This study presents the performance of carbon textile reinforcement used as strengthening layers for reinforced concrete (RC) slabs under repeated impact loads. In order to reveal the contribution of carbon textile reinforcement to the behavior of RC slabs under impacts, five identical RC slabs with the dimensions of 1.5 m × 1.5 m × 0.20 m were manufactured and tested at the Technische Universität Dresden. To understand failure mechanisms of RC slabs under impact loadings, two specimens were kept unstrengthened and tested under different impact velocities. The rest of the specimens was strengthened with three different carbon textile reinforcements embedded in an additional 2 cm fine‐grained concrete layer and subjected to impact loads with the same striker velocity. The results observed from the tests revealed that the carbon textile reinforcement is very effective at increasing the impact capacities of the specimens. Additionally, displacement–time histories and crack profiles are highly affected due to the carbon textile reinforcement types and ratios during the impact loadings.

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In this study, effects of steel fibers on the bending behavior of reinforced concrete beams of varying longitudinal reinforcement ratios and without stirrups are investigated experimentally and analytically. In the experimental work, two groups of simply supported beams of low and high longitudinal reinforcement ratio were manufactured. Each group had 0%, 0.5%, 1.0% and 1.5% steel fiber ratio in volume. Eight beams were tested under a load applied at midspan. In the group with lower longitudinal reinforcement ratio, steel fibers increased the bending capacity by almost 50%. However, since deformations were concentrated on a single crack, longitudinal reinforcement has ruptured and the beams could not displace as much compared to the one without steel fibers. In the group with higher longitudinal reinforcement ratio, steel fibers acted like stirrups and changed the brittle shear failure mode to a ductile bending failure. Although increasing the steel fiber ratio affected crack distributions, it did not cause a significant difference in the behavior. When analytically modeled using a common model that assume constant tensile stress at crack, computed bending capacities were lower than actual, although on the safe side. More precise models that relate tensile stresses to the crack width could give better estimations.

Eight slabs with two different longitudinal reinforcement ratios and varying steel fiber ratios were tested  Steel fibers increased the ultimate load capacity for all slabs  Contribution of steel fibers to the displacement capacity was more significant for slabs with higher longitudinal reinforcement ratio Addition of steel fibers in concrete mixture is known to increase the punching resistance of slabs. There are numerous studies, both analytical and experimental, in the literature investigating the effects of steel fibers on the punching behavior of steel fiber reinforced concrete slabs. Figure A. Load-displacement curves for slabs Purpose: This study is concentrates on the effects of steel fibers on the punching behavior of reinforced concrete slabs with different longitudinal reinforcement ratios. Experimental studies on the subject were usually performed with either no or constant longitudinal reinforcement. This study aims to investigate the coupling effects of steel fibers with varying longitudinal reinforcement ratios. Theory and Methods: Reinforced concrete slabs in two groups, having 0.004 (D1 series) and 0.002 (D2 series) longitudinal reinforcement ratios in two orthogonal directions, were cast with concrete mixes containing 0%, 0.5%, 1% and 1.5% steel fiber ratios in volume. Slabs were 2150x2150x150 mm in dimensions. Eight slabs were tested in total under static loads applied at their midpoints. An analytical study of the test specimens were also performed using Critical Shear Crack Theory and based on comparisons of experimental and analytical results some improvements in the model were proposed. Results: For slabs without steel fibers, the slab with higher reinforcement ratio showed punching failure before the yielding of longitudinal bars, whereas the slab with lower reinforcement ratio displayed a significantly higher ductility before final punching failure. Addition of steel fibers increased the punching load capacity up to two times. However, although addition of steel fibers also increased the maximum displacements in D1 series slabs, it did not make any significant effect on the maximum displacements of D2 series slabs. Maximum displacements were still controlled by the yielding of longitudinal reinforcement. Increasing the steel fiber ratio increased both the punching capacity and the maximum displacements in D1 series slabs, but it did not make a significant difference in behavior of D2 series beyond 1% fiber ratio (Figure A). Conclusion: Role of steel fibers on the behavior of slabs is dependent on the longitudinal reinforcement ratio. For slabs with low reinforcement ratio, steel fibers increase the load capacity but do not have a significant effect on the displacement capacity since displacement capacity is still controlled by the yielding of the longitudinal reinforcements. For slabs with high reinforcement ratio, which do not show yielding before punching, steel fibers increase both punching capacity and displacement capacity. Increased punching capacity in these slabs allows yielding...