The emerging interest in the architectural applications of cast glass components reveals a knowledge gap on the mechanical properties of cast glass. Apart from its chemical composition, cast glass is characterized by its manufacturing history and thermal profile, often inheriting a set of defects that define its properties. The role that inhomogeneities in the bulk of voluminous glass components have on the strength of the final product is also uncertain. Systematic testing is therefore necessary for the safe structural application of cast glass. Towards this direction, the presented research aims to experimentally investigate the fracture resistance of cast glass under sharp contact loading, by means of a customized splitting test using a sharp linear indenter. Cubic specimens with 50 mm sides are kiln-cast at low forming temperatures, employing a variety of silicate-based cullet and firing schedules and their inherent defects are documented. The results of the splitting tests show that the borosilicate specimens fail at the highest splitting force, followed by the soda lime float specimens, while the fused or porous specimens have a significantly lower resistance to fracture. The strength order of the various glasses, as this results from the splitting tests- is opposite to that found earlier in four-point bending tests, due to the different fracture mechanisms activated. The fracture resistance of a glass specimen is governed, first by its ability to deform around the indenter to relief the developing stresses and then by its bond strength to resist crack propagation. Thus, a good balance between glass network flexibility and high bond dissociation energy is required, explaining why the tested homogeneous borosilicate and soda lime glasses are more resistant than the modified soda lime compositions with high alkali content. In addition, the fractographic analysis indicates that the non-stress inducing flaws in the bulk have a negligible contribution to the fracture resistance of the specimens.

A unique structural design was made for the glass façade of the Co-Creation Center building in Delft. The roof is completely carried by the glass fins. The fins are laterally stabilized by being included in the triple glazed façade. To certify the safety of the design full scale tests on the fins were done at Delft University of Technology. Due to a transportation accident the fins were damaged at one end. This allowed an additional study into the effect of this pre-test damage on the residual compressive stressed induced by the tempering. It was found that the residual stresses were not significantly affected by the damage. During the compression tests no cracks developed at the damaged ends. A load of 200 kN, more than double the maximum design load did not produce failure in the prototypes. After intentionally seriously damaging all plies of the fins, the fins could still carry the 200 kN load for 30 min without buckling or other failures being noted. Measurement of the residual stress in the outer plies of the fins after damage showed that sufficient residual stress was present in the larger fragments of the prototype to provide enough stability in combination with the Sentryglass laminating foil.

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.

The investigation of new compositions is crucial for the expansion of possible applications of glass, from the typical applications for building engineering, in the form of cast blocks or float glass, to more advanced technologies, such as 3D-printed glass or glass-to-metal connections. Since high melting temperatures and brittleness are two important drawbacks of glass, this work aims to improve both properties. Characterisation techniques, such as thermal analysis, nano-indentation, and UV/VIS spectroscopy, are used to evaluate the properties of the samples. The modification of the properties is achieved via changes in the composition of the glass, using compounds such as phosphorus pentoxide, aluminium oxide and boron oxide. Then, the choice of different glass formers and modifiers contributes to the development of compositions with lower melting and glass transition temperatures. The reduction of the melting temperature allows a saving of energy during the manufacturing. The structures of the glasses differ from the standard soda–lime–silica and borosilicate glasses, leading to a different mechanical behaviour. Furthermore, these new compositions incorporate up to 35% of fly ash in their formulas. The valorisation of these by-products reduces costs and gas emission.

Connecting glass with heat bonds is a way to create all-transparent glass structures. Two methods have been researched in theory and practice, glass welding, through local heating, and glass fusion through global heating. Both methods have been applied to produce 10 mm thick T-sections of soda lime glass while preventing thermal shock failure and minimizing residual stress. These specimen, and specimen with an adhesive joint, have been tested destructively. It is concluded that it is possible to connect 10 mm thick soda lime glass by welding, if the glass is preheated and the surrounding temperature remains elevated during the welding process. Additionally, glass fusion of a similar product through global heating is possible for the applied temperature schedule. The mould has a paramount influence on the quality of the product. For both production methods, the annealing schedule was adequate to reduce residual stress. The average strength of the fused specimen was 44% larger. The standard deviation of the welded specimen was smaller: the standard deviation relative to the mean value was 9% for the welded specimen and 60% for the fused specimen. However, the amount of tested specimen is little. This research is a proof of concept for heat bonding soda lime glass of a structurally relevant thickness.

Currently, tons of high quality commercial glass are down-cycled or landfilled due to contaminants that prevent close-loop recycling. Yet, this glass is potentially a valuable resource for casting robust and aesthetically unique building components. Exploring the potential of this idea, different types of non-recyclable silicate glasses are kiln-cast into 30 × 30 × 240 mm beams, at relatively low temperatures (820–1120∘C). The defects occurring in the glass specimens due to cullet contamination and the high viscosity of the glass melt, are documented and correlated to the casting parameters. Then, the kiln-cast specimens and industrially manufactured reference beams are tested in four-point bending, obtaining a flexural strength range of 9–72 MPa. The results are analysed according to the role of the chemical composition, level of contamination and followed casting parameters, in determining the flexural strength, the Young’s modulus and the prevailing strength-limiting flaw. Chemical compositions of favourable performance are highlighted, so as critical flaws responsible for a dramatic decrease in strength, up to 75%. The defects situated in the glass bulk, however, are tolerated by the glass network and have minor impact on flexural strength and Young’s modulus. The prerequisites for good quality recycled cast glass building components are identified and an outline for future research is provided.

It is not obvious to talk about glass recycling when we realize that a mature recycling procedure for glass bottles is already working well. However, apart from glass bottles, unfortunately, that a large amount of glass will disappear into landfills. This large quantity of unrecycled glass indicates that there is a large potential in upgrading the glass recycling process. In the field of architecture, we see a fast-growing interest in using glass, also for structures. The glass bricks of Crystal Houses in Amsterdam are a good illustration. Aiming at maximizing the recyclability of glass, this paper focuses on the structural use of the glass components made from recycled glass through kiln casting method. An overview of the existing glass recycling industry is given at the beginning, followed by a discussion of glass type to be recycled. After this the experimental process of the glass recycling is introduced, which uses coated float glass with tints as the basic material to be recycled. Following this, a further exploration in three structural properties of the recycled products is conducted, namely: Young’s modulus, coefficient of thermal expansion and the fracture strength, with mechanical experiments. Finally, the test results are analyzed together with the chemical composition of the recycled products, which is derived from X-ray fluorescence (XRF) analysis. The result contains the value of mechanical properties and it evaluates the possibility of the structural use as a recycled-float-glass beam. In the end of this paper, the future possibility and feasibility in structural application of recycling waste float glass are discussed.

The majority of glass used in structures is as planar elements. Some projects exist that use linear glass elements. This paper discusses in broad terms the design, engineering and fabrication of a unique vector active glass structure.

This paper presents a novel approach to modelling and documenting design knowledge: to use parametric technology to explicitly store knowledge which exists in a group of people (such as a company), so that it can be reused over many projects and grow over time when more projects are designed. This approach has been applied and tested on a test case of common concrete viaducts. The outcome constitutes the first iteration of the development of a parametric viaduct design platform, aimed for architects and structural engineers. The motivation was to counter the fragmentation of the Architecture, Engineering & Construction (AEC) industry, where each discipline encapsulates different knowledge areas, which results in miscommunication and the loss of valuable information and time. The suggested methodology aims at combining the BIM principles [1] with the concepts of parametric and associative design, as well as visual programming [2] to develop a common design platform for the architect and the structural engineer. Such a platform ensures that both disciplines are working on the same design and merges their different knowledge areas into one model. The knowledge model evolves from a top-down UML diagram into a user-friendly, parametric platform for viaduct design implemented in Dynamo [3].

In many famous architectural works, it is the structure and materiality of the building that manifest the project’s innovation. In such works, the structural system of the building becomes the primary form of expression. Ergo, the ability to understand the principles of structural engineering and design, and the motivation to experiment with new types of structures and materials are invaluable assets for both architects and structural engineers. Towards this goal, a series of elective courses (Shell structures, Glass structures, Bridge Design) have been integrated in the curriculum of the MSc of Building Technology at the Faculty of Architecture and the Built Environment (BK) and of the MSc of Building Engineering at the Faculty of Civil Engineering and Geosciences (CiTG) at TU Delft. Aim is to bridge the gap between architects and structural engineers. Each of these courses lasts 10 weeks and focuses on the design, engineering, calculation and materialization of a different type of structure. This paper will discuss the set-up, learning objectives, methodology and output of the “Technoledge-Glass Structures”(BK) and the “Structural Glass” (CiTG) courses. Aim of these parallel courses is to effectively teach students, of both architectural and civil engineering backgrounds, how to design, engineer and evaluate the behaviour of structures made entirely out of glass elements and how to tackle problems related to the practical aspects of a construction.

The success of projects such as the Crystal Houses façade in Amsterdam has triggered an increasing interest from architects, engineers and glass producers in the development and application of structural cast glass components. This interest raises, simultaneously, the needs for a controlled manufacturing process, a system for quality control and structural validation, to guarantee the production of safe components. Manufacturing-related flaws, such as stones, cord inclusions, or air-bubbles, occurring in the mesostructure of the components, form weak zones within the material and may lead to “spontaneous” cracking. The casting parameters such as the forming temperature and corresponding glass viscosity, the dwell time at this temperature and the cooling rate, largely determine the homogeneity of the final product. Additional complexity arises once the use of waste/recycled glass is considered, due to the probable presence of variable glass compositions and miscellaneous contaminants in the initial batch. The risk of inhomogeneity and resulting eventual mechanical failure, indicates the necessity of understanding the causes of flaw-formation and the impact of the developed flaws on the structural performance of the cast components. Therefore, a series of 50mm cubic glass components are cast at the TU Delft Glass Lab, using a selection of already formulated discarded soda-lime glasses from different commercial applications. The cubes’ meso-structure is documented and- when required- scanned employing a Computer Tomography scanner and a polariscope to identify possible density differentials and internal stresses respectively. Then the cubes are tested for splitting strength and their performance is analyzed in relation to the previously documented flaws. The destructive tests suggest that there is a correlation between the meso-structure, structural performance and failure pattern of the cast glass components.

The majority of glass used in load-bearing structures is as planar elements. Some projects exist that use linear glass elements. This paper discusses in broad terms the design, engineering, and fabrication of a unique vector active glass structure consisting of glass bundles and partly printed steel connections. A structure was conceived that utilizes the glass bundles in a way that can be directly experienced by the users: a swing. To create a non-standard form for the swing, a structural optimization procedure was used. To realize the structure, a novel steel node was developed and produced using an additive manufacturing technique in steel. These novel applications have made the project innovation heavy, particularly considering the limited timeframe for its development and construction. Description is given of the several optimization techniques incorporated in the digital process, the assembly and testing of the glass bundles, and the manufacturing of the steel nodes by Wire and Arc Additive Manufacturing.

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.

Although in theory glass can be endlessly re-melted without loss in quality, in practice only a small percentage gets recycled, mainly by the packaging industry. Most of the discarded glass fails to pass the high quality standards of the prevailing glass industry – due to coatings, adhesives, other contaminants or incompatibility of the recipe – and ends up in landfill. However, using discarded glass in cast components for building applications can be a good way to reintroduce this waste to the supply chain. Such components can tolerate a higher percentage of inclusions, without necessarily compromising their mechanical or aesthetical properties. This paper explores the potential but also the limitations of recycling glass in order to obtain load-bearing components. First, an overview is provided regarding which types of glass reach the recycling plants and which not, arguing on the reasons behind this selection. Afterwards, a series of experiments is presented, exploring the possibilities of recycling everyday glass waste, from beer bottles and Pyrex trays to mobile phone screens. Each type of glass waste is cast at different temperatures and firing/cooling rates to define its flow capability and risk of crystallization. The above information is linked to the X-ray fluorescence (XRF) analyses of the samples prior to recycling. The results point out the types of glass with potential in structural applications, and the overall feasibility of the concept. This paper is an extension of previously reported work by Bristogianni et al. 2018.

Structural Glass is defined as an application of the material glass in a main bearing structure of for example a building or a bridge. Involvement started for the author in 1986, with designing and building of the Sonsbeek pavilion and continues, up to present, with the completion of the Taipei Performing Arts Centre expected in 2019. This editorial is divided in four chapters; the first one concentrates on bridges, the second on facades, the third on cast glass and the last chapter is on future developments. Ongoing research is discussed at the end of each chapter. One could say that the Roman, bronzed framed, glass panels, known from excavations in Pompeii, were the first application of glass as “structure”: they had to withstand wind load and the influences of the outside climate. However, this is a secondary structure, what we are now looking for is the use of glass in primary structures and, very important, because glass is a delicate material, these primary glass structures have to be robust, according to the demands of the Eurocodes.

A Glass Truss Bridge has been constructed on the Green Village on the campus of Delft University of Technology (TU Delft) by the Glass & Transparency Research group (faculties of Architecture and CiTG). The bridge has been fitted with as many glass components as was structurally feasible, showcasing the group’s research into the structural application of glass in the built environment. The diagonals in the truss are glass bundle struts and the nodes of the truss are cast glass components. The lenticular truss will serve as a temporary bridge. Because of the experimental nature of the truss, with its unusual and novel applications of structural glass, a number of demonstrative proof loadings were performed to ease concerns about the safety of the structure. The glass bundles have been proof-loaded to twice their maximum expected load just prior to their installation in the structure. The whole bridge, once installed, has then been proof-loaded for several critical load combinations (static and dynamic) just after installation. During the proof-loading the strains in the glass diagonals have been measured. These lie well within the acceptable limits. In the paper the structural design of the bridge, in particular the glass node connector and the glass bundle diagonals will be explained. Then the proof-loading of the bridge will be described and the results of the proof-loading are presented and discussed.

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.

Steel-to-glass laminated connections, which have recently been developed, limit stress intensifications on the glass and combine strength and transparency. Transparent Structural Silicone Adhesive (TSSA) connections have been used in several projects worldwide; however, the hyperelastic and viscoelastic nature of the material has to date not been fully investigated. In this work, the first objective is to investigate the mechanical response of TSSA connections under static and cyclic loading by means of experimental tests. Firstly, the shear behaviour of TSSA circular connections is characterized by means of monotonic and cyclic loading tests. The adhesive exhibits significant stress-softening under repeated cycles that becomes