Mechanical analyses of hooked fiber pullout performance in ultra-high-performance concrete

• The pullout response of straight and hooked fibers in ultra-high-performance concrete is investigated.
• Spalling due to fracture propagation is proposed which corresponds to the experimental results.
• Friction due to bending, slip-hardening and tunnel damage are explicitly taken into account.
• Pullout behavior in different matrix with variable fibers is properly modeled.

In this study, a practical model to simulate the pullout performance of hooked steel fiber in ultra-high-performance concrete is proposed. Straight and hooked fiber pullout tests were performed to evaluate the pullout mechanism, based on which slip-hardening, matrix spalling and tunnel damage assumptions are made. With energy conservation, static and fracture mechanical analyses, this model investigates the pullout load due to mechanical deformation as well as additional friction caused by bending. Model predictions are compared with the experimental results of hooked fiber pullout data and reasonably good correlation is observed.