Numerical investigation of the impact of nonuniform corrosion on dynamic characteristics and nonlinear cyclic behaviour of circular RC bridge piers

Insufficient detail in the numerical modelling of reinforced concrete (RC) bridge piers can lead to oversimplification between simulated and real column behaviour under seismic loading. This paper describes the development and validation of an advanced and computationally efficient numerical model for circular RC bridge columns. First, the lateral stiffnesses, natural frequencies and damping ratios of three differently configured RC columns at various stages of degradation were evaluated by means of quasi-static cyclic and sledgehammer tests in loading cycles of increasing lateral drift amplitude. Normalised column lateral stiffness and first mode natural frequency were found to reduce nonlinearly with increasing column drift ratio. The two variables were also correlated to link RC column degradation with natural frequency reduction, which could allow rapid post-earthquake assessment of residual capacity. RC columns suffering from heavy corrosion were found to have a higher natural frequency and a tendency to fail prematurely under cyclic loading, whereas the damping ratio was generally unchanged. A set of nonlinear beam-element models employing fibre-discretised cross-sections was then developed and validated against experimental measurements. The model simulates buckling, fracturing, low-cycle fatigue, and bond-slip of vertical reinforcements, as well as nonuniform geometrical and mechanical deterioration of critical column sections. Individual fibre responses in the numerical model offered explanations for specific features of the experimental column stiffness and natural frequency reduction curves. Underlying mechanisms included the redistribution of compressive stress between concrete and rebars during cyclic loading, crushing of cover concrete, and yield of vertical reinforcements. Overall, the model accurately simulates the hysteresis response of the differently configured RC columns, without the need for column-specific adjustments.