Fragility-based effectiveness evaluation of reinforced concrete bridge piers strengthened with UHPC jackets

The use of ultra-high-performance concrete (UHPC) jackets as a seismic strengthening method for reinforced concrete structures has become increasingly prevalent. Specifically, these jackets are applied to plastic hinge regions of the structures to improve overall earthquake resistance. This study evaluates the effectiveness of UHPC jackets in strengthening reinforced concrete columns through fragility curves. The columns are modeled numerically, accounting for material nonlinearity, and various strengthening scenarios, including those without UHPC jackets and with UHPC jackets of different heights, are modeled and validated with cyclic loading tests. Subsequently, a case study of a two-column reinforced concrete bridge pier is examined. Time-history dynamics analyses are conducted on 140 ground motion records to develop probabilistic seismic demand models of the column with different strengthening designs. Fragility curves obtained using the cloud method indicate a significant impact of the strengthening method on the failure probability of the column. The research findings presented in this paper provide engineers with a basis for selecting appropriate UHPC jacket parameters, including thickness, height, and material strength in a rational manner.