Slenderness effects in reinforced concrete (RC) beams are not comprehensively accounted for in the prevailing design codes on concrete. The existing recommendations are limited to prescriptions of limiting slenderness ratios, which are semi-empirical in nature. No reduction in flexural moment capacity is recommended for beams whose slenderness approaches these limits. This paper attempts to address the aforementioned shortcomings for rectangular beams. In a recent paper, the authors proposed a formulation to predict the critical buckling moment, which is found to agree closely with experimental results. Based on this formulation, an expression for limiting slenderness ratio (to predict sudden buckling failure) is explicitly derived for under-reinforced rectangular RC beams. The proposed expression for limiting slenderness ratio accounts for beam end conditions, loading conditions, concrete strengths, and steel, as well as tension and compression reinforcement and transverse reinforcement ratios. It is found that a wide range of slenderness limits is feasible for different sets of design variables, in contrast to the constant value prescribed in the existing codes of practice for specified end conditions. Based on experimental studies carried out on eight moderately slender beams, it is observed that, like steel beams, RC slender beams also exhibit slenderness effects (lateral deflections and twist), even in beams with moderate slenderness. The ultimate moment capacity is found to reduce on account of these effects. An empirical reduction factor ? is proposed to account for such slenderness effects.
|Journal||ACI Structural Journal|
|Publisher||International Concrete Abstracts Portal|