Application Of Optic-Fiber Sensing Technology To Civil Engineering

Based on the theory of optic-fiber bending attenuation and Bragg grating reflecting theory, this paper studied the application of distributed fiber crack sensor system and Bragg grating sensor system to civil engineering. As for distributed fiber crack sensor system, discussed is its basic sensor theory ----micro-bending effect theory, which lays the theoretical foundation for the model tests of mechanics-optics relation, the sensitiveness tests of fiber to the surrounding temperature, longitude tension and other factors, as well as the fiber embedment technique. The establishment of the mechanical-optic constitutive model is the key to the application of distributed fiber crack sensing in civil engineering practices, thus a digital and automatic test system for testing mechanics-optics relation was formed. This mechanics-optics coupling test system includes two subsystems as follows: mechanical system and optical system. The mechanical system consists of the test system of MTS815 rock-concrete mechanics test, mainly providing loading system and recording cracks. And the optical subsystem consists of the source of laser light and the optical power meter, chiefly collecting the changes of fiber signals. In the test progress of the tensile test for distributed fiber crack sensing and fiber Bragg grating sensors, Instron-4302 digital tensile test machine was used as the mechanical subsystem, used to extend the fiber and the fiber Bragg grating sensors. And in the temperature sensitiveness test for distributed fiber crack sensing, the combined system of optical and digital temperature controlling box were adopted. Based on modal tests, the successful application results of fiber Bragg grating sensors to model experiments of engineering structures was carried out, some conclusions have been drawn in the this paper as bellows: 1. Fiber micro-bending effect theory can be used to monitor concrete cracks. And the fiber crack sensing system is infected by surrounding temperature factor. Using the model tests, the mechanical-optic constitutive model of the distributed fiber crack sensing has been built. 2. High sensitivity and good distinguishing ability of crack width resolution and localization are the characters of the distributed fiber crack sensing. 3. In engineering application, the distributed fiber crack sensing realizes distributed monitoring, which are unable and incomparable functions for traditional sensors and other separated apparatus. 4. By use of fiber Bragg grating theory, fiber crack sensors, fiber slip sensors, and fiber life sensor can be made. These sensors are characterized by their high sensitiveness, good practicability, strong anti-destroy capacity and great livability of embedment. 5. The fiber Bragg raster sensor system has very simple structure, with a grating strain sensor head as the core. It can be produced a sensor net to implement quasi-distribution monitoring, which has the ability to take large capacity tests with the advantages of credibility, stability, free of the inflection of light strength and attenuation of the system. 6. The system has been used in the model tests of the steel-concrete compositebridge deck, and the structural strains especially the damage of the steel-concrete interface including slip and disengaging(lift) and concrete cracks of the deck have been successfully detected, to the extent that traditional equipment can never or has little possibility to measure this kind of damages. The results show that the fiber Bragg grating sensor system has many advantages for the safety monitoring of the steel-concrete composite structures.