Numerical investigations on the performance of ultra-high performance concrete (UHPC) subjected to projectile impacts have attracted extensive attention, but there are still deficiencies in the accuracy and computational efficiency of related simulation methods. To make up for these deficiencies, a mesoscale equivalent model for UHPC is developed to simulate the response of UHPC under projectile impacts. In this model, an equivalent treatment is conducted on steel fibers to reduce their quantity under the premise that the interfacial shearing force between the fibers and the matrix remains equal. Based on the mesoscale equivalent model, numerical simulations of uniaxial compressive tests and projectile penetration tests on UHPC specimens are performed in LS-DYNA, and the numerical results are compared with the corresponding experimental results to verify the developed model. It is found that the mesoscale equivalent model could accurately reproduce the failure mode and stress-strain curve of UHPC specimens when the amplification factor of steel fibers is lower than 5. When the amplification factor is 5, the computational efficiency of the numerical models for penetration tests is significantly improved, and the maximum relative error between the numerical results of the crater diameter and penetration depth and experimental results is 11.7%. The successful application of the mesoscale equivalent model provides a more precise and in-depth perspective in simulating the response of UHPC with steel fibers subjected to projectile impact. Then, the influence of projectile striking velocities, UHPC compressive strengths, and volume percentages of steel fibers on the depth of penetration (DOP) are further numerically assessed. Based on the simulated data, modifications of the Young equation for predicting the DOP are conducted, and the maximum relative error of the modified equation is 13.9%. This demonstrates that the modified Young equation can accurately predict the DOP of UHPC subjected to projectile impacts.

Ultra-high performance concrete (UHPC) has a promising application in resisting projectile penetration due to its excellent mechanical properties. In the present study, a three-dimensional equivalent model of UHPC was developed to simulate the dynamic response of UHPC with steel fibers when subjected to projectile impact. The reliability of the numerical model developed in this paper was verified by uniaxial compression tests and projectile penetration tests on UHPC specimens. The results showed that the failure mode, stress-strain curve, depth of penetration (DOP) and crater diameter of the specimens were consistent with the experimental results. To further investigate the impact resistance of UHPC, the effects of projectile impact velocity, UHPC compressive strength and volume content of steel fibers on DOP were investigated by numerical modeling. The Young's equation for predicting DOP was modified, and the modified equation could accurately predict the DOP of UHPC subjected to projectile impact. The successful application of the equivalent model provided a more accurate and in-depth perspective for simulating the response of UHPC containing steel fibers subjected to projectile impact.