What is the introduction of tensile structure?

Structure whose members are only in tension

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In structural engineering, a tensile structure is a construction of elements that only experiences tension, with no compression or bending forces involved. It's important to differentiate tensile structures from tensegrity systems, which incorporate both tension and compression elements. Essentially, tensile structures represent a widely used category of thin-shell constructions.

Typically, tensile structures rely on supporting elements that apply compression or bending forces, such as masts, which are exemplified by The O2 (formerly known as the Millennium Dome), as well as compression rings or beams. A tensile membrane structure is often utilized as a roof due to its ability to economically and aesthetically cover large spans. Common applications for these structures include sports facilities, storage buildings, and exhibition venues.

History

This method of construction gained significant analysis and popularity in the latter half of the twentieth century. Historically, tensile structures were commonly seen in tents, which use guy ropes and tent poles to pre-tension fabric and allow it to bear loads.

One of the pioneers of practical computations for tensile structures, shells, and membranes was Russian engineer Vladimir Shukhov. He engineered eight tensile and thin-shell structures for the Nizhny Novgorod Fair, covering an impressive area of 27,000 square meters. The Sidney Myer Music Bowl is another notable implementation of a membrane-covered tensile structure.

A reverse approach was introduced by Antonio Gaudi, who created a compression-only structure for the Colonia Guell Church by utilizing a hanging tensile model to determine compression forces and the geometries of columns and vaults. The work of German architect and engineer Frei Otto, who designed the West German pavilion for Expo 67 and later the roof for the Olympic Stadium during the 1972 Summer Olympics in Munich, also played a critical role in promoting tensile structures. A group of renowned designers and engineers, including Ove Arup, Buro Happold, and others, furthered the development of tensile structures. The advent of advanced technology has made fabric-roofed structures increasingly appealing, as the lightweight materials facilitate ease of construction and cost-effectiveness, particularly for large open spaces.

Types of Structure with Significant Tension Members

Linear Structures

Three-Dimensional Structures

• Bicycle wheels (can serve as roofs in a horizontal orientation)
• 3D cable trusses
• Tensegrity structures

Surface-Stressed Structures

• Prestressed membranes
• Pneumatically stressed membranes
• Gridshells
• Fabric structures

Cable and Membrane Structures

Membrane Materials

Commonly used materials in doubly curved fabric structures include PTFE-coated fiberglass and PVC-coated polyester. These woven fabrics exhibit varying strengths depending on the direction. The warp fibers, which run straight along the loom, can bear greater loads compared to the weft or fill fibers.

Other structures utilize ETFE film, either as a single layer or in cushion form, which can be inflated for enhanced insulation or aesthetic appeal, as demonstrated in the Allianz Arena in Munich. The translucency of fabric membranes provides soft, diffused natural lighting during the day, while artificial lights can create a warm glow at night. However, these structures typically require a supporting framework since they do not gain strength through double curvature.

Cables

Cables may be constructed from mild steel, high-strength steel, stainless steel, polyester, or aramid fibers. They consist of a series of small strands twisted or bound together, forming a larger cable. Steel cables can be either spiral strand or locked coil strand, both varying in strength and construction methods.

Structural Forms

A category of tensile structures are air-supported structures, in which the fabric is upheld solely by pressurized air. Most fabric structures derive their strength from doubly curved forms, which must be pretensioned or prestressed to withstand loads, such as wind or snow.

Issues relating to the design of such structures have made it crucial to conduct physical modeling and form-finding exercises to better understand their behavior. Scale models, often made from stocking or soap film, showcase structural properties similar to that of actual fabrics, as they cannot withstand shear forces.

Different curved forms, including the saddle shape, exhibit special mathematical properties crucial for structural integrity. Saddle shapes, not to be confused with other forms, provide solid foundations for tensile structures.

Pretension

Pretension refers to the tension deliberately exerted in structural elements beyond the loads they typically bear. This technique aims to maintain stiffness under various loads. Examples of pretension can be seen in systems like cable-supported shelving units. Membrane pretension can be achieved by stretching it from its edges or pre-tensioning the supporting cables.

Notable Structures

Gallery of Well-Known Tensile Structures

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