptural act of emptying out the construction, stripping it of anything “that does not contribute to its strength”. He takes as his starting point the image of the chimney, almost metaphorically, as the optimum form for absorbing lateral loads and studies the process of transformation that turns it into a habitable tower block. In this process, he defines two parameters, the indices of rigidity under flexion and shearing, and investigates the form required by the “structural mass” to produce maximum efficiency.
What essentially defines the limits of each structural morphology (of each typology) is, then, its geometry. Material thereby becomes a simple multiplier. The typological limits we
work with today, which were defined more than half a century ago by Myron Goldsmith and Fazlur Khan, are what they are because we have the materials that we have. If we were capable of manufacturing much stronger, more rigid structural materials, our typological scales would move forwards, though obviously not linearly.
Further, each geometric configuration involves a different state of equilibrium. That of traction is stable, that of compression, unstable, and that of flexion, indifferent. It is, then, no coincidence that the typological variants used to span large spaces are those that fundamentally employ systems of traction, followed by compression. Systems of flexion follow at some distance, since compression and traction coexist in a single element (one in each flange of the beam); in this way, the distance between the two stresses and, therefore, the efficiency of the compression/traction pair are limited to the depth of the beam. If these two forces act on different elements, conversely, this efficiency grows in accordance with the distance between the elements.
If it were possible to construct skyscrapers stabilized by cables anchored hundreds of metres away from their bases (compression in the building and traction in the cables), they would be much more slender and, therefore, much taller (like the telecommunications tower in Collserola, Barcelona, designed by Norman Foster). This attempt to establish similarities and differences was essayed in one of the exercises in the first term of the 2010-2011 academic year at the BIArch, in the form of a critical comparison of five singular constructions: the basilica of Hagia Sophia in Istanbul, Eladio Dieste’s market in Porto Alegre, Dulles Airport by Eero Saarinen, the roof structure of Frei Otto’s Olympic Stadium in Munich and the sports hall in Huesca by Enric Miralles.
Finally, our approach to structural design has to be underpinned by two partially complementary concepts: the order of magnitude required for analysis and the determination of the important variables. The first tells us the level of precision that we expect and need to achieve in each phase of the project (schematic design, conceptual design, design development, etc.) and, consequently, the intensity required for analysis in the respective phases. The second refers to the obvious concept that, of all the variables involved in the concretion of the form of the structure, only a few ultimately have an essential bearing on the process, whereas the vast majority simply nuance the result.
All of these factors point to the need to adopt new positions. The desirable communion between technology and architecture posited by Mies will only be possible if our essential approach sees the structure as an indissoluble part of the building, in which the scientific concept is not undermined by its technological instrumentation.
All of these considerations were developed in the Building Structure class during the first term of the 2010-2011 academic year at the BIArch and are addressed at much greater length in Agustí Obiol’s forthcoming book, which will be published by BIArch Press.
Agustí Obiol
Member of the BIArch Board of Directors, Professor at the Universitat Politècnica de Catalunya and co-founder of BOMA
Photo: Structural proposal for a larg span building using 4 supports (detail). Building Structures course project by MBIArch students M. Chapman-Smith (USA), I. Petkovic (Montenegro), and G. Kallis (Cyprus)
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