An Experimental Investigation on Flexural Behavior of Reinforced Concrete Beams Strengthened by an Intelligent CFRP Plate with Built-In Optical Fiber Bragg Grating Sensors

The difficulties induced from high-durability package, large-scale measurement, and sensor installation make it a big challenge but an urgent need to predict the mechanical behavior of strengthened reinforced concrete structure with the externally bonded fiber-reinforced polymer (FRP) plate under harsh environments and rough construction process. In an effort to solve this challenge, this paper proposes a novel end anchored self-sensing CFRP plate assembly with built-in optical fiber Bragg grating (FBG) sensor. The self-sensing principle is presented and a demonstration test was carried out in the laboratory in order to investigate the self-sensing properties of the intelligent CFRP plate. Three-point flexural tests of a total of ten RC beams were carried on: six strengthened with the bonded or unbonded posttensioned intelligent CFRP plates, one strengthened with the ordinary CFRP plate, and three strengthened with the control beams. The full-range CFRP plate strain at the maximum moment was measured utilizing the FBG interrogator. Using this monitoring data, the short-term prestress loss attributed to anchorage set and the relationship between the external load and the CFRP strain at the middle span associated with the integral response of the strengthened member were investigated. Besides, the objective of the tests was also to gain a better understanding of the failure mode and the flexural behavior of RC beams strengthened with posttensioned CFRP plates taking into account the different strengthening methods, initial damage, and the dead load before strengthening. The experimental results showed that the developed CFRP plate with built-in FBG sensors not only can be the reinforcement of the RC structures, but also provide an effective way to monitor the full-range behavior of the CFRP plate with the excellent self-sensing property shown in the demonstration tests.