Structural Optimisation of Concrete Shells Reinforced with FRP Bars

Since the early 20th century, reinforced concrete shells have been widely used in large-span roofing systems for industrial and public buildings, including hangars, sports facilities, and theatres. While these structural solutions have long fascinated designers, they also present significant challenges. Problems during fabrication arise from the complexity of forming and assembling the formwork, reinforcing, and casting large concrete surfaces. Structural modelling and analysis are further complicated by the unconventional shapes and unique behaviour of these structures. Concrete shells are typically designed as thin, slender elements to meet aesthetic and efficiency goals. However, this design approach often conflicts with the need to provide adequate concrete cover over the steel reinforcement to prevent corrosion and ensure long-term durability. As a result, the use of concrete shells has diminished, leading to a loss of both architectural innovation and structural efficiency. This paper presents a structural optimisation procedure for concrete shells, with a focus on shape optimisation. It employs two computational form-finding methods -Force Density (FD) and Dynamic Relaxation (DR)- to determine the optimal shape capable of primarily carrying loads through a membrane stress field. This shape will serve as the basis for further structural optimisation, specifically regarding the integration of reinforcement using fiber-reinforced polymers (FRP).