Experimental and Nonlinear Finite Element Simulation of Compressive Behavior in Natural FRP-Concrete-Steel Double-Skin Rectangular Tubular Columns

Abstract

This study addresses the research gap regarding using natural fibre-reinforced polymers (FRPs) to construct hybrid Double-Skin Tubular Columns (DSTCs). Experimental testing on twelve rectangular specimens revealed critical failure mechanisms primarily due to the rupture of FRP tubes under excessive stress. This rupture led to the loss of lateral support for the concrete, resulting in severe crushing and localized buckling of the inner steel tube. The experimental results also showed an 18% increase in axial stress and 18 times enhancement in axial strain within confined concrete specimens compared to unconfined concrete specimens because of the effective confinement provided by the outer natural FRP tube (hemp fibre). By integrating experimental and nonlinear finite element simulations, this study highlights the structural performance of these hybrid DSTCs under axial compression, with an average deviation of 1% at the peak axial load, demonstrating the effectiveness of the numerical simulation model. Additionally, a parametric study using validated nonlinear finite element analysis (NLFEA) models to investigate the influence of outer tube cross-sectional aspect ratio, inner steel tube shape, and outer FRP tube thickness on the confined concrete in rectangular DSTCs has been carried out. The finding highlighted that rectangular DSTCs with thicker FRP tubes exhibit higher ultimate axial stress and strain in the confined concrete. Moreover, rectangular DSTCs with square inner steel tubes showed notably lower ultimate axial stress and strain in the confined concrete than rectangular DSTCs with circular inner steel tubes. This comprehensive study emphasizes the importance of stress–strain models, offering valuable insights for the design and construction of hybrid rectangular DSTCs.