Manufacturing cost optimization of welded steel plate I-girders integrating hybrid construction and tapered geometry

Abstract Steel plate I-girders are widely used in the construction industry worldwide. While numerous studies have explored ways to enhance their benefits, few have simultaneously optimized both key mechanical components—geometry and material—to develop novel and more efficient typologies. This research employs metaheuristic optimization to explore alternatives to traditional I-girders, formulating optimization problems that integrate geometric and material variables in both transverse and longitudinal planes. The objective is to minimize manufacturing costs, accounting for material expenses and seven key production activities such as welding, cutting, or painting, while ensuring compliance with Eurocode 3 specifications. The results indicate that material selection dominates in short-span girders, whereas geometric optimization becomes more critical for longer spans. The most cost-effective solution identified is the transversely hybrid with variable section (THVS) girder, which features tapered geometry and hybrid material distribution between the flanges and the web. Based on these findings, practical design recommendations are provided, including optimal span-to-depth ratios, hybrid ratios, taper angles, and transition positions for variable cross-section configurations. A proposed design methodology incorporating these recommendations is validated through a case study, demonstrating that THVS elements can reduce costs by up to 70% compared to traditional designs. However, challenges related to material availability, fabrication complexity, and local buckling risks must be addressed to fully realize the potential of these designs. Future research should prioritize FEA and experimental testing to refine these typologies and update design codes to better account for tapered and hybrid girders.