EFFECT OF SUPPLEMENTARY REINFORCEMENT ON FLEXURAL STRENGTH OF REINFORCED CONCRETE BEAMS

Abstract

This study investigates the flexural behavior of reinforced concrete (RC) beams, modeled using a nonlinear deformation-based fiber method, in accordance with Vietnamese Standard TCVN 5574:2018. The analysis focuses on the effect of supplementary longitudinal reinforcement added to satisfy the code’s vertical spacing requirement. The fiber method enables accurate simulation of reinforcement distribution and material nonlinearity across arbitrary cross-sections. Three typical RC beam types-rectangular, T-shaped, and I-shaped-were analyzed under varying reinforcement strategies. The results show that, beyond ensuring serviceability, supplementary reinforcement can significantly enhance structural capacity. Specifically, for the representative reinforcement layouts examined in the case studies, the maximum observed increases in ultimate moment capacity reached 47.74% for rectangular beams, up to 20.36% for T-shaped beams, and nearly 64% for I-shaped beams. This finding demonstrates that a detailing constraint originally intended for crack control can be reframed as a strength optimization opportunity. Although developed under TCVN 5574:2018, the numerical method is essentially code-independent, requiring only idealized stress-strain input and thus applicable to standards such as Eurocode 2 and ACI 318. This adaptability supports broader adoption of performance-based structural design.