Fiber and engineered cementitious composites (ECC) hollow sections for structural members

Experimental and analytical works were conducted in this study. Both focus on the flexural behavior of hollow beams. Two types of concretes were investigated, steel fiber-reinforced high strength concrete and engineered cementitious composites (ECC). The experimental work of this research is composed of three parts. In the first, the materials properties including the basic mechanical tests in addition to the flexural performance and fracture behavior were investigated. The second experimental part investigated the flexural behavior of steel fiber-reinforced high strength solid and hollow beams. The load-deflection behavior, cracking pattern and failure type, ductility, toughness and stiffness were among the beam bending test results. The hole cross-sectional size reduction (16, 28.4 and 44.4 %) and the steel fiber volumetric content (0, 0.5, 1.0 and 1.5%) were the main variables, while other variables such as the tension and shear reinforcement ratios, the effective shear span ratio and hole shape were also investigated. The third experimental part consists of casting and testing of solid and hollow ECC reinforced beams. The parameters investigated using the ECC beams are the cross-sectional size reduction (16, 28.4 and 44.4 %) and the type of fiber. Three types of synthetic fibers were used, which are the nylon monofilament, polyvinyl alcohol and polypropylene. The analytical part of the thesis focused on the strength sectional analysis of the tested beams. The test results showed that the flexural behavior of steel fibrous beams was superior to that of beams without fiber. The best enhancement in load carrying capacity was recorded for the 1.5% fiber content for both solid and hollow beams. For the same beams, the ductility indices of hollow beams with size reductions of 16% and 28.4% were approximately 15 to 24% higher than that of solid beam, while that of 44.4% recorded a ductility index that is quite comparable to that of the solid beam. It was also noted that hollow beams with size reductions up to 44.4% were tougher than solid beams when 1.0% steel fiber was included. Using the strength formulas introduced in this study, good agreement was found between the predicted and experimental cracking and peak loads. For the ECC beams, it was recorded that hollow beams with cross-sectional size reductions of 0.16 and 0.28% retained higher cracking and ultimate loads and noticeably higher ductility compared to solid beams.