Acoustic emission monitoring and damage assessment of FRP-strengthened reinforced concrete columns under cyclic loading

Fiber-reinforced polymers (FRPs) have been widely used for the seismic strengthening of reinforced concrete (RC) structures in seismic regions across the world during the last decades. However, the crack states of concrete inside the strengthened regions are wrapped by FRP sheets and are not visible to inspectors after earthquakes. Aiming to solve this problem, the crack process of FRP-strengthened large-sized RC column under lateral reversed cyclic loading was investigated based on acoustic emission (AE) techniques in the present study. It was found that AE techniques were effective in revealing the crack process of both FRP-strengthened and unstrengthened RC columns. The AE hits analysis revealed that the damage process of the FRP-strengthened column could be divided into four damage levels qualitatively, and the distribution of AE amplitudes had an obvious relationship with the peak displacements of the strengthened column under cyclic loading. The b-value analysis showed that the variation of the crack magnitude during the cyclic test could be reflected effectively by the trend of b-values. The accumulative AE energy exhibited a good correlation with the accumulative hysteretic energy dissipated during the cyclic test for the FRP-strengthened column. Based on fractal theory, a concise but reliable damage index was proposed to predict the damage levels of FRP-strengthened RC columns and the efficiency of the damage index has been verified through the test results.