A new design of distributed crack sensors is presented for the condition assessment of reinforced concrete (RC) structures during and immediately after an earthquake event. This study is mainly focused on the performance of cable sensors under dynamic loading, particularly their ability to memorize the crack history of an RC member. This unique memory feature enables the post-earthquake condition assessment of structural members such as RC columns, in which the earthquake-induced cracks are closed immediately after an earthquake event due to gravity loads and they are visually undetectable. Factors affecting the onset of the memory feature were investigated experimentally with small-scale RC beams under cyclic loading. Test results indicated that both crack width and the number of loading cycles were instrumental in the onset of the memory feature of cable sensors. Practical issues related to dynamic acquisition with the sensors were discussed. The sensors were proven to be fatigue resistant from the shake table tests of RC columns. They continued to show useful signal after the columns can no longer support additional loads.
Configuration-based coaxial cable sensors have recently been developed to detect cracks in reinforced concrete (RC) structures. These sensors have shown a high sensitivity when applied to several short RC flexural members. However, the signal losses resulting from a long cable sensor may distort the initial waveform of the electromagnetic wave propagating along the cable, thereby compromising the spatial resolution and sensitivity of this sensor. The signal losses consist of the contributions from the skin effect of conductors, energy absorption in the dielectric material, and impedance mismatch loss due to multiple signal reflections resulting from discontinuities caused by the separation between the adjacent spirals, which acts as the outer conductor of a cable sensor. This paper summarizes the basic physics of signal losses in cable sensors, and investigates the impact of the signal losses on the spatial resolution and sensitivity of a cable sensor over distance. Several methods are proposed to simulate and quantify various factors affecting the signal losses.