FRETTING FATIGUE CHARACTERISTICS IN THE CURVED LAYOUT OF LARGE-CAPACITY PRESTRESSING STRANDS

Fatigue tests were carried out on the fretting of prestressing strands S15.2 given a small radius of curvature, in external tendons of a prestressed concrete bridge. It was confirmed that the fretting associated with high bearing stress and relative slipping at the contact points between prestressing strands causes the ruptures of strands, and fretting mark and crack were found at the point of origin of rupture. It was learned that the lifetime under these conditions is shorter than the usual fatigue lifetime in which fretting effects are negligible. From the test results, we propose a design fatigue strength formula of prestressing strands that takes fretting in small radius of curvature into account and show that a cable grouted with cement mortar is effective in suppressing fretting fatigue.