Monitoring the stress of the post-tensioning cable using fiber optic distributed strain sensor

We applied a Brillouin-OTDR, which is a fiber optic distributed strain sensor, to measure the stress of four post-tensioning cables. The fiber optic sensor was bonded to one steel strand and three aramid fiber reinforced plastic (AFRP) cables, which were later installed in three precast beams. The monitoring test was performed both in the tension procedure and the load procedure. The experimental results showed that the fiber optic distributed sensor holds high accuracy, and the relative deviation of the measurement results between fiber optic sensor and strain gauge is under 2.7%. The stress distribution of the post-tensioning cable obtained under all loads can be used to evaluate the health state of the beam. Furthermore, the prestressing loss occurred in post-tensioning cable can be calculated. The initial prestressing loss of steel strand is 8.98% and the initial prestressing loss of AFRP cable is 6.32%. After 30 days, the prestressing loss of steel strand is 8.81% and the prestressing loss of AFRP cable is 9.61%.