Concrete damaged plasticity-based numerical study of flexural, shear and cyclic behaviour of ultra-high-performance fibre-reinforced concrete beams with high-strength steel

Ultra-high-performance fibre-reinforced concrete (UHPFRC) has attracted increasing attention for earthquake-resistant structures due to its high strength, crack control and energy dissipation capacity. However, the combined influence of steel fibre content and high-strength steel (HSS) reinforcement on the cyclic–flexural–shear behaviour of UHPFRC beams remains insufficiently understood. In this study, a numerical framework is presented coupling a Matlab-based random fibre distribution model with the concrete damaged plasticity (CDP) approach implemented in Abaqus. The proposed model was validated against experimental results reported by Pourbaba and co-workers and by Kodur and co-workers, demonstrating less than 8% deviation in peak load predictions. A parametric investigation was then performed to assess the effects of compressive strength, fibre volume fraction and reinforcement ratio under monotonic and cyclic loading. The results indicate that increasing the fibre content to 4% enhances load capacity by approximately 20% and energy absorption by about 24%. Beams reinforced with HSS exhibited improved ductility, reduced stiffness degradation and superior energy dissipation under cyclic loading. The numerical framework effectively captures the flexural, shear and cyclic responses of UHPFRC beams, providing a reliable basis for performance-based design and optimisation of UHPFRC–HSS structural elements.