New findings on fatigue strength of prestressed concrete under very high load cycles

For the fatigue verification of older existing prestressed concrete bridges or new structures, S-N-curves for prestressing steel embedded in concrete are required. Previous tests with curved prestressing tendons embedded in concrete cover the current S-N-curves mainly in the range of fatigue strength for finite life. Only very few tests achieved a number of load cycle of more than 10 million, whereby a real endurance strength is not detected. For this reason, the course of the S-N-curves in the area of endurance strength was essentially determined hypothetically. In the course of the research project SFB 823 Statistics of Nonlinear Dynamic Processes, the fatigue strength of embedded prestressing steels in the range of up to about 10(8) load cycles is experimentally investigated at the TU Dortmund for the first time. Furthermore, on the basis of a very extensive database of various measured physical values, prognosis using mathematical statistical methods for estimating the service life of test girder were developed. They allow the estimation of a prognosis interval with mean and quantile regression curves for the service life on the basis of the damage course with a distinct probability.