Experimental and analytical study on heat transfer characteristics of fireproof panels with air layer and Low-E film protecting FRP strengthening

This study proposes a fireproof panel to protect Fiber-reinforced polymer (FRP) in FRP-strengthened structures from fire. The panel, installed beneath the FRP, consists of a steel plate, an air layer enclosed by a low-emissivity film (Low-E film), and a fireproof material, enhancing fire resistance. The study quantifies the heat transfer characteristics of the fireproof panel under fire conditions and presents a conceptual design process to determine optimal material layer thicknesses, ensuring the FRP surface remains below its critical temperature. The panel's effectiveness was verified through heat transfer experiments and numerical analysis using ANSYS software, considering air layer thickness and surface emissivity as variables. The ISO 834 fire curve was applied, and parametric analysis was conducted using total panel thickness and individual material layer thicknesses as variables. Results identified an optimal air layer thickness of 4 mm, preventing the FRP surface from exceeding its critical temperature while minimizing surface temperature. The effects of the steel plate and fireproof material layer thicknesses were analyzed and expressed as a thickness coefficient. The relationship between the thickness coefficient and FRP surface temperature ratio enabled a quantitative evaluation of heat transfer performance. The design process was developed to determine material thicknesses for fireproof panels, ensuring compliance with the 2-h fire resistance requirement while minimizing overall thickness. This approach improves fire protection efficiency and allows for the prediction of FRP's residual strength after fire exposure without complex calculations.