Evaluation of Torsional Capacity of Square RC Columns Strengthened with CFRP Using Finite Element Modeling

Abstract

Researches on behavior of reinforced concrete (RC) columns subjected to torsion including mechanical properties like cracks and failure modes are not commonly studied and investigated well. It is necessary to investigate the mechanical properties and characteristics for RC columns subjected to torsion during different types of loading including earthquakes. Also, as a reinforcing method to existing RC structures, the application of Carbon Fiber Reinforced Polymers (CFRP) became common. CFRP has properties of high tensile strength, light weight and easy execution. CFRP is easy to adjust the reinforcement volume whenever necessary and considered excellent in endurance because the rust will not occur. The purpose of this study is to present a model suitable for analyzing square RC columns strengthened with CFRP under torsional effects and developing a reasonable method for calculating angles of twist for square concrete columns using the finite element method. Final available version of finite element analysis software [ANSYS 14 – 64 bits] is used to solve the problem and to predict the torsional behavior 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 CFRP under torsion are studied in parametric study. These parameters include: the presence (distribution type) of CFRP, CFRP number of layers (thickness), type of interface between CFRP layers and concrete surface, CFRP orientation and effect of applying axial load in addition to torque. The results showed that zebra shape (where sheets are straight and fibers are inclined with 45o) is the best way to increase the torsional capacity of RC columns.