# Smart Sensing of PSC Girders Using a PC Strand with a Built-in Optical Fiber Sensor
## 2 Fabrication and Test  
### Fabrication of Full-Scale BH Girder Bridge and Installation of OSPC Strand  
Figure 3 shows the conceptual drawing and a photograph of the manufactured OSPC strand. Since the OSPC strand had shapes and dimensions identical to a conventional steel strand, the same anchoring device could be used. In addition, considering that the OSPC strand exhibits performance equivalent or superior to that of the conventional steel  
Figure 4: Shape and dimensions of full-scale bulb-T-shaped half-deck (BH) girder bridge prototype for the test.  
Figure 3: Optical sensor PC (OSPC) strand: (**a**) Conceptual drawing; (**b**) Actually manufactured product.  
strand, the OSPC strand offers the advantage of being able to play both roles of sensor and reinforcing member.  
The full-scale BH girder bridge prototype constructed for the test had a length of 35 m and a deck depth of 2.5 m (Figure 4). The anchorages were disposed at the top and bottom of the cross-section and near the connections between the segments. To observe the overall state of the prestressing force in the bridge, one OSPC strand was installed at each anchorage. Considering the profile of the tendon involving straight and curved parts, each sensor was set to have three to seven sensing points. Figure 4 depicts the shape and dimensions of the BH girder bridge applying the OSPC strand and indicates the locations of the anchors (A, B, C). Figure 5 shows the position of the OSPC strand in the cross-section for each of the anchors, A, B, and C, of Figure 4, as well as the numbering of the tendons. Table 1 provides the details of the tendons one, two, three, and four, like the profile and length, the number of sensing points, and the prestressing method.  
Table 2 shows the specification of the FBG sensor and measurement equipment used for manufacturing the OSPC. The FBG sensor used in OSPC fabrication distinguished the wavelength intervals so that the wavelengths did not overlap when a tension force was applied. Data was acquired once per second using an interrogator, and then the change in wavelength was converted to strain using the wavelength-strain formula from Equation (1)  
\[\frac{\Delta\lambda}{\lambda_{B}}=(\alpha+\xi)\Delta T+(1-P_{\epsilon})\epsilon^{m} \tag{1}\]  
where \(\lambda_{B}\) is the reference wavelength before tension force is introduced, and \(\Delta\lambda\) is the change in wavelength from the measurement. \(\epsilon^{m}\) is the elastic strain. \(P_{\epsilon}\) is effective photoelastic constant for the fiber and generally 0.22 is applied. Although the FBG sensor was sensitive to temperature, the temperature change was not considered. This is because the tension force as introduced for a short time, and the wavelength change by the tension force was quite large [14]. In this paper, after converting the measured wavelength into strain, the tension force was estimated by applying the elastic modulus (195 GPa) from the basic tensile test of OSPC and the cross-sectional area.  
Figure 6 shows pictures of the fabricated full-scale BH girder bridge prototype installed with the OSPC strand. Figure 7 presents the tensioning process of the girder bridge and the measurement of the prestressing force during the process.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Tendon No.** & **Number of Sensing Points** & **Wavelength (nm)** & **Reflectivity** & **Interrogator** \\ \hline One & Seven & 1520, 1525, 1530, 1540, & over 90\% \\ Two & Three & 1520, 1540, 1560 & over 90\% \\ Three & Three & 1520, 1540, 1560 & over 90\% \\ Four & Five & 1520, 1530, 1540, 1550, 1560 & over 90\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Specification of FBG sensor and measurement equipment.  
Figure 6: Full-scale BH girder bridge prototype: (**a**) Assemblage of precast segments; (**b**) Installation of OSPC strands.  
Figure 7: Full-scale BH girder bridge prototype: (**a**) Prestressing process; (**b**) Measurement of prestressing force during tensioning.