Numerical investigation on the torsional improvement of reinforced concrete beams strengthened with various techniques.

Abstract

This study digitally investigates the torsional behavior of reinforced concrete (RC) beams strengthened with near-surface bracing (NSM) and external bracing using Abaqus/CAE software. Finite element analysis (FE) was developed based on a previously validated experimental program, encompassing five tested beams, thus providing a realistic basis for model validation. The numerical results showed strong agreement with experimental trends, with deviations of less than 5%, confirming the model's accuracy and reliability. The analysis utilized the concrete deterioration plasticity (CDP) model, realistic surface bonding properties, and the elastic steel behavior to effectively monitor cracking and stiffness degradation. The grid sensitivity indicated that a 25 × 25 mm element size achieved optimal accuracy and efficiency, while an extension angle of ψ = 37° best represented the torsional response. The results showed that overlap lengths between 0.6d and 0.8d in the NSM stirrups enhanced torsional strength and elasticity, achieving a 110-138% increase in ultimate moment and a 14-86% increase in torsional angle compared to the control beam. Furthermore, combining the NSM stirrups with externally bonded steel mesh layers improved torsional performance up to three layers, after which the improvement stabilized. The developed finite element (FE) model proved to be a reliable and practical tool for analyzing, predicting, and optimizing torsional reinforcement systems in reinforced concrete beams. The study also investigated the effect of inclined bracing on beam faces compared to vertical bracing, demonstrating that inclined bracing exhibited a very high efficiency in resisting torsional stress, reaching 338%, a significantly higher percentage compared to vertical bracing, thus confirming its effectiveness.