Abstract: An advanced modelling technique is developed to model the nonlinear cyclic response of circular RC columns using fibre-based section discretisation method. A comparison between different reinforcing steel models is made. Through a comprehensive parametric study the influence of inelastic buckling of vertical reinforcement on the cyclic response of circular RC columns is investigated. The results have been compared and validated against a set of experimental datasets. The proposed calibrated model accounts for the influence of inelastic buckling of vertical reinforcement, stiffness of horizontal ties and their interaction with vertical reinforcement, and fracture of vertical bars due to low-cycle fatigue on cyclic degradation of circular RC columns. The results show that the existing uniaxial material models of reinforcing bars that are calibrated using stress-strain behaviour of isolated bars cannot represent the behaviour of reinforcing bars inside RC columns. Moreover, it is found that the buckling length of vertical reinforcement has a significant influence on pinching response of RC columns and also reduces the low-cycle fatigue life of buckled reinforcement.

Keywords: Nonlinear analysis, Finite element method, Reinforcing steel, Buckling, Force-based element, Postbuckling, Reinforced concrete, Bridge piers, Low-cycle fatigue, Cyclic degradation 

Abstract: A numerical model is presented that enables simulation of the nonlinear flexural response of reinforced concrete (RC) components with corroded reinforcement. The model employs a force-based nonlinear fibre beam-column element. A new phenomenological uniaxial material model for corroded reinforcing steel is developed and used. This model accounts for the impact of corrosion on buckling strength and simulates the post-buckling behaviour and low-cycle fatigue degradation of vertical reinforcement under cyclic loading. The basic material model is validated through comparison of simulated and observed response for uncorroded RC columns. Cover concrete strength is adjusted to account for corrosion induced damage and core concrete strength and ductility are adjusted to account for corrosion induced damage to transverse reinforcement. The model is used to explore the impact of corrosion on the inelastic response of corroded RC columns under monotonic and cyclic loading. It is found that corrosion has more significant effect on ductility loss of corroded columns than strength loss. Results show that considering the effects of corrosion damage on both reinforcing steel and confined concrete can change the failure mode of corroded RC columns.  

Keywords: Corrosion; RC bridge pier; Inelastic buckling; Reinforcing steel; Cyclic behaviour; Low-cycle fatigue; Fibre model