Thickness of shear flow zone in a circular RC column under pure torsion

This study proposes a rational method capable of analyzing the behavior of circular reinforced concrete (RC) columns under pure torsion with or without axial compression. The developed method is based on the concept of the rotating-angle softened truss model (RA-STM) and incorporates the recently updated material models. In particular, the most important factor in estimating torsional capacity of RC structures–thickness of shear flow zone–is investigated in-depth for the circular RC column and discussed together with other mechanical aspects. The concept of thickness of shear flow zone for rectangular RC members is theoretically well established, while it is not clearly understood for circular RC members. This is due to the lack of existing experimental and analytical research work in this area. Recently, a circular RC column under pure torsion was tested at Missouri S&T. Test results of the column were used to validate the proposed method in terms of overall column behavior and local behavior of each component (concrete, both longitudinal and transverse reinforcement). The comparisons proved that the proposed method was in reasonable agreement with experimental results. In addition, the concept of the proposed method can be applied for any arbitrary section and is free from mechanical assumptions such as concrete cover spalling.