A Multi-objective Optimization-based Novel Design Framework for Permanent Formwork-integrated Reinforced Concrete Beams balancing Structural, Economic, and Environmental Criteria

The use of precast concrete permanent formwork systems in reinforced concrete (RC) construction can deliver meaningful benefits only when their design is optimized by balancing structural, economic, and environmental objectives. This study proposes a multi-objective optimization framework for RC beams with permanent formwork, simultaneously considering flexural performance, material cost, and CO2 emissions. A case study is conducted in which key geometric and material parameters are treated as variables and the results are compared with those of reference RC beams using reusable steel formwork. Parametric and sensitivity analyses reveal trade-offs among cracking resistance, flexural capacity, cost, and emissions, with formwork thickness, concrete strength, and reinforcement ratio identified as dominant factors. The multi-objective optimized solutions achieve up to 250% higher cracking moment and over 30% increases in yield and ultimate capacities while maintaining comparable or lower material cost and CO2 emissions than reference beams.