Structural Behavior of Fiber

An indirect J-integral technique for measuring the tension softening curve of non-yielding materials like concrete is presented and is applied to mortars reinforced with various short fiber types (steel and synthetic). The tension softening curve serves to characterize and measure material fracture resistance. The dependence of structural behavior on material fracture resistance is investigated through third-point loading tests on unreinforced fiber mortar beams which fail in flexure and through center-point loading tests on longitudinally reinforced fiber mortar beams without shear stirrups which fail in shear. Conclusive evidence, relating improved structural performance directly to improvements in material fracture resistance due to fiber reinforcement, is presented. Semi-empirical formulae are proposed which relate flexural toughness indices directly to parameters involving just the flexural strength, the splitting tensile strength and the fiber length. Also, semi-empirical design formulae are proposed which relate the ultimate shear strength of longitudinally reinforced beams with fibers as shear reinforcement, to the material fracture resistance (represented by a combination of flexural and splitting tensile strengths), the shear span/effective depth ratio, the longitudinal reinforcement ratio and the beam depth. All proposed formulae are suitable for the purposes of design and quality control. Thesis Supervisor: Dr. Victor C. Li Title: Associate Professor of Civil Engineering