Structural Deflection Monitoring Using an Embedded ETDR Distributed Strain Sensor

Feasible application of the electrical time domain reflectometry (ETDR) technique for distributed strain measurement is investigated in this study. A prototype coaxial ETDR distributed strain sensor is embedded into a laboratory-scale reinforced concrete beam specimen, and three-point bending tests are conducted. The ETDR signal waveforms of the embedded sensor are used to determine the deflection profiles of the beam under various bending loads. The resulting deflection profiles are validated by their good agreements with the deflection measurements by LVDT displacement sensors at four discrete locations. It is shown that the ETDR distributed sensing technique has the capability to capture the variation of the load-induced axial strain along the sensing line. In addition, the ETDR distributed sensor could also clearly capture the location of localized high strain points.