Enhancing the resistance of composite sandwich panels to localized forces for civil infrastructure and transportation applications

This paper presents the details of an experimental and numerical study that was conducted to evaluate different methods of increasing the punching resistance of glass fiber reinforced polymer (GFRP) composite sandwich panels with balsa wood cores. A total of four large-scale panels were subjected to concentrated loads in a two-way bending configuration. Different techniques of locally stiffening the panels were investigated including bonding a steel coupling plate to the loaded surface of the panels and embedding steel tubes within the panel core. The experimental program was supplemented by a finite element study to evaluate the location, magnitude, and extent of stress concentrations in the panels. The experimental program demonstrated that the failure modes of the stiffened panels shifted from local punching to delamination of the loaded GFRP skin which initiated at the discontinuities of the panel stiffness. The finite element analysis indicated that the delamination failure was due to stress concentrations which formed at these critical locations. The local stiffening of the panel approximately tripled the concentrated load carrying capacity of the panels. The research findings suggest that, through careful design and detailing, composite sandwich panels can be used to resist large-magnitude concentrated loads such as those found in civil infrastructure and heavy freight transportation applications.