The degradation of seismic performance for RC bridge piers induced by chloride corrosion has previously been studied by treating the earthquake as a unilateral cyclic loading. Such studies do not consider the true response of the pier under the joint effect of corrosion damage and real multi-dimensional earthquake action. Thus, in the present study, the cyclic behavior of rectangular bridge piers subjected to the coupling effects of chloride corrosion and bidirectional loading was numerically investigated. First, the corrosion-induced deterioration of material mechanical properties is introduced. Second, the numerical model of two corroded piers is built and validated with the test results in the literature. Then, the time-dependent biaxial seismic performance of a rectangular bridge pier under the circular-shaped (CS) biaxial displacement pattern, square-shaped (SS) biaxial displacement pattern, uniaxial displacement in the X-direction (UX) pattern, and uniaxial displacement in the Y-direction (UY) pattern is analyzed using the validated model. The simulation results conclude that the trajectory of biaxial loading paths and corrosion levels significantly influence the peak force, deformation capacity, and dissipated energy of the piers. The biaxial loading path effect for the corrosive pier includes two stages with different biaxial force trajectory characteristics. Compared with the uncorroded pier, the corrosion level of 13.7% and biaxial loading induces up to a 40% reduction in strength and a 54% decrease in the residual ultimate displacement of the corroded pier. For the same corrosion degree, the dissipated energy under the SS biaxial displacement path is the largest among the four loading paths.

Offshore reinforced concrete (RC) structures, such as bridges and high-piled wharves, are frequently subjected to the coupled action of steel corrosion and ship collision loads. However, existing studies lack systematic quantification and in-depth revelation of the synergistic degradation mechanism under this coupling effect, resulting in an insufficient scientific basis for engineering design and reinforcement. To address this gap, this study established a refined three-dimensional numerical model of drop hammer-reinforced concrete beams based on ABAQUS, comprehensively considering the strain rate effects of steel and concrete, steel–concrete bond–slip behavior, and the trilinear constitutive model of corroded steel. After validating the model’s reliability against experimental data from the existing literature, parametric simulations were conducted to investigate the coupled effects of different corrosion rates and drop heights (0.25–1.5 m). Key findings include: (1) corrosion reduces the peak impact force by 9.7–58.9% and increases the maximum mid-span displacement by 6.6–35.7%, with this effect amplified by higher drop heights; (2) shear performance degradation (16.14–35.19%) is significantly more severe than flexural performance degradation (13.28–28.93%), confirming that shear performance is more sensitive to corrosion; (3) corrosion causes cracks to propagate from a localized distribution to a global distribution, while higher drop heights accelerate structural evolution toward brittle failure; (4) the synergistic degradation law of “corrosion exacerbates impact damage, and impact amplifies corrosion defects” is revealed. By quantifying the corrosion–impact coupling effect, this study advances research in the field and provides critical technical support for damage assessment and service life prediction for offshore RC structures. In engineering practice, it is recommended that offshore structures in high-corrosion environments prioritize shear resistance enhancement and adopt targeted protective measures for high-impact-risk areas to mitigate the risk of brittle failure.