Numerical Model for Predicting the Flexural Performance of Plate Bonded Retrofitted RC Beams

Abstract

This study presents the development of a numerical model for predicting the flexural behaviour of reinforced concrete (RC) beams strengthened with externally bonded steel plates. The objective is to improve understanding of the structural response and effectiveness of plate-bonding retrofitting techniques, particularly with respect to flexural capacity, deformation behaviour, and failure mechanisms. A finite element model (FEM) was developed using an eight-noded interface element to represent the steel to adhesive to concrete interface, whose thickness is assumed negligible. The formulation is based on isoparametric elements with parabolic shape functions and a two-point Gaussian integration scheme. The numerical simulations accurately capture the load–deflection response, ultimate load capacity, and failure modes of plate-strengthened RC beams. Comparison with experimental results shows strong agreement, with predicted ultimate loads deviating by less than −3.27% to +6.0% from measured values across all specimens. Beams strengthened with relatively thin steel plates (t ≤ 3 mm) exhibited conventional flexural failure typical of under-reinforced RC beams, whereas increasing the plate thickness beyond 3 mm resulted in a transition to bond-controlled failure modes, including plate debonding and interface-induced cracking. This transition highlights the dominant influence of plate thickness on the interaction between flexural capacity enhancement and bond performance. Statistical validation was performed using Analysis of Variance (ANOVA) based on a linear regression model at a 95% confidence level. The computed F-value of 62.5 exceeds the critical value of 18.51, confirming a statistically significant relationship between experimental and numerical results. The coefficient of determination (R²) of 0.969 indicates that the FEM explains 96.9% of the variation in experimental data, while a correlation coefficient of 0.9844 demonstrates excellent predictive accuracy. The proposed model provides a reliable tool for predicting flexural behaviour and failure mode transition in plate-bonded RC beams.