Sustainable Bridge Retrofit for Coastal Municipality: A Case Study

Thesis Abstract

Coastal infrastructure networks face increasing risks from climate-induced hazards, aging articulation joints, and corrosion-driven material degradation, threatening bridge reliability, service life, and community resilience in coastal municipalities. This study addresses the gap between sustainability objectives and retrofit decision-making for medium-span bridges exposed to saline environments, high tidal ranges, and traffic loading variability. The aim is to develop a decision-support framework for sustainable retrofit of coastal bridges, integrating structural performance, life-cycle environmental impacts, and social-vulnerability considerations. Specific objectives are (i) to evaluate the current condition and corrosion status of ten medium-span bridges in the Atlantic Coastal Municipality, (ii) to compare retrofit options—concrete cover remediation, steel jacketed reinforcement, fiber-reinforced polymer (FRP) wrapping, and hybrid composite decking—using life-cycle assessment (LCA) and life-cycle cost analysis (LCCA), (iii) to quantify structural reliability and predicted service life improvements under projected sea-level rise scenarios up to 1.2 m, (iv) to assess climate adaptation value through resilience indicators and stakeholder risk perceptions, and (v) to develop a composite decision model that integrates technical, economic, and sustainability metrics under uncertainty. Methodologically, the study adopts a mixed-methods design anchored in a structural engineering assessment, environmental accounting, and stakeholder analysis. The population comprises all operational coastal bridges within the municipality, with a stratified sample of ten bridges representing varying ages, materials, and traffic loads. Primary data are collected through nondestructive evaluation (NDE) surveys, chloride profile testing, half-cell potential measurements, and in-situ capacity tests. Instrumentation includes corrosion rate meters, covermeters, and structural health monitoring sensors deployed for twelve months. Secondary data consist of bridge maintenance records, geotechnical reports, climate projections from regional downscaled models, and cost data from regional suppliers. For the environmental dimension, the study performs cradle-to-grave LCA using SimaPro with CML-IA and ReCiPe 2016 methods and conducts LCCA incorporating discount rates, depreciation, replacement, and salvage values. For the structural performance assessment, probabilistic reliability analysis is conducted using Monte Carlo simulation to propagate uncertainties in material properties, corrosion progression, and load combinations, coupled with finite element modeling in OpenSees to estimate ultimate capacities under service and extreme-event limits. The decision model employs multi-criteria decision analysis (MCDA) with weighted aggregations, incorporating sustainability indicators, risk-based resilience scores, and community exposure metrics. Uncertainty is addressed through scenario analysis reflecting climate, economic, and policy changes. The study analyzes data with regression-based trend analysis to link corrosion indicators to structural reliability, ANOVA to compare retrofit options, and sensitivity analyses to identify dominant factors. Theoretically, the research draws on the Theory of Planned Behavior to interpret stakeholder acceptance, and on the System Resilience framework to evaluate the integration of redundancy and robustness in retrofit design. The expected findings include (i) quantified corrosion progression and remaining service life for baseline conditions, (ii) comparative life-cycle environmental impacts and costs across retrofit strategies, with FRP and hybrid options presenting favorable durability and lower maintenance in saline environments, (iii) improved reliability indices and extended service life under sea-level rise projections, and (iv) a robust, stakeholder-informed MCDA model that guides optimal retrofit choice under uncertainty. The study contributes to knowledge by bridging structural retrofit engineering with sustainability assessment and resilience planning in coastal contexts, offering a transferable framework for municipalities facing climate-driven deterioration. Policy implications include guidance on material selection, audit protocols for coastal bridges, and integration of resilience criteria into municipal asset management. The main conclusion anticipates that integrated FRP-wrapped retrofit combined with low-embodied-energy decking yields superior life-cycle performance and resilience benefits relative to conventional repairs, while ensuring social acceptance through transparent stakeholder engagement. Recommendations emphasize the standardization of NDE protocols for corrosion mapping, adoption of region-specific LCA databases for marine environments, routine climate-adaptation planning in bridge asset management, and the development of a decision-support tool that can be generalized to other coastal municipalities with similar climatic and load conditions.