Numerical Response of Concrete-Filled Steel Tubular (CFST) Columns Externally Strengthened with FRP Composites Subjected to Cyclic Loading

The ultimate load-carrying capacity of concrete-filled steel tubular (CFST) columns exposed to monotonic loadings can be greatly increased by strengthening those columns, and the occurrence of the steel tube's outward buckling can be postponed. The current research aims to study the possibility of improving the structural characteristics of CFST columns exposed to cyclic loadings in terms of lateral load capacity and absorbed energy by strengthening them with different patterns of fiber-reinforced polymer (FRP) sheets. The ABAQUS software was used to create a three-dimensional (3D) non-linear finite element model (FEM) to simulate the behavior of FRP-strengthened CFST columns exposed to monotonic and cyclic loadings. After ascertaining the accuracy of the proposed model's results in successfully predicting failure patterns and lateral loads compared to the experimental results of tested specimens available in the literature, the model was used to create a parametric study. The parametric study focused on the impacts of the thickness, location, and length of the strengthening sheets on the failure pattern, lateral load-carrying capacity, stiffness, cumulative energy, absorbed energy, and viscous damping factor of the CFST columns exposed to cyclic loadings. The results revealed that the un-strengthened specimen displayed a maximum lateral load of 185 kN and a viscous damping factor of 45.2% at a lateral drift of 5.7%. On the other hand, strengthening the CFST column using five layers of FRP sheets exhibited the highest lateral load of all investigated columns (50% more than the un-strengthened specimen). Additionally, at a lateral drift of 5.7%, the decrease in viscous damping factor of CFST specimens due to strengthening using 1, 2, 3, 4, and 5 layers of FRP sheets with respect to the control specimen was 7.9%, 14.9%, 20.8%, 27.7%, and 30.3%, respectively.