International Journal of Space Structures

Frei Otto (1925 – 2014) is one of the most decorated architects in the 2nd half of the 20th century in the world. He built lightweight structures as the German Pavilion in Montreal 1967, the roofs for the Olympic games in Munich 1972 and numerous tents and shell structures. In his pioneering research he described the growth and form of natural structures in living and non living nature. This contribution highlights Frei Otto’s approach and works.

The contribution presents design approaches based on analog models and experiments in architecture and science and on the works of Frei Otto and his teams, in particular. Starting with the classification of self-forming processes, three thesis are described to show the influence of the physical experiment on the quality of the design. The first thesis - the design tools define the architecture - opposes T-square and compass versus self-forming physical experiments, tracing back the invention of the grid shell to the search for a tool to define the proper shape of compression stressed shell structures. The second - in working with self-forming processes, the will to design a particular shape is linked to the understanding of the influence of boundary conditions - emphasizes that the use of self-forming processes never holds you from making design decisions. The third - in shapes, defined by self-forming processes, the balance of power according to the principle of minimal energy expenditure results in a harmony of form - reflects on the esthetical quality of shapes, deriving from self-forming processes. The verification is given by an example of evidence: describing the design process for a tent according to the form of a minimal surface the interplay between willful decisions and inherent laws within the shape are show. The choice of suitable boundary conditions results in a shape which does equal justice to the original design ideas and the structural specifications. Finally its shown that the role of physical design models in times of computer-based virtual 3D models appear as three dimensional sketches.

Physical modeling as a developmental iterative process was one of the primary legacies of Frei Otto in his quest for a formfinding design tool. Exploring first hand knowledge of his sketching, and then incremental physical modeling techniques, we look at Otto’s global approach to problem solving through design. Numerous actual projects of Otto including the BP Dyce Tent in Scotland and the KOCOMMAS project in Saudi Arabia are described in terms of this process as a better way of understanding his approach. A comparison of the formfinding and shape making approach to design is examined. In contrast to Otto’s physical modeling, digital modeling & parametric approaches are also investigated to show Otto`s influence and evolution in contemporary modeling of complex surface geometries, but also to point out the seismic change that is presently occurring in the architectural profession.

Short presentation of the key topics of research of Frei Otto and his teams at IL, with emphasis on the comprehensive investigations on form generating processes, the mutual interdependence of forms as a geometrically measurable, space creating entities and their structural qualities. This was one of the primary research topics at IL, which was studied in different contexties, like prestressed membranes, grid shells, form generation in living nature. Similar questions lead also to the investigations on structures of non-planed settlements, their form generation processes and their characteristics. The article conclude with a short presentation of the author’s latter investigations at the University of Innsbruck, “Institut für Konstruktion und Gestaltung” - “koge” on the phenomena of irregularity and on multilayer membranes, studies which are based on the experiences winned at IL.

Urban structures encompass settlements, characterized by the spatial distribution of built-up areas, and also transportation structures, to connect these built-up areas. These two structures are very different in their origin and function, fulfilling complementary needs: (1) to access space and (2) to occupy space. Their evolution cannot be understood by looking at the dynamics of urban aggregations and transportation systems separately. Instead, existing built-up areas feed back on the further development of transportation structures, and the availability of the latter feeds back on the future growth of urban aggregations. To model this co-evolution, we propose an agent-based approach that builds on existing agent-based models for the evolution of trail systems and urban settlements. The key element in these separate approaches is a generalized communication of agents by means of an adaptive landscape. This landscape is only generated by the agents, but once it exists, it feeds back on their further actions. The emerging trail system or urban aggregation results as a self-organized structure from these collective interactions. In our co-evolutionary approach, we couple these two separate models by means of meta-agents that represent humans with their different demands for housing and mobility. We characterize our approach as a statistical ensemble approach, which allows to capture the potential of urban evolution in a bottom-up manner, but can be validated against empirical observations.

In this article, formfinding theories for different structures are considered. The beginning of analytical formfinding theories coincides with the analysis of the Olympic Roof in Munich (1972). Therefore, this article starts with the derivation of the force-density method with respect to cable net calculations as those procedures were used for the cable net calculation of the Munich stadium. Later on, the formfinding theories were adapted to textile membranes and foils, so the constitutive equations are extended by crimp- and shear-stiffness. The crimp-stiffness produces a correlation between warp- and weft-stiffness in textile membranes. The shear-stiffness causes shear-stresses because of angle-deformations. Pneumatic structures such as air-halls, air-domes, and ethylene tetrafluoroethylene cushions are widely used. The formfinding calculation of those pneumatically stressed membranes is also demonstrated. An important formfinding input value for those structures is the size of the volume itself. Therefore, an additional constraint in the volume formfinding strategy is the so-called volume equation, which is related to the internal pressure. Minimal surfaces such as soap films (and pneumatically stressed bubbles) have a very specific material behavior which is extensively described. The analytical formfinding theories were always developed due to physical modeling procedures. Mixed formfinding tools combine stiff elements with soft surface materials, as is often done in physical models when, for example, a stiff timber bar is used together with a soft nylon mesh.

Designing and building the stadium complex for the International Olympic Games 1972 in Munich in only five years, may be characterized as a singular challenge. The futuristic and huge tensile structure, covered with Plexiglas became to be designed by engineers and architects of different fields: Günther Behnisch, Frei Otto, Fritz Leonhardt, Jörg Schlaich, John Hadji Argyris, Klaus Linkwitz with Carl Mertz responsible for the management. Based on written reports and testimonials from witnesses of the process, the paper analyses all phases, starting from the skepticism of many that the most spectacular part, the roof, would be buildable. After Leonhardt/Schlaich also Otto/Bubner became part of the design team. At the start of building the engineers registered that the technical models of the Frei Otto team could not bring exact data for (all) cutting patterns, which was a crucial problem. Both Argyris and Linkwitz delivered feasible computational methods for calculating cable lengths and joint locations. The executed result was criticized by its authors for different reasons, in the same time respecting the unique mutual achievement. The spectacular Olympic stadium complex was much appreciated by visitors, and critics ranked it as one of the most impressive and innovative examples of German architecture.

The search for lightweight constructions is the search for boundaries. Designing the lightest possible constructions can be equated with feeling one’s way towards the limits of what is physically and technically possible. It is about the aesthetics and physics of the minimal, and it is about stepping across the dividing lines between scientific disciplines. Using the concept of ultra-lightweight structures developed by the author, it becomes possible to reduce the use of material to a minimum hitherto considered unachievable. Moreover, it leads to the reduction in distortions and helps to dampen vibrations – an enormous progress opening up interesting new perspectives for architecture. This article describes the theoretical considerations underlying the concept of ultra-lightweight structures and presents a selection of experimental structures demonstrating the potential of this new concept.