# Smart Sensing of PSC Girders Using a PC Strand with a Built-in Optical Fiber Sensor
## 2 Fabrication and Test
### Test and Measurement of Full-Scale BH Girder Bridge
Moreover, some differences in the material properties adopted in the analysis might also possibly have caused this discrepancy. The data above are those obtained by vibrating the structure sufficiently using the actuator and allowed clear identification of the natural frequency. In general, data related to the longitudinal direction along the girder in bridge structures present poor sensitivity compared to the vertical acceleration response of the bridge, which made them improper for identifying the natural frequency. However, [PERSON] et al. [18] determined the impact factor  
Figure 12: Identified natural frequencies of the first mode using: (**a**) Accelerometer data; (**b**) FBG sensor data. Figure 13: Dynamic analysis: (**a**) Three-dimensional FE model; (**b**) First-mode shape of BH girder bridge prototype [13]. of an actual in-service railway bridge structure based upon data measured by electrical resistance gages installed longitudinally in the girder near a FBG sensor during the crossing of train convoys. Moreover, prior to the test presented in this study, the OSVC strand was already installed inside the girder of a road bridge with a span length of 60 m and in operation. Figure 14 shows the layout and a photograph of this bridge together with its natural frequencies extracted from dynamic acceleration data acquired during the crossing of a truck. Several months after the completion of the bridge shown in Figure 14, the wavelength variation in the structure was measured by the OSVC strand under the crossing of a truck. Figure 15 plots the dynamic data obtained during the measurement and the identified natural frequency. The wavelength variation plotted in Figure 15a was obtained by removing the Direct Current (DC) content from the raw data and applying a high pass filter. The natural fre  
Figure 14: Real bridge applying the OSVC strand: (**a**) Overview of bridge and layout of sensors; (**b**) Photograph of the completed bridge and dynamic data acquisition equipment; (**c**) Natural frequencies extracted from acceleration data. Figure 15: Data acquired on the road bridge in the previous test: (**a**) Dynamic data (wavelength variation) measured by OSVC strand; (**b**) Identification of natural frequency. quency in Figure 15b was computed by FFT. The natural frequency obtained from the OSPC data differed slightly from that of the acceleration response in Figure 14c, but this difference was probably due to the effects of the time elapsed between the two measurements like temperature and change in the state of the bridge in operation. In view of such results, installing semi-permanently the OSPC strand in the railway BH girder bridge appears to offer a fair and sufficient solution enabling to observe and evaluate the change in the prestressing force as well as the natural frequencies of the structure without other accelerometers nor electrical resistance gages. These features will allow effective maintenance since it is possible to detect any abnormal change of the structure. Furthermore, the flexural performance of the BH girder bridge was evaluated through the four-point bending test, as shown in Figure 16.  
Figure 17 shows the comparison of the strain measured during the four-point bending test by the optical sensor located at the center of tendon one among the OSPC strands and by the electrical resistance strain gage bonded on the closest reinforcement in the cross-section. Linearly varying strains were measured by both types of sensor at early loading until the plastic zone. Beyond a value of about 3600 \(\mu\varepsilon\), the strain provided by the electric resistance gage showed a steep increase, which indicated yielding of the steel reinforcement arranged at the bottom of the girder bridge. On the other hand, the OSPC strand continued to behave normally and measure the strain even after the yield of the reinforcement and until the final loading stage at approximately 6000 kN. A deflection of about 350 mm was finally observed at mid-span.