Low cycle fatigue crack propagation and damage evolution of concrete beams reinforced with GFRP bar

This paper studies the low cycle fatigue (LCF) behavior of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) beams by utilizing experimental and analytical investigation. Static and LCF three-point bending tests were carried out on 12 over-reinforced GFRP RC beams and six under-reinforced steel RC beams. The failure modes, fatigue lives, load-deflection, strain, and crack propagation were analyzed. The fatigue life of the steel RC beam with the same maximum stress level was lower than the GFRP RC beam, while the GFRP RC beam illuminated a larger failure mid-span deflection. For GFRP RC beams, the average fatigue lives with the maximum stress levels S-sigma max = 0.85P(u) , 0.70P(u) , and 0.65P(u), were 896, 8491, and 19949, respectively (P-u = the ultimate static flexural loading capacity). The average fatigue life of the highest stress level (0.85P(u)) was approximately 22 times the lowest stress level (0.65P(u)). Bending shear failure, and concrete crush were the dominant fatigue failure mode for GFRP and steel RC beams. The relationship between fatigue stress range and fatigue life was investigated based on fitting and reliability analysis. The stress intensity factor of the type I crack of the GFRP RC beam was deduced theoretically. The fatigue crack clarified a three-stage development trend (crack initiation, stable crack propagation, unstable crack propagation). When the crack continued to expand until it ran through the whole section, the beam was damaged. The fatigue crack propagation was fitted according to the experimental data. The deflection, dynamic stiffness, and damage evolution law of steel and GFRP RC beams were deducted. The fatigue life prediction models based on crack propagation and damage evolution were derived.