Practical study on shear strength of reinforced concrete haunched beams

Abstract In structural engineering, the behavior and strength of reinforced concrete haunched beams (RCHBS) are crucial, especially when shear strength governs design. Despite the advantages of RCHBS, several building codes do not identify the critical section for shear strength calculations, and some of them neglect the effect of the inclined part on the shear strength of RCHBS leading to uneconomical and conservative design. This paper aims to highlight the contribution of inclined reinforcement at the haunch zone to the shear strength of RCHBS and suggest a new empirical equation for identifying the critical section and predicting the shear strength. An experimental program involving nine positively RCHBS and two prismatic beams divided into three groups was conducted to understand how different parameters such as inclination angle, shear span to depth ratio, and the web reinforcement ratio affect the shear strength and behavior of RCHBS. Measurements of steel strain, deflection, mode of failure, and crack propagation were taken for all beams, which all failed in shear. The results showed that increasing inclination angle from 0° to 18° enhanced the shear strength by 67%. Additionally, the existence of stirrups enhances the shear capacity by boosting the inclined reinforcement's effectiveness. The shear transfer mechanism is significantly influenced by the shear span-to-depth ratio (a/d), where reducing the a/d ratio from 4 to 2 resulted in a 25% increase in shear strength. The experimental ultimate shear loads were compared with the theoretical ones that were determined according to ACI 318 Code, and six formulas proposed by previous researchers. Finally, a new empirical formula was proposed to determine the critical section location and predict the shear strength for positively RCHBS.