Impact of Corrosion and Smooth Reinforcement on the Nonlinear Cyclic Behaviour of RC Columns

Research aims and scopes:

Under the supervision of Dr. Mehdi Kashani, this parallel experimental research programme investigates the combined impact of accelerated corrosion and the use of smooth reinforcing bars on the nonlinear cyclic behaviour of reinforced concrete (RC) columns. The scope of the investigation evaluates two distinct infrastructure profiles: modern, code-conforming columns detailed to Eurocode 8 standards, and substandard, pre-1970s columns featuring inadequate transverse confinement and non-seismic detailing. The primary aim across both studies is to characterise how corrosion influences stiffness degradation, deformation capacity, energy dissipation, and structural failure mechanisms, ultimately informing more reliable seismic assessment and rehabilitation strategies for vulnerable, ageing bridge piers and infrastructure.

Main body of work:

The research team manually fabricated large-scale reinforced concrete column specimens equipped with smooth reinforcing bars. To effectively simulate decades of severe environmental exposure, selected specimens underwent an accelerated electrochemical corrosion process utilising a 7% sodium chloride solution and a constant 3A external current. During the structural testing phase, the columns were heavily instrumented using a 250kN servo-hydraulic actuator, Linear Variable Differential Transformers (LVDTs), and two-dimensional Digital Image Correlation (DIC) to capture full-field surface strains and visually track damage propagation. High-Resolution Distributed Acoustic Sensing (HR-DAS) with fibre optic sensors was also employed to dynamically measure internal strains directly within the longitudinal reinforcement.  The columns were subjected to a rigorous, displacement-controlled cyclic loading protocol, enduring repeated push-and-pull load reversals at increasing drift ratios up to 7%. Subsequent data analysis revealed that the accelerated corrosion caused severe, spatially variable pitting, particularly at the corners of transverse ties, which heavily compromised structural confinement. While the peak lateral strength of the columns experienced only moderate reductions, the corrosion significantly accelerated stiffness degradation and severely reduced the overall deformation capacity. In both the code-conforming and substandard designs, the uncorroded columns were dominated by a bond-slip and rigid body base-rotation failure mechanism. In stark contrast, the corroded columns exhibited a distinct shift to a distributed, damage-controlled flexural response characterised by extensive concrete crushing, premature bar buckling, and the sudden fracture of the deteriorated transverse hoops.