Determining the decay of frictional shear bond strength in the fiber duct of a single straight steel fiber in cementitious composites using an experimental and numerical data calibration method

Abstract

When straight steel fibers (SSFs) are embedded in a cementitious matrix, the frictional shear bond strength increases the safety factor against brittle fractures in the fiber/matrix regime. This study presented three methods for evaluating the frictional shear bond strength performance based on the pullout work principle. First, theoretical approaches defined the SSF regime in concrete matrices using an analytical model. Second, experimental pullout tests were used to control the proposed theoretical approaches. Third, numerical simulations were used for validation purposes. These three methods were calibrated using an empirical decaying coefficient. Various parameters were used to evaluate the pullout work and frictional shear bond strength. The effects of the fiber geometry, such as the diameter, embedded length, and aspect ratio, were investigated. The results showed that increasing the diameter of the fibers by six times increased the pullout capacity by 3.75 times and decreased the frictional shear bond strength by 62.4%. Thus, decreasing the fiber diameter improved the resistance of the fiber duct against decay. However, increasing the embedment length and aspect ratio of the fibers by 1.8 times increased the pullout capacity by 2.1 times and decreased the shear bond strength by 7.9%. Therefore, increasing the embedded length of the fiber increased crumbling in the fiber duct. © 2025 American Society of Civil Engineers.