Analytical investigation of axial-moment interaction behaviour of GFRP-RC piles made of high-strength and ultra-high-performance concrete

An analytical investigation into the behaviour of GFRP reinforced fibre-reinforced concrete for pile application using either high strength concrete (HSC) or ultra-high-performance concrete (UHPC) is implemented. The study focused on capturing the behaviour of such members and validating against a series of experimental and analytical results. This was followed by a parametric study to investigate the effects of various parameters influencing the piles’ behaviour. An innovative analytical method was used to determine the maximum strain of concrete based on which it was found that a larger maximum compressive strain of around 0.005 is more suitable for non-conventional concrete such as UHPC. It was shown that depending on the properties of the cross-section, using a strain of 0.003 instead of 0.005 can result in overly conservative designs or in some situations even unsafe design. For lower ranges of reinforcement ratios, this increased compression strain capacity can result in transition from compression-controlled to tension-controlled mode of failure, making the design unsafe if lower strain values are assumed. For larger reinforcement ratios, assuming a strain of 0.003 results in an underestimation of the capacity. The findings of this study will contribute to a better understanding and design of GFRP-RC piles using non-conventional concrete. Recommendations were provided to enhance the design of these structural members.