A Numerical Investigation on the Behavior of RC Columns with Spiral Stirrups

In recent years, the use of helical screws in reinforced concrete components has been developed. Practical results of these experiments have shown that spiral reinforcement (SR) has improved seismic performance compared to other conventional methods. Experience has shown that by applying torsion in concrete members, due to the principal tensile stresses in the diameter of each element, the member elements of torsional structures with spiral patterns will expand. Due to the design of the expansion of torsional cracks in the cross-section, these cracks are relatively ideally perpendicular to the cross-section of the torsion reinforcement. The research results so far clearly show that the use of rectangular helical bolts increases the bearing capacity. Also, in this method, with a constant ratio of transverse reinforcement, the ductility condition is improved compared to conventional bends in workshops. Finally, the use of helical reinforcement in structural members increases the shear, flexural and axial strength. Commonly used braces require two end hooks to support the anchor. For the length of these two hooks, a large amount of steel material is needed for each closing brace, which increases the weight and price of the steel. This process is not required, and this type of reinforcement reduces the weight of the steel and saves money due to the reduction of steel consumption compared to conventional braces. The effect of SR on the formation of cracks and the member's behaviour after cracks has also been tested.
According to the researches, it is observed that so far, the effect of continuous closures as well as the effect of changing different parameters in the enclosure in columns with a square cross-section with continuous rebars has not been done. Regarding the confinement of concrete members with reinforcement, considering the cases mentioned about the importance and role of transverse struts in the performance of structural components, the purpose of this study is to investigate the performance of helical reinforcement in comparison with conventional transverse reinforcements in square reinforced concrete columns.  Also, the effect of changing various parameters such as yield stress of reinforcements (high-strength steel with normal strength), cross-section reinforcement and cross-sectional column dimensions on behavioral performance, including load-bearing capacity and ductility, in columns with this type of arch and analysis. In this study, the finite element analysis method has been used. The results show that the capacity and ductility of the column enclosed by the winding is higher than that of the column retained by the conventional tension. Also, in the column held by the twist, the column withstands less stress after loading, so it can be said less damage in this column will be obtained. In the load-displacement curves drawn for the column, at the beginning of the vertical branch up to a certain load, the behaviour of the columns is the same. Until the peak is reached, the stiffness decreases with increasing stiffness, and in the area after the apex, the softening behaviour increase. As the spacing of the bolts and the pitch of the windings increases, the behaviour of the columns in the two modes becomes closer to each other. It shows a relatively similar behaviour, and the difference in their capacity also becomes much smaller. Ductility is also reduced. Increasing the pitch of the windings has a greater effect on the capacity of the column than increasing the distance of the windings. By increasing the distance of the turns, the capacity of the column enclosed by the tortoise decreases sharply. However, in these conditions, the column enclosed by the tortoise performs better than the column enclosed by the arch. The results show that by increasing the cross-sectional dimensions of the column, the rebars withstand less stress, and the column capacity also increases. Also, keeping the number of rebars constant and increasing the cross-sectional dimensions to a certain extent increases the capacity, and then increasing the dimensions without increasing the number of rebars does not have much effect on the column capacity. The results show that with the increasing yield stress of the rebars, the capacity of the column has increased. Increasing the strength of the rebars reduces the stress in the concrete, resulting in less damage.