Seismic resilience of corroded mid-rise reinforced concrete structures under mainshock-aftershock sequences

Numerous existing structures exposed to an aggressive environment would also face to a threat from potential strong earthquakes. The coupling effect of environmental aggression and earthquakes could significantly increase the structural damage and failure probabilities of aging buildings. This paper presents a practical methodology of seismic resilience assessment for the corroded reinforced concrete (RC) buildings under mainshock-aftershocks. In this methodology, a piecewise resilience function is introduced, and the structural resilience will drop to zero when performing replacement. An economic loss ratio is adopted to determine the boundary point in the piecewise resilience function. Moreover, a vector-valued approach is employed to evaluate the structural fragility under mainshock-aftershock sequences. To illustrate the proposed methodology, a RC frame building designed according to Chinese codes is used as an example, and four cases with no, low, moderate, and high degrees of corrosion damage are considered with the corrosion rates (ηs) of 0%, 5%, 10% and 15%, respectively. A set of 662 real mainshock-aftershock sequences are selected as the input ground motions from PEER database. The resilience curves are then developed for the uncorroded and corroded RC frame cases under mainshocks alone and mainshock-aftershock sequences. The results show that the coupling effect due to both corrosion and aftershocks lead to a more significant reduction on the structural resilience (ΔR) than the individual effect due to either corrosion or aftershocks. For the condition of ηs = 15% and the PGV of aftershock equals to 0.1 m/s, it is found that there is a 95% of increase on the ΔR due to the coupling effect which is larger than either aftershock (31.6%) or corrosion alone (70%). Moreover, the reduction scale of the structural resilience due to both factors is even larger than the summation of those due to any individual factor alone. The results of this study highlight the importance to consider the two scenarios of aging and aftershocks simultaneously when evaluating the seismic resilience of structures in the lifespan.