Reliability analysis and parametric study for axial strength models of concrete-filled tube columns with FRP reinforcement

The study aims to investigate the structural behavior of Concrete-Filled FRP Tube (CFFT) columns internally reinforced with GFRP/CFRP bars, focusing on enhancing axial load capacity and deformation resistance. The research addresses the challenge of accurately predicting the axial performance of FRP-wrapped compressive members, which is crucial for designing durable and reliable CFFT columns. To address this problem, a comprehensive dataset of 650 FRP-wrapped compressive members was compiled from existing literature. Several previously developed strength prediction models were evaluated using key statistical indicators, including the root mean square error (RMSE) and coefficient of determination (R2), to assess predictive accuracy. Subsequently, a new analytical model was formulated to estimate the axial load capacity of CFFT columns, which was validated using finite element analysis (FEA) in ABAQUS. The FEA incorporated refined constitutive relationships for the concrete core, FRP tube, and longitudinal FRP reinforcement based on experimental data. Results showed that the proposed model outperformed previous models, achieving an R2 of 0.95 and an RMSE of 0.20, demonstrating its high accuracy. FEA results were in good correlation with experimental findings, with discrepancies of only 1.3% in axial deformation and 3.0% in ultimate axial load. The parametric study showed that increasing the FRP bars ratio from 1.2% to 2.2% enhanced axial strength by 179.01% and deflection by 15.75%. Similarly, increasing the GFRP tube thickness from 0.5 mm to 3 mm improved axial load by 64.02% and deformation by 34.74%. Moreover, raising the unwrapped concrete strength from 15 MPa to 65 MPa increased axial strength by 222.23% and deflection by 27.49%. Notably, increasing the column diameter from 100 mm to 350 mm led to a 2157.44% rise in axial strength and a 30.69% increase in deformation.