Form-finding framework for monocoque sandwich composite bridges

Abstract

FRP is increasingly utilised in the built environment, following successful implementations in the aerospace and marine industry. However, it exhibits poor stiffness and stability compared to conventional materials such as steel, making it challenging to satisfy serviceability and comfort requirements. Optimising FRP to address these challenges will allow for lightweight solutions with long service lives which could contribute to a cost-efficient reduction of carbon footprint. To this end, an optimisation tool for the preliminary design of bridges using FRP is presented in this thesis report.

The research explores the feasibility of adopting FRP in the main load-carrying system of pedestrian bridges and develops a framework for the concurrent geometry and material architectural optimisation of said structures. The study aims to achieve significant cost- and carbon footprint reductions in
monocoque FRP bridges by employing a numerical optimisation approach.

The optimisation tool utilizes the computer-aided geometric design (CAGD) software Rhino® and its parametric interface, Grasshopper®, to concurrently optimise the shape and material architecture of the bridges. Through the use of genetic algorithms, the framework overcomes FRP’s poor stiffness and
stability, and maximizes its unique advantages, including lightweight and high-strength properties, enabling free-form designs. This feat is achieved by implementing hybrid sandwich panels, comprising glass fibre-reinforced polymer (GFRP) and carbon fibre-reinforced polymer (CFRP) face sheets.
Satisfactory stiffness is ensured by defining deflection constraints, whereas constraints on the fundamental frequency and critical buckling load factor ensure adequate stability.

The research demonstrates promising results, showing potential cost reductions of up to 17% and carbon footprint reductions of up to 27.4% compared to a real case design carried out by FiReCo. However, certain limitations and areas for improvement are acknowledged, including the required run-time and the complexity of the solution space. Suggestions for enhancing the framework’s efficiency are proposed, including implementing orthotropic failure criteria and reducing the solution space through adjustments to ply thicknesses and foam core configurations.

Overall, the developed optimisation tool provides valuable insights and serves as a valuable resource for researchers and practitioners seeking sustainable and economically viable bridge designs. By embracing innovative solutions and eco-friendly materials, this study contributes to global efforts towards carbon neutrality and sustainable infrastructure development in the built environment.