C. J. Burgoyne
Department of Civil Engineering, Imperial College,
London, UK
The material will be useful where a
tension member is required in situations in which it is difficult or expensive
to protect steel from corrosion. It will also be useful where steel is excluded
by virtue of its weight, or by its electro-magnetic properties.
With these factors in mind, we can
look at specific examples. We shall not present here detailed calculations for
each application, since this would need to be derived from assumptions about
particular structures; rather, we shall concentrate on general principles.
Prestressed concrete is an obvious
use for a high strength, high stiffness material like parafil. The prestressing
tendon is very highly stressed, but the tension is virtually constant. This
allows maximum use to be made of the strength of the tendon, since only a small
allowance has to be made for variations in the force, and the maximum force is
applied in a controlled and measurable way by a jack.
Conventional prestressing places
the tendon inside the concrete, in order to provide maximum corrosion
protection to the tendon. In prestressing terms, the use of external cables is
quite acceptable, and leads to significant savings in weight, since the
thicknesses of the webs, and to a certain extent the flanges, do not have to be
artificially increased to provide cover to the tendon.
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