Seismic Fragility Analysis of Aged Bridges with RC Piers

Abstract

Bridges are one of the most important elements in a transportation network. A major concern regarding bridges is their susceptibility to corrosion. Maintenance, repair, and rehabilitation of these structures constitute a huge part of the total expenditure. Studies regarding carbonation induced corrosion on structures are limited because it propagates slowly and is less dangerous compared to chloride induced corrosion. However, in industrial and urban locations, carbonation induced corrosion may be the driving factor that determines the service life of the structure. Corrosion causes cracking and spalling of the concrete cover, deteriorates the bond between concrete and rebar, and also affects the strength and ductility properties of rebar. These effects cause a reduction in the flexural capacity of the structure. The reduction in ductility of the structure is catastrophic in earthquake prone regions as it may cause brittle failure of the structure. In the present study, the mechanism of carbonation induced corrosion and the deterioration induced by it on the structure is reviewed. Perspectives regarding the acceptable limits that indicate the end of the service life of the structure is studied. Various models of corrosion and carbonation by researchers are examined. Then, a model is used to predict the rate of corrosion with time. Finite element software, ABAQUS and SAP2000 are used to model corroded RC columns and tests are simulated to verify their behaviour. Incremental Dynamic Analysis (IDA) is performed on a bridge pier considering the effect of corrosion, as case study, to derive the fragility curves of the pier at different ages during the lifetime of the pier. The probability of collapse of the pier at different ages are derived from the fragility curves considering MCE intensity (2% probability of exceedance in 50 years), intensity corresponding to 2% probability of exceedance in 75 years and a target intensity corresponding to 2% probability of exceedance in 250 years. This helps in determining the safety of the structure and the need for repair and rehabilitation of corroded structures.