بررسی اثرات خوردگی کلرایدی با لحاظ تغییرات زوال چرخه‌ای بر ظرفیت فروریزش قاب‌های خمشی ویژه بتن‌آرمه در زلزله‌های متوالی

This study evaluates the simultaneous effects of reinforcement corrosion and earthquake sequences on the seismic performance of reinforced concrete structures. The main objective is to quantify the reduction in seismic capacity caused by corrosion of longitudinal reinforcement and to investigate the intensification of cumulative damage under consecutive seismic excitations. For this purpose, incremental dynamic analysis and fragility assessment were employed to provide a probabilistic evaluation of the collapse-related response of the studied structures under different corrosion and seismic loading conditions.

n the first step, the hysteretic behavior of reinforced concrete columns at different corrosion levels was extracted, calibrated, and validated using available experimental data. The calibration process was aimed at representing the main deterioration mechanisms associated with corrosion, including reduction in effective stiffness, strength degradation, and cyclic deterioration. Based on the validated member-level results, an equivalent cantilever-column model was developed to reproduce the nonlinear cyclic response of deteriorated members with sufficient accuracy. The calibrated parameters obtained from this stage were then implemented in the numerical models of two benchmark reinforced concrete special moment frames with different heights and structural configurations. This procedure allowed the local effects of corrosion observed in experimental specimens to be consistently transferred to the structural models used in the dynamic analyses.

To evaluate the influence of seismic sequences, nonlinear dynamic analyses were performed using a selected suite of far-field ground-motion records. The analyses were conducted in two general cases: single earthquake excitation and sequential earthquake excitation. In the sequential case, the mainshock record was first applied to the structure, followed by a time interval with zero acceleration, and then the aftershock record was imposed as the second seismic event. This procedure made it possible to examine the effects of initial damage caused by the main earthquake and the subsequent redistribution of seismic demand during the aftershock. The structural response was assessed for three corrosion conditions, including intact, slight corrosion, and moderate corrosion.

The results show that increasing the level of corrosion leads to a noticeable reduction in the initial stiffness and ultimate strength of the structural members. It also increases lateral displacements close to collapse and weakens the cyclic energy dissipation capacity of the system. These effects are reflected in the fragility curves, where increasing corrosion severity shifts the curves toward lower spectral acceleration values and increases the probability of reaching severe damage states at lower seismic intensities. The results further indicate that the presence of aftershocks can intensify accumulated damage and reduce the collapse capacity compared with the single-event earthquake case. The observed trends were more pronounced for moderate corrosion, whereas the response of slightly corroded frames remained closer to that of the intact condition in several cases.

For the two-story structure, the median collapse capacity of the frames with slight and moderate corrosion under earthquake sequences was estimated to be approximately 16% and 33% lower than that of the intact structure, respectively. Overall, the findings emphasize the importance of considering both reinforcement corrosion and earthquake sequences in seismic vulnerability assessment and retrofit planning of existing reinforced concrete moment-resisting buildings.