Integrated Assessment of a Distressed Reinforced Concrete Monorail Pier: Condition, Durability and Strengthening

Ageing and increasing traffic demands, combined with aggressive environmental exposure, can significantly deteriorate reinforced concrete bridges. In coastal regions, chloride ingress is a major threat due to its role in initiating reinforcement corrosion. This study was carried out to evaluate the existing condition of the Mumbai Monorail. The visual inspection with non-destructive tests, including ultrasonic pulse velocity, rebound hammer test and natural-frequency measurement, was utilised, while the chloride-ion penetrability was assessed using the rapid chloride permeability test (RCPT). The RCPT results were used to characterise chloride-ion penetrability at the tested locations. However, due to cracks in pier 2A-70, the measured reduction in natural frequency corresponds to an effective global stiffness reduction of approximately 25%, based on the assumption of comparable mass distribution and boundary conditions between the reference and distressed piers. The strengthening was carried out by near-surface mounted (NSM) bars and carbon fibre reinforced polymer sheets (CFRP), and the results demonstrate reductions in concrete stress of 62.12% and 68.77% in the compression and tension zones, respectively, while the corresponding reductions in steel reinforcement stress are 56.90% and 65.89%. These reductions indicate an improved serviceability response of the strengthened pier within the adopted numerical assessment framework, which employs an experimentally informed equivalent-stiffness model for the comparative evaluation of the strengthening schemes. The study provides an integrated approach for evaluating the condition and durability of existing reinforced concrete infrastructure by combining visual assessment, non-destructive testing, and chloride-ion penetrability measurements. The findings can assist in identifying vulnerable locations, interpreting durability-related risks, and supporting condition-based maintenance and rehabilitation decisions. The methodology provides a useful framework for durability assessment of similar ageing reinforced concrete infrastructure under variable environmental exposure.