Tension Membrane Structures

Tension membrane structures offer an aesthetic,  practical, and cost-effective way to provideroofing to either new or existing areas. These shade  supporting structures have been put into usefor most  part of the twentieth centuryand have found wide  spread applicationsincluding,
sports facilities,  convention centers, concert halls, shade roofs of large commercial buildings, airport roofs, gas stations and terminals, tomention only a few.  The membrane part inthe structure is pre-stressed and thus enables the structure to maintain itsform.

Two types of shapes are found in tension membrane  structures. The first type is the’anticlastic structures’ with two double curvatures in the  opposite direction while the second is a   ‘synclastic structures’ with the doublecurvatures  in the same direction.Anticlastic structures can  take avariety of shapes and forms including, the arched vault, hyper and cone. Technically speaking a tensionmembrane  structure is a combination ofelements, which carry only tension and no compression or bending. This  is the reason why the use of compressionrings or  beams, that form the bending or compression elements,  is used in mosttensile structures.

Why Tension Membrane Structures?
The semi-translucent nature of fabric structures is  what makes them a favourite with engineersand architects looking for roofing systems to cover large  areas, such as sports stadia or terminals.Fabric  structures help in increasing thesustainability quotient of  a building inmore ways than one. The fabric allows for entry of natural light, while cutting down the  transmission of heat. The high reflectivityof the  membrane makes it an idealalternative to glass as a  roof glazingsystem.  Tension membrane structures areusually reinforced  using either PVC/Polyester or PTFE based coatings. This makes the fabric structure perform wellfrom the fire  performance perspectivetoo. For example, a tension membrane structure with PTFE coating is ratednon  combustible as per ASTM 136, makingthem completely safe. Additionally the inert nature of the fabric aids in  self-cleaning, a characteristic which makesthem  perfectly suited for applicationover large areas.

The  dependency onartificial lighting is vastly reduced. The unique properties of lightreflectance and  transmission also offerexciting possibilities for lighting after dark. Directing lights under the canopy to reflect  off the underside is a great way to useuplighters, but  more even lighting canbe achieved under the fabric by  shininglights down on the fabric from above.
The thermal insulation achieved with a single layer  of either PVC/Polyester or PTFE membrane witha typical weight of around 1200gm per sq metre and a  U value of approximately 4.5 W/m2K, is moreor less  similar to that of glass. Whiteis mostly the preferred  colour when itcomes to tension membrane structures. This is because with dark coloured membranes, the  absorption of heat is very high. Darkcoloured  membranes can also re-radiateheat. White is  therefore the preferredchoice in the case of tension  membranefabrics.

Roofing and Cladding
With tension membrane structures, it is possible to  have both the roofing and cladding in onesingle structural element. Typically the seam and curve of the  fabric structure that reflects the tension isaesthetically  pleasing, while also beingimportant for the structural  integrity.Due to the integration of the roofing and  cladding, the structures are also easy toclean and  maintain, when compared toglaze glass roofing. The  roof, in thecase of tensile membrane structures is  factorywelded and therefore easy to install, apart from  acting as a weatherproof skin that does notcontain  expansion joints. All thesefactors enable rapid  construction andcoverage of large areas. 
Span Capabilities
An excellent span capability is another factor that  puts fabric ahead of other materials. Whileevery other  possible roofing materialrequires rigid intermediate  support, itis not the case with fabric structures. The  fabric can span from one boundary to anotherin one  unbroken (sweep). This ensuresthat there are no sealing  related issuesthat need to be addressed. The amazing tensile capacity of fabric helps to  reduce the number of components that make upthe  supporting framework to a minimum,thus enabling a  structure that is muchmore light-weighted when  compared toother types of construction. On the flip side  though, the structures incorporating theconcept need  large foundations in orderto prevent wind currents  lifting thecanopy. This factor is offset by the fact that in  terms of cost foundations are cheaper toprepare, than  the visible above groundconstruction components that  are exposedto the vagaries of weather and therefore,  more prone to damage. 


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