Self-sensing and quantitative assessment of prestressed concrete structures based on distributed long-gauge fiber Bragg grating sensors

Quantitative assessment of strengthened concrete structures using self-sensing fiber-reinforced polymer sheets is presented in this article. First, strain distribution along the height of a structure induced by pre-tension force (initiate state) is theoretically estimated. Second, the procedure for parameter estimation of prestressed fiber-reinforced polymer–strengthened structures under external load using measured and pre-tension force–induced strain is established, and nonlinearity caused by random cracks is considered in the method. Both local parameters (neutral axis position, bending stiffness distribution, strain distribution along the cross section, etc.) and global parameter (deflection) of structures can be accurately estimated by measured long-gauge strain responses. Finally, both prestressed fiber–reinforced polymer–strengthened and reinforced concrete beams installed with long-gauge fiber Bragg grating sensors have been experimentally investigated to prove the effectiveness of this method. Experimental results indicate that the estimated neutral axis height and local bending stiffness can reflect initiation of random cracks and deterioration process of structures under increasing external load. Meanwhile, the estimated strain along the beam height and deflection at mid-span agree well with the measured ones, which further verifies the accuracy of the estimated neutral axis position affected by randomly appeared cracks. Hence, the method can be utilized for assessment and maintenance of fiber-reinforced polymer–strengthened structures.