Optimum Seismic Retrofit of Deteriorating RC Bridge Columns Based on Risk, Cost–Benefit, and Real Option Analyses

Continuous exposure to aggressive environmental stressors, deterioration mechanisms, and natural hazards subjects existing bridges to a multitude of detrimental impacts on structural performance throughout their service life. In order to effectively address uncertain situations leading to structural performance deterioration, strategic approaches involving maintenance, repair, and retrofitting have become essential for managing deteriorating bridges. This paper presents an approach for seismic retrofit optimization of reinforced concrete bridge columns under corrosion and earthquakes using a real option analysis. The proposed approach consists of (1) time-variant risk assessment considering corrosion and earthquakes; (2) machine learning (ML)–based time-variant vulnerability assessment; (3) estimation of the effect of retrofit on time-variant vulnerability assessment; and (4) optimization to determine the retrofit application time for the RC bridge columns. The seismic responses of the RC bridges with and without retrofitting are obtained using a three-dimensional finite-element model. An ML technique is applied for the cost-effective time-variant risk assessment. The seismic retrofit optimizations are based on several objectives including minimizing the cumulative expected seismic risk, maximizing the cumulative benefit, maximizing the benefit ratio, and maximizing the real option value, which are estimated with the expected risk. The benefit ratio indicates the ratio of the cumulative benefit to retrofit cost. The optimum retrofit application times associated with these objectives are compared. The proposed approach is illustrated using an existing multispan RC girder bridge.