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How Do Tensile Structures Work and What Are the Different Types?

2019-09-24

The tensile structure usually refers to roofs which are made of a membrane which is fastened in place using cables of steel. Tensile structures carry only tension, without bending or compression. Commonly, a tensile membrane structure is used as a roof due to its ability to span a large area attractively and with minimal cost. Tensile structures have the following characteristics:

 

•They can work under tensile stress

•They can cover large spans

•They have ease of pre-fabrication

•They are capable of malleability

•Due to their thin canvases, their structure system uses a small amount of material.

•They can overcome the forces exerted upon them when stretched using steel cables.

 

How tensile structures work

 

The tensile construction system is achieved by joining three things, namely cables, masts/poles or rigid structures plus membranes. There are two types of support in this system, namely: direct and indirect support. In direct support, building structure is in direct arrangement with the construction. In indirect support such as a mast, the arrangement happens to be from a raised point.

 

The cables, responsible for distributing tensile stresses and canvasses hardening, are also classified in two ways depending on the role which they play: these are stabilization and load-bearing cables. To avoid deformations and ensure strength into two directions, both of these two types of cables cross orthogonally. The cables responsible for receiving external load directly are the ones called load-bearing cables. On the other hand, the stabilizing cables cross the load-bearing cables orthogonally, and their role is to strengthen the load-bearing cables. By using a fixation cable, you can avoid a situation where you have to attach the stabilization cables on the ground.

 

Depending on their positions, different nomenclatures for different cables can be manufactured. For example, the uppermost cable will be referred to as the ridge-line cable, while cables fixed below other cables are referred to as valley cables. Valley cables are used to support wind loads, while ridge line cables anchor gravitational loads. Cables in the form of a ring called radial cables are stabilizer cables.

 

Types of Tensile Structures

 

Depending on the plane on which the forces act on the structure, tensile structures can be classified into the following:

 

Three-dimensional tensile structures

•A tensile structure that compiles elements that are basically tensed and then the compression is directed to a mast at the center before it is taken to the ground.

•They often in sports arenas, usually acting as roofs for such structures.

 

They include the following categories:

•3D cable trusses

•Tensegrity structures

•Bicycle wheel which in its horizontal orientation can be used as a roof.

 

Surface –stressed tensile structures

 

•Tensile structures similar to 2 tensile structure only that, tension bearing members are the surface members.

•Great examples of surface-stressed structures are fabric tensile structures.

•A specially designed fabric is held in tension by vertical pillars.

 

They are categorized into the following:

•Grind shell

•Fabric structure

•Pneumatically stressed members

•Pressurized members

 

Linear Tensile Structures

•All the members all in linear tensile forces

•Tensile members carry out significant loads.

•Compression members support linear members

 

A cable suspended bridge is an excellent example of these structures. The cables which are in tension carry the load, while the main pillars act as the compression members.

 

Linear tensile structures entail the following categories:

•Cable trusses

•Draped cables

•Straight tension cables

•Suspension Bridges

•Cable-stayed beams/ trusses

 

Again there are three classifications of tensile structures when it comes to the tensile construction systems field. These are:

•Pneumatic structures: this involves membrane that serves the protective role being anchored by an air pressure means.

•Mesh structures: there is a network of cables carrying the tensional forces, to transmit them to different elements in separate places. A good example is a sheet of wool or glass.

•Membrane tensioned structures: in this class, cables support a membrane, giving way for tensile stresses to be distributed throughout the entire form of the structure.

We are going to discuss going to discuss pneumatic structures and tensile membrane structures.

 

Pneumatic structures

 

Pneumatic structures date back to the late 1940s. Walter Bird first invented them during World War II and used by the United States Army. Initially, they were used for decoys and shelters. They were then later used to set temporary radar stations by the army. Today, pneumatic structures find their everyday use in temporary art installations, warehouses, sports stadiums, and swimming pools.

 

They are also called Air-Supported Structures. To guarantee their structural integrity, these buildings or structures utilize air pressure. To ensure maximum interior space volume, pneumatic structures have a shape that resembles the look of a dome or a bubble. The air pressure inside the structure is increased evenly so that it is slightly above the atmospheric pressure to realize this dome or bubble shape. Then cables, which are anchored to the ground, are used to make the exterior membrane more sturdy and rigid.

 

Types of pneumatic structures

 

There are two types of pneumatic structures:

 

•Air-supported structures: this structure has one continuous membrane that is anchored on the ground, or attached to a support wall or beam to create an airtight seal. Through a constant loss of air pressure through openings, this structure is firs inflated like a balloon, and then pressured continually by using fans to compensate for the lost air.

 

•Air-inflated structures: these are composed of multiple layers of membranes and are used in more advanced structures. These layers of membranes are linked in a perpendicular way. They are erected through increased air pressure using a fan. Unlike air-supported structures, these air-inflated structures are self-erectable and self-supporting. They do not entail pressurizing the entire interior space. Only a portion called the "pillow" is pressurized to carry the load of the membrane layers.

 

Tensile membrane structures

 

They include:

•PTFE Fiberglass: this is also called polytetrafluoroethylene. It is coated with Teflon woven fiberglass membranes. This makes it extremely durable and resistant to weather. Due to this, it is a highly suitable material for roofing. This membrane can be installed in climates that range from scorching desert heat to the frigid arctic with an estimated project life of at least thirty years.

 

•PVC: it is also called polyvinyl chloride. You can find it either as a non-woven or woven material. Canopies made of PVC membrane fabric are cost-effective and can be produced in many colors to fit match the individual need of the building project. They offer an alternative to façade or traditional roofing systems.

 

•ETFE Film: this stand for Ethylene Tetrafluoroethylene. It is applied in various tensile architecture layers ranging from single, double or triple. It is light in weight, has high transparency, and it is durable compared to glass structures.

 

•Insulated tensioned membrane: it is a composite system which is also called tensotherm. It comprises of a thin translucent insulation blanket embedded with aerogel, an exterior skin of PTFE membrane and a lighter and thinner barrier interior liner made of vapor or acoustic.

 

•ePTFE: it is a coated membrane with high transparency. This fabric membrane is unmatched when it comes to its tensile dynamism, durability, and aesthetics. It is a woven material that is non-flammable, and it uses 100% coating of fluoropolymer. It can offer up to 40% light transmission. This eliminates glare allowing wide illumination via a particular interior space.

 

Shapes of tensile structures

 

The following are the four basic shapes used in tensile structures:

•Conical tension structures: they have a tent-like form, and are ideal for covering large areas. Suitable for a shade over high traffic walkways or seating areas.

 

•Hypar or anticlastic structure: most common due to a pleasing aesthetic look. For stability, they rely on two opposing curvatures.

 

•Parallel arch or barrel vault structure: they form a canopy that can span broad and extended areas — ideal for sports arenas or entryways.

 

•Cable net and membrane structure: they are common in stadiums or large spaces.

 

Car parking shades

 

Usually, tensile structure car parking shades are durable, affordable, and reliable. Car shades are popular and widely used around the world. They can be installed for a lot of cars in a series or just for one car. They are usually available in a double bay or single bay parking slots.

 

There are different types of car parking shades. Some of them include:

•Pergola shades

•Umbrella shades

•Tensile shades

•Sail shades

•Paddock shades

•Beach shades

•Swimming pool shades

•Awning shades

Advantages of car parking shades

 

•Helps in maintaining the shine and gloss of the vehicle

•Reducing direct heat on the car

•Helps in keeping the electronics in the car safe

•Protecting the car win screen

•They protect against harsh UV sun rays, snow resistant and wind-resistant

•They are durable and robust and sturdy to resist anti-aging

 

Advantages of tensile structures

 

•Simple to maintain and easy to replace or repair

•They are lightweight and durable

•Large spans

•Recyclability and eco-friendliness

•Endless form possibilities and catching character

•They can adapt to exciting building technologies

•Short building time, less site interruption time and off-site manufacturing of structure

•Provide options to design light effects due to translucency

•Environmental shelter from wind, rain or sum

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