Numerical simulation and load-bearing capacity of concrete-filled steel tubes strengthened with CFRP grid-reinforced ECC under axial compression

A numerical study on the compressive behavior and load-bearing capacity of the concrete-filled steel tube (CFST), strengthened with a carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (ECC), is presented. The numerical simulation, which was based on a previous test performed by the authors, indicated that an increase in the number of CFRP grid layers results in a significant increase in the bearing load on the concrete core. The confinement is provided to the concrete core by the strengthening layer only after the yielding of the steel tube, which occurs because of the contact pressure between the steel tube and ECC. Parameter studies that considered the effect of the number of CFRP grid layers and the strength of the CFRP, compressive strength of the ECC and concrete core, diameter-to-thickness ratio, and yield strength of the steel tube were conducted. The increase in fcu and decrease in Ds/t weakened the function of the confinement of the strengthening layer, and the influence of fcu was more significant. Furthermore, an analysis model that considered the nonlinear confining behavior and stress history for predicting the load-bearing capacity of the CFST columns strengthened with CFRP grid-reinforced ECC was established. The stress increment iteration method was employed to determine the varying confining pressure during loading. The proposed model showed high accuracy for predicting the load-bearing capacities of the strengthened columns.