Performance-Based Seismic Design for Retrofitting Deficient Bridge Bents: Developing Performance-Based Damage States

Abstract

The performance-based seismic design (PBSD) approach is implemented to achieve the desired structural performance over a wide range of seismic hazard levels. It requires a set of targeted performance levels and their corresponding limits to be defined. Because the current codes and guidelines do not prescribe these limits for different performance levels for old bridges with seismic deficiencies, such as inadequate ductility and low shear strength, this study aims to develop them. In this study, quantitative damage states that are expressed as drifts and damage indices (DIs) at various performance levels are developed using incremental dynamic analyses for retrofitted bents. Four retrofit options: (1) steel; (2) carbon–fiber-reinforced polymer (CFRP); (3) concrete; and (4) engineered cementitious composite (ECC) jackets are considered in this study. The concrete and longitudinal reinforcement of all bents cracked and yielded at limiting drifts of 0.06% and 0.38%, respectively. In addition, the ECC-jacketed bent experienced core crushing of the concrete at the highest limiting drift of 4.16%. In addition, a detailed example complements this study, which presents how retrofitting could be designed by considering the target seismic performance that uses the proposed damage states. The first-mode spectral accelerations of the bents were the optimum intensity measures (IMs) to study their relative performance for noncumulative and cumulative damage measures (DMs) at various hazard levels. Drift is considered noncumulative, and the DI that includes the combined effect of maximum drift and absorbed hysteretic energy is considered cumulative. The steel jacket was the most effective when decreasing the median maximum drift of the retrofitted bent, and the ECC jacket reduced the median DI of this type of bent the most.