Investigation of flexural behaviour of steel fiber reinforced concrete beams by experimental and statistical methods

Concrete is the most preferred building material today. In the design of structural elements, the resistance of concrete against compressive loads is high. In order to increase its low resistance against tensile loads, to control cracks formed under load and to improve its performance, steel fiber can be added to the concrete mixture. Within the scope of this thesis, the effect of steel fiber addition on the flexural behavior of concrete and reinforced concrete beams under load was investigated experimentally and the experimental results were evaluated statistically. In experimental study, steel fiber length/diameter ratios and steel fiber adding ratio by volume were selected as variables. nine different steel fiber concretes were produced by adding steel fiber 0,5%, 1% and 1,5% by volume and steel fibers have length/diameter ratios of 40, 65 and 80 and a control concrete containing no steel fiber for comparison purpose. So totally ten different concretes were produced. Compressive strength, flexural strength, static modulus of elasticity, dynamic modulus of elasticity, Poisson's ratio and flexural toughness of the concretes were determined experimentally. Steel fiber reinforced concrete beams with under-balance reinforcement ratio were produced from the concretes whose properties were determined. The steel fiber reinforced concrete beams samples were subjected to four-point flexural tests to determine the load-displacement relationships, moment-curvature relationship, fracture energies of the samples. Cracks that occurred in the samples due to load were visually examined. Acording to test results, In steel fiber concretes samples, static elasticity modulus, dynamic elasticity modulus, flexural toughness and Poisson ratio increased with the increase of steel fiber ratio and length/diameter ratios. In steel fiber reinforced concrete beams load carrying capacity increased up to 110,12% compared to the control sample with steel fiber addition. With steel fiber addition, the displacement and fracture energy values increased up to 245% and 605% according to control sample, respectively. Quadratic regression models with high correlation coefficients were created and variance analyses of the experimental results were performed to determine the effect weights of the variables. While length/diameter ratio was the most dominant variable with 77,27% effect weight on the load carrying capacity; binary interaction of the steel fiber ratio and length/diameter ratio was determined as the most dominant variable with 48,1% effect weight on the displacement value. Multi-Objective Optimization study was conducted and the experimental results were estimated with the desirability function that can represent the optimum production criterias and expected results for steel fiber reinforced concrete beams.