Review on behaviour of under-reinforced shallow fibrous concrete solid beams under pure torsion

In this paper, the methods for evaluating torsional strength of fibrous concrete beams are reviewed and highlighted the basic assumptions in these methods.The variables which include in the proposed model in these methods for predicting of torsional strength in shallow under-reinforced and plain fibrous concrete beams are explained. The proposed models indicated that volume fraction of steel fibre, aspect ratio of fibres, tensile strength of fibres, geometry of the section and inclination angle of spiral crack have an impact on the torsional strength in pre-cracking stage, whereas longitudinal and transverse reinforcement ratios, enclosed area by stirrups as well as stirrup spacing have influence on the ultimate torsional strength.Likewise, the impact of these variables on the torsional strength in prior of cracking and post-cracking stages improved by the experimental researcher’s .It was noticed that there is a gap between assumption and experimental variables. While in space truss analogy method, the enclosed area by stirrups is considered in the prediction of ultimate torsional strength, whereas according to the basic assumptions the same area is ignored. Likewise, the area of concrete outside of stirrups is considered as a basic assumption whereas this area is completely ignored in the evaluating ultimate torsional strength. Moreover, the material’s strength is limited in the predicting models. Consequently, these limits make an efficient torsion design of fibrous concrete beams difficult.