Nonlinear fibre element modelling of RC bridge piers considering inelastic buckling of reinforcement

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 and interaction of stiffness of horizontal ties reinforcement with vertical reinforcement. The model also accounts for the fracture of vertical bars due to low-cycle high-amplitude fatigue degradation. Therefore, this model is able to predict the nonlinear cyclic response of circular RC columns up to complete collapse. The results show that the existing uniaxial material models of reinforcing bars that are calibrated using stressstrain 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 the pinching response of RC columns and also reduces the low-cycle fatigue life of buckled reinforcement.

Influence of non-stationary content of ground-motions on nonlinear dynamic response of RC bridge piers

“…The failure mode in column 1015 starts with buckling (not as severe as columns 415 and 815) but is followed by fracture of bars in tension without any severe core concrete crushing. This behaviour was observed in the experimental testing by Lehman and Moehle (2000) and numerical modelling by Kashani et al (2016) and also reported by other researchers Eberhard 2003, 2006). Similar differences are appreciated in the nonlinear dynamic response of column 1015 in the IDA graphs.…”

“…Therefore, this combined model accounts for the influence of inelastic buckling and low-cycle fatigue degradation. Through a comprehensive parametric study the 'optimum' pinching parameters of the model under cyclic loading are obtained (Kashani et al 2016). A more detailed discussion of the model development and calibration can be found elsewhere , Kashani et al 2016).…”

“…Therefore, the accuracy of the nonlinear model of RC components and structures is greatly influenced by the accuracy of the uniaxial material model. Accordingly, several researchers have developed material Kashani et al (2015a) and Kashani et al (2016) that have been extensively validated against a variety of experimental datasets. In this research the effect of geometric nonlinearity and large deformation is also considered in addition to the material nonlinearity.…”

“…The finite element model is validated against the experimental data of RC bridge piers conducted by Lehman and Moehle (2000). The fibre element modelling technique that is used in this research was developed by Kashani et al (2016), which employs the uniaxial material model developed in Kashani et al (2015a). This bridge pier model is a generic distributed plasticity nonlinear fibre beam-column element which is capable of predicting multiple failure modes (confined concrete crushing, inelastic buckling and/or tension failure of longitudinal reinforcing bars, low-cycle fatigue) of RC components simultaneously.…”

Design of transverse reinforcement to avoid premature buckling of main bars

“…() This may result in a reduction of section moment capacity, thereby adversely affecting the section/member ductility. () In cyclically loaded RC members, when unloading from tension, concrete does not carry compressive stress until the cracks are completely closed, but the longitudinal bars develop large compressive stress well before the cracks close (ie, when the strain is still tensile). Hence, during most inelastic cyclic response, cracked concrete does not contribute much to the section equilibrium, and the tensile force carried by bars and the applied axial compression force are balanced only by the compressive forces carried by bars in the compression side.…”