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Is There a Future for Carbon-Fibre-Reinforced Plastic Cables in Load-Bearing Structures?
Because of the fatigue and corrosion to which metal cables are subject, suspension structures are usually designed to allow a relatively simple replacement of these members. This is not always easy with cable-stayed bridges, however; nor does it make sense economically to have to renew structural members every 20–30 years. In the early 1980s, the Swiss institute for materials testing and research (EMPA), suggested the use of carbon-fibre-reinforced plastics (CFRP) for cables. The material does not corrode; it is relatively light (1.5 t/m3), is extremely strong (3,300 N/mm2) and has great rigidity (150,000–300,000 N/mm2). A graded granular material was also developed that acts as a load-transmitting medium for anchoring the cables in parallel sheaves (ill. 1). Since little practical experience of the behaviour of these cables exists, building authorities are reluctant to grant permission for their use. The only way experience can be gained is by replacing individual steel cables in existing structures with CFRP cables. The first opportunity for this presented itself in the Storchen Bridge in Winterthur, Switzerland (ills. 2, 3), where two of the 24 cable stays are in CFRP. Other examples include the Kleine Emme bridge in Lucerne (ill. 4), the Ponte Ri di Verdasio and the Passerelle des Neigles in Fribourg. Scenarios for the future foresee a substantial reduction of production costs and a greater readiness to use these cables on the basis of experience gained from present test objects.