To improve the impact resisting performance of reinforced concrete (RC) components, three strengthening designs based on ultra-high performance concrete (UHPC) are proposed in this study. Drop hammer impact test was conducted to evaluate the dynamic response and failure modes of RC beams and UHPC strengthened RC-UHPC beams. Test specimens included two control RC beams, a RC beam with UHPC layer retrofitted on the tension surface, a RC beam with UHPC layers retrofitted on both the compression and tension sides, two RC beams with UHPC layer that was not directly attached to the tension surface, but with 5 mm gap between the interfaces. Test results showed UHPC strengthened beams had a good impact resistance. Under the impact from 641 kg weight dropping from 0.5 m, with a 15 mm UHPC layer directly attached to the tension surface of the RC beam, the crack pattern shifted from concrete spalling to diagonal shear failure, and the maximum and residual displacements decreased by 9.1% and 25.3%, respectively. RC-UHPC beams with non-attached interfaces exhibited even better impact resistance, the UHPC layer was able to develop multiple energy dissipating tensile cracks prior to failure, and the gap ensured a larger moment resistance leading to reduced beam deflections. The repeated impacts were performed on RC-UHPC beams. With the same total impact energy, the single impact was found to be more hazardous than the repeated impacts. Nonlinear finite element modelling was developed to further interpret the experimental results. With the validated numerical model, energy absorption curves, dynamic shear force and bending moment distribution diagrams were derived. Based on the experimental and numerical data, the shear mechanisms of RC beams and RC-UHPC beams were studied. The effects of non-attached spacing length, spacing depth and UHPC layer thickness were investigated in the parametric study.

为了提高钢筋混凝土（RC）构件的抗冲击性能，本研究提出了三种基于超高性能混凝土（UHPC）的加固设计。进行落锤冲击试验以评估 RC 梁和 UHPC 加强 RC-UHPC 梁的动态响应和破坏模式。试验样品包括两根控制 RC 梁，一根在受拉面上加装了 UHPC 层的 RC 梁，一根在受压侧和受拉面上都加装了 UHPC 层的 RC 梁，两根带有 UHPC 层但未直接连接到受拉面上的 RC 梁，但接口之间有 5 毫米的间隙。试验结果表明，UHPC 加固梁具有良好的抗冲击性能。在 641 kg 重物从 0.5 m 落下的冲击下，15 mm 的 UHPC 层直接附着在 RC 梁的受拉面上，裂缝模式从混凝土剥落转变为斜向剪切破坏，最大位移和残余位移分别减少了 9.1% 和 25.3%。具有非连接界面的 RC-UHPC 梁表现出更好的抗冲击性，UHPC 层能够在失效前产生多个耗能拉伸裂纹，间隙确保更大的抗弯矩，从而减少梁的挠度。对 RC-UHPC 梁进行了反复冲击。在总冲击能量相同的情况下，单次冲击比重复冲击更危险。开发了非线性有限元建模以进一步解释实验结果。通过验证的数值模型，推导出能量吸收曲线、动态剪力和弯矩分布图。基于实验数据和数值数据，研究了RC梁和RC-UHPC梁的剪切机理。在参数研究中研究了非附着间距长度、间距深度和UHPC层厚度的影响。