Despite the increased popularity of the application of load bearing glass in the built environment, its design does rarely address sustainable or circular aspects. This Master’s Thesis analyses what the inﬂuence of connections is on the sustainable performance of structural glass and informs about the limitations and possibilities of sustainable glass design. To answer this question, sustainability has been deﬁned from literature which resulted in ten sustainable, circular design methods. The role of load bearing glass and its connections is discussed in these methods, and it is concluded that there are two main possible design strategies for a sustainable design. First, the biggest impact in design can be made when focus is on reuse as an afterlife application to increase the lifetime of glass elements. Secondly, impact can be made by limiting the
environmental footprint of the structure in the initial design by material minimization and selection. Recycling is left out of the scope since recycling on a world-wide scale barely occurs. Even in a country with a well developed recycling network like the Netherlands, just 5-10% of discarded ﬂat glass waste ends up back in the ﬂoat glass industries and the rest is downcycled to container glass or glass ﬁbres. Besides, the sustainable impact from recycling compared to reuse is far smaller, and measures to limit contamination are out of control of the designer. At ﬁrst, in order to design for reuse as an end-of-life application, demountable connections are essential and adhesive based connections should be avoided. Although demountability is a key to the circular economy, this study concludes that there are various technical barriers to overcome to make glass elements actually reusable. One important barrier is the lack of standardization in glass structures. As is shown in the redesign of "Kasteel Ruurlo", implementing standardization leads to a modular design and is integrated by using minimum size deviation and the use of a single type of connection. However, as a result of standardization, the design freedom of the architect is taken away and the mechanical connections lead to a less elegant design. Therefore, it is recommended to further development these modules and discuss elegance and design freedom in standardization. Another technical barrier to overcome is the performance and quality of glass elements which makes current reuse impossible: insulated glass units will loose their insulating performance due to failure of the edge sealant after 20 to 25 years, and laminated glass is prone to delamination over time. There is a lack of legislation which sets requirements to the quality and performance of these elements. Only for laminated glass, there is a potential reuse strategy which has been used in the redesign of "Kasteel Ruurlo". It is proposed to use a high quality interlayer as SentryGlas or Troﬁsol. For both interlayers, delamination problems should be further researched in order to assure a long technical lifetime.
Secondly, in order to minimize the environmental impact of the structure, the impact has been quantiﬁed using Life Cycle Analysis data and Environmental Product Declarations. With the method by "Stichting Bouwkwaliteit", this data is converted to shadow costs which is used to calculate the environmental footprint of a connection. Different structural connections are considered: various facade connections, different moment rigid frame connections and various ways to connect a panel. From this calculation, the different connections are compared and it is concluded that adhesive based connections have both a smaller environmental footprint than mechanical connections, and that these result in less material use in the overall structure and thereby limiting the environmental footprint. This is also reﬂected in the redesign of "Kasteel Ruurlo", where due to the mechanical demountable connections, the environmental impact increases compared to the current design. With current possibilities, the relation between the connection and a sustainable design depends on the type of connection: an adhesive based connection will result in an overall low environmental impact but makes reuse unlikely. A mechanical connection could be an outcome here, but with current possibilities, reuse cannot be guaranteed either. The application of current demountable connections on the reuse possibilities can therefore be argued. In order to succeed with structural glass in the circular economy, this research emphasizes the need for legislation, standardization and to solve problems like delamination and leaking insulated glass units which now determine the lifetime of glass structures. It also shows the need for demountable connections which increase the reuse potential and which ideally do not increase the environmental footprint.