Giuseppe Guimarães
Dept. of Civil Engineering, Pontifical
Catholic University of Rio de Janeiro, Brazil
Claudia Campos
Dept. of Engineering, University
of Cambridge, Cambridge, UK
Chris Burgoyne
Department of Engineering, University of Cambridge,
Cambridge, UK
External prestressing techniques
have been used both in new structures and for rehabilitation. Some advantages
are the possibility of controlling and adjusting the tendon forces; ease of
inspecting, replacing or adding tendons and lower weight of the structures.
Many bridges have been designed and built using external tendons in Europe, USA
and other countries over the last twenty years.
The steel tendons used for the
reinforcement need careful protection against the various type of corrosion
attack. Corrosion is one of the most problems that affect the durability of the
structures. Innovations include progress in design procedures, in corrosion
protection systems and in materials.
With the development and
commercialisation of organic fibres with good corrosion resistance, high
strength and high elastic modulus in the early 1970s, interest in using new
materials has increased. One example which has already been used for prestressing
tendons is Parafil, made of Kevlar fibre and produced by Linear Composites Ltd.
Tests of full scale concrete beams prestressed with these tendons were carried
out (Burgoyne et. al., 1991), showing that Parafil is a very suitable material
for use as a noncorrodable prestressing tendon. However, more studies are
necessary for understanding the overall behaviour of these structures because
the behaviour of externally prestressed structures is itself complex and the
failure criteria for Parafil differ from those of steel tendons.
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