PC tendon is a vital component for strength of prestressed concrete structure. However, there is no warning sign when it is degraded or damaged, because of its invisibility from outside. Vibration-based method is one of the technique for damage detection due to simplicity. However, the extensively used method such as modal-based analysis is still insensitive to such damages. Recently, phase space-based analysis, a novel method for damage detection, was adopted in Civil engineering and a new index called Change of Phase Space Topology (CPST) has been developed. It is effective in identifying the damage existence regardless a known of damage location. Therefore, this paper adopted such technique to investigate damages of PC tendon. A pretension concrete girder with artificial PC tendon damages was used in experiment and it was excited by two vibration tests; free vibration and impact hammer test. The CPST values and the results from modal-based analysis were investigated and compared. The index shows increasing trend with increasing of damage levels. Moreover, it is more sensitive to the PC tendon damages than the results from modal-based analysis. This implies that CPST might be an effective index to detect the damages of PC tendon.
