Effective flange width of reinforced concrete T‐beams: Experimental study and international code evaluation

Abstract

The effective flange width is a fundamental parameter in the flexural design of reinforced concrete (RC) T‐beams, directly affecting strength, stiffness, ductility, and crack control. Nevertheless, current international design standards adopt markedly different formulations, leading to significant variability in predicted structural performance. This study presents a comprehensive investigation combining international code comparison, full‐scale experimental testing, and statistical evaluation of crack width predictions. Provisions from 15 international design codes are first examined, revealing substantial dispersion in effective flange width estimates for identical beam configurations, ranging from 750 to 1803 mm. An experimental program involving 13 full‐scale, simply supported RC T‐beams is then conducted to assess the influence of flange width, flange thickness, and shear span‐to‐depth ratio on flexural behavior. The results show that increasing the flange width from 300 to 1280 mm enhances the ultimate load capacity by up to 28%, accompanied by a noticeable increase in mid‐span deformation and ductility, while increasing flange thickness from 40 to 80 mm results in a 15.7% improvement in ultimate strength. The beneficial contribution of the flange is found to increase at a diminishing rate, indicating that excessively large effective flange widths assumed in some codes may not be fully mobilized in practice. Crack width predictions from selected design standards are statistically compared with experimental measurements, demonstrating that AS 3600 provides the closest agreement, with a coefficient of variation of 0.119, compared with higher variability for ECP 203‐2020 and JSCE 2007. The findings highlight the need for more consistent and experimentally calibrated effective flange width provisions and offer practical insights for improving the reliability and economy of RC T‐beam design in current codes, particularly for monolithic slab–beam systems subjected to positive bending.