In this research, efforts were made to study the effects of water to cement ratio (W/C) and steel fibre volume fraction (V_f (%)) on the fracture parameters of self-compacting steel fibre-reinforced concrete using both Work Fracture and Size Effect Methods. In an experimental program, a variety of water to cement ratio and volume of steel fibres were considered and five mix designs were prepared in two series. In the first, water to cement ratio were altered (Includes values: W/C=0. 42, 0. 52, and 0. 62) with a constant volume of steel fibre (V_f=0. 3%), and in the second, varied volume of steel fibres (Includes values: V_f=0. 1, 0. 3, and 0. 5%) with a constant water to cement ratio (0. 52) were considered. Results have shown that an increase in the water to cement ratio reduces the fracture energy, However, we see a different behaviour in the lower water to cement ratio, while an increase in the volume of steel fibre not only increases the fracture energy causing the concrete to become more ductile, but it can also reduce the size effect greatly. G_F⁄ G_f has been found for all mix designs about 11. 81 and it has been concluded that the work fracture method yields more fracture energy than the Size effect method.

Reinforced concrete with steel fibers has been widely used in concrete and reinforced concrete structures to improve the properties of concrete. The reason for this widespread use is the myriad technical and economic advantages of using steel fibers in concrete bodies. Reinforced concrete with steel fibers includes a concrete body composed of cement, stone materials, water as well as a percentage of short steel fibers that are mixed in a completely randomly and in different directions in the mixture that the presence of steel fibers characterizes the concrete compared to pure Improves. Determining the optimal percentage of fibers is one of the important factors in terms of economics and efficiency of concrete. In this study, to determine the percentage of optimal fibers in different strength classes, 24 mixing designs were prepared and a mechanical laboratory and fresh concrete were performed. The flexural strength of samples containing 0. 9% of steel fibers for categories C40, C50 and C60 was 1. 91, 3. 86 and 5. 14 times higher than the control sample, respectively. Among the self-compacting concrete specimens reinforced with steel fibers, the most optimal mixing design belongs to the specimen in which 0. 9% of steel fibers are used,So that the corresponding compressive strength is equal to 71. 19 MPa. Among the typical concrete samples reinforced with steel fibers, the most optimal mixing design belongs to the sample in which 0. 9% of steel fibers are used,The corresponding compressive strength is 63. 7 MPa.

The application of fiber and nano to improve the performance of concrete is common in the construction industry. In this study, the glass and steel fibers were selected, and their performances were investigated in combination with nano-montmorillonite. The purpose of this paper is to use glass fibers instead of steel fibers with the same strength. For this purpose, the weight ratio of nano-montmorillonite to cement was varied from 0 to 2. 7%, and the weight ratio of fibers to cement was varied from 0 to 4. 5%. Compressive strength tests were performed at the ages of 7, 28, and 90 days, flexural strength and water absorption tests were performed at the ages of 28 days. Nano-montmorillonite has increased the compressive strength of steel fiber concrete by 8 percent and the flexural strength by 15 percent. The influence of nano-clay on the mechanical properties of glass fiber concrete is greater than that of steel fiber concrete. Nano-montmorillonite has increased the compressive strength of glass fiber concrete by 40 percent and the flexural strength by 19 percent. Comparison of the effect of Nano-montmorillonite on the behavior of glass fiber reinforced concrete and steel fiber reinforced concrete shows that nanoclay not only improves the strength of the concrete but also eliminates the strength reduction caused by increasing volume fraction of glass fiber. The compressive and flexural strength tests showed that the optimal amount of steel and glass fibers is 3 percent. The optimum amount of nano-montmorillonite is dependent on the type of fiber and experiment.

In order to select the most suitable concrete for the construction of high-rise buildings, method of analytic hierarchy process (AHP) based on expert knowledge has been used.In this study conducted a series of laboratory works, to compare the effect of steel fibers used in various categories of resistance on concrete behavior parameters. Mixing the samples is set for the three categories of resistance 25, 35 and 45 MPa. Strength parameters that are chosen to identify concrete actions are tensile strength, impact strength, compressive strength and flexural strength. Also the samples in each resistance category are made with four fibers quantity: without fibers, 15, 25 and 35 kg fibers per cubic meter. The results suggest that using of steel fibers, increases the impact resistance, time of the first crack and ultimate strength of concrete significantly. Also the addition of this type of fibers, increases tensile strength and flexuralstrength but don’t have significant effect on the compressive strength of concrete.

Concrete and steel are materials with extensive use in human construction activities. Concrete is a material with high stiffness which is less expensive than other available construction materials, and steel is a material with high strength and ductility. Steel-concrete composite structural systems have been utilized in the construction of high-rise buildings due to their superior structural behavior. Fibrous concrete-encased steel columns are one of the most important composite structural members in which the axial load is carried by the steel and concrete at the same time. These columns are attracting the interest of many researchers due to their excellent structural performance under both static and seismic loading conditions. The steel-concrete interaction enhances the performance when carrying monotonous and earthquake loading. Reinforcing steel fibers help control crack propagation and prevent brittle failure in concrete through improving aggregate interlocking and thus enhance the properties of concrete including the tensile strength and ductility. This paper aims to investigate the axial capacity of fibrous concrete-encased steel composite stub columns. A total of 36 specimens with different cross-sectional shapes of steel profiles, including H-shaped and C-shaped, were tested, and axial parameters and compressive behavior were investigated. The variables of the research included the shape of the steel profile (H-shaped and C-shaped), steel fiber volume ratio (0%, 0. 75%, and 1. 25%), and the stirrup spacing (40, 65, and 130 mm). The results showed that the loading capacity of fibrous concrete-encased steel columns was affected by the shape of the steel profile inside. In this regard, the use of the H-shaped steel profile in the columns led to a higher axial loading capacity than the use of the C-shaped steel profile, due to greater confinement provided by concrete in columns with this section type (H-shape). Moreover, the addition of fibers significantly increased the ductility of these columns in comparison with those without fibers, and also, the addition of fibers increased the axial capacity of the steel-concrete composite columns by 6%. On the other hand, given the results, it is found that the stirrup spacing had a considerable effect on the load-carrying capacity of these columns, in that by increasing the stirrup spacing, due to the lower confinement of the column, the axial load-carrying capacity declined. In this regard, as the stirrup spacing increased, the decline in this parameter reached up to 11% for the columns with the H-shaped profile and 9% for the columns with the C-shaped profiles. Furthermore, the results of this study showed that the specimen with the H-shaped steel sections, 1. 25% fibers, and the stirrup spacing of 40 mm generally were the optimal specimens in terms of the axial load-carrying capacity and ductility in comparison with the other specimens under study. All the specimens had almost similar damage patterns up to their failure. The difference was that the specimens containing fibers experienced failure mainly in the form of the crushing of concrete cover and its breakage from the middle of the column height, due to greater integrity of the concrete structure in these specimens. However, in the specimens without fibers, a considerable portion of the concrete cover was completely detached from the column.

Concrete has the lowest ratio of cost with respect to strength compared to other materials, so it is widely used in construction industry. However, it has some disadvantages, such as low tensile strength and high brittleness, which limit its application in some cases. To improve these negative properties of concrete, adding short discontinuous randomly oriented fibers to the concrete mix is an effective way. Among different types of fiber, steel fibers are used in practice more than others. Steel fibers and concrete form a composite, known as steel fiber-reinforced concrete (SFRC), which has an improved post-cracking behavior compared to plain concrete.In this study, the effect of hooked-end steel fibers on the shear behavior of simply supported concrete beams without stirrups is investigated. Nonlinear finite element method is used to analyze the behavior of specimens under shear. In numerical simulation, the effects of fibers on the tensile strength, compressive strength, compressive and tensile post-peak behavior, and bond between concrete and longitudinal reinforcement are considered. At first, finite element model is validated with experimental data. Then, the e ects of adding steel fibers (0, 0.5, 0.75, and 1 percent) and of beam's height (350, 675 and 915 millimeters) on the average ultimate shear stress are studied.The results demonstrates the considerable effect of fibers on the shear strength. It was observed that adding the maximum amount of %1 percent of fibers can increase the shear strength about 77, 91, and 131 percent in beam having 350, 675, and 915 millimeters height, respectively. On the other hand, the efficiency of fibers depends on the height of the beam. The deeper the beam is, the more efficient the fibers are. Moreover, using fibrous concrete results in more ductile failure having ultimate deflection 3 to 4 times larger than that of plain concrete. Finally, it was understood that using fibers can mitigate well-known size e ect on ultimate shear stress in beams without stirrups.

Fiber reinforced concrete (FRC) has been used widely due to its advantages over plain concrete such as high energy absorption, post cracking behavior, flexural and impact strengths, arresting shrinkage crack.This research discusses the effect of increasing the percentage of polypropylene fiber on flexural toughness and strength of FRC. Three percentages of polypropylene fiber were substituted in 1% steel fiber reinforced concrete (SFRC). Finally, the mechanical properties of three types of hybrid fiber reinforced concretes were compared with each other and with steel fiber reinforced concrete by measuring their flexural toughness and flexural strength. A four-point bending test was adopted to determine the effect of hybrid fibers on crack arresting and post crack behavior.The research results show that the more the percentage of polypropylene fiber which is substituted in SFRC is, the less the amount of energy absorption and flexural toughness with FRC will be.

Concrete is one of the widely consumed building materials in the construction industry, Among the specifications of the concrete which have been paid attention to by the researchers are compressive strength and tensile strength. So, to attain this goal, in the recent years, using a less ratio of water to cement with superplasticizers and natural and or synthetic pozzolans and also with fibers of different materials and specifications in the concrete mixture is a normal method. In this research, the effect of the combined use of fibre microgels and steel fibres on the mechanical properties and durability of concrete has been studied in a laboratory. Fiber microgels include micro-silica (silica fume), polypropylene fibers (pp fibers) and superplasticizers. Consumable steel fibers are 5 cm long and 0.8 mm in diameter with a hooked end. The effect of microgels and steel fibers were each compared and evaluated in five ratios of fibrous microgels 0, 0.5, 1, 2, 5% and steel fibers in ratios of 0, 05, 1, 1.5, 2%. A total of 25 mixing designs were tested for compressive and flexural strength to evaluate mechanical properties. The results of compressive and bending strength tests have shown that by adding different percentages of fibers, the percentage of increase in compressive strength in most of the 7-day samples has improved more than the 28-day samples. The highest resistance growth was related to the samples containing 5% fibrous microgel and 2% steel fibers.