Matthias Seel

In general, flat glass can only be thermally pre-stressed up to a minimal thickness of 3 mm. Lower thicknesses can also be realized by using tempering furnaces without the classic roller transport, but at a minimum only up to 1.5 mm. Achieving fully tempered glass (FTG) quality (criteria fine fracture pattern) becomes more and more difficult as the thickness is reduced. However, a prestressing process of lower glass thicknesses can be realized with the chemical pre-stressing process. The disadvantage of this process is that it is very time-consuming (8 to 48 h) and therefore also cost-intensive. Another disadvantage especially with soda lime glass is the low pre-stressing depth of 10…30 μm. Microdefects caused by the manufacturing processes involved in flat glass processing (cutting, lamination,…) are often deeper, which means that the full potential of chemically pre-stressed glass with high pre-stressing values cannot be exploited in practical construction terms.
A special tempering technique provides rapid chemical strengthening of flat glass. The process time is around 30 minutes. Through a new combination of the distribution of compressive and tensile stress in the glass, the lower depth of pres-stressing of the chemical tempering is significantly compensated for with similar strength values. This technique can also be used to pre-stress thin glass up to 0.5 mm and the geometrically undesirable changes in geometry (e.g. roller waves) are significantly less in comparison to thermally pre-stressed glass.
The paper presents the results of a study on small samples (100 x 100 x 4 mm³). The following aspects are examined in the investigations: Fracture pattern analysis; strength (double ring bending tests), anisotropy, toughening values (via Scattered Light Polariscope) and flatness of the glazing.
For the comparison, the following series of identical base glass are compared with each other (glassX; fully tempered glass, annealed glass).

Glass façades constructions typically uses plane panes. The main reasons lies in the flat glass manufacturing process, the practical handling in production and on-site installation in combination with low resulting cost. However, high deformation and stresses are inherited from the mechanical behaviour of that flat glass construction sytle due to activating only the eigen stiffness (and in case of glass laminates: Steiner-parts and shear coupling) of the glass panes. Today, glass layouts and especially the thickness of the glass panes are mostly determined by requirements for serviceability limit state (SLS) with a focus on maximum deflections, inducing thick glasses. This leads to high dead loads in façade constructions and induces increased economic and ecologic disadvantages while the potential of glass is not fully exploited. More efficient glass structures could be realised in the future if glass panes were locally reinforced by additional glass elements or local geometry reshaping (e.g. like profiled sheets) aiming at increasing the bending stiffness while reducing the glass thickness. Such approaches become possible with emerging technologies such as additive manufacturing or the local forming of glass panes without the need for expensive moulds. This article first reviews the current state of the art in various manufacturing technologies and approaches for the structural optimisation of glass panes. Then examples and experimental tests are presented to demonstrate the potential of structural optimisation in the field of glass façades. Glass structures that deviate from a flat configuration require more attention in a stress analysis. This aspect is also addressed in the paper. As a conclusion, the reviewed technologies will allow the significantly reduction of glass thicknesses, which represents an important contribution to the future design of customised and sustainable glass façades.