Smart-monitoring capabilities of CFRP strips in civil structures based on width-to-length ratio optimization

Abstract Structural health monitoring is critical for ensuring the serviceability of in-service structures. However, mainstream monitoring technologies have inherent limitations. In this study, a novel approach was investigated by using carbon fiber reinforced polymer (CFRP) by leveraging its self-sensing properties. Six groups of CFRP smart strips were designed and applied to high ductile concrete (HDC) columns subjected to axial compression, with the view to ascertain the strain and damage sensing capabilities of the CFRP strips having different width-to-length (w/l) ratios and gauge lengths. Experimental results show that the longitudinal and transverse resistances of all CFRP smart strips decrease with increasing compressive strain, attributing to the Poisson effect as well as the change in fiber-to-fiber contact rate within the microstructure. Abrupt changes in resistance occur upon the fracture of the HDC column. The w/l ratio emerges as a crucial factor affecting the sensing performance of the CFRP smart strips. A w/l ratio of smaller than 0.1 corresponds to a small gauge factor (GF) of less than 35, with the maximum coefficient of determination of 0.78829. When the w/l ratio is between 0.1 and 0.125, the GF averagely increases to 224.1, with the average coefficient of determination of 0.96082. For the CFRP smart strips having the same w/l ratio of 0.125, the GF increases from 158.76 to 194.89 as the gauge length rises from 80 mm to 120 mm, while the coefficient of determination slightly decreases from 0.97842 to 0.97381. As the gauge length extends to 160 mm, an enormous improvement from 194.89 to 445.5 in the GF is achieved, accompanied by a reduction in the coefficient of determination from 0.97381 to 0.93459. Compared with the transverse resistance, the longitudinal resistance exhibits the superiority in both the GF and the coefficient of determination. The established model of fiber-to-fiber contact rate theoretically interprets and validates the influence of w/l ratio on the smart properties of the CFRP strips.