Seismic Retrofit of Nonuniformly Corroded Coastal Bridge Piers with FRP and Engineered Cementitious Composite Overlays

Coastal bridge piers are prone to corrosion attack owing to their exposure to marine environments, particularly in the splash and tidal zone, which is rich in chloride, oxygen, and moisture. Severe corrosion in this area results in the transfer of plastic hinges and evidently impairs the structural performance under seismic loading. Previous seismic retrofitting typically focused on the area of the pier end with the greatest bending moment. However, the location of the splash and tidal zone varies with the change in season and is generally not in the pier end. This study investigated for the first time the seismic retrofit of such piers using fiber-reinforced polymer (FRP) and engineered cementitious composite (ECC), where the middle part of the pier subjected to NaCl solution corrosion was simulated as the splash and tidal zone. Reversed cyclic loading tests of nine bridge piers with various corrosion rates, FRP types, and retrofit areas were performed. The seismic behaviors in terms of failure mode, crack pattern, load-carrying capacity, ductility, energy dissipation capacity, and stiffness degradation were compared and discussed. The experimental results of mildly corroded specimens indicated that seismic retrofitting with combined FRP and ECC significantly improved the seismic performance of bridge piers. The retrofitted specimen exhibited an even higher ductility and energy dissipation capacity than the noncorroded specimen. For severely corroded piers, the plastic hinge was transferred from the pier end to the corroded area and then transferred back to the pier end after retrofitting. The seismic performance of the specimens retrofitted from the corroded area to the foundation was better than that of the piers retrofitted only in the corroded area.