Seismic retrofitting of rectangular bridge piers using ultra-high performance fiber reinforced concrete jackets

An innovative seismic retrofitting technique for “as-built” reinforced concrete (RC) bridge piers was proposed, by using ultra-high performance fiber reinforced concrete (UHPFRC) jackets. One “as-built” and two UHPFRC jacket-retrofitted rectangular cross-section RC piers were fabricated and cyclically loaded. Damage evolutions, skeleton curves, strength and stiffness degradations, ductility, self-centering and energy dissipation capacities were derived and analyzed. The two jackets mitigated the concrete damage and enhanced the self-centering capacity of a RC pier. The 850 mm-height jacket significantly increased the strength, but ductility and cumulative energy dissipation capacity. On the other aspect, the 400 mm-height jacket exhibited superior performances in ductility and cumulative energy dissipation capacity. Three strengthening mechanisms were brought by a UHPFRC jacket, and they were cross-section enlargement effect, gap opening effect, and passive confinement effect. Among them, formulas for the confinement effect are analytically obtained. The fiber-based finite element (FE) model for the UHPFRC jacket-retrofitted RC pier is developed within OpenSees framework. The simulation agrees well with the experimental results and can benefit further researches involved in the seismic retrofitting with a UHPFRC jacket.