Evaluation of the Condition of Prefabricated Pretensioned Prestressed Beam Forming the Load-Bearing Structure of Bridges after About 60 Years of Use

The paper summarizes results of diagnostic work on approximately 6 bridges constructed from prestressed standardized precast elements used in the 1960-1990s for the construction of bridges in the Czech Republic. These are mainly the standardized girders of KA type (Type documents for prefabricated girders KA-73, Dopravoprojekt 11/1973, digital copy) for clearances of 9–18 m and I girders (Type documents for prefabricated girders I-73, Dopravoprojekt 11/1973, digital copy) for clearances of 21–30 m. The assessment focused mainly on the actual strength class of concrete in relation to the design strength, visual inspection of the outer face and inner chambers of the girders with the help of videoscopes, and last but not least, checking the condition of the prestressing reinforcement and the state of cable ducts grouting. The condition of the prestressing reinforcement was checked firstly by means of mechanical probes and secondly by means of the half-cell method in the place of visual defects. Results were supplemented by a corrosion survey of the prestressing reinforcement with regard to content of chloride ions in the grout mixture.