Bond‒Slip Behavior and Pullout Capacity of Bundled Ribbed GFRP Rebars in Concrete

The use of a large number of reinforcing bars in one layer in reinforced concrete (RC) flexural elements can create difficulties for concrete consolidation on-site. Using larger bar sizes instead of smaller bars to provide the same reinforcement ratio is not always a practical solution because of their supply shortage and their lower perimeter, which increases their development and splice lengths. Placing the same reinforcement in multiple layers will reduce the capacity of the RC section in serviceability and ultimate limit states and can add complexity to the bar placement on-site. In such situations, bundling the rebar can be a practical solution. Glass fiber reinforced polymer (GFRP) rebars are used in applications where corrosion of steel rebars in RC structures is of concern. Most of the research on bundled reinforcing bars was conducted on steel rebars. However, there is a lack of knowledge about the bond behavior and anchorage capacity of bundled GFRP bars. This research aims to investigate the effect of bundling on the pullout capacity, bond–slip behavior, and bond strength of ribbed GFRP rebars in concrete. To achieve the objectives of this research, 12 pullout specimens, including 6 individual and 6 bundled GFRP rebars, were cast and tested. The specimens were cast in dimensions of 200 × 200 × 200 and 300 × 300 × 300 mm. Ribbed GFRP rebar of 16 mm (No. 5) and 25.4 mm (No. 8) diameters and 9.5 mm (No. 3) and 12.7 mm (No. 4) diameters were used for individual bar and three-bar bundle specimens, respectively. During the test, the load and slip of the rebar were measured and recorded. The experimental results were analyzed, compared, and discussed in terms of the pullout strength, bond–slip behavior, and failure mode. Based on the experimental results, all the specimens experienced brittle concrete splitting failure. Similar to bundled steel reinforcing bars, the experimental results showed that the equivalent sectional area method provides close predictions for the pullout capacity of bundled ribbed GFRP bars when compared to corresponding individual bars. The bond strength of the bars and concrete increased noticeably as the dimensions of the specimens increased.