A comparative study on hybrid fatigue stress-life model of RC beams strengthened with NSM CFRP

Abstract

Near Surface Mounted Carbon Fiber-reinforced Polymers (NSM FRP) are becoming widely used in the rehabilitation field of concrete structures. Several studies were conducted to evaluate the fatigue performance of Reinforced Concrete (RC) bridges strengthened with NSM FRP composite materials. Most stress-life (S-N) fatigue models of RC beams are based on fatigue testing that has been conducted in the region of load cycles ranging between 10³ and 10⁷. This might cause an inaccuracy in the stress-life predictions when the common S-N formulations are used. This paper presents a review of the recent research on the fatigue behavior of RC beams and proposes a hybrid fatigue stress-life model of RC beams strengthened with NSM CFRP. An analytical fatigue S-N model was developed based on experimental fatigue data of constant amplitude of tension-tension cyclic loading obtained from the literature. A hybrid formulation was used, combining both exponential and power regression analyses to enhance the accuracy of prediction in low and high cycle fatigue regions. Moreover, Muratov’s method was used to determine the endurance limit of strengthened RC beams. A three-dimensional finite element RC beam strengthened with NSM CFRP was modeled to investigate the accuracy of the proposed hybrid model. The RC beam was modeled in ANSYS with similar dimensions and material properties to experimental specimens in the literature. The hybrid model was compared to experimental and numerical data, and satisfactory precision was observed with a correlation coefficient of 0.86. The proposed hybrid model helps to provide comprehensive fatigue stress-life estimation for design purposes.

Keywords:

• Fatigue
• S–N curve
• fiber-reinforced polymers
• near-surface mounted RC bridges