Numerical study on inelastic cyclic behavior of CFRP wrapped substandard RC columns

Few numerical investigations have been carried out on fiber-reinforced polymer (FRP)-jacketed substandard RC columns with characteristics not normally met in properly designed structural members. Three columns were modeled through finite element method (FEM) by means of ATENA and OpenSees considering their cyclic lateral-load displacement hysteretic responses, where i) the first column (S) represents the typical characteristics of substandard columns violating rules of their construction time (i.e. 1975 Turkish Seismic Design Code) in terms of compressive strength of concrete (fc ≈ 10 MPa) and transverse reinforcement detailing (s=250 mm, where s is stirrups spacing), ii) the second column (C) represents the columns of buildings thoroughly complying with the requirements of their construction time (i.e. 1975 Turkish Seismic Design Code) (fc ≈ 20 MPa and s=80 mm), and iii) the third column (RS) is identical to a substandard column (S), but retrofitted with a CFRP jacket of 1 ply thickness. High axial load-to-axial capacity ratio (0.75 fcbh) together with high shear demand were among main features of the substandard column (S). Also, the Ve/bhfct value for S, C, and RS were 0.87, 1.43, and 1.64, respectively. Note that b, h, Ve, and fct are column width, column height, shear force corresponding to bending moment, and direct tensile strength of concrete, respectively. In OpenSees model distributed plasticity, slip (due to strain penetration into the foundation of longitudinal bars at the column-foundation interface), cyclic stiffness, strength degradations and buckling of rebars in compression are considered. In ATENA, the columns were modeled as a single macro element and discretized by fine meshes capturing both flexure and shear deformations. The results obtained through the numerical modeling both in ATENA and OpenSees are in good agreement with the experimental ones. As per the nonlinear analyses, member damage levels are assessed by means of the strain-wise performance limits given in Turkey Building Earthquake Code (2018). The pros and cons of the modeling approaches and their accuracy are discussed as well.