Shear Behavior of Macro-Synthetic Fiber-Reinforced Concrete Panels

Abstract

Macro-synthetic (polypropylene or polyolefin) fibers are often added to concrete mixtures as secondary reinforcement, designed to control shrinkage and temperature cracks. The contribution of these fibers to the strength of structural elements and the interactions and synergies between distributed fiber and deformed bar reinforcement are not well understood. This research investigated the behavior of macro-synthetic fiber-reinforced concrete panels subjected to in-plane shear stresses. Twelve panel specimens were tested using the Panel Element Tester located in the Structure Engineering Testing Laboratory at the University of Washington. The panel specimens varied in their transverse reinforcement ratio (ranging from 0% to 1.1%) and fiber content (ranging from 0% to 0.5%). Additionally, companion specimens were cast and tested alongside each panel to determine material properties, including compressive strength, modulus of elasticity, and flexural toughness and strength. The results of the tests showed that macro-synthetic fibers, at the dosage rates used, were effective at reducing both the average and maximum crack widths observed throughout testing. Generally, the addition of fibers led to finer, more distributed cracking in the panel specimens and no significant change to the panels’ shear strengths. Comparisons to existing empirical shear equations from the literature showed overestimations of shear strength in panels containing no transverse reinforcement and tended toward more accurate estimates as the reinforcement ratio increased. In the larger project, the experimental data that was collected will be used to develop rational design guidelines for the shear strength of members that contain both macro-synthetic fibers and transverse deformed bar reinforcement.