This paper explores a novel restoration approach for consolidating historic structures using structural glass to substitute for the missing elements, preserving at the same time the structural integrity of the structure. A restoration design is proposed for the hypothetical consolidation of the remaining tower of Schaesberg Castle, in Limburg, The Netherlands. The masonry walls suffer from a significant loss of material and a temporary steel structure currently prevents the tower from collapsing. It is proposed to use stacked float glass to fill the missing parts of the wall. The connection between the old masonry and new glass is the most challenging aspect given the different physical and mechanical properties of the materials, which need to work together in a coherent way. Shear tests of various connecting materials are carried out in order to evaluate the performance of this connection with respect to aspects of compatibility and feasibility.

A novel, reversible structural system comprising interlocking, dry-assembled cast glass components is currently being developed at the TU Delft Glass & Transparency Lab. This paper, in continuation of the research conducted by (Oikonomopoulou et al. 2018a), investigates the mechanical properties of different materials that function as dry interlayers for interlocking cast glass structures. The interlayers should be preferably transparent, able to be pre-formed to the desired shapes, and resistant to UV-radiation-induced colour shifts, long-term compressive loads and creep. Based on the above criteria, polyurethane (PU) rubber with a shore hardness between 60A - 80A is chosen as the most suitable material. Accordingly, different readily available PU interlayers are selected and cast in the desired shape. Each interlayer is introduced between two interlocking osteomorphic cast glass components (bricks) and the assembly is tested under compression in series of 3 specimens. The experiments indicate that for the harder interlayer variants, failure mainly occurs due to peak stresses occurring at the shortest section of the brick, where the manufacturing tolerances of the concave-convex surface are the highest, leading to mismatch, i.e. incomplete contact at that area of the interlayer with the glass units. The stiffer interlayers further contribute to the failure due to the increased shear stresses induced at the edges of the interlocking surface while they are deforming. This is evident by the radial breaking pattern of the failed glass blocks. Interlayer variants with low tear resistance fail due to the perforation of the interlayer leading to glass-to-glass contact. Still, all specimens with interlayer in between presented a considerably higher failure stress than an assembly with no interlayer, highlighting the critical contribution of the PU to the structural performance of the system.

The applicability of glass in structures is continuously ascending, as the transparency and high compressive strength of the material render it the optimum choice for realizing diaphanous structural components that allow for light transmittance and space continuity. The fabrication boundaries of the material are constantly stretching: visible metal connections are minimized and glass surfaces are maximized, resulting to pure all-glass structures. Still, due to the prevalence of the float glass industry, all-glass structures are currently confined to the limited forms and shapes that can be generated by planar, 2D glass elements. Moreover, despite the fact that glass is fully recyclable, most of the glass currently employed in buildings is neither reused nor recycled due to its perplexed disassembly and its contamination from coatings and adhesives. Cast glass can be the answer to the above restraints, as it can escape the design limitations generated from the 2-dimensional nature of float glass. By pouring molten glass into moulds, solid 3-dimensional glass components can be attained of considerably larger cross-sections and of virtually any shape. These monolithic glass objects can form repetitive units for large all glass-structures that do not buckle due to slender proportions and thus can take full advantage of the stated compressive strength of glass. Such components can be accordingly shaped to interlock towards easily assembled structures that do not require the use of adhesives for further bonding. In addition, cast glass units–due to their increased cross section– can tolerate a higher degree of impurities and thus can be produced by using waste glass as a raw source.

This paper explores the potential of a novel, reversible all-glass system consisting of dryassembly, interlocking cast glass components. Owing to its interlocking geometry, the proposed system can attain the desired stiffness with the aid of minimal, if any, metal framing. The use of adhesives is circumvented in the system by employing a dry, colourless interlayer as an intermediate medium between the glass components. The interlayer can accommodate by deformation surface asperities; furthermore, it allows for an even stress distribution and for the eventual disassembly and reuse of the components. To validate the concept, various component geometries and interlocking mechanisms are developed. The interlocking forms are kiln cast in 1 : 2 scale and are comparatively assessed in terms of mechanical interlocking capacity, mass distribution, residual stress generation and ease of fabrication. In parallel, research is conducted on different materials for the dry, transparent interlayer. From the developed designs, osteomorphic blocks are selected as the most promising concept and are further assessed by numerical modelling to investigate the influence of the interlocking geometry to the overall structural performance. The results of the numerical model indicate that lower bricks are more susceptible to bending, whereas for higher brick variants the shear lock failure is more critical. To further validate the concept, two specimens of stacked glass columns comprising osteomorphic blocks and different interlayers are tested in compression until failure. The failure mode of the specimens suggests an increased fracture toughness of the proposed system compared to a monolithic variant, preventing cracks propagating from one brick to another and an inherent robustness The experiments also suggest that an interlayer of increased shear strength is recommended to prevent tearing under compression and thus avoiding direct glass-to-glass contact.

This research investigates the potential of glass as a new design tool to highlight and safeguard our historic structures. Current restoration and conservation treatments with traditional materials bear the risk of conjecture between the original and new elements, whereas the high consolidation demands often result in visually invasive and irreversible solutions. Nowadays, aspects of materiality and aesthetics appear as integral parts of the restoration practices, indicating new materials and technologies in the form of ambiguous gestures rather than absolute and permanent manifestations that prevail over the historic structures. The inherent transparent properties render glass a distinct material that enables the simultaneous perception of the monument in both its original and ruinous state. The emerging technologies have set the ground for using glass in a structural way minimizing the need for substructure and maximizing transparency, while protecting the sensitive historic materials. The paper explores the feasibility of this concept addressing aspects of structural compatibility, reversibility and aesthetics, through a review of realized examples. Finally, a methodology is developed to relate the glass products, available in the market today, to the possible consolidation treatments in respect to the degree of intervention and representativeness, stressing the potential of using and considering glass as a promising restorative material.

This research investigates the potential of glass as a new design tool to highlight and safeguard our historic structures. Current restoration and conservation treatments with traditional materials bear the risk of conjecture between the original and new elements, whereas the high consolidation demands often result in visually invasive and irreversible solutions. Nowadays, aspects of materiality and aesthetics appear as integral parts of the restoration practices, indicating new materials and technologies in the form of ambiguous gestures rather than absolute and permanent manifestations that prevail over the historic structures. The inherent transparent properties render glass a distinct material that enables the simultaneous perception of the monument in both its original and ruinous state. The emerging technologies have set the ground for using glass in a structural way minimizing the need for substructure and maximizing transparency, while protecting the sensitive historic materials. The paper explores the feasibility of this concept addressing aspects of structural compatibility, reversibility and aesthetics, through a review of realized examples. Finally, a methodology is developed to relate the glass products, available in the market today, to the possible consolidation treatments in respect to the degree of intervention and representativeness, stressing the potential of using and considering glass as a promising restorative material.

Cast glass components are a promising solution for engineering pure glass structures of high transparency and load-carrying capacity due to their large cross-sectional area and monolithic nature. Currently, the few realized structures employing cast glass components rely either on a steel substructure or on an adhesive of high bonding strength and typically less than 2 mm thickness, to ensure the stiffness and stability of the construction. Whereas the first solution compromises the overall level of transparency, the second results to a permanent construction requiring intensive and meticulous labour and extreme accuracy. This paper explores the potential of a novel, reversible all-glass system comprising dry-assembly, interlocking cast glass components as a promising and sustainable solution that can avoid the above-mentioned challenges. Owing to its interlocking geometry, the proposed system can attain the desired stiffness and stability with the aid of minimal, if any, metal framing. Furthermore, the suggested system circumvents the use of adhesives by using a dry, colourless interlayer as an intermediate between the glass components to accommodate any dimensional tolerances and allow for an even load distribution; moreover, it allows for the disassembly and circular use of the components. To validate the concept, different component geometries and interlocking mechanisms are developed. As a proof of concept, the most promising interlocking forms are kiln cast in 1:2 scale and assessed in terms of mechanical interlocking capacity, mass distribution, residual stress generation and ease of fabrication. In parallel, research is conducted on different materials for the dry, transparent interlayer. From the developed designs, blocks with osteomorphic interlocking mechanisms are selected as the most promising concept and are further assessed by numerical modelling to study the influence of the interlocking geometry to the overall structural performance. The results highlight the structural potential of the proposed system and demonstrate its feasibility.

This research investigates the potential of glass as a new design tool to highlight and safeguard our historic structures. Current restoration and conservation treatments with traditional materials bear the risk of conjecture between the original and new elements, whereas the high consolidation demands often result in visually invasive and irreversible solutions. Nowadays, aspects of materiality and aesthetics appear as integral parts of the restoration practices, indicating new materials and technologies in the form of ambiguous gestures rather than absolute and permanent manifestations that prevail over the historic structures. The inherent transparent properties render glass a distinct material that enables the simultaneous perception of the monument in both its original and ruinous state. The emerging technologies have set the ground for using glass in a structural way minimizing the need for substructure and maximizing transparency, while protecting the sensitive historic materials. The paper explores the feasibility of this concept addressing aspects of compatibility, reversibility and transparency, through a review of realized examples. Finally, a developed methodology relates the, available in the market today, glass products to the possible consolidation treatments in respect to the degree of intervention and representativeness, stressing the potential of using and considering glass as a promising restorative material.

This paper investigates the potential of cast glass structural components in architectural applications. Initially, the commonly applied casting methods, glass types and mould types are discussed. To address both the possibilities and limitations in the size and form of cast glass components, an overview of the largest monolithic pieces of cast glass ever made is presented, from giant telescope mirrors and nuclear glass blocks to massive artifacts. Weighing several tons each, these cast glass pieces are assessed with comparative charts of technical data collected from literature, industry and field research, regarding their geometry, materialization, manufacturing method and annealing process. The data highlight not only the potential but also the practical implications involved due to the meticulous and time-consuming casting and annealing process of three-dimensional glass elements. Learning from the extreme, proposals are made for optimizing the size, shape and casting process of cast glass components suitable for architectural applications. Subsequently, the state-of-the-art architectural examples employing cast glass are analyzed and evaluated in terms of manufacturing, structural system, level of transparency, ease of assembly and disassembly. Based on the findings the authors suggest new design concepts for cast glass components that can take full advantage of the glass’ properties and can result in novel, transparent, yet load-bearing architectural applications.

This paper investigates the application of structural glass in restoration and conservation practices in order to highlight and safeguard our built heritage. Cast glass masonry is introduced in order to consolidate a half-ruined historic tower in Greece, by replacing the original parts of the façade that are missing. Dry connections between the elements contribute to a completely reversible system that complies with the conservation guidelines suggested by the Venice Charter, while the interlocking nature of the glass units ensures the overall stability and the desired structural consolidation of the monument.

The application of structural glass as the principal material in restoration and conservation practices is a distinguishable, yet discreet approach. The transparency of glass allows the simultaneous perception of the monument at both its original and present condition, preserving its historical and aesthetical integrity. Concurrently, the material’s unique mechanical properties enable the structural consolidation of the monument. As a proof of concept, the restoration of Lichtenberg Castle is proposed. Solid cast glass units are suggested to complete the missing parts, in respect to the existing construction technique and aesthetics of the original masonry. Aiming for a reversible system, the glass units are interlocking, ensuring the overall stability without necessitating permanent, adhesive connections. This results in an elegant and reversible intervention.