Nonlinear analysis of columns with insufficient shear resistance strengthened by RC jacketing and CFRP

It has been experienced during past earthquakes that many buildings collapsed due to serious damages on columns. Therefore, the columns having insufficient shear strength and/or deformation capacity in existing structures should be strengthened. Additionally, although experimental studies are one of the most effective methods to investigate actual behavior of reinforced members under various loads, due to their high cost and requirement of developed infrastructure and skilled human labor, finite element programs are an alternative, reliable and mostly preferred method with an advancing computer technology. In this study, finite element models of reinforced concrete (RC) columns with an insufficient shear strength and strengthened by RC jacketing and carbon fiber reinforced polymer (CFRP) confined RC columns were created and their nonlinear behaviors under horizontal reversed cyclic loading were investigated. OpenSees finite element program was used in nonlinear analyses. Modeling steps were explained, and the constitutive relation of the materials used in the models were presented. The deformation components consisting of shear and reinforcement slip playing an active role in the behavior of reinforced concrete columns were also integrated into the models. According to the analysis results, nonlinear models were highly successful to represent experimental behavior of the tested members in terms of strength, lateral stiffness, ductility, cyclic stiffness degradation, and pinching. By using these models, a parametric study with the reference samples having insufficient shear strength and different axial load levels were performed by using RC jacketing and CFRP confinement strengthening methods. The effects of jacket concrete strength and jacket stirrup spacings in by RC jacketing and the effects of maximum tensile strength and thicknesses of FRP wraps CFRP confinement were comparedd in terms of strength, rigidity, ductility, and energy dissipation. As a result of the study, while RC jacketing strengthening method significantly increases the strength, stiffness, deformation capacity and energy dissipation capacity of the reference sample, strengthening with CFRP confinement contributes an apparent improvement in ductility and energy dissipation capacities. It is understood that CFRP reinforcement method can be preferred in case where significant increases in the deformation capacities of the elements are desired, while the RC jacketing strengthening method is a more suitable option that it is desired contributions of strength, rigidity and energy absorption capacities in addition to the contribution in the ductility of the element.