Civil Engineering Reference
In-Depth Information
weave which may produce higher tensile strength may at the same time reduce its tear
strength.
There are different kinds of tears; some are in plane and some are out of plane, like
tearing a sheet of paper. Some of the more common tests are shown in Figure 3-12.
Figure 3-12 (a, b, c)
Tear Tests
There is a strong interaction between tensile strength and tear strength, so that some
fabrics may have high tensile strengths and low tear strengths, such as the PTFE
coated glass fabrics. This is due to the high modulus of elasticity of the glass
combining with the high adhesion of the glass to the PTFE coating. The high
modulus prevents the fibers from stretching and the high adhesion prevents the fibers
from slipping in the coating, thus properties which would be expected to transmit
high strength to the performance of the structure can actually contribute to a reduced
usable strength. In the PVC polyester, the trapezoidal tear properties are stronger, but
the fibers are weaker and elongate under load.
Most failures of tensile structures are caused by tears, so it is important to understand
the relation between the tensile strength and tear properties and this is also the reason
why in the design of fabric structures, the factor of safety remains relatively high
(FOS 5 - 8).
3.6 Sustainable & Environmental Qualities
In the past few years, the awareness of the carbon footprint of buildings is gaining
new importance in architectural design. Tensile fabric structures since their inception
in the mid 1960's have used synthetic materials to create longer lasting fabrics in
contrast to the traditional cottons which lasted only a couple of years. Most of these
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