Automatic Deflection Inspection of Composite Structures Using Fiber Optic Strain Sensing

Deflection is a crucial indicator for structural safety assessment and maintenance of engineering structures. Traditional deflection inspection methods are confronted with the difficulty in selecting reference points, and therefore these methods are usually applied in short-term monitoring of structures. In this context, a novel strategy for automatic deflection inspection of beam-like composite structures which overcomes the difficulty in selecting reference points is put forward in this article. First, deflection assessment of composite structures using long-gauge fiber optic sensing was theoretically established. The relationship between vertical displacement and monitored average strain is irrelevant to external loads. The approach is applicable to both linear and nonlinear stages of structures, and deflection distribution along the structures can be estimated. Second, a four-point loading experiment on a wood–concrete composite beam which was installed with long-gauge fiber optic sensors was performed to verify the reliability of the deflection inspection method. Deflection was estimated under three conditions: (1) without considering composite action; (2) considering composite action but neglecting interface slip; and (3) considering both composite action and interface slip. Meanwhile, displacement meters were also installed to verify the calculated results. Experimental results indicate that the presented strategy has high precision. Hence, the presented method serves as an innovative option for assessing composite structures in both the short and long term.