Abstract:
Structural health monitoring helps to protect infrastructure by guiding timely
interventions. Distributed Fibre Optic Sensing (DFOS) is one such monitoring
technique with significant advantages such as continuous measurement capability,
small size and lightweight. This is the first time introducing the Fibre Optic Monitoring
technology to Sri Lanka. A recently developed FOS technique, Brillouin Optical
Frequency Domain Analysis (BOFDA), provides advantages such as smaller sized
analyser unit and faster measurements, however, it lacks experimental evidence on the
measurement accuracy. FOS, in general, also has unestablished workmanship
practices on pre-straining and placing of fibre optic cables. This study is particularly
aimed at BOFDA-based instrument calibration and verification of the accuracy of the
BOFDA-based strain and temperature measurements. Firstly, laboratory experiments
were performed to investigate the accuracy the measurements provided by the
BOFDA-based DFOS system using the strain cable calibration test setup and
temperature cable calibration test setup. These calibration tests indicated that actual
maximum spatial resolution of the selected BOFDA unit is in the range of 0.4 - 0.6 m.
The strain and temperature measurements provided by BOFDA were found to be
reliable, since constant strain and temperature coefficients were observed. The
workmanship practices were examined using a set of four-point beam bending tests
with different configurations of FO cable locations and pre-tensioning levels. The
results showcases that the location of the fibre cables, whether on the surface or
embedded in concrete either near or away from the reinforcement, had no significant
effect on the accuracy of strain measurements. However, contrarily to the practice,
clear evidence was found on the need for pre-straining of strain cables to obtain
accurate compressive strain measurements. This research therefore showcases the
reliability of BOFDA technique and encourage future fibre optic monitoring
deployments to ensure pre-straining of fibre optic cables as a good workmanship
practice.
Citation:
Gowshikan, A. (2023). Experimental analysis on the workmanship factors and performance of fibre optic infrastructure monitoring cables embedded in concrete structures [Master's theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/22089