In construction, three significant forces act on a structure. These forces are tension, compression, and bending. The forces dictate the architectural and structural design of any structure. A tensile structure is constructed to withstand only tension. Therefore, the structure cannot take on compressional or bending forces. However, the structures can be supported by compressional or bending elements.
For instance, a dome is an excellent example of a tensile structure. The main forces acting on the dome are tensional forces. But to support the dome, you will need compression elements like the pillar or bending elements like the beam. Predominantly tensile structures are used as roofs but can also be used as complete structures by themselves with applications in structures like sports arenas, warehouses, storage facilities, and exhibition venues.
These tensile systems are created by utilizing tensile membranes, tension rods, and cables.
Tensile structures have been built since man evolved to create any form of shelter. In those ancient times, they used animal skin as their material. But in recent years, especially in the last half of the previous century, tensile structure technology has gained momentum, and many technological advances are being made.
The material used in tensile structures is constantly being improved and upgraded.
There are two types of fabrics commonly used in tensile structures. They are coated structural fabric and mesh fabric. A coated structural fabric is made using a base cloth and a coating on both sides. The coating is used for the protection and stabilization of the base cloth. Warping threads make the base cloth along the length of the fabric, and weft threads run across the width.
On the other hand, mesh fabric is a coated cloth but has its thread bundles spaced. It is mostly used in interiors. The threads are coated before weaving to create an aesthetic in the space spanned by the tensile structure.
Different materials are used to make the woven fabric a tensile material. There are two main materials for external use: PVC (Poly Vinyl Chloride) coated cloth, and PTFE (Poly Tetra Fluro Ethylene) or Teflon coated glass cloth.
A PVC fabric contains additives such as UV stabilizers, anti-fungicides, coloring, and fire retardants. They have a 20-year structural lifespan.
Since it is glass, a PTFE fabric is inert and more natural, and suitable for structures with more than 15 years lifespan maintaining its buff color that bleaches white in strong sunlight. Still, the anticipated lifespan is 25-30 years.
Structural tension rods efficiently transfer large tensile forces over long distances with minimal material. However, tension rods are usually loaded with significant force; hence, they have a high chance of affecting the structure’s integrity if not correctly connected or are misaligned.
Cables are made of small strands of either mild steel, stainless steel, high strength steel, aramid fibers, or polyester bound together to make a larger cable. They can either be a spiral strand or a locked coil strand. Spiral strand is where they are twisted and glued using a polymer, whereas locked coil strand is where the strands are individually interlocking to form a cable.
Having understood what tensile structures are made of, there are different membrane structures. They are hypar, conical, and barrel vault.
A hypar structure is more suitable for a shading structure. It is usually constructed by attaching two high points and two low points, creating a three-dimensional flying shape. For a hypar to be functional, it needs a high tensile load to avoid rainwater ponding, fabric damage, or flapping.
The conic structure is created by utilizing the high center point to create a large ambiance covered with minimal columns. It is ideal for outdoor structures that aim to offer eye-catching views. Conical structures can also cover extensive areas.
A barrel vault is an asymmetrical parallel arch design that is very cost-effective and offers pleasing aesthetics to your structure. The canopy formed by such a structure can span long distances and be implemented in small areas.
Tensile systems are of great application to modern structures. Despite being revitalized just over a century ago, they have been applied to create some of the most iconic designs today, including The O2 in London, formerly the Millennium Dome, Denver International Airport, Sidney Myer Music Bowl Melbourne, and the Olympiapark in Munich, among many others.