An evaluation method for the hygrothermal effect on fatigue crack propagation in CFRP–strengthened RC beam

Hygrothermal effects on the fatigue crack propagation behavior of Carbon fiber reinforced polymer (CFRP)–strengthened reinforced concrete (RC) beam was studied based on experimental and numerical methods. Quasi-static tests and hygrothermal fatigue tests of RC beams were conducted to investigate the coupling effect of the hygrothermal environment and fatigue load on the crack propagation behavior. Digital image correlation (DIC) method was applied to track the whole process of fatigue main crack initiation and propagation in real time, in order to obtain the fatigue crack length and crack propagation rate. Stress intensity factor (SIF) of main crack was calculated through finite element method considering material nonlinearity and hygrothermal influence. Results showed that SIF considering hygrothermal influence slightly increased compared to that at indoor atmospheric environment, and the influence of temperature on SIF was greater than that of relative humidity. The fatigue crack propagation curves showed a segmented phenomenon and different fitting function were adopted. It was found that the fatigue crack propagation rate increased with the increase of temperature at the same maximum stress intensity factor K_max. However, the increase of relative humidity had a limited effect on the fatigue crack propagation curves, showing less influence on the fatigue crack propagation behavior compared with that of temperature. Finally, environmental equations based on Paris Law were proposed to quantify the effect of temperature and humidity on fatigue crack propagation in RC beams strengthened with CFRP.