Development of innovative optical-fiber sensors suitable for civil engineering applications

In this research, innovative optical fiber sensors measuring displacement, strain, acceleration and pressure, which are suitable for monitoring civil structures, have been developed and tested in the laboratory and the field. Representing a significant advancement, the developed optical fiber sensors eliminate the practical problems associated with conventional sensors when being used in civil engineering applications, such as weak resistance to electromagnetic interference (EMI), heavy and cumbersome cables, high cost of cabling, etc.; Two types of sensing mechanisms have been developed. The first type uses a vibrating string and the second uses a LC oscillating circuit as the sensing element. Both take advantage of well-understood mechanisms of proven reliability and accuracy to transduce the physical quantity into frequency modulated signals, which are robust over long distance transmission. The power and signal transmission is by optical fibers, which are immune to EMI, light in weight, and easy to be installed.; Prototype for verifying the sensing mechanisms, and working versions of optical fiber displacement sensors, accelerometers, strain gauges and pressure sensors have been fabricated, extensively tested in laboratory in terms of static and dynamic characteristics, and applied in the field to monitor a number of civil structures. Shake table tests were performed for a steel frame on which the optical fiber strain gauge was installed to measure its dynamic strain response to earthquake ground excitations and the measurements were compared with the results by the conventional strain gauge. The optical fiber strain gauges were also embedded in concrete cylinder specimens to measure the strain changes during compression tests. The dynamic performance of the developed optical fiber accelerometer was compared with that of a servo accelerometer through shake table tests. The optical fiber pressure sensors were applied to monitor the ocean wave pressure acting on a wave breaker. The optical fiber accelerometers were installed on a 310-meter tall concrete TV tower, to measure its ambient vibration, based on which the dynamic characteristics and finite element models of the tower have been successfully identified using system identification techniques.; This interdisciplinary research has produced optical fiber sensors that are truly suitable to civil engineering applications.