The demand for resilient materials in impact-prone structures has increased interest in UHPC reinforced with steel fibers. Known for its strength and energy absorption capacity, UHPC is a promising construction material that can be used under dynamic loading. However, a lack of tensile data at high strain rates (>100 s⁻¹) limits the development of predictive models and safe structural design. This study addresses this gap by investigating the strain-rate-sensitive tensile behavior of UHPC reinforced with smooth (SF) and hooked-end fibers (HF), using direct tension tests across a wide strain-rate range (quasi-static to ∼200 s⁻¹). Results demonstrate that, while matrix strength controls the first peak stress, fiber geometry governs post-cracking behavior, energy dissipation, and ductility. UHPC SF achieved up to 35 % higher second peak loads and 18–22 % greater dynamic toughness than UHPC HF, reaching 674 kJ/m³ at 195 s⁻¹. In contrast, UHPC HF reached higher maximum peak loads (up to 32 kN) and more stable first-peak responses, but suffered abrupt post-peak stress drops, with toughness values limited to ∼572 kJ/m³. At higher strain levels, UHPC SF benefited from its uniform fiber distribution and frictional pull-out, while UHPC HF relied on mechanical anchorage that was less effective beyond ∼100 s⁻¹. The Dynamic Increase Factor (DIF) for peak load ranged from 2.7 to 4.2 for UHPC HF and from 3.3 to 3.9 for UHPC SF, significantly exceeding by up to 40 % the typical DIF range (1.5–3.0) reported for conventional concretes. Ultimate strain reached up to 4.5 % at 195 s⁻¹, with UHPC SF exhibiting a more stable strain evolution, while UHPC HF showed sudden cracking and steeper load drops. This behavior highlights the crucial role of fiber bridging in absorbing high-velocity impacts. This comprehensive experimental campaign also supported the calibration of a numerical simulation by the Concrete Damage Plasticity (CDP) model with strain rate dependence, which reproduced the key post-peak features of both UHPCs and predicted peak loads with less than 8 % deviation across the entire strain-rate range, including interpolated intervals lacking direct experimental data. Numerical predictions aligned with experimental DIF trends, confirming the robustness of the model for dynamic tensile loading. In addition, the predictive model for DIF captured experimental behavior across all strain-rate ranges, confirming its applicability for UHPC under extreme dynamic loading. This integrative approach, combining mechanical characterization and numerical modeling, advances the understanding of mechanical behavior and damage evolution under dynamic tension, providing a foundation for more reliable design strategies in UHPC structures subjected to extreme loading scenarios.
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