Finite element modeling of steel bar buckling in FRP-confined RC columns

Abstract

Fiber-reinforced polymer (FRP) confining jackets offer an attractive solution for the seismic retrofit of reinforced concrete (RC) columns. For an accurate prediction of the strength and ductility of FRP-confined RC columns, it is necessary to understand the interaction between the FRP jacket and the RC column at all deformation levels under seismic loading. In particular, when widely-spaced steel stirrups/spirals are used as the transverse steel reinforcement, the longitudinal steel bars are likely to develop buckling deformations, which are however restrained by the FRP-confined concrete cover. This paper presents a “beam-on-elastic foundation” model for simulating the buckling behavior of longitudinal steel reinforcing bars laterally supported by FRP-confined concrete using the finite element (FE) approach. In addition, a curved beam approximation is proposed to evaluate the stiffness of the lateral springs that are used to represent the restraining effect offered by the FRP-confined concrete cover. The proposed FE model is verified through comparisons between the predicted and the experimental average stress-strain relationships of steel reinforcing bars, the latter of which were obtained from compression tests of FRP-confined RC columns. The proposed FE model provides an effective method for simulating the buckling behavior of laterally supported longitudinal reinforcing bars for a more accurate analysis of the behavior of FRP-confined RC columns.