Structural Performance–Based Framework for Seismic Retrofit Strategies of Reinforced Concrete Bridge Columns

Abstract This study evaluates seismic retrofit methods for reinforced concrete bridge columns within a structural performance–based framework and introduces a unified key indicator linking component-level retrofit design to structural seismic response. A multilevel performance-based retrofit design was first established for bridge columns. The seismic performance of a prototype bridge, incorporating columns with different retrofit types (categorized by seismic performance enhancement indices) and postretrofitting performance levels, was assessed using incremental dynamic analysis and fragility analysis. Results show that a higher postretrofitting performance level of bridge columns is essential for effectively reducing structural damage in less severe damage states. Although the combined confinement and flexural ability–enhancing retrofit method can effectively prevent pier anchorage loss at higher postretrofitting performance levels, none of the performance levels successfully prevented concrete cracking and spalling associated with minor damage in the piers. The degree of reduction in exceedance probability is influenced not only by earthquake intensity but also by the increment in postretrofitting performance level. Enhanced column retrofit performance allows the structure to derive greater benefits when subjected to higher seismic intensities. By focusing exclusively on the enhancement of stiffness and peak load in retrofitted bridge columns, it is possible to accurately evaluate the fragility of the retrofitted bridge structure. Based on this research framework, a single indicator, termed the Key Indicator Enhancement Rate (KIER), is proposed as an effective measure for capturing the combined effect of column stiffness and peak load. The distributions of maximum reduced probability and earthquake intensity associated with KIER follow a natural exponential function and a linear function, respectively.