Quantifying prestressing force loss due to corrosion from dynamic structural response

In prestressed concrete structures, corrosion of prestressing strands is a major durability concern. In advanced stages, corrosion may result in the rupture of strands. At early stages, corrosion of strands results in microcracking, deterioration of bond between strands and concrete, and therefore, in the loss of prestressing force. These effects, in turn, result in the change of dynamic response of prestressed elements. In this paper, we investigate whether the prestressing force of prestressed beams can be estimated indirectly using dynamic vibration test. For this purpose, six prestressed concrete beams were manufactured. Two beams were kept as control, two beams were corroded along the entire length of the strand, and two beams were corroded along one-third of the strand length. The induced accelerated corrosion was monitored by corrosion current measurements and passive acoustic emission. Two system identification approaches were developed where both utilize the free vibration response of an Euler-Bernoulli beam to estimate prestressing force of strands. Due to the ill-possedness of the identification problems and the presence of random and systematic errors in the experiment, Tikhonov regularization method was used. Finally, results were compared with analytical solution of vibration of a simply supported beam with external compressive force. It was concluded that using dynamic vibration of prestressed concrete beams and using indirect estimation approaches, it is possible to quantify the loss of prestressing force due to corrosion.