Equation Model for Predicting the Load Capacity of RC Hollow Beams

Abstract

- A reinforced concrete hollow beam has a void along its span. The void reduces the beam’s weight while increasing its strength-to-weight ratio. It also reduces the moment of inertia and cross-sectional area, affecting the beam's load capacity. This effect is not considered by the existing beam theories, especially when the void is present in the tension zone. In this study, an equation model is derived to predict the load capacity of hollow beams. The reduced moment of inertia and cross-sectional area are considered while computing the moment and shear capacities, respectively. The model is then validated using experimental data from 11 specimens tested under a four-point load setup. In the specimens, PVC pipes of 25 mm to 75 mm in diameter were placed between 39 mm and 139 mm from the beam's soffit. From the validation analysis, the load capabilities are incorrectly predicted. The variation exceeds 10% of the experimental results, with a 36.1% average absolute error. Only four out of the eleven specimens' failure modes are correctly predicted. The model has a 95.4% chance predicting a 20% lower load capacity than the actual hollow beam. Thus, it could be used to design hollow beams. However, due to limited data, the hollow beam's shear strength is not verified. Thus, the model should not be used for hollow beams prone to shear failure.