Designing for safety and sustainability: Optimization of fire-exposed steelconcrete composite footbridges

This study introduces a novel framework for the multi-objective optimization of steel-concrete composite footbridges, integrating fire resilience with sustainability metrics such as cost, CO2 emissions, and pedestrian comfort. While previous research has largely focused on ambient or simplified fire conditions, this work uniquely incorporates six fire exposure scenarios, ranging from 200 to 1500 seconds, to assess structural performance under extreme conditions. Employing a customdeveloped Multiobjective Harmony Search (MOHS) algorithm, the optimization identifies Pareto-optimal solutions that balance economic and environmental efficiency with pedestrian comfort and fire safety. The results reveal a linear relationship between cost and CO2 emissions, demonstrating that each US$ 1.00 saved reduces emissions by 0.7727 kg per meter. Additionally, a moderate 23% cost increase enhances fire resistance, preventing collapse during 10 minutes of fire exposure, while smaller investments of 3.91% and 15.06% extend safety for 200 and 400 seconds, respectively. These findings highlight the critical trade-offs between slender, cost-effective designs and compact, fire-resilient configurations. By addressing both fire scenarios and sustainability in a single optimization process, this research offers new insights into designing safer, more sustainable footbridges, with practical implications for urban infrastructure development.