Structural design and experimental validation of an innovative hybrid lightweight sandwich glass panel

This thesis focuses on the design of a sandwich panel with thin glass faces and a 3D-printed plastic core in between. To validate the structural behaviour evaluated with FEM models, two prototypes have been built and subjected to experimental tests. The combination of these material is perfect for a sandwich structure, two thin and strong faces with a low-density core. In this way lightness, transparency and a good structural behaviour can be achieved at the same time, creating an alternative to traditional glass structures. Thin glass has great mechanical features due to chemical tempering processes, that through the immersion in a molten salt induce compression stresses on the sheets surfaces, reducing the sensibility of glass to flaws and microcracks which may cause brittle failures. In this way glass is able to absorb tensile stresses and exploit all of its potential. Because of its thinness it is necessary to increase the flexural stiffness, for this reason between the thin glass faces a thick core of a plastic material has been placed with the function to absorb shear stresses. The chosen material for the core is PET-G, because it is cheap, it does not require particular precautions during the 3D-printing and it has good mechanical features. Different geometrical patterns were taken into account for the core design, evaluating advantages and disadvantages of each pattern. The choice has fallen on truss cores, because they provide a good structural behaviour, they can be defined by a few number of parameters and they ensure a good transparency of the sandwich panel, which is the most important goal while designing with glass. In particular the chosen pattern is a tetrahedral core with cylindrical elements. The geometry has been defined in the parametric software Grasshopper to evaluate the influence of geometrical factors as the core thickness, the volume of material used and the slope of tetrahedrons vertices. It was also made a first sizing of the panel, with the help of simplified models and analytical formulas for the equivalent elastic modules of the core. To optimize the structural weight and the transparency, two strategies were applied at the same time: the diameter of each element varies from the ends, where it is maximum to the mid-section, where it reaches its minimum value, in this way the manufacturing and the assembly are improved; on the other hand, the sizes of the truss elements are maximum near the supports and they decrease until the mid-span section, where shear stresses are lower. To validate the calculations, besides FEM analysis, two panels of 700x400 mm were built, the first with elements of constant dimensions, while in the other panel were applied all the optimization strategies. The panels were subjected to both distributed load tests and 3PB tests. The results have been successfully compared with numerical models and the optimization strategies have been confirmed. Lastly the developed technology has been applied in a case study, the entrance of the Berkeley Hotel in London and the conclusion of this thesis have been drawn