Design of solid reinforced concrete beams

Higher experimentally measured load resistance of a solid beam than a hollow one, with similar reinforcement, led to theoretical and experimental investigations on how the concrete core participates in stress resistance. Stress analysis was carried out on solid beams subjected to combined load of bending, shear and torsion. The beams were 300 × 300 mm in cross-section and 3800 mm in length. A three-dimensional in-house non-linear finite-element program was used for numerical analysis. From this analysis, a stress distribution was selected and used in computational experiments. It was found that the concrete core participates in the beams' behaviour and strength and cannot be ignored when combined loads of bending, shear and torsion are present. Its participation depends partly on the ratio of the torsion-to-bending moment and the ratio of shear stress caused by torsion to the shear stress caused by shear force. This computational study was followed by experimental testing of three beams designed using the selected stress distribution. Experimental results on the behaviour and ultimate load showed an acceptable agreement with the design values. Most of the longitudinal and transverse reinforcement in the front side, where shear stresses are additive, reached yield stress near failure load. The longitudinal reinforcement in the rear side, where shear stresses are subtractive, reached near yield stress but the transverse reinforcement did not reach yield stress, especially in the beams where bending was dominant. In addition, it was found that the smaller the ratio of torsion to bending, the larger the failure load.