Abstract
Advances in emerging fi bre-optic sensing technology have contributed to the recent development of innovative systems for monitoring the health of civil engineering structures. The main reasons for this development are the reduced weight and dimensions of fi bre-optic sensors, their strong immunity to electromagnetic interference, their improved environmental resistance and their scale fl exibility for small-gauge and long-gauge measurements. In companion papers, an overview of the challenges related to the design and mechanical characterization of a novel fi bre-optic plate sensor for crack monitoring was explained and discussed. The proposed sensor does not require prior knowledge of the locations of cracks, which is a signifi cant advancement over existing crack-monitoring techniques. Moreover, several cracks can be detected, located and monitored using a single fi bre. In this paper, we will fi rst present the results of calibration tests on the crack sensor, which aim at determining the relationship between optical intensity loss and crack opening under static conditions. Then, the performance of the sensors with respect to the detection and monitoring of internal and external fl exural cracks in concrete, masonry and bituminous elements is assessed. Two versions of the sensor were examined. The fi rst version was externally attached to fi bre-reinforced concrete beams and reinforced masonry slabs; the second version was embedded into fi bre-reinforced concrete beams and bituminous slabs. The results presented in this paper demonstrate the viability of implementing the attached and the embedded plate sensors to detect the formation and propagation of internal and external cracks and to measure the crack opening width in a wide range of applications.
Highlights
Sensors and Materials, Vol 21, No 2 (2009)displacement of the crack surfaces perpendicular to the plane of the crack
Occasional deviations in the alignment of the plates when clamping the specimens. Despite all these sources of uncertainty, the comparison of the performance characteristics obtained from the calibration tests performed in this study indicates that the results achieved by both direct and backscattered power measurements exhibit reasonable agreement
To compare the crack measurements with the measurements obtained in the concrete beams, the masonry slab was tested using the sensor with the optical fibre at an angle of 15°
Summary
Displacement of the crack surfaces perpendicular to the plane of the crack. The shearing mode of loading is due to in-plane shear loads, which cause the two crack surfaces to slide on one another. Cracks are repaired after the cause is established, and after determining whether the observed cracks are indicative of current or future structural problems, taking into consideration the present and anticipated future loading conditions This firstly involves a field observation to identify the location and extent of cracking, a review of the design elements (drawings, specifications, etc.), inspection records and maintenance history. It is important to recognize the type of cracking as this will affect the placement of sensors for the effective detection and monitoring of the cracks Under special conditions such as high friction and a large drop in temperature (or moisture content), longitudinal cracks can develop, and in such cases typical block cracking patterns are found. The guidelines for pavement evaluation[8] recommend that the crack opening width and spacing and changes in the crack opening width should be measured while considering possible changes in the climatic conditions (temperature and moisture)
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