Torque – Twist Behavior of RC Columns Retrofitted with GFRP Laminates Under Combined Torque & Axial Loads: A Parametric Study

As one of the most important topics that have not been sufficiently studied to investigate the structural behavior of concrete columns is the mechanical properties of concrete members resulting from the torsional effects that caused mainly from the exposure of buildings to earthquakes, especially the cracks resulting in the structural members and overall torque-twist behavior. However, concrete columns are elements that are difficult to replace when exposed to earthquakes, so the role of developing applicable and useful methods for maintaining and strengthening columns has emerged after exposure to torsion. FRP laminates like CFRP and GFRP are one of the most successful and widespread of these methods nowadays. To achieve the goal of this paper, a finite element 3D model suitable for analyzing square RC columns strengthened with GFRP under combined torsional moment and axial loads has been adopted and a reasonable method for calculating angles of twist for square concrete columns using the finite element method has been developed. [ANSYS] software as a useful tool is used to solve the problem and to predict the Torque – Twist relationships of the columns under investigation. The results are compared and verified with an experimental study and the numerical results showed acceptable agreement with the experimental results. Several important parameters affecting the torsional capacity of square columns strengthened with GFRP and subjected to combined torque & axial load are studied in parametric study. These parameters include, GFRP distribution, GFRP thickness, and GFRP schemes (orientation). The results showed the efficiency of finite element software to estimate the torque twist relationships after developing modified formulas to calculate the angles of twist, on the other hand, the fixing of GFRP sheets in 45 degree opposite to the cracks orientation is the best way to increase the torsional capacity of RC columns.