High mechanical strength and ductility of fibre reinforced ultra-high performance concrete (UHPC) are beneficial to its loading capacity under static and dynamic loads. To further improve the material performance, especially the crack restraint capability and flexural capacity, hybrid fibre reinforcement in UHPC is investigated in the present study. This study first investigated the influence of hybrid straight steel fibres on the static mechanical performance of UHPC. Four mixtures with single and hybrid fibre reinforcement were developed. Fibres with three different lengths (6, 10, 15 mm) but identical diameter (0.2 mm) and volume dosage (2.5%) were incorporated. Quasi-static compression and flexural tests were conducted on these mixtures. The findings in this study indicated that while longer fibre provided an improvement of both compressive strength and elastic modulus, UHPC with hybrid fibres demonstrated better flexural performance. With notched three-point bending test results, tensile softening curves and fracture energy of UHPC were obtained and discussed. The flexural strength and fracture energy of mixture with hybrid long and short fibre was 21.84% and 20.13% greater than those with single long fibre reinforcement. Subsequently, the dynamic behaviour of UHPC beams (2000 × 168 × 168 mm) with a single and hybrid fibre reinforcement was investigated against low-velocity impact. The impact scenario was modelled with 641 kg drop hammer falling freely to the mid-span of the UHPC beams. The test results showed all specimens exhibited flexural response with minimal damage. The impact resistance of UHPC beams reinforced with hybrid fibres was found better than that with single long fibre reinforcement. The maximum and residual displacement of the mixture with hybrid long and medium fibre was 16.08% and 23.95% lower than that with long fibre reinforcement.

纤维增强超高性能混凝土（UHPC）的高机械强度和延展性有利于其在静态和动态载荷下的承载能力。为了进一步提高材料性能，特别是裂纹抑制能力和弯曲能力，本研究对 UHPC 中的混合纤维增强材料进行了研究。本研究首先研究了混合直钢纤维对 UHPC 静态力学性能的影响。开发了四种具有单纤维和混合纤维增强材料的混合物。包含三种不同长度（6、10、15 毫米）但直径（0.2 毫米）和体积剂量（2.5%）相同的纤维。对这些混合物进行了准静态压缩和弯曲试验。本研究的结果表明，虽然较长的纤维提高了压缩强度和弹性模量，但含有混合纤维的 UHPC 表现出更好的弯曲性能。通过缺口三点弯曲试验结果，得到并讨论了UHPC的拉伸软化曲线和断裂能。长短纤维混合增强的抗弯强度和断裂能比单长纤维增强的高21.84%和20.13%。随后，研究了具有单纤维和混合纤维增强材料的 UHPC 梁（2000 × 168 × 168 mm）在低速冲击下的动态行为。撞击场景是用 641 公斤落锤自由落到 UHPC 梁的跨度中点来建模的。测试结果表明，所有试样都表现出最小损伤的弯曲响应。发现混合纤维增强的 UHPC 梁的抗冲击性优于单长纤维增强。混合长中纤维混合料的最大位移和残余位移比长纤维增强混合料低16.08%和23.95%。