A Master of Science thesis in Civil Engineering by Yousef Ayman Awera entitled, “Compressive Behavior of Slender Circular Columns with Double GFRP Spirals and Bars”, submitted in April 2021. Thesis advisor is Dr. Mohammad AlHamaydeh. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Despite the recent research efforts and developments, many building codes and standards, e.g. ACI 440.1R-15 and CSA S806-12, recommend ignoring Fiber Reinforced Polymer (FRP) reinforcement in design for compression. This research investigates the feasibility of utilizing Glass Fiber Reinforced Polymer (GFRP) rebars as compression and confinement reinforcement in slender circular RC columns, subjected to concentric loading. A group of 18 circular columns are instrumented and tested to failure in axial compression. The specimens’ reinforcements (longitudinal bars and spirals) were mainly arranged in double layers and compared to single layer control counterparts. The double-layer longitudinal reinforcements were all-GFRP, all-steel, or hybrid (outer GFRP layer and inner steel layer). The slenderness ratio of all columns is 38.5, made of 21 MPa concrete. The investigated parameters included: reinforcement type (steel/GFRP), ratio, and configuration (single/double-layer); spiral pitch and diameter. Upon conclusion, it is found that substantial improvements to confinement and ductility levels are directly associated with double-layer configurations. This cannot be achieved unless the recommended maximum spiral pitch (75 mm) is maintained. At higher pitch values, the double-layered hybrid columns outperformed their all-GFRP counterparts. This could be attributed to the greater confinement provided by the higher modulus of elasticity of the inner steel reinforcement and the additional concrete volume surrounding it, thus minimizing the potential for rebar local buckling. Moreover, at constant volumetric reinforcement ratios, smaller diameter spirals at smaller pitches greatly outperform larger diameters at higher pitches. Furthermore, when the 75 mm pitch limit is maintained, single and double-layer GFRP specimens successfully achieved higher strength, confinement, and ductility compared to their steel or hybrid counterparts. Reliable performance of the GFRP reinforcement in compression is demonstrated in this experimental study. It may be attributed to substantial improvements achieved in GFRP quality and manufacturing processes. Future studies are expected to provide further confirmation that GFRP reinforcement can be reliably used in compression design.