Axial Loading Tests and Simplified Modeling of Sandwich Panels with GFRP Skins and Soft Core at Various Slenderness Ratios: Fid-Bau Portal

Axial Loading Tests and Simplified Modeling of Sandwich Panels with GFRP Skins and Soft Core at Various Slenderness Ratios

Mathieson, Hale / Fam, Amir

Abstract

Experimental and analytical studies were conducted to investigate the axial strength and failure modes of sandwich panels with glass fiber reinforced polymer (GFRP) skins and soft polyurethane core. A total of 45 specimens of $78 \times 150 mm$ cross-section and of lengths $L_{e}$ varying from 500 to 2,400 mm [i.e., slenderness ratio ( $K L_{e} ∶ r$ ) of 15–70, where $r$ is the radius of gyration] were tested concentrically using pin-ends ( $K = 1$ ). The effects of skin thickness and an internal GFRP rib on axial behavior were studied. The study first assessed the level of out-of-straightness and concluded that all specimens generally fall within an acceptable limit of $span / 1,000$ . A model based on sandwich panel theory, accounting for excessive shear deformations of the soft core, was used to predict axial strength at a wide range of $K L_{e} ∶ r$ and then used in a parametric study. It was shown that short panels with $K L_{e} ∶ r$ of 15–17 experienced local failure, outwards skin wrinkling in non-ribbed panels, or skin crushing in ribbed panels. Slender panels with $K L_{e} ∶ r$ of 41–70 experienced global buckling followed by secondary local failure. Panels with intermediate slenderness (17–41) showed mixed failure modes. The load at which local failure governs at low $K L_{e} ∶ r$ appears to be a constant, independent of $K L_{e} r$ , whereas the global buckling load decreases significantly with increasing $K L_{e} ∶ r$ . Increasing skin thickness appears to be more effective at high $K L_{e} ∶ r$ whereas increasing core shear modulus appears to be more effective at low $K L_{e} ∶ r$ .