Tensile structure -Tension in structures

Tensile structures or Tension in structures refers to the internal force created within a structure due to an applied load that tends to pull or stretch the structural members apart. When a force is applied in tension to a structure, the structural elements experience a stretching effect, which creates tensile stress within the material. This stress can cause the material to deform, and if the tension becomes too great, it can cause the material to fail or break.

Tension is a critical consideration in structural design, and engineers must carefully calculate and account for the amount of tension that a structure will experience in order to ensure that it can withstand the anticipated loads without failing. Materials such as steel, which have high tensile strength, are often used in structures that will be subjected to significant tensile forces.

Tensile structure – Working principle

When studying architecture/civil engineering, you often come across the concepts of tension and compression, which are two types of forces. The majority of structures we construct are in compression, meaning that they rely on the downward pressure and squeezing of materials such as bricks and boards to remain stable on the ground. In contrast to compression, tension involves the pulling and stretching of building materials.

Some of the earliest human-made shelters have historically influenced tensile structures. For instance, the nomads of the Sahara Desert, Saudi Arabia, and Iran developed black tents using camel leather. Native American tribes also built various structures. Compared to other structural models, tensile structures provide several advantages, and they are inspired by these ancient shelters.

The principle of tensile structures is that they rely on tension to create a stable structure. Tensile structures use tensioned elements, such as cables, ropes, or membranes, to transmit loads and create a self-supporting structure. These tensile elements are anchored to supports, such as poles or columns. The supports resist the tensile forces and keep the structure in place. The tensioned elements work together to distribute the load and create a structurally efficient system. Tensile structures are known for their lightweight and flexible design, which allows them to span long distances while using minimal materials.

Types of tensile structure

Tensile structures can be classified based on the plane in which the tensile forces act, which determines the shape and form of the structure. The three main classifications of tensile structures based on the plane of tension are:

Linear Tensile Structure

Tensioned cables or rods support a linear tensile structure, which is a type of lightweight and flexible structure characterized by long, narrow spans. These structures are often used to provide shade or cover for outdoor spaces such as pedestrian walkways, seating areas, or parking lots. Designers typically aim for a simple, minimalist aesthetic and can use a range of materials, including steel cables, high-strength polyester fabric, or PTFE-coated fiberglass. The design of linear tensile structures is important to ensure stability and resistance to wind, snow, and other loads. Engineers use computer simulations and physical testing to determine the optimal shape, size, and materials for the structure.

1. Shade sails: Tensioned fabric structures used to provide shade in outdoor spaces.
2. Tensile canopies: Lightweight fabric structures used to provide shade or cover for outdoor events.
3. Tensile bridges: Tensioned cables or rods support pedestrian or cycle bridges.
4. Tensile roofs: Tensioned fabric structures used to cover large outdoor spaces.
5. Tensile facades: One can attach external lightweight fabric or cable structures to a building’s exterior. Their purpose is to provide shade or reduce solar heat gain.

Three-dimensional tensile structures

Designers create a three-dimensional tensile structure with multiple curved surfaces in three dimensions. Manufacturers make 3D tensile structures from various materials such as fabric, steel, and composites. Architects frequently utilize these structures in large-scale projects such as stadiums, airports, and exhibition halls.

1. Cone-shaped structures: Three-dimensional structures shaped like a cone, often used for small pavilions or temporary structures.
2. Hyperbolic paraboloid structures: Curved structures with a saddle shape that can span large areas, used in roofs and canopies.
3. Geodesic dome structures: Spherical structures made of interconnected triangles, used for large span structures such as greenhouses or exhibition spaces.
4. Cable-net structures: Three-dimensional networks of tensioned cables that can form complex curved shapes, used for roofs and facades.
5. Pneumatic structures: Three-dimensional structures made of airtight materials, inflated to create a stable shape, often used for temporary structures such as exhibition booths.

Surface-Stressed Tensile Structures

Designers create surface-stressed tensile structures with pre-stressed fabric or membrane panels.” They tension the panels in all directions to create a stable and self-supporting three-dimensional surface.”Large-scale projects like stadiums, arenas, or exhibition halls often use this type of structure, which designers can make from various materials such as PVC-coated polyester, PTFE-coated fiberglass, or ETFE foil.”The pre-stressing of the fabric panels allows for the creation of complex shapes and curves, making surface-stressed tensile structures a popular choice for architects and designers looking to create visually striking and functional structures.

1. Single-curved surface-stressed structures: Designers often use a pre-stressed membrane to create a stable, self-supporting structure with a single curved surface for roofing applications or canopies.
2. Double-curved surface-stressed structures: These structures have two curved surfaces that intersect, creating complex shapes and curves. They are often used for large-scale architectural projects such as stadiums, exhibition halls, or museums. The designer creates a stable, self-supporting structure by tensioning a pre-stressed membrane in multiple directions for double-curved surface-stressed structures.

Shapes of tensile structures

The basic shapes of tensile structures include:

1. Cone – a structure shaped like a cone with a pointed top.
2. Hyperbolic paraboloid – a saddle-shaped structure that can span large areas.
3. Cylindrical – a structure shaped like a cylinder with rounded ends.
4. Spherical – a structure shaped like a sphere.
5. Pyramid – a structure with a base that is a polygon and triangular sides that meet at a point.
   One can create more complex shapes and designs for tensile structures by combining or modifying these shapes.

Major tensile structures around the world

1. The Sydney Opera House – a famous example of a double-curved surface-stressed tensile structure, with sail-shaped roofs.
2. The Denver International Airport – a cable-net structure featuring a white fabric roof spanning over 500,000 square feet.
3. The Olympic Stadium in Munich – a tensile membrane structure with an acrylic glass roof held by a steel tension ring.
4. The Burj Khalifa – a skyscraper featuring a helix-shaped tensile structure at its base, designed to withstand high wind loads.
5. The Kauffman Center for the Performing Arts – a cone-shaped tensile structure that covers an outdoor courtyard and serves as a performance venue.

Advantages of Tensile structures

Tensile structures offer several advantages over traditional building structures, including:

1. Lightweight: Compared to traditional building materials, tensile structures are lightweight, which can lead to lower transportation and installation costs.
2. Flexibility: The flexibility of the materials used in tensile structures allows for the creation of unique and complex shapes, which can be difficult or impossible to achieve with traditional building materials.
3. Durability: Designers create tensile structures to endure harsh weather conditions, which makes them a durable and long-lasting option.
4. Cost-effective: The lightweight materials and quick installation time of tensile structures can result in lower construction costs compared to traditional building structures.
5. Energy efficiency: Tensile structures allow for natural light to penetrate, reducing the need for artificial lighting and making them energy-efficient.
6. Sustainable: Manufacturers can make tensile structures from recyclable materials and can easily dismantle and reuse them, making them a sustainable option for construction.