A Sneak Peak in to the Notions of Tensile Structures – Part 1

Posted On :- 2 June 2017

Tensile Structures are assembling of tensioned elements carrying no bending or compression. These structures are the most commonly used thin-shell structures and often used as roofs in common erection due to their economical feasibility. They can be stretched over a large roof area and look appealing than any other form of roofing. Tensile structures are supported by tensioned elements such as compression rings or beams and as masts in case of Millennium Dome. Modern architects have been using it since a long time for temporary tents as it can endure loads. Technological revolution in construction industry has made fabric-made structures popular. Flexibility and lightweight nature of tensioned structures make roof construction cheaper than any traditional way of building roof system, particularly when a large area is to be covered.  Environmental adaptability and reflective or translucent properties these structure are something to be taken advantages of. 

Criteria and concept Design

Proper planning is required at the design process as the slightest mistake will reverberate all the way through the process of designing the structures and installing them, which will in turn affect the performance and appearance of these fabric structures. Following aspects are needed to be mulled over: 

•    Statistical limitations of the construction site and nearby buildings 
•    Sun angles to be installed for the required Sun-shading levels
•    Designs and cut outs for the ventilation and proper air flow inside the structure
•    In-space light transmission requirements
•    Evaluation of anchorage points positions and availability 
•    Recognizing the continuous-sealed perimeter anchorages requirements 
•    Structure compatibility with adjacent elements 
•    Aesthetic consideration of the construction elements 
•    Sufficient bend achievement that would lessen movement and stresses in fabrics
•    Proper channeling to drain out rainwater and pass up ponding  
•    Achieving self cleaning with apt fabric slopes
•    Evaluating the characteristics of tensile structures to be used 

Nature of Tensioned Structures

To achieve planar tensile forces on the structure, a two-dimensional compressed fabric can be used. However this way of binding the elements on the structure is not significantly effective. For which, a certain three-dimensional and pre-stressed fabric elements are being used to form a stable structure. This method is in use since many years and makes possible to design two tensioned shapes such as Synclastic Shapes and Anticlastic shapes.

Synclastic Shapes
 This form of tensioned structure is characterized by having ambit of the prime curve in the same side as of the upper form of the fabric there by offsetting the external pressure and forces of the total structure. Air inflated structures are the best example of synclastic shapes. Pressure and force difference escalate the external forces in the form of wind. 

Anticlastic Shapes
This is the opposite of synclastic shape, where shapes are formed by having ambit of the prime curve in the opposite side as of the upper form of the fabric, thus increasing the tension on one particular curve of the structure avoiding the upper part of the structure when loaded at a particular point of elements. This method of tensioning creates equilibrium and keeps the whole structure unwavering. Sequentially, to maintain the pressure of anticlastic shapes, there comes the necessary of structure support in the form of steel beams or metal cables. Cone, saddle and wave forms are the best example of Anticlastic Shapes.