Time-Dependent Seismic Fragility of Coastal RC Frames Considering Effect of Distance from Coastline

Reinforced concrete (RC) structures in coastal atmospheres commonly suffer the penetration of chloride ions, which can lead to the corrosion of reinforcements and, thus, a reduction in their structural performance under earthquakes. In recent years, time-dependent seismic fragility analysis has been widely used as an effective tool to represent the deterioration in the seismic performance of aging RC structures. However, few studies have considered the influences of varying chloride ion exposure environments due to the different distances of structures from a coastline. In light of this, this study performs a time-dependent seismic fragility analysis for aging RC frames, considering varying distances of the buildings from the coastline. To conduct this, a time-dependent reinforcement corrosion rate model that can consider the effect of the distance of a building from the coastline is established by combining a concrete surface chloride ion concentration model, an initial corrosion time model, and an electrochemical corrosion rate model. By integrating material deterioration models for reinforcements and concrete, the seismic fragility relationships for structures with different degrees of corrosion damage can be developed. A corrosion deterioration factor is then proposed to quantify the relationship between the seismic fragility function parameters and the corrosion rate. Subsequently, time-dependent fragility functions considering the effect of the distance from the coastline can be established. A nine-story RC frame designed according to the existing Chinese codes is used for illustration. The time-dependent seismic fragility relationship of the structure is developed considering different distances of buildings from the coastline. The results show that the effect of the distance of a building from the coastline varies under different categories of environment. The seismic fragility results for a structure under a III-a environment are more significantly influenced by the structural distance from the coastline compared to those for a structure under a II-a environment.

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