PSI - Issue 64

Mingyang Xi et al. / Procedia Structural Integrity 64 (2024) 515–522

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

adhesive layer thickness of 0.3 mm, can achieve optimal and efficient monitoring.

Fig. 1. Embedded FBG Self-sensing strand

Fig. 2. Schematic Diagram of FBG Embedding

The design of this encapsulation structure aims to enhance the survivability and monitoring range of FBG within the strand. By using a groove-embedded encapsulation method, direct contact between the FBG and the hard surface is avoided, reducing the risk of breakage due to compression. The key advantages of the self-sensing strand, including improved monitoring range, the ability to monitor stress and strain throughout the entire lifecycle of the strand, and enhanced fatigue life, highlight the potential of this technology in the application of prestressed concrete beams. 2.2. Calibration of Self-sensing Strand Data For the data calibration of self-sensing strands, due to the slight deviations in manufacturing processes and varying degrees of coupling, each strand undergoes precise data calibration before application. This process includes the assembly of anchorage tools, stress control, and data recording to ensure the accuracy and reliability of the data in subsequent use.

Fig. 3. Anchorage Tools Installation

Fig. 4. Stress Control

To calibrate the precise wave-force value conversion for each self-sensing strand, data calibration is conducted before the use of the self-sensing strands by using graded verification points. A formula is established to describe the relationship between force value and wavelength change: F A  =  (1) Where: F = Loading force (kN); A = Wave-force conversion coefficient; = Wavelength variable (pm). During the data calibration process, before the loading force is applied (i.e., when the verification point is 0 MPa), the initial reflection wavelength of the fiber Bragg grating is measured and recorded. This initial wavelength serves as a baseline for subsequent data processing. Then, the loading force is gradually and uniformly increased in a stepwise manner. During the loading process, the reflection wavelength of the fiber bragg grating is measured and recorded at fixed verification points using a fiber optic spectrometer. The calibration data for the 5 self-sensing strands used in