Experimental investigation of the effect of reinforcement types and placements on torsional behavior in reinforced concrete beams

Reinforced concrete systems are among the most widely used structural systems in the construction sector today, and a detailed investigation of the behavior of their fundamental components is of great importance in terms of structural safety. Beams, as critical load-bearing elements in reinforced concrete structures, transfer loads from slabs to columns and are subjected to various internal forces such as bending, shear, and torsion. Although the torsional effect is often considered a secondary action, it becomes a dominant internal force in structures with irregular geometries, edge beams, and cantilever elements. In this context, damage assessments conducted after past earthquakes have revealed the critical role of torsion in structural behavior and the inadequacies in reinforcement detailing within the existing building stock. In this study, the effect of non-ribbed reinforcement bars, which were commonly used before the year 2000, on the torsional behavior of reinforced concrete beams was experimentally investigated in comparison with ribbed bars currently preferred in practice. A total of 16 beam specimens were prepared using different longitudinal reinforcement ratios (2ɸ12 and 3ɸ12) and various stirrup spacings (none, 5 cm, 10 cm, and 20 cm), and were subjected to torsion tests using a specially designed experimental setup. The experimental data were evaluated in terms of rotational capacity, torsional moment, energy dissipation, and stiffness parameters. The results revealed that beams with non-ribbed reinforcement exhibited significant weaknesses in terms of torsional strength and ductility compared to those with ribbed reinforcement; moreover, the influence of longitudinal reinforcement amount and stirrup spacing on torsional behavior was clearly demonstrated. This study aims to contribute to the literature by supporting the evaluation of the existing building stock in terms of safety and by guiding the determination of effective reinforcement detailing in new reinforced concrete designs.