Effectiveness of Glass Fiber-Reinforced Polymer Stirrups as Shear Reinforcement in Glass Fiber-Reinforced Polymer-Reinforced Concrete Edge Slab-Column Connections

Recent years have seen a great interest in testing concrete slab-column connections reinforced with glass fiber-reinforced polymer bars (GFRP-RC). Yet, current fiber-reinforced polymer (FRP) codes and guidelines have not addressed the design of slab-column connections with FRP shear reinforcement. Results from an experimental investigation aimed at evaluating the effectiveness of glass fiber-reinforced polymer (GFRP) stirrups as shear reinforcement in edge slab-column connections reinforced with GFRP bars are presented. Four full-sized slabs with and without stirrups as shear reinforcement were tested to failure under combined vertical load and unbalanced moment. The effect of the GFRP stirrup type and extension on the punching shear response of the tested slab-column connections are analyzed and discussed. In addition, simplified design provisions to predicate the ultimate shear capacity of the tested specimens are proposed. The test results revealed that the presence of GFRP shear reinforcement as either closed or spiral stirrups within the slab around the column perimeter improved the punching-shear response of the tested connections. The results also indicated that the performance of the spiral stirrups was equivalent to or better than that of the closed stirrups in reducing the brittleness of the tested specimens with the same amounts of flexural and shear reinforcement. The proposed design provisions as extensions to those in CSA S806 design code yielded good, yet conservative predictions with an average V-test/V-pred of 1.28 +/- 0.24 for test specimens with FRP shear stirrups, as well as others with different types of FRP shear reinforcement found in the literature. This represents a step forward for engineers in designing two-way concrete slabs reinforced with FRP stirrups.