Large-scale sandwich panels made of GFRP facings and recycled PET core: Cyclic bending tests, design optimization, and feasibility for building applications

The objective of this paper is to evaluate the structural performance of sandwich panels composed of recycled polyethylene terephthalate (R-PET) cores and glass fiber reinforced polymer (GFRP) facings under cyclic four-point bending loading. This study involves the testing of three large-scale specimens, each measuring 8 feet (2438 mm) in length with an unsupported span of 2286 mm, a width of 4 feet (1219 mm), and a core thickness of 6 inches (152 mm) along with a GFRP facing thickness of 2.5 mm. The study aims to evaluate the feasibility of using R-PET, a sustainable alternative to non-recycled plastics, as the core material of structural insulated panels (SIPs) designed for building applications, including walls, roofs, and particularly floors. While the mechanics of materials and the material properties of both the core and the facings were individually examined—testing the facing axially and the core in shear—such assessments provide preliminary insights into the anticipated structural behaviour of the large-scale FRP-faced SIPs under transverse loads. However, building codes and regulatory officials mandate comprehensive full-scale testing to validate these findings and preclude premature failures in large-scale components. Consequently, this study tested full-scale FRP-faced SIPs under transverse loading, incorporating cyclic loading to evaluate under real-world loading conditions. Additionally, the experimental results were validated through a model, which was then used to create a detailed design table. This table offers essential guidance for designers, specifying the maximum allowable spans for the panels under typical specified dead and live loads uniformly distributed, considering strength and deflection criteria. The design table considers variations in facing thickness, core thickness, and core density, making it an invaluable resource for the preliminary design of floors using these innovative SIPs.