Consequence-based safety requirements for structural glass members

Glass is generally considered to be an unsafe material to use in building structures. To limit the risk associated with glass structures, there has been a focus on the probabilistic approach. This is insufficient for structures in general and for glass structures in particular. Much more than common structural materials like steel and reinforced concrete, glass is highly susceptible to a wide range of incidents causing glass breakage. Therefore, one should not (only) ask ‘when will the glass break?’ (probabilistic approach), but (also) ‘what will happen when is does?’ (consequence-based approach). Analysis of projects realized in practice show that structural engineers are aware of this, and use varying strategies to limit the consequences of glass failure. However, such strategies are applied to varying extent, depending on the engineer’s experience and opinion, location, structure type and probably on many more factors. Hence, an explicit consequence-based approach is proposed for structural glass members, in addition to the existing probabilistic approach. This approach sets specific requirements to the residual strength of structural glass members for a certain period of time, at prescribed levels of damage. The concept of Member Consequence Classes (MCC) is introduced, in order to be able to differentiate requirements for members based on their role within a structure and the function and accessibility of the structure at hand. The presented approach allows for an open discussion on the required level of residual strength at varying levels of damage. Furthermore, it provides a basis for comparing design options in terms of safety. Finally, because it sets requirements for the application of structural glass in any (building-) structural application, it provides a fundamental basis for the development of structural glass beyond the existing small scale glass structures like entrances, pavilions and conservatories.