Strategic use of steel fibers and stirrups on enhancing impact resistance of ultra-high-performance fiber-reinforced concrete beams

In order to investigate the static and dynamic flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams, twelve half-scale beams (125 × 250 × 2438 mm) were fabricated and tested under quasi-static and drop-weight impact loading conditions. Four different volume fractions (v_f) of steel fibers, i.e., 0, 0.5, 1.0, and 1.5%, and shear reinforcements were considered as test variables. Force-displacement relations and energy dissipating capacity were derived to evaluate and compare the impact resistance of the UHPFRC beams. The force-displacement curves, excluding inertial effects, were obtained by a proposed process using D'Alembert's dynamic equilibrium principle, and energy dissipating capacity was calculated by integrating the overlapped force-displacement curves of sequential impact tests. Furthermore, the equivalent blast load was converted from the impact force to extend the utilization of impact test results for substituting difficult blast tests on structural specimens. Lastly, the test results indicate that the addition of steel fibers and stirrups enhanced the static and impact resistances of the UHPFRC beams in terms of higher load carrying capacity, higher energy dissipating capacity, and lower maximum and residual displacements. As for specimens without steel fibers and stirrups, brittle shear failure occurred under static and impact loading conditions.