## 2 Ospec Performance Verification
### Experiment for Temperature Compensation  
_Calculation of Thermal Expansion Coefficient and Data Analysis_  
The optical fiber sensor has excellent advantages in terms of its accuracy and durability, but it also has a disadvantage in terms of being vulnerable to temperature change. Therefore, temperature compensation is absolutely necessary where an optical fiber sensor is used. The OSPC strand behaved with materials with various coefficients of temperature expansion as it was a structure that was combined not only with the CFRP rod but also with the steel outer wire outside the strand, finally forming a composite structure with poured concrete. Therefore, this study attempted to extract only the pure change in prestress force in OSPC through a separate thermal calibration experiment. For the experiment for thermal calibration, composite and non-composite concrete beams were fabricated to match the conditions as similar as possible to the beam specimens fabricated for long-term performance verification. Figure 11 below shows the dimensions of the specimens and the production. A chamber capable of temperature and humidity control was used for the temperature compensation experiment. In order to minimize the effects other than temperature change, a Teflon sheet with a small coefficient of friction was laid on the floor, and the test objects were placed on it to perform the experiment. Figure 12 shows the installation and measurement of a specimen in the temperature chamber. The temperature was maintained at 50 \({}^{\circ}\)C for 1 h, then lowered to \(-15\) \({}^{\circ}\)C for 60 min, maintained at \(-15\) \({}^{\circ}\)C for 60 min, and then increased to 50 \({}^{\circ}\)C for 60 min, where the humidity was fixed at 0%, and the temperature inside and outside the specimen and the strain of the OSPC strand were measured by repeating the same temperature pattern four times. Figure 11: Dimensions of specimens and their production (**a**) Dimensions and appearance of specimens, (**b**) Fabrication of specimens. Figure 12: View of temperature–compensation experiments (**a**) Installation of specimen, (**b**) View of measurement. Figure 13 shows the temperature change measured by the thermocouples installed inside and outside the specimens and the change in strain calculated by the wavelength value of the optical fiber sensors, measured in the composite and non-composite specimens. As shown in the figure, the thermal expansion coefficient of the composite specimens in which the entire OSFC strand was embedded in concrete was about 17.266 \(\mu\varepsilon/\lx@math@degree\)C. This was a slightly smaller value than the sum of the thermal expansion coefficients of the steel and optical fiber used for the normal concrete and PC strand. The thermal expansion coefficient of the optical cable may have been almost consumed, owing to the influence of the CFRP rod, with a thermal expansion coefficient close to zero, thereby being mainly affected by the thermal expansion coefficient of the steel outer wire and the concrete surrounding the CFRP rod. On the other hand, for the non-composite specimen in which the middle part formed a tube, the thermal expansion coefficient was about 9.933 \(\mu\varepsilon/\lx@math@degree\)C. Compared to the composite specimen, the behavior with respect to temperature did not show a constant pattern, but the thermal expansion coefficient was somewhat smaller than that of the composite specimen, owing to the existence of the non-composite section in the hollow tube. Figure 14 below shows the results obtained by applying the thermal expansion coefficients calculated in the above thermal expansion coefficient experiment to the actual long-term prestress force-loss data to remove the amount of change due to heat. As shown in Figure 15, the range of change in prestress force was significantly reduced in the upper and lower parts after removing the change in prestress force according to temperature. [PERSON] et al. (2019).