Recently, fiber has been incorporated into concrete mixtures, where its distribution in the concrete matrix helps to improve and enhance the mechanical properties of fiber-reinforced concrete (FRC). The aim of this study is to investigate the influence of steel and synthetic fiber parameters, along with different coarse aggregate maximum sizes (CAMZs) on FRC performance. Additionally, in past research, the empirical relationships among the compressive, tensile, and flexural strengths of plain concrete and FRC were assessed, and correlations between these mechanical properties of FRC were examined. For each CAMZ, four fiber dosages for each fiber type were considered. The results demonstrate the mechanical properties of FRC enhanced as the fiber length increased from 13 mm to 60 mm, the CAMZ increased from 9.5 mm to 37.5 mm, and the ratio of the fiber length to the CAMZ was in the range of 0.35–5.68. All mixtures have been intended to exhibit similar compressive strengths; however, the synthetic/steel fiber advanced the brittleness ratio of specimens with G10, G19, and G38 to approximately 36.8%, 40.7%, and 47.4% greater than the contral specimens, respectively. In addition, from the regression analysis investigation, there are strong correlations from the regression analysis of the mechanical property results of FRC.

Fiber-reinforced concrete is widely acknowledged for its ability to resist cracking effectively and limit its propagation. By preventing cracks from spreading, the addition of fiber composites to concrete can enhance its extensibility and tensile strength, not only at the initial point of cracking but also at its maximum capacity. Additionally, the fibers in fiber-reinforced concrete are capable of binding the matrix, even when exposed to significant cracking. However, there is limited information available about the behavior of fiber-reinforced concrete under a bending moment combined with torsion. This study aims to investigate the structural behavior of fiber-reinforced concrete members subjected to a bending moment with a torsion to moment ratio equal to 1. Synthetic and steel fibers of 1.0% content with different lengths (19, 35, and 55 mm for synthetic fiber and 13 mm for straight and hook steel fibers) were mixed with concrete mixtures to examine the effects of fiber lengths and types on the concrete beam performance. Test results indicated that the fiber-reinforced concrete beams showed higher cracking moments than the normal-strength concrete beam. The steel fiber with a hooked configuration reinforced beam showed increased moment capacity and total torsional toughness higher than that of the straight steel fiber-reinforced beam. The synthetic fiber of a 55 mm length reinforced beam exhibited the highest first-crack and ultimate moment values among other tested beams. The test results were compared with past research models for the moment capacity of beams under the compound effect of bending and torsion and we modified these values with another factor that represented the fiber length influence on beam capacity, as suggested in past research. The comparison between the ultimate moment of the test results and the moment predicted from the modified past research model presented a good correlation.

Over the past few decades, numerous studies have explored the use of steel fiber (SF) as an alternative to transverse reinforcement rebars in reinforced concrete beams, either partially or completely replacing them. However, there are limited studies that have investigated the effect of fiber dosage and length on reinforced concrete beam performance under torsional loads without the use of transverse reinforcement rebars. In this study, experimental investigations were conducted to examine the performance of reinforced SF concrete beams subjected to torsional load, utilizing SFs as a complete substitution of transverse reinforcement rebars. Ten different concrete mixes with varying dosages of SFs, namely 0%, 0.5%, 1.0%, and 1.5%, were examined while maintaining the same aspect ratio for fiber length and diameter. The results revealed that the addition of SFs in the concrete mix had an impact on its properties, reducing workability but increasing flexural, tensile, and compressive strengths. By incorporating 1.0% of SFs in the concrete mix, the missing torsional strength resulting from the absence of stirrups was adequately compensated. Moreover, the presence of SFs significantly influenced the ductile behavior beyond the point of cracking in the tested beams. Hence, it is recommended that SFs are incorporated with dosages of 1.0% and 1.5% in the concrete mixture, particularly for beams subjected to torsion, as a viable substitute for stirrups.

Structural engineers have used V-shaped columns based on technical requirements. The inclination of the V-shaped column underlines the individual purpose of the base floor. However, there is no any specification or guidance on the design of V-shaped columns to date. The aim of this study is to investigate the behavior of V-shaped reinforced concrete columns with three angles between columns (30°, 60°, and 90°) in order for the results to be used in the design and analysis of the V-shaped column. The impact of using a 1.5% dosage of micro-straight-steel fiber (MSSF) in the concrete mixture was also studied. The results showed that the V-shaped column with 30°, regardless of the concrete type (with and without MSSFs), exhibited crushing at legends when the sample reached the ultimate load, while no cracks occurred at the legends during the test for the other V-shaped columns. Upon increasing the angle of inclination of the V-shaped columns, the ultimate load capacity was decreased by 24%, 23%, and 20% for V-shaped columns with 30°, 60°, and 90° angles of inclination, respectively. The addition of MSSFs in the concrete significantly improved the ultimate axial load and the bending moment compared to the reference specimens with the normal reinforced concrete (NRC). The steel-fiber-reinforced concrete (SFRC) vertical column specimen demonstrated the highest increase in axial load, and the other SFRC V-shaped and flexural specimens showed a minor increase compared to the NRC specimens.

This study investigates the torsional performance of reinforced concrete beams with transverse circular openings and examines methods to mitigate the detrimental effects of these openings using Ultra-High-Performance Concrete (UHPC) and diagonal reinforcement. The experimental component involved casting and evaluating eight beams with dimensions of 150 × 200 × 1200 mm under pure torsion. Among these, two beams were solid (without openings), one was made from normal-strength concrete (NSC), and the rest were cast with UHPC. The beams with openings were categorized into two groups based on the size of the openings—small and large. Each group comprised three beams: the first was cast from NSC and included diagonal reinforcement, the second from UHPC with diagonal reinforcement, and the third from UHPC but without diagonal reinforcement. Results indicated that all beams with openings cast from UHPC exhibited a substantial increase in ultimate torque compared to the control NSC solid beam. NSC beams with small openings showed a marginal decrease in ultimate load capacity by 1.47%, whereas those with large openings experienced a significant reduction of 17.65%. UHPC effectively compensated for the strength lost due to the absence of diagonal reinforcement in both small and large openings. Initial stiffness in NSC beams decreased by 19.4% and 70.1% for small and large openings, respectively. Conversely, UHPC beams demonstrated improved initial stiffness, with increases of approximately 64% for small and 34% for large openings. This study proposes ultimate torsional equations for UHPC beams with various opening sizes. These equations are validated by comparing them with results from previous experimental research, examining the performance of UHPC beams with and without openings.

Flat slabs supported by columns without beams are widely used in construction owing to their economy and efficiency. However, brittle punching shear failure at slab–column connections can cause progressive collapse. UHPC has a higher tensile strength than NSC and, when appropriately reinforced with steel fibers, exhibits strain hardening after initial cracking. These properties make Ultra-High-Performance Concrete (UHPC) ideal for durable, thin, low-cost bridge decking and heavily loaded elements and an excellent choice for improving slab–column connections that have experienced punched shear failure. This study explores the impact of UHPC layers on the punching shear behavior of reinforced concrete slabs. Sixteen slab specimens were tested with variations in UHPC layer thickness, placement, and column shape. Results demonstrate that incorporating UHPC layers significantly enhances punching shear resistance, increasing ultimate load capacity by 27–91% compared to reference specimens. Notably, thicker UHPC layers (75 mm) and bottom-placed layers exhibited superior performance in terms of ductility and toughness. Square columns outperformed circular ones in resisting punching shear. Additionally, thicker layers reduced initial stiffness, while debonding issues in 25 mm layers adversely affected structural performance. This research provides valuable insights for optimizing UHPC configurations to improve the punching shear resistance of concrete slabs, offering promising solutions for high-load structures in modern construction.