Life-cycle monitoring on compressively loaded ductile concrete structures based on CFRP self-sensing

This study is concerned with smart monitoring on ductile concrete structures based on self-sensing performance of carbon fiber reinforced polymer (CFRP) strips. The CFRP smart strips were fabricated and applied to a highductility concrete (HDC) column subjected to axial compressive and cyclic loading with the view to investigate the strain and damage sensing properties of the CFRP strips having different off-axis angles and width-to-length ratios. The experimental results show that the electrical resistances in both longitudinal and transverse directions of the CFRP strips vary as the compressive load increases. The slope of the real-time resistance changes slightly when the column cracks, and a dramatic change occurs in resistance when the column fails. When compared to the transverse resistance, the longitudinal resistance changes more significantly; exhibiting higher sensitivity and linearity with respect to the strain in the elastoplastic stage of the monitored structures. The sensing properties of the CFRP strips are significantly influenced by the off-axis angle and width-to-length ratio. A CFRP strip with an off-axis angle of 0 degrees and a width-to-length ratio of 0.125 exhibits the most favorable sensing properties in resistivity, linearity and hysteresis. Moreover, the fractional change in resistances of the CFRP strips is significantly influenced by the Poisson effect and fiber-to-fiber contacts within the microstructure of the strip. This is in contrast to the trend of resistance change in longitudinal and transverse directions during the monitoring period. It is found that the transverse resistance of the on-axial CFRP strips is always less sensitive to vertical loading and structural state as compared to the longitudinal resistance.