La utilización de nuevos materiales en hormigón pretensado: Una experiencia a escala real

A full scale experience on prestressing concrete structures with high strength fibres

Recently, the external prestressing became a subject of increasing interest in the area of bridges. The actual trend in diminishing dead load in the superestructure by reduction of cross-section dimensions (mainly the width of webs) seems to be perfectly linked with using external prstressing. However, the durability aspects about the long-term behaviour of steel tendons non protected by concrete are not yet well known, and recent investigations about corrosion effects in the stays of some cable-stayed bridges have shown that does not exist yet a perfect protection system against corrosion and in any way all the actual methods of protection have failed to one extent or another. Therefore, investigation and experimentation concerning new materials available in the substitution of prestressing steel should be carried. By now, the most important alternative to the use of steel tendons in external prestressing seems to be the use of man-made fibres with high ultimate strength and low elasticity modulus and without corrosion problems when used in aggressive environments (atmospheric polution, presence of chlorides, etc...). Because most of experimetnal work has been done in laboratory, in the present not so much is known about long term behaviour of prestressing fibres when used in real construction and environments. The paper deals with the applicattion of man-made fibres in prestressing approximately 20 meters of cantilever structure, spanning 4 m, which have to be designed to support the upper traffic in the North Ring-Road in Barcelona. This construction is an important key in order to acieve a solution in the city traffic problems involved in the celebration of the summer Olympic Games in 1992. Technological requirements in the use of this new material and durability aspects will be derived from this full-scale experience.