Structural Behaviour of Spliced GFRP-RC Piles Subjected to Combined Axial Load and Biaxial Bending

The increasing demand for durable and corrosion-resistant structural systems in marine environments has motivated the development of advanced splicing techniques for precast concrete piles (PCPs). This study presents an experimental investigation on spliced PCPs reinforced with glass fibre-reinforced polymer (GFRP) subjected to combined eccentric axial loading and cyclic flexural loading. A total of seven piles were designed, manufactured, and tested, including five spliced ones (where epoxy and dowels were used to connect the segments), as well as two continuous (unspliced) ones as control specimens. The test parameters included dowel size, embedment length, dowel arrangement, and the level of eccentric axial loading. The results indicate that all spliced piles exhibited lower flexural capacity than the unspliced ones. However, increasing the embedment length of the spliced piles from 18.75 dowel bar diameters ( d ) to 30 d enhanced the load-carrying capacity from 56% to 80% of that of the unspliced piles. The embedment length of 30 d provided full bond development and failed through compression-controlled mode of failure in the compression zone of the splice section, without evidence of dowel slip. However, a reduction in strength was observed, which was attributed to the relatively low elastic modulus of the epoxy and slight movement of the dowels within the ducts. Conversely, inadequate embedment lengths of 18.75 d and 20 d resulted in premature bond slip, localized spalling, joint opening and stiffness degradation of up to 55%-65%. Moreover, piles subjected to out-of-plane eccentricity exhibited approximately 5% and 14% reduction in strength and stiffness compared to their counterparts under concentric loading. In addition, an analytical method was applied to predict the axial load and biaxial moments interaction behaviour to evaluate the accuracy of the current methods. The comparison showed that the analytical predictions were consistently conservative, with experimental capacities exceeding analytical estimates by approximately 13%-15% for both spliced and unspliced piles, except in spliced piles with insufficient splice length where premature bond deterioration resulted in large capacity reduction. The findings of this paper contribute to a better understanding of the behaviour of epoxy-FRP dowel connections in piles and support their practical implementation in precast concrete.