AbstractsEngineering

The use of glass has been limited to windows for a long period of time. However, since the nineties of the 20th century, façades became more complex to cope with energy efficiency and also the use of structural glass became popular amongst designers. In both cases, thermal fracture of glass elements imply considerable costs and safety risks. In general, thermal fracture is caused by a temperature gradient in the glass pane. For example, the latter may appear because the part concealed within the surrounding frame remains colder, while the temperature of the central part increases due to solar radiation. Consequently, the edges are subjected to tensile stresses, which cause failure when exceeding the edge strength. For simple window configurations, the application of the existing empirical verification method is sufficient to avoid thermal fracture. However, these rules do not provide an accurate probability of failure, and are not applicable to the more complex façade constructions of today. Also, for structural elements, the combination of thermal actions and other actions must be considered. Therefore, a general and accurate method according to the safety principles of the Eurocodes should be developed. The safety against thermal fracture is determined by on the one hand the magnitude of the edge stresses caused by the climate actions and on the other by the glass edge strength. The latter is highly dependent on the defects, induced by the edge finishing process, including cutting, arrissing, grinding and polishing. Furthermore, humidity has a significant influence on the strength of glass when the edge is stressed during a long period of time; this phenomenon is known as stress corrosion. To estimate the edge strength of glass and the influence of humidity, a large experimental campaign was launched in the current study. Hereby, the influence of stress corrosion, load duration and load history, size and stress distribution on the edge strength was estimated. Next, a complex double skin façade (DSF) was simulated with real climate data at two locations in the Netherlands to investigate the environmental influence on the stresses at the edge. During the lifetime of the façade, the stress history was computed. From this, the distribution of the maximum yearly stresses was evaluated. Finally, the verification according to the Eurocodes was performed to estimate the safety against thermal fracture. This verification was performed with the distribution of the maximum values, but also with an equivalent lifetime stress, derived from the complete stress history. The latter method involves damage accumulation caused by reloading. The state of the art about thermal fracture is mostly empirically based, on the action side as well as on the resistance side. The theory of linear elastic fracture mechanics and stress corrosion describes well the edge strength of glass as it is strongly dependent on the damage caused by cutting and processing the edge and on the environmental environment. The approach in this theory can be…