Use of DIC and AE for Monitoring Effective Strain and Debonding in FRP and FRCM-Retrofitted RC Beams

The effective strain in composites, along with their potential rupture and debonding, plays a crucial role in predicting the strength of retrofitted reinforced concrete (RC) beams. However, only limited experimental data on these phenomena are available, mainly because of the inadequacy of traditional deformation and strain measurement techniques. This paper presents a comparative analysis of instrumentation for monitoring retrofitted RC elements. In particular, the paper addresses beams retrofitted with composite materials, FRPs (fiber-reinforced polymers), and FRCMs (fiber-reinforced cementitious mortars). It also considers strain gauges, fiber Bragg grating (FBG) sensors, LVDTs, digital image correlation (DIC), and acoustic emission (AE) sensors for monitoring strain, displacement, cracking, and debonding. Experiments on six beams are carried out, and the measured data from the monitoring devices are compared. The accuracy of DIC for strain and displacement monitoring is shown to match the performance of traditional methods, with the added benefit of providing full-field monitoring. The use of AE for detecting cracks and debonding, which is not readily possible using traditional methods, is also demonstrated. This is of particular interest for composite-strengthened RC elements, where accurate measurements of effective strain and debonding of the composite material can lead to the development of more precise design formulas.