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PurposeThe purpose of this paper is to present experimental investigations on the structural behaviour of composite sandwich panels for civil engineering applications. The performance of two different core materials – rigid plastic polyurethane (PU) foam and polypropylene (PP) honeycomb – combined with glass fibre reinforced polymer (GFRP) skins, and the effect of using GFRP ribs along the longitudinal edges of the panels were investigated.Design/methodology/approachThe experimental campaign first included flatwise tensile tests on the GFRP skins; edgewise and flatwise compressive tests; flatwise tensile tests on small‐scale sandwich specimens; and shear tests on the core materials. Subsequently, flexural static and dynamic tests were carried out in full‐scale sandwich panels (2.50×0.50×0.10 m3) in order to evaluate their service and failure behaviour. Linear elastic analytical and numerical models of the tested sandwich panels were developed in order to confirm the effects of varying the core material and of introducing GFRP ribs.FindingsTests confirmed the considerable influence of the core, namely of its stiffness and strength, on the performance of the unstrengthened panels; in addition, tests showed that the introduction of lateral reinforcements significantly increases the stiffness and strength of the panels, with the shear behaviour of strengthened panels being governed by the ribs. The unstrengthened panels collapsed due to core shear failure, while the strengthened panels failed due to face skin delamination followed by crushing of the skins. The models, validated with the experimental results, allowed simulating the serviceability behaviour of the sandwich panels with a good accuracy.Originality/valueThe present study confirmed that composite sandwich panels made of GFRP skins and PU rigid foam or PP honeycomb cores have significant potential for a wide range of structural applications, presenting significant stiffness and strength, particularly when strengthened with lateral GFRP ribs.

Reducing the dependency from petroleum-based monomers and crosslinkers is an increasingly important goal for the plastics industry. This is being enabled by the growing diversity and availability of alternative biobased products derived from renewable resources, some of which are compatible with the production of more sustainable resins for high-performance applications. This paper presents the development of unsaturated polyesters (UPs) and their crosslinked resins (UPRs) based on 2,5-furandicarboxylic acid (FDCA) and other biobased building blocks. The original features of these UPs are derived from (i) the use of FDCA as an aromatic monomer replacing phthalic anhydride, (ii) the introduction of a FDCA–isosorbide (ISO) block into the polyester backbone with the presence of unsaturations provided by biobased fumaric acid, (iii) the use of ISO and 1,3-propanediol instead of ethylene glycol and 1,2 propylene glycol, and (iv) the reduction of styrene content using 2-hydroxyethyl methacrylate. The developed UPRs have a similar thermal and mechanical behavior to the petrochemical ones, presenting glass transition temperatures up to 102 °C, tensile modulus and strength up to 3.9 GPa and 63.3 MPa, respectively, and viscosity between 800 and 1250 cP, making these resins greener alternatives to fully petroleum-derived UPRs for high-performance applications.

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This paper presents experimental and analytical investigations about the creep behaviour of sandwich panels comprising glass-fibre reinforced polymer faces and rigid polyurethane foam core for civil engineering applications. A full-scale sandwich panel was tested in bending for a period of 3600 h, in a simply supported configuration, subjected to a uniformly distributed load corresponding to 20% of the panel's flexural strength. Additionally, specimens of polyurethane foam core were tested in shear for a period of 1200 h, for three different load levels corresponding to 10%, 20% and 30% of the foam's shear strength. Experimental results were fitted using Findley's power law formulation. Creep coefficients, shear modulus reduction factors and time-dependent shear moduli were obtained for the polyurethane foam in shear. A composed creep model is proposed to simulate the sandwich panel's long-term creep deformations by considering the individual viscoelastic contributions from (1) the core material in shear and (2) the glass-fibre reinforced polymer faces in tension/compression. The composed creep model predictions adequately reproduced the full-scale panel's experimental results. In addition, a good agreement was found between the composed creep model predictions and the extrapolation of the power law fitting obtained from the full-scale panel test, for a 50-year period.