Nonlinear finite element analysis of concrete columns confined by fibre-reinforced polymers

Abstract

The use of fibre-reinforced polymer (FRP) is an efficient and technically sound method for strengthening the damaged structures or upgrading the inadequately designed members or retrofitting of seismically damaged reinforced concrete structures. Although there is a large amount of experimental data available on the compressive behavior of fibre-reinforced polymer (FRP) confined concrete columns, a full understanding of the behavior of FRP confined rectangular concrete columns is somewhat lacking. This study aims to generate a 3D finite element model for FRP confined concrete columns under axial loading to overcome the deficiencies in the available experimental database. The nonlinear finite element analysis on FRP confined plain concrete was performed using ABAQUS/Standard (HKS 2009) finite element code. Both material and geometric nonlinearities were included in the model. A damage plasticity model was used to simulate the behavior of confined concrete. The interface between FRP and concrete was simulated using contact pair algorithm. Two different types of formulation: cohesion based surface interaction and friction type perfect bond interactions were defined at the FRP-concrete interface. A static Riks formulation was implemented to trace the stable load-displacement history of FRP confined concrete up to failure. The load was applied through displacement control technique. The numerical model was successfully applied to simulate the behavior of eleven columns from three experimental programs including square, rectangular and circular columns. The model reliably reproduced the peak axial stress, axial deformation at the peak stress, the post-peak behavior and the failure mode observed in the tests. A parametric study was conducted to investigate the influence of several geometric parameters such as aspect ratio, corner radius and the thickness of the FRP wrap on strength and ductility of FRP confined rectangular columns. The maximum effect of confinement was achieved for square columns. Decreasing the aspect ratio from 1 to 0.7 and 0.5 reduces the ultimate capacity of the confined column by 20% and 30% respectively with respect to the square column. Moreover, the axial capacity and ductility of the rectangular columns were found to increase significantly with the increase in corner radius and thickness of the FRP laminates. Finally, a simple form of polynomial equation was proposed to predict the confined compressive strength and the ultimate axial strain of concrete.