Torsional behavior of solid and hollow concrete beams reinforced with inclined spirals

Enhancing the torsional capacity of reinforced concrete (RC) beams while maintaining reasonably economic and efficient cross-sections poses a practical challenge in the design of such elements. Thus, developing and testing economically viable reinforcing techniques for enhancing the torsional capacity of RC beams is a significant aspect. Among these techniques is the continuous spiral reinforcement system that has shown promising results in enhancing the torsional capacity of rectangular RC elements. In this study, the role of continuous rectangular spiral stirrups, as a transverse reinforcement with a controllable pitch (P) and inclination angle (θ), in enhancing the torsional behavior of rectangular solid and hollow RC beams has been investigated experimentally. The applied torque was directed to lock the spirals for all specimens. The experimental program of this investigation included testing of ten specimens of normal strength RC beams; two of which were solid with closed and spiral rectangular stirrups. While the rest of specimens were hollow specimens included one beam reinforced by closed stirrups and seven beams reinforced by rectangular spiral stirrups with different reinforcing ratios. Different variables were considered to develop a wide range of the beams’ reinforcing scenarios. This includes stirrups type (conventional closed stirrups and rectangular spiral stirrups), inclined stirrups ratio, pitch, inclination angle and finally the longitudinal reinforcement ratio. In addition, a three-dimensional finite element model using ANSYS-15.0 was developed to examine the capability of the model to capture the observed torsional behavior of the experimentally tested beams. The obtained results showed that using inclined spiral rectangular stirrups in reinforcing RC solid and hollow beams greatly enhanced the torsional capacity by about 16% and 18%, respectively compared to using the conventional closed stirrups. Moreover, the results showed that using that technique leads to higher twist- angles, more ductile failure and increased strain energy by about 27% and 16% for solid and hollow beams, respectively. Lastly, the comparison between the results obtained from numerical model and experimental results showed good agreement and thus the numerical model can be used to extend the experimental work for investigating different reinforcing schemes.