When architects and designers approach us with a tensile fabric structure idea, sometimes they know what type of fabric they want, other times, they look to us for direction. This article provides an overview on the fabrics we design & build with. Today’s fabrics are innovative, allowing you to create iconic spaces.
A coated structural fabric consists of a woven base cloth stabilised and protected by a coating on both sides. The base cloth consists of warp threads running the length of the roll and weft threads running across the width.
A mesh fabric is a coated cloth with spacing between the thread bundles. With some meshes for interiors use the threads are coated before weaving.
A typical structural fabric would have a tensile strength of 10 tonnes in the warp and weft direction. A factor of safety of 6 on a maximum design loads is used select a cloth although this may be reduced if the circumstances are well understood ie. if the maximum strength of the membrane is 10 tonnes/linear metre the maximum permissible load would be 1.7 tonnes/metre, and the typical pre-stress load would be 150-350kg/metre.
All fabrics will stretch under load although some exhibit different characteristics as a function of time. A structural fabric would not creep under load once it has reached full pretension.
Each roll of fabric is tested in a biaxial rig to measure the stretch in both thread directions at load ratios derived from the form generation computer model.
These figures would then be used as compensation percentages to be factored into the patterning software. The canopy is manufactured undersize so that when installed to its final dimensions it tensions out correctly.
For External Use: – Coated fabrics
For external Use there are two main choices PVC (Poly Vinyl Chloride) coated polyester cloth and PTFE (Poly Tetra Fluro Ethlene) (Teflon) coated glass cloth.
The PVC coating contains additives that include UV stabilisers, fire retardants, colouring and antifungicides.
There is a choice of protective PVDF (fluorinated Polymer) lacquers that enhance the cleanability of the PVC membrane. With the Non weldable PVDF version we remove the lacquer before welding the seam. It will give 15-20 year lifespan compared to 10-15 years for the weldable PVDF type.
Although a PVC/Polyester fabric will have a structural lifespan in excess of 20 years its quoted lifespan is based on visual appearance. Plasticisers in the PVC will migrate towards the surface over a period of time making the surface harder to clean.
The French fabric supplier Serge Ferrari will coat the fabric whilst keeping the warp and weft threads in tension known as the precontraint method. This will result on more even stretch characteristics in both thread directions than a conventional coated fabric
The components of PTFE/glass are inert and are therefore the natural choice for permanent structures with design life over 15 years. When new PTFE is a buff colour that will bleach white in strong sunlight in a matter of weeks, weld discolorations will also disappear in a similar period. The anticipated lifespan of the membrane is 25-30 years.
Meshes are available in both PVC/polyester and PTFE/glass. They are essentially shading fabrics but a version of the PTFE/glass mesh is available with clear laminate on both sides giving a weatherproof fabric with translucency of 50%.
ETFE Foil is not a coated woven cloth and is not covered in these notes.
For Internal Use: – Mesh Fabrics
For interiors there are three main fabrics:
Cottons are most economical and are available in a wide range of colours. Due to their susceptibility to staining and shrinkage they are ideally suited for short term use or where a softer and more natural texture is required.
PVC coated glass mesh is very durable and acts like a theatre gauze or sunscreen.
Polyurethane coated glass cloth which has benefits of durability and similar appearance to cotton.
Silicon coated glass cloth is being used for its high fire resistance and low relative fore toxicity but tends to attract dirt.
All these fabrics meet BS476 Part 7 class1 and part 6 class 0 which is normal requirement for internal finishes. In some instances other fabrics with lower fire rating such pvc/polyester, CS trevira and cotton Lycra and silk have been approved.
Pure glass meshes can be used in exhibition halls when fire standards are very stringent. Some ceiling systems demand open meshes that allow water sprinkler systems to operate through them. Unfortunately other exciting fabrics such as rip stop nylon and mylars do not achieve an adequate fire rating.
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