Numerical study on impact resistance of NC–UHPC composite beam

Ultrahigh-performance concrete (UHPC) has become the most promising high-performance material, and has achieved excellent application in the field of impact and explosion protection engineering. Normal reinforced concrete (NC) beams subjected to impact load are prone to local punching shear failure. However, although the impact performance can be improved using UHPC beams, their application is limited by high costs. To achieve impact resistance at a lower cost, this work proposes a design scheme for locally replacing and wrapping NC beams with UHPC, with the aim of improving the impact resistance of NC beams. In this study, differing research conditions were employed (NC, UHPC, and NC–UHPC composite beams), and the impact resistance of specimens was compared and analyzed. Numerical models of NC and UHPC beams under impact loads were first established to verify the reliability of the modeling method, which is contact method, load application, initial velocity, boundary conditions, etc. The NC, UHPC, and NC–UHPC composite beam models were then established, and the impact performances of different NC–UHPC beam combinations were analyzed. The results revealed that compared with NC beams, the UHPC local replacement scheme effectively avoided local punching shear failure of beams. Under impact load, bending and shear cracks occurred on both sides, and the damage degree on both sides decreased with the increase of the local replacement length. For the UHPC wrapping, the failure mode of the beam changed from punching shear failure to bending failure. With an increase in UHPC thickness, the damage degree of the beam span increased, and it gradually reached that of the pure UHPC beam. Furthermore, both schemes effectively reduced peak displacement and residual displacement in the mid-span. Compared with the UHPC wrapping scheme, the peak displacement and residual displacement in the mid-span of the UHPC local replacement beam were reduced, and the mid-span bearing capacity was improved. Thus, we recommend that a local replacement length of more than twice the beam height should be selected to avoid the occurrence of local punching shear failure.