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Pneumatic and Tensile Structures: The Work of Frei Otto

Pages: 5-8
Dr. Ida Rolf Institute

Bulletin of Structural Integration Ida P. Rolf


Fur nearly thirty years German architect Frei Otto has devoted himself lo the theoretical and practical development of tension based and pneumatic structures. Ottos reputation as a visionary and as a remarkably adept technician rests on the fact that his lightweight structures are radical depart in design from the dominant architectural style.

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All structures employ both tension and compression if they are to remain integral. All structural elements exhibit relative degrees of both tensile and compression characteristics, some being primarily tensile while others are primarily compression based. The chief feature of Otto’s style is that he has shifted his focus away from compression materials such as concrete and steel beams to tension based materials such as high strength steel cable, cable nets and thin members of synthetic fabric.

In most of the structures we see around us, the sheer volume and the combined weight of the materials used are vastly disproportionate to the actual loads they must bear. The esthetic of such a massive structure as, say, a Gothic cathedral is quite different from the basic shelters the average person lives it but they share a common design feature in that they do not employ gravity as a potential source of structural economy. Quite the contrary they are built with the intention to eliminate gravity as a technical or esthetic consideration.

Otto has attempted to reverse this disproportion. As you will see, the design possibilities and his technical accomplishments reveal quite a different relationship between gravity and design integrity. The results have primarily been temporary structures, highly efficient with respect to over all weight and volume of materials relative to the intended function of the structure.

Using a few lightweight compression members in conjunction with tensile members, the shapes and arrangements that a few cables hung with fabric may assume appear to be nearly unlimited. The purposes to which such designs have so far been put include pavilions tents, open-air theaters. Stadium roofs and public recreation areas. Each is unique grateful and economical often appearing to be more art than architecture.

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Despite the fact that cash of these designs necessary begun as tabletop sculpture. Otto himself resists being labeled all artist. Only after meticulous calculation of all the stresses involved in a design can large scale construction begin. Preferring to be viewed more as a technician. Otto maintains that his designs are but the manifestation of the physical laws governing the nature of his materials.

At the first glance this stay not appear to be a particular revolutionary statement. Every architect must account for nature in developing any design that is to remain functional. Perhaps more accurately. Otto has occupied himself by exploring the limits of these natural laws expressing a unique kind of genius by evoking forms in whit It the relative influence of technical design and physical nature are less distinguishable. Further, Otto s explorations into pneumatic structures reveal principles more directly related to out own understanding of biological structure and function.

The oldest pneumatic system known to humankind is most likely the sail. The sail functions as a result of the air pressure difference across the sail material. Tension in the sail material produced by this differential is transmitted through the rigging to the mast and thence to the hull of the vessel. More generally, a system is pneumatic whose energy source is provided by fluid (gas or liquid) pressure upon a closed or controlled access membrane. A balloon is a simple pneumatic system that does not require any cables or rigid members, yet anchoring this balloon to the ground would not change its essential pneumatic character.

The viability of any pneumatic system is determined In the weight and tensile strength of the membrane fabric, its ability iii withstand predictable loads such as wind and water, and mainly the energy required to maintain the functioning inflated state. Common pneumatic systems include auto shock absorbers, blood vessels, the chambers of the heat t, citrus fruits soap bubbles tires, the stalk of a delicate plant and Perhaps even muscles themselves. In short, the pneumatic principle is found throughout the biological and technical world.

The critical functional principles of a pneumatic system are few. Consider, for example a simple inflated balloon. We all know dial if a pin is stuck into the surface of a balloon with sufficient force, the balloon will burst. The stress in this cast is highly localized. Suppose for a moment that we were able to distribute this saint quantity of stress curly oven the entire surface of the balloon. The effect, taking into account the force exerted from within would be to decrease the total stress on the balloon membrane. If we were able to increase the external sows on the balloon uniformly, we would theoretically be able to reach a point at which there would be zero stress on the balloon membrane. The fabric of the balloon will have been completely neutralized as a structural member insofar as it becomes a boundary separating equal loads.

This neutralization of the structural member is, however a theorem al ideal. As far as technical structure, are concerned, asymmetrical loading is invariably the case. Total neutralization does not occur, and the same is probably true of organic structures as well. Because this is so the character of technical pneumatic structures must account for the possibilities of sudden and radical asymmetrical load differences across structural members. Like wise biological systems possess a range of limited adaptabilities to changing circunstances.

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If we were to con tine an outdoor inflatable structure such as a greenhouse we would have to consider the weight and tensile strength of the material used for the enclosure taking into account possible changes in weather conditions, and whether these factors could be adequately compensated for by all energy source capable of maintaining the inflated state. This can become a delicate problem. A membrane equipped to withstand broadly distributed loads cannot also be expected to withstand highly local loads without requiring a great deal more available energy to keep the structure inflated. Like wise, the greater the area we wish to enclose the lighter the material must be the less likely it would withstand local load changes.

Further, let us presume that we wish to maintain a constant temperature and constant ventilation within. These conditions may require the use of a slightly permeable membrane. Otherwise, a large temperature difference across the membrane might produce condensation on the inside (or the outside creating an undersirable additional load on the fabric. All of these hypothetical considerations merely sear to illustrate Otto’s point that the critical feature of an efficient pneumatic system is that the load upon the membrane he minimized. That is energy is expended from within immediately and appropriately only to counteract changes in real external loads and in such a way as to neutralized the membrane itself as a structural member as much as possible.

Going one step further into Otto’s thought it is useful to mention two simple principles. Any rigid structural member has a characteristic buckling length, the point at which, when erected vertically, it will break under its own weight. Similarly any tensile material has a characteristic rupture length, the point at which, when suspended freely, it will likewise break under its own Weight. Nylon thread for example. will rupture at a length of about 35 miles. Steel cable will rupture at closer to 20 miles. Otto demonstrated that in combining both compression and tensile members in certain designs, each was mutually strengthened. Their respective buckling and rupture lengths were increased. A free-standing compression strut capable of hearing, say, fifty pounds, would, when enclosed in a pneumatic envelope- bear 60 or 70 pounds. The total compression is shared by both members.

The relevance of these principles to Rolling should by now he apparent. Frei Otto speaks directly of the analogy to human structure: The body structure of humans is a composite of rigid and compression based members surrounded by numerous tension elements such as sinews and membranes forming highly braced and reinforced struts. The lengths of the bearing can he adjusted by muscular action which permits activation of the entire system. Muscles form bundles of tissue which are enclosed in sheaths holding them close together. Since the tissues whose individual cells are distended wider osmotic pressures exercise a load on the enveloping membranes similar to that exercised by gas or fluid pressure, it is not surprising that all tissue elements enclosed by sheaths constitute pneumatically formable shapes. That is the obvious relationship of all pneumatic structures to these natural shapes is not accidental, but inherent in the structure.

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The view that Otto offers of the body is that connective tissues organized as fascial planes constitute functional pneumatic membranes. Muscle action generates internal pressures within fasciculi in response to external loads placed upon them. His pneumatic model implies that the body is a balloon tilled with fluid and rendered its shape by the arrangement of the hones within and the influence of gravity without. Since fascia is a continuous organ. binding all tissues into a single functional unit, we are fret to consider the body as a single balloon, or as an aggregate of many such muscle/balloons acting tit coordinated fashion.

Whether sleep fascia in the living state actually functions as a membrane in Ottos sense is open to interpretation. Loosely stated, its fibrous nature and its necessary permeability world support this view, as well as the fact that fascia is considered a boundary in the sense that it separates discrete functions. Resisting the temptation to over generalize from this model, however, ironically throws us hack to a more dynamic and fluid image of structural integrity in which fascial “harriers” are being effectively, neutralized as structural members by an efficient pneumatic system. Even at a cellular level where mitosis is triggered partly as a function of the ratio of volume to surface area. it is as though the cell “knows’ when the differential load across the cell membrane reaches a point beyond which further growth is no longer viable.

The current analogy applies further to the Rolf understanding of the dynamics of structural aberration. Our view is that fascial planes increasingly become the solid boundaries previously described as progressive aberration takes its toll. Local areas undergoing chronic stress represent load differentials that threaten the integrity of the pneumatic system. Even though biological systems are equipped to adapt to such conditions the cost becomes increasingly high and eventually the system begins to break down.

Otto’s theories would suggest that the function of the myofascial system is to distribute stress in the body as broadly and as evenly as possible, approaching the ideal condition of neutralizing itself as a structural member. Progressive adaptation to assymetrical loads brings the fascial system more and more into play requiring the absorption of increasing amounts of compressive force, interfering with this self neutralizing process and eventually making it altogether impossible. The capacity of the pneumatic system to “choose” its response to “real” loads is progressively diminished. Structural adaptations eventually dictate he movement response whether the load is real or not.

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Frei Otto is one of the few people who have managed to transcend the lever and pulley theory of body mechanics in order to see the body in a new way, which accords the tensile members, the soft tissues, the status of being the paramount structural elements. The elegance of his metaphor lies in the paradox that a biological system approaching ideal structural integrity has largely neutralized its most important structural elements. Further, he weds his theory to a model with which we are already familiar, tensegrity, implying that locomotion and support are functions of a pneumatically activated tensegrity mast. Finally, since Otto acknowledges that there is no such thing as a perfectly neutralized pneumatic membrane in either technological or biological system, he implies that as long as it remains functional or alive, imperfection is inherent in any structure.

If we are to learn anything from Frei Otto, i think it would be more than his affirmation of the importance we place on returning the physical structure to a state of greater choice exists only to the degree to which the body is able to deal with gravity in a broad and uniform way rather than in a local and irregular way. Through his eyes, you can see that what we understand to be structural integration is a process of evoking a more authentic expression of the universal laws governing the behavior of the material of the body itself.

“Otto has never forced or attempted to pervert the intrinsic logic of structural form to achieve an architectural effect.”

“The viability of any pneumatic system is determined mainly by the energy required to maintain thefunctional state.”

“… the function of the myofascial system is to distribute stress as broadly and as evenly as possible, neutralizing itself as a structural member.”

Gary Horvitz is a Certified Rolfer and editor of the Bulletin of Structural Integration, working in Berkeley, California

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