Experimental Study on the Impact Resistance of Steel Fiber Reinforced All-Lightweight Concrete Beams under Single and Hybrid Mixing Conditions

An impact action can cause local, or even overall, damage to structural components. This paper investigates the effect of flat and wavy steel fibers on the mechanical impact resistance of all-lightweight concrete beams under single and mixed conditions. Four all-lightweight concrete beams were subjected to drop hammer impact tests. From the failure mode, local shear-type damage occurred at the midspan of the all-lightweight concrete beams, with mainly shear cracks. The steel fiber has an inhibitory effect on the generation and development of cracks and improves the phenomenon of concrete crushing and spalling after the impact of the beam. Different mixing methods will have different effects on the crack-inhibition effect of steel fiber. The mixed addition of steel fiber has a more prominent effect on crack-development inhibition, making the cracks finer. Under the conditions of adding the flat steel fibers alone, the wavy steel fibers alone, and the mixed addition of steel fibers, the peak displacement at the midspan was reduced by 14.29%, 22.86%, and 37.14%, respectively; in comparison, residual displacement was reduced by 18.18%, 50.91%, and 54.55%, and the peak impact force was increased by 6.98%, −2.62%, and 1.89%. In addition, the stiffness loss of the steel fiber-added specimens is slight, which can have a higher impact response when the drop hammer falls. The results show that the addition methods of the steel fibers have different effects on the improvement of the impact resistance of the all-lightweight concrete beams, and the mixed addition has a better effect than the single addition.

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