INVESTIGATIONS ON PRESTRESSED CONCRETE STRUCTURES WITH POST-TENSIONED STEEL MEMBERS

摘要

In Germany in recent years failures of more than 30-year-old prestressed concrete structures with post-tensioned steel members were observed. In all these cases a quenched and tempered steel type, strength class St 1420/1570 was used. Failure analysis has shown that the fracture appearance indicates characteristic signs of hydrogen-induced stress corrosion cracking, both macroscopically and microscopically. In order to clarify whether corrosion-induced crack initiation and propagation of this steel type can develop in sufficiently grouted ducts over long service times and to limit the risk of older prestressed concrete structures failing due to stress corrosion cracking, a number of on-site investigations were performed. These investigations were carried out as part of planned demolitions, rehabilitation measures, damage analyses or precautionary inspections. The main aim was to assess the prestressing members, i.e. prestressing steel, the quality of injection, and the properties of the injection grout. Investigations were carried out on altogether 21 structures. The lifetime of the structures was between 20 and 40 years at the time of the investigation. From the results which are described below it can be concluded that the specific susceptibility of certain prestressing steels is the determining factor with respect to crack initiation and propagation rather than environmental factors.