Design optimization of a composite typology based on RC columns and THVS girders to reduce economic cost, emissions, and embodied energy of frame building construction

Abstract

The construction industry significantly contributes to global energy consumption and emissions, necessitating sustainable alternatives to conventional practices. In this context, this study introduces a novel composite structural typology that combines reinforced concrete (RC) columns with transversely hybrid variable section (THVS) steel girders as beam-type elements. The proposed building frame leverages the high horizontal stiffness of RC columns and the reduced weight of steel girders to lower material consumption. The THVS variant has proven to be one of the most sustainable steel I-girder configurations. Two arrangements are analyzed: one with fixed beam-column connections and another with pinned joints. Structural design optimization problems are formulated, targeting three objectives: economic cost, CO₂(e) emissions, and embodied energy. These indicators are evaluated using a “cradle-to-site” approach. Results demonstrate that the fixed connection typology is optimal for buildings with shorter spans (4 m), achieving reductions in economic cost (6 %), emissions (16 %), and embodied energy (11 %) compared to traditional RC structures. The pinned variant is more suitable for longer span buildings (8 m), resulting in economic gains of around 5 % and a 6 % reduction in emissions despite higher energy requirements. Optimal THVS configurations indeed employ higher-grade steels in flanges than in the web, with tapered geometries varying by span length and connection type. The study also highlights that the THVS girders’ lighter weight significantly lowers axial loads on columns and foundations, further reducing construction costs and environmental impacts of the structural assembly. These findings underscore the potential of composite designs to enhance sustainability in building construction.