Environmental boundary conditions for prediction of temperature distribution in hybrid GFRP sandwich panels under service conditions

Abstract

Understanding and accurately predicting the thermal behaviour of fibre-reinforced polymer (FRP) composites is critical for their reliable application in structural systems. This study focuses on predicting temperature distributions within hybrid FRP sandwich panels composed of a pultruded glass fibre-reinforced polymer (GFRP) box, a closed-cell polyurethane foam core, and a steel fibre-reinforced self-compacting concrete (SFRSCC) topping layer. An extensive experimental programme was conducted under both controlled and external environmental conditions. The controlled phase involved thermal cycling and exposure to a high-pressure sodium (HPS) lamp to simulate radiant heating effects, while the outdoor phase captured real-world thermal fluctuations. Temperature was monitored using embedded PT100 sensors, and additional equipment was used to record ambient conditions, including solar radiation. Through meticulous experimental analyses and numerical simulations, this research evaluates the boundary conditions and thermal loads affecting the specimens, enabling the development and validation of numerical models. These models were designed to replicate transient heat transfer within the panels, accounting for convective heat exchange, direct and reflected radiation, and the influence of surface moisture during and after rainfall. The models achieved over 92% accuracy compared to experimental data, based on the mean absolute percentage error. Key findings show that disregarding reflected solar radiation from surrounding surfaces resulted in peak temperature underestimations of up to 13.9 °C, while neglecting evaporative cooling reduced the overall accuracy by approximately 6%. These results highlight the importance of calibrated numerical models for thermal analysis, ensuring the reliability of FRP-based structures under operational conditions. Furthermore, this research offers valuable insights for defining temperature distribution assessment methodologies regarding FRP composite structures in real-world applications.