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Tim van Driel

Date and time: 22-10-2021, 16:00

Track: Building Engineering

Topic: Investigations on the Cold Bending Behaviour of a Double Glazing Unit with a Rigid Edge-Spacer Frame

Location: CiTG Hall G

Description: Free-form façades with bent glass have become increasingly popular in recent times. As bent glass is stiffer against out-of-plane loads, it can result in thinner glass and lower embodied carbon. A promising new technique is to cold bend thin glass plates with a stiff structural edge into a hyperbolic paraboloid (hypar), and to subsequently lock the corners to create a self-contained, self-stressed system. In this research, the physical bending process of IGUs with a particular local instability phenomenon is investigated. This instability is hypothesised to be delayed by stiffening the edges of the plate, which is done here by using 30x30mm GFRP profiles as spacers. These were bonded to the glass using Dow 993 silicone adhesive. Four IGUs of 1.5x1.5m were produced, three with 4mm fully toughened glass, and one with 1.1mm chemically toughened glass. In a series of experiments, the panels were supported on two opposite corners, and pulled down on the others. A numerical model was developed to predict the outcome of the experiments.
It was found that with the sizes used it was difficult or impossible to get close to a hypar. Due to the small thickness of the glass, one the diagonals would always be straight or mostly straight throughout the loading process, making the panel not resemble a hypar. The bottom plate of the 4mm panels broke at a corner displacement of around 150mm and a total load of 2.6kN, and the top plate around 200mm and 0.7kN. The bottom plate of the 1.1mm also broke first, at a corner displacement of 120mm and a total load of 1.4kN. The top plate broke at a much higher corner displacement of almost 400mm, when the loaded diagonal was fully straight. It was also found that the top and bottom plates would make contact around 50mm corner displacement for the 4mm panels, and around 30mm corner displacement in the 1.1mm panel. The numerical model could predict this contact and the overall behaviour of the panel until a corner displacement up to 60mm. From the experiments and the model it was concluded that the glass was too thin for the size of the panels and the applied edge stiffening. Changing the parameters (e.g. thin glass in smaller sizes or higher edge stiffness) could result in a viable product.