How the Tensile-Yome Works

"We put up too many buildings. We squander space, land, mass & energy. We still build the unnatural buildings of past epochs. Our times demand lighter, more energy saving, more mobile and more adaptable - in short more natural buildings, without disregarding the demands for safety and security." –Frei Otto

"Compression is that "realistic core" that men love to refer to, and its reality was universal, ergo comprehensive. Man must now break out of that habit and learn to play at natures game where tension is primary and where tension explains the coherence of the whole. Compression is convenient, very convenient, but always secondary and discontinuous."–Buckminster Fuller

    In order to understand how tensile structures in general work, we must first learn some basic principles and terms that apply to all building structures.

      The purpose of all building structures is to channel the load on the building to the ground. This action is similar to water flowing down a series of pipes; columns, beams, joists, cables, membranes and other structural elements act as pipes for the flow of the load. A structure will always channel its loads to the ground by the easiest of the many paths available. In structural language, the loads are said to stress the structure, which strains under stress.

      As complex as the structure may be and as varied as its loads are, there are only two ways in which a structure can perform the task of channeling the load; pulling and pushing. The pulling action is called tension and the pushing action is called compression. Tension lengthens a material while compression shortens it. This may not be visible to the naked eye, but this lengthening and shortening always occurs in buildings for there are no perfectly rigid structural materials.

      Tension and compression never occur independently, although most reactions to stress produce predominately a tension or compression. A cable being stretched is mostly under tension with very little compression (the strands of cable are being pushed together) while a supporting column is subject to mostly compression with little tension.

    The history of Western architecture has focused almost exclusively on using compression to transfer loads, leaving tension as a secondary element. Even today, tension remains predominately the undiscovered principle in architecture. Although Buckminster Fuller didn’t invent the geodesic dome, he drew attention to it, realizing it is unique in that it allows tension and compression to work together in equal harmony. This is why a geodesic dome can carry the same loads as a compression structure of several times its weight and mass.

      The one application of tensile principles in architectural history has been in the suspension bridge. Large span suspension bridges began in the early 1800’s applying the same suspension principles that had been used for thousands of years in the rope bridges of the Far East and South America. Another traditional use of tensile principles has been tent technology. From the "black tent" of the Bedouins to the grand three ring circus tents of the turn of the century, elaborate systems using tension to support fabric covered structures evolved. See History of Tensile Architecture.

      In Germany in the 1960’s, Frei Otto pioneered the new era of tensile fabric architecture. Frei Otto developed the idea of using a cable net or a stretched (prestressed) woven fabric membrane to form a load bearing structure. It allows buildings to span larger areas and use much less materials. See History of Tensile Architecture.

      As structural elements, tensile members are more efficient than compression members are. Unless they have a certain minimal thickness, compression members will bend out of shape and fail regardless of their material strength. Structures made of tensile members, on the other hand, become more stable with increasing stress levels. The stress pulls each member into line, making the structure taut. In fact, these structures are capable of maintaining several times the ratio of applied loads to self-weight compared to traditional steel, wood or concrete structures of equal spans.

      Conventional structures rely upon two main principles, gravity and internal rigidity to achieve stability and carry loads. Tensile fabric architecture uses neither of these principles; instead a flexible, lightweight membrane is stretched between a fixed set of support points. These structures, consisting of elements that have little or no stiffness, rely on their form and internal tension alone to carry their loads.

      In fact, they work because they are flexible. This flexibility means that the entire fabric membrane responds to a load applied to any part of it. This load carrying ability actually increases as the fabric deforms. Making full use of the materials strength, tensile membranes, using their inherent tension, will efficiently carry a load.

      To keep a curved surface in tension while carrying upward loads of wind and downward loads of snow requires a careful balance of curvature in opposite directions. This solution to this problem is to determine the curved shape that represents the minimal surface area possible for the flexible membrane given a fixed set of endpoints. This is the form where all points are in equal tension. The membrane's ratio of tension applied in perpendicular directions can then be adjusted to respond to various load conditions. The more the chosen endpoints will create a shape that deviates from a flat plane, the greater the load carrying capacity (up to a point). Given the endpoints and tension ratio, the shape of the structure is not arbitrary, but derives from structural function. Form and function, architecture and engineering become one.

    Tensile roofs, by their nature, will transfer a tremendous load to the points which they are attached. Because of this, it is not uncommon in tensile architecture for the elegantly curved fabric membrane to seem out of place compared to their large compression load bearing supports. In the new Tensile-Yome by Red Sky Shelters, the tensioned roof membrane is attached to the same framework as the original Yome. Based on the principles of the geodesic dome, the load is elegantly transferred to the ground using only a lightweight continuous triangular framework. It works because it forms that perfect balance of tension and compression. The Tensile-Yome represents a step into the future of architecture; it is sturdy, lightweight, uses a minimum of materials and is an elegant work of art.