Compression lap splices of GFRP bars in reinforced concrete columns
Other titre : Étude sur le recouvrement (ou le chevauchement) de barres longitudinales en PRFV dans des colonnes en béton sous charge axiale
Tabatabaei Kashani, Amirhomayoon
Corrosion of concrete structures reinforced with steel bars is a concern in regions where weather condition is harsh. Fiber-reinforced-polymers (FRP) reinforcement has proven its feasibility through different civil structural elements as an alternative reinforcement to overcome corrosion. Recent advances in the applicability of GFRP reinforcement in axially loaded members has lightened the need for further investigation into detailing of GFRP bars under compression. Due to the lack of experiments, present guidelines for FRP structures have not yet addressed this issue. This research takes charge of providing experimental database as well as extensive analyses and design recommendations to estimate the required splice length of GFRP reinforcement under compression for concrete columns. A total of thirty large scale circular RC specimens were fabricated and tested experimentally under concentric axial load. The 300 mm diameter columns with total height of 1600 mm were designed according to CAN/CSA S806-12 (2012) code requirements. The specimens were divided into four series; series I contained three columns reinforced with steel bars and one plain concrete column. Series II contained seven specimens internally reinforced with GFRP bars, while series III included nine specimens with different amount of transverse reinforcement. Series IV is comprised of ten columns reinforced with different longitudinal reinforcement ratio. The test variables were bar type (steel and GFRP), spacing of transverse reinforcement (40 mm, 80 mm, 800 mm), bar diameter (#5, #6, #8) and splice length as a factor of bar diameter (0, 4, 8, 12, 24, 36). The experimental results were reported in terms of failure modes, load displacement behavior and the components of splice strength. Based on the findings of experimental investigation, the splice length of GFRP bars is much less than that of steel bars. It was found that the specimens reinforced with spliced bar at a specific splice length can behave the same as those reinforced with continues longitudinal bar. The use of condensed GFRP spirals (spacing at 40 mm) provided sufficient restraint against the buckling of the spliced GFRP bars up to the limit of concrete crushing in the post peak stages. The well confined specimens were also able to achieve the second peak load at a specific splice length. The results revealed the splice strength is comprise of end bearing and bond stress. Both components were evaluated precisely, and effect of variables on these components were determined. Despite spliced steel bars, end bearing stress has a prominent role in the strength of spliced GFRP bars. An analytical model capable of predicting the required splice length, was developed and verified with the experimental results. Moreover, a simplified design equation was presented including the effect of bar diameter, transverse reinforcement, elasticity modules of GFRP reinforcement and compressive strength of concrete. This equation accurately and simply predicts the required splice length.