Early-Stage Design of Concrete Girder Bridges Using Set-Based Design: Parametric Exploration of Design Alternatives Considering CO2 Emissions, Cost, and Buildability

Abstract

This thesis investigates the application of parametric multi-criteria optimization in the early-stage design of reinforced concrete girder bridges using a set-based design (SBD) approach. As the construction industry faces increasing pressure to reduce greenhouse gas emissions in line with Sweden’s 2045 net-zero targets, methods that allow sustainable solutions in the initial stages of a project are encouraged. However, minimizing the use of carbon-intensive materials, such as concrete, can present challenges for buildability, particularly when more geometrically complex structures are introduced. To address this situation, the study incorporates both environmental impact and buildability into the optimization criteria, enabling identification of solutions that balance these potentially conflicting objectives. A developed parametric Python algorithm was used to generate a wide design space based on geometry parameters from a reference project. The study focused on cross-sections with two main girders—either of rectangular or I-shaped profiles. Each alternative was structurally verified by the algorithm through finite element analysis using BRIGADE/Plus, and subsequently evaluated in terms of investment cost, CO2 emissions, and buildability. The analysis of over 100,000 cross-section alternatives revealed groups of material-efficient solutions that reduced both emissions and cost, although some with buildability that was negatively impacted due to increased production complexity. The results underscore the trade-offs between key criteria and demonstrate the ability of the SBD method to identify solutions that meet multiple performance targets. Overall, the study highlights the value of SBD in supporting early-stage decisionmaking, enabling more informed trade-offs, and reducing risk in tendering processes aimed at sustainable infrastructure development.