Cyclic behaviour of an innovative cap beam to column pocketless connection in GFRP-RC precast structures

This study examined the cyclic performance of innovative connection details for precast cap beam-to-column connections reinforced with glass fibre-reinforced polymer (GFRP). It aims to address the shortcomings identified in the performance of the previously examined pocket connections, where premature failure around the pocket was the governing failure mode, subsequently led to a reduced capacity. Three pocketless specimens were cast and assembled using epoxy resin and bolts/bars as connecting reinforcement in ducts (epoxy duct connection). Epoxy resin was used for its non-shrinkage properties and high early strength which can contribute to the acceleration of the construction process. A unique test setup that represents the cap beam-column connections in real-life scenarios where the beam at the joint end is free to rotate was used. The cyclic performance in terms of hysteresis behaviour, energy dissipation, stiffness, and residual drift was evaluated, and the results were compared to those of pocket connections. The test specimens exhibited a concrete failure at the column region away from the column end, indicating a strong connection with no sign of failure/slippage of the GFRP reinforcement. The proposed pocketless connection outperformed the pocket one, achieving a greater lateral capacity of 48%. It has the potential to prevent premature failures observed in pocket connections, relocating the failure from the connection region to the column. Additionally, the proposed epoxy duct connections dissipate more energy than the pocket connection and exhibit a low stiffness degradation rate with fewer residual deformations. This study concluded that the epoxy duct connection using epoxy resin and connecting reinforcement in ducts can be effectively utilized to assemble GFRP-RC precast structures with proper integrity of precast elements. The findings of this research can be used to accelerate the construction of GFRP-RC elements in aggressive environments, particularly in structures located in coastal regions, such as jetties.