Connection development and in-plane response of glass fiber reinforced polymer sandwich panels with reinforced cores

This paper presents the findings of an experimental research project that was conducted in two phases to study the behavior of glass fiber reinforced polymer (GFRP) sandwich panels with reinforced cores under in-plane loading conditions. The tested panels consisted of two GFRP face skins separated by a polymeric foam core. The foam core was reinforced with different configurations of through-thickness fiber insertions and through-thickness GFRP web skins. In the first phase the performance of three different types of structural connections was tested - namely, bolted, bonded, and so-called enhanced bolted connections. The findings indicate that bolted connections to thinner and more flexible panels exhibited lower strength and a higher degree of nonlinear behavior compared with the bonded connections to the same panels. In contrast, the bolted connections to thicker and stiffer panels were generally stronger and stiffer than their bonded counterparts. The findings further indicate that the ultimate strength of the connections can be increased by up to 26% by bonding a steel reinforcing plate to the face skins of the panel prior to bolting. In the second phase three full-scale sandwich panels (1400 mm x 1400 mm) with different panel configurations were tested under proportional, biaxial, in-plane loading. The applied loads were selected to simulate the in-plane loading conditions in sandwich panels that are subjected primarily to in-plane loads, such as webs of deep beams and shear walls in lightweight structures. The full-field strains and displacements of the panels were measured using a digital image correlation-based (DIC) non-contact measurement system. The findings indicate that the through-thickness core reinforcements effectively prevented localized buckling, debonding, and separation of the panels' face skins. The findings also demonstrated that slender panels exhibit shear-compression buckling failures, whereas less slender panels exhibit shear-tension rupture failures.