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Cable and tensile structures
- 1. CABLE &TENSILE STRUCTURES Rohan Joshi -Assignment 3
- 2. Cable structures Cables are made of a series of small strands twisted or bound together to form a much larger cable. Steel cables are either spiral strand, where circular rods are twisted together and "glued" using a polymer, or locked coil strand, where individual interlocking steel strands form the cable. Cable is a flexible structural component that offers no resistance when compressed or bent in a curved shape. Technically we can say cable has zero bending rigidity. A cable is the main component of cable supported bridge or suspended roof structures. Classification of cable structures Suspension type cable structures : The basic structural components of a suspension bridge system include stiffening girders/trusses, the main suspension cables, main towers, and the anchorages for the cables at each end of the bridge. ... The main load carrying member is the main cables, which are tension members made of high- strength steel. Cable-stayed type structures : A cable-stayed bridge is a structural system with a continuous girder supported by inclined stay cables from the towers. Form the mechanical point of view, the cable- stayed bridge is a continuous girder bridge supported by elastic supports.
- 3. Tensile structures A tensile structure is a construction of elements carrying only tension and no compression or bending. The term tensile should not be confused with tensegrity, which is a structural form with both tension and compression elements. Tensile structures are the most common type of thin- shell structures. Tensioned Fabric Structure : A structure where the exterior shell is a fabric material spread over a framework. The fabric is maintained in tension in all directions to provide stability. Tensile Structures : Tension roofs or canopies are those in which every part of the structure is loaded only in tension, with no requirement to resist compression or bending forces.
- 4. Advantages of tensileStructures Flexible Design Aesthetics - Tensile membrane structures provide virtually unlimited designs of distinctive elegant forms that can be realized because of the unique flexible characteristics of membrane resulting in an iconic and unique structure or feature for any building owner, city or even region. Outstanding Translucency – In daylight, fabric membrane translucency offers soft diffused naturally lit spaces reducing the interior lighting costs while at night, artificial lighting creates an ambient exterior luminescence. Excellent Durability – With several different membranes in the market place such as PTFE fiberglass, ETFE film, PVC, and ePTFE, the durability and longevity of tensile membrane structures have been proven. Lightweight Nature - The lightweight nature of membrane is a cost effective solution that requires less structural steel to support the roof compared to conventional building materials, enabling long spans of column-free space. Low Maintenance – Tensile membrane systems are somewhat unique in that they require minimal maintenance when compared to an equivalent-sized conventional building. Cost Benefits – Most tensile membrane structures have high sun reflectivity and low absorption of sunlight, thus resulting in less energy used within a building and ultimately reducing electrical energy costs.
- 5. A two-dimensional tension fabric membrane can take planar tensile forces, but it cannot take significant forces perpendicular to this plane. Therefore, in addition to being pre-stressed, tension fabric must take a certain three-dimensional shape, in order to remain stable. These shapes were discovered by Otto and Berger during their investigation of natural forms, such as soap bubbles.There are two types of general shapes: Types of Tensile structures Anticlastic Shapes : Anticlastic Shapes are created by having the radii of the principal curvatures on opposite sides of the tension fabric surface. As a result, when loaded at a particular point, tension will increase on one curve of the membrane and leave the opposite curve. Thereby, preserving equilibrium and keeping the structure stable. In order to keep anticlastic shapes, some kind of structural frame or support is necessary in the form of cables or steel beams. Some examples of anticlastic shapes are saddle, cone and wave forms. Synclastic Shapes : Synclastic Shapes are characterized by having the radii of the principal curvatures on the same side of the fabric. In order to counteract external forces, pressure from the within is necessary. This is why synclastic shapes are associated with air-inflated structures. The difference of pressure created by air pumped into the building is able to counteract the external forces, in the form of wind or snow.
- 6. Whether it’s a permanent durable structure that needs to last longer than 30 years, an insulated membrane system for thermal performance or a deployable flexible application, there are a variety of tensile membranes to choose from to meet specific performances for your next building project. By using translucent tensile fabric membranes like PTFE, PVC, Insulated Tensile Membrane or transparent ETFE films, daylight is maximized in building interiors, thus reducing the costs for electric lighting. The following are types of tensile membranes which are widely used in India – • PVC (Poly-vinyl Chloride) • FRP (Fiberglass Reinforced Plastic) • PTFE (Polytetrafluoroethylene) • FILM Types of Tensile Membranes
- 7. PVC (Poly-vinylChloride) PVC coated polyester can be a great material choice for both permanent and temporary tensile fabric structures. PVC coated polyester is known for its excellent strength, flexibility, translucency and affordability compared to FRP and PTFE. The PVC coating, which is applied to polyester includes UV stabilizers, fire retardant additives, and anti-fungicides. PVC coated polyester fabrics have a structural lifespan greater than 20 years. PTFE (Polytetrafluoroethylene) PTFE coated glass cloth was developed by DuPont in the 1960s and has been used to create tensile fabric structures since the early 1970s. Originally, the material had a lifespan of 25 years; however, this has already been exceeded, with present day expectations lying somewhere between 30 and 50 years. Today, it is considered to be the highest quality material for creating tensile fabric membranes and the best choice if you desire a long lifespan and low maintenance.
- 8. FRP (Fiberglass Reinforced Plastic) FRP (Fiber Reinforced Polymers) material is a type of composite material that is increasingly used in the construction industry in recent years. Due to their light weight, high tensile strength, and corrosion resistance and easy to implementation makes these material preferred solutions for strengthening method of reinforced concrete structural elements. In this study it is aimed to discuss advantages of FRP usage as a composite material. It is noted that the mechanical properties of these materials shows a useful behavior for strengthened theoretically to satisfy safe cross-section with FRP materials. NAME FEATURES BUILT TYPE SPAN MARKET RATE PVC Easily assembled Eco friendly Prefab 20-30m 300/sq.ft PTFE Superior quality Water proof easy installation Panel Build Modular 25-45m 1750/sq.ft FRP Light weight High tensile strength Corrosion resistance Prefab 40-60m 75/sq.ft Film Waterproof Easily available Post- stressed 25-45m 350/sq.ft The following table constitutes the properties of different tensile membranes in the Indian market
- 9. References • https://www.rstensile.in/tensile-structure-manufacturer-in-india.html • https://www.rstensile.in/tensile-fabric.html#tensile-fabric • https://architizer.com/blog/product-guides/product-guide/tensile-fabrics/ • https://www.slideshare.net/MimiAlguidano/cable-and-tensile-structures-for-architecture- and-engineering