Wzmacnianie konstrukcji żelbetowych wstępnie naprężonymi materiałami kompozytowymi FRP

Debonding of the CFRP extemal reinforcement and concrete cover delamination is the most common mode of failure observed in the experimental tests. These premature failure significantly limit the efficiency of the CFRP strips. Application of prestressed FRP strips on the tension face of concrete members control the cracks distribution, limit deflection of the concrete elements and increase the ultimate strength of the strengthened specimens by preventing premature debonding failure. The paper presents several prestressing and anchorage systems that required special end anchorage systems. A new technology of anchorage with gradually reduced prestressing force was developed and successfully tested in the Swiss Federal Laboratories for Materials Research (EMPA) in Duebendorf-Zurich. This method allows variation of the prestressing levels in the CFRP strip, eliminating the risk of shearing-orf in the concrete. The paper presents state of the art of the experimental tests in the field of strengthening RC members with initially prestressed strips.