Challenging Glass Conference 9 is held 19 & 20 June 2024 at Delft University of Technology (TU Delft).
Organisers:
Prof. Christian Louter (TU Delft)
Dr Freek Bos (TU Munich)
Prof. Jan Belis (Ghent University)
Co-Hosts:
Prof. James O'Callaghan (TU Delft)
Prof. Mauro Overend (TU Delft)
Dr Fred Veer (TU Delft)
Cover image: Mirage - Apple Park - by Katie Paterson and Zeller & Moye
Photo by: Dr Faidra Oikonomopoulou
Welcome at Challenging Glass!
At this 9th edition of the conference, we are thrilled to welcome no less than 120 presentations - a record since the first edition of this international event back in 2008.
Ever since, we have been keeping up our high standards in sharing knowledge, science and best practices on glass engineering and design. Thanks to the great work of bright authors and sharp reviewers, that is not different this time.
What actually ís different this edition, is the introduction of a Glass Circularity Debate. We have seen several trends come...
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In comparison to traditional glass casting, glass additive manufacturing (AM) presents an opportunity to increase design flexibility and reduce tooling costs for the production of highly variable geometries. While the latter has been extensively explored for masonry units, there is minimal research on the former for its viability to produce structural building components. This paper encompasses design, manufacturing, and experimental testing to assess the feasibility of using glass AM to produce interlocking masonry units for the construction industry. The glass 3D printer employed in...
This study investigates the feasibility of 3D printing with recycled glasses, focusing on comparing viscosity characteristics and extrusion behaviors of studio soda-lime glass, recycled soda-lime container glass, and recycled float produced window glass. Employing multiple methodologies, we analyzed the temperature-viscosity curves of these glass types, providing an understanding of their thermal properties in relation to 3D printing process and applications. We employed infrared (IR) thermography to calibrate the glass printer and gain insights into the characteristics of each glass...
Additive manufacturing (AM) has opened new possibilities in many disciplines. Complex geometries can now be created from a variety of materials and material compositions that were previously unimaginable. As a result, there is also the potential for customization and personalization for each user. The present paper and the related research provide insight into the possibilities to further process glass by additive manufacturing methods and thereby exploring the potential for the built environment. This research focuses on developing AM glass components to be used as point fixings for...
The brainwave of spray printing glass (SPG) emerged in September 2021 and has become a feasible way of applicating glass in thin layers in June 2022. The whole idea started from a sustainable motive: Can we use less material and less energy for glass elements? Based on the theoretical background of repairing old diesel engines, physical tries were made with acetylene torches blowing glass powder on a glass plate, fusing the glass powder particles to a glass panel. The first result of SPG was an opaque substrate on a transparent panel. From there on...
Structural glazing joints in glass construction are subject to dynamic earthquake loads in certain regions. To date, however, there is no recognized proposal for the design of such situations. The verification for earthquake loads is either neglected for glass structures or carried out with equivalent values for the entire building. Not considering the behaviour of the bonded joints under dynamic loading might be insufficient, especially in the presence of heavy glass elements. Dynamic loads on bonded glass constructions with silicones or polyurethanes influence the structural design...
This work aims to characterise the behaviour of structural adhesives for timber-glass connections by performing experimental tests and calibrating numerical models. An adhesive bond between timber and glass can solve two conflicting requirements in timber frame structures.: i) horizontal stability provided by shear walls/vertical diaphragms; ii) large open spaces to maximize the flexibility of the building's use. One solution to this challenge is to increase the number of diaphragms in the timber frame building's façade, which can be achieved by structurally activating the glass panels....
In addition to static loads, structural glazing joints in glass and facade construction in many regions are subject to extraordinary effects such as earthquakes. Seismic actions are characterized by a randomly recurring and dynamic load that affects the structural behavior of the viscoelastic material. Publications on the load-bearing behavior and design of structural glazing joints against seismic loading have not systematically considered these effects. In this paper, relevant parameters influencing the seismic loading of structural glazing joints are determined, evaluated, and...
Integrating glass as a load bearing part of the structure of a ship requires methods of connecting glass to the ship’s structure which are novel within shipbuilding practices. Adhesive bonding is a suitable method of connecting glass to metal in ships and is typically used to bond window panes to metallic frames, although usually with a flexible adhesive. This paper presents the findings of the evaluation of an epoxy adhesive for structural glass to steel continuous bonds. The epoxy adhesive is chosen for its high strength and load transferring capabilities. To accommodate geometric...
In Structural Silicone Glazing (SSG) when applied to unitised curtain wall systems typical practice incorporates a pair of dead load plates intended to carry the glass self-weight and so avoid subjecting structural silicone to permanent shear. However in reality, due to the fabrication sequence and system behaviour some loads can occur which will be resisted permanently by the structural silicone. In a hung and sworded system (H&S), designers typically assume that slab deflection, or inter-story drift will cause a unitised panel to lift off from one support and so change the load...
Given the need to create a sustainable future with limited resources and growing environmental concerns, high-strength adhesives offer an alternative and potentially more efficient load-bearing connection to conventional bolted connections in glass structures. However, there is a lack of knowledge on the elevated-temperature effects on the mechanical strength of these connections. Therefore, in this paper, an experimental program was conducted to evaluate and compare the performance of transparent bonded glass joints. A transparent epoxy adhesive Loctite EA 9455 and two glass types...
This study aims to explore innovative structural applications involving the bonding of glass to concrete. To date, academic literature has provided limited insights into the adhesive bonding between glass and concrete. This investigation focuses on understanding the bond behaviour of glass-concrete joints through small-scale three-point bending tests. The analysis shows how variations in the adhesive joint configuration and the selection of adhesives impacts the bond behaviour. By systematically examining these factors, the aim is to provide valuable insights into optimising the design...
Fluids in the cavity can be used to integrate additional functions into insulating glazing. However, the high permanent load exerted by the fluid on the glazing and surrounding components is problematic. Conventional design methods result in large adhesive joints, which are not desirable from an aesthetic point of view. ETAG 002-1 is typically used for the design of structural adhesive bonds for use in structural glazing façades. However, the calculation is considered to be conservative. In particular, it is criticised for its deterministic safety...
It has been identified that current standardised method for structural sealant joint dimensioning is applicable to flat rectangular panels only and no provisions are made for panels with curved surfaces. The purpose of this study is to investigate the stress distribution along the sealant joint of a cylindrically curved glass panel subjected to wind pressure and to establish if the panel curvature influences the stress distribution along the joint length. Using numerical method, several curved units were analysed and the results have shown that the out of plane wind action generate...
This study is part of a comprehensive research to develop a better understanding of the structural performance of Glass-GFRP composite façade panels. Composite sandwich façade panels exhibit significant potential for replacing non-composite counterparts, attributed to their superior structural strength and higher stiffness. These sandwich panels not only offer higher structural efficiency but also present the opportunity for a more visually appealing façade panels, allowing for slimmer profiles and greater spans. Nevertheless, the use of composite façade panels is to be investigated more...
Sustainability, and more specifically embodied carbon emissions, have become one of the most prominent challenges for the facade industry. Discussions around the topic focus on the global warming potential of materials and their recycled content, whilst efficiency and innovation in design as a way to reduce embodied emissions have not yet received the same level of attention. This article proposes evolved structural design and detailing methods for glass-metal facades that minimise the amount of materials needed to meet their serviceability and structural integrity requirements. The...
For glass constructions with a high degree of transparency, facade systems with structural sealant glazing are increasingly being used. However, the use of bonded joints is also suitable for many other applications in glass construction. Even today, the design of bonded joints is still based on the outdated global safety concept according to ETAG 002. Although the safety and predictability of hyperelastic
silicone bonds have been continuously shown by research activities during recent years, high levels of safety are still required in the design, which is mainly due to the expected...
Light Forms is a compressive glass block system aimed at creating site-specific architectural structures that investigates three-dimensional forms studied for light transmission and structural performance. Building on the success of previous cast glass architectural blocks, Light Forms expands this work by adhering two components to create a single glass modular unit that offers the following unique opportunities. First, through the process of industrial press forming, mass production on the industrial...
Advances in structural glass have enabled a new paradigm in expressive and transparent architecture. Cast glass can further extend the possibilities of structural glass by allowing for more complex and sophisticated shapes than the current planar geometries of structural float glass. However, the use of cast glass is currently limited because of the lengthy annealing process, making massive component sizes impractical to fabricate. Topology optimization (TO) has been proposed as a solution to this problem, as it is known to
generate structurally efficient designs with a low volume...
Cast glass represents a captivating material for artistic expression and innovative façade elements. However, the allure of cast glass comes with its own set of challenges. One of the foremost difficulties lies in achieving secure and durable bonds between individual glass components. Unlike other materials, the smoothness of glass surface requires specialized techniques and materials to maintain
both the structural integrity and aesthetic cohesion. Furthermore, the brittle nature of glass demands that the movements of the structure be absorbed by the bonding material to mitigate...
Glass casting displays great forming potential allowing for the realisation of three-dimensional glass elements of virtually any shape and size, as showcased in glass art. Disposable mould technology seems to be ideal for the fabrication of such customised and complex geometries, including for architectural and structural cast glass components deriving from structural Topology Optimization (TO), since it offers great shape freedom and cost effectiveness. However, currently, glass casting on disposable moulds faces the major drawback of a resulting rough and opaque glass surface quality,...
Glass is an energy intensive material that is essential to buildings and their energy consumption. Its transparency allows for natural daylighting and the use of solar heat gains. In the context of the refurbishment politics of the EU as a result of the Paris Agreement on climate goals, significant amounts of glass waste in form of windows and façades are to be expected. In order to minimize the environmental impact of glass by preserving the embodied carbon and substitute newly produced glasses, the Re-use of glass is considered to be of highest potential. When reusing panes, energy and...
This article presents the metric avoided carbon for the reuse of aluminium unitised curtain wall façades from a donor building in a receiving building. The metric is used to compare seven proposed circular reuse strategies, each showing a different gradation of reuse. Based on literature and reference studies, we identify those parts of the façade where reuse has the most impact and is technically feasible. The seven reuse strategies and the avoided carbon method are applied on a real case study building as donor project and a fictive building as receiving project. We...
The adoption of glass reuse in construction faces challenges due to higher costs and more perceived risks compared to new glass. This conflicts with the goal of a circular economy. To challenge this status quo, this article explores a hypothetical scenario where glass becomes a scarce commodity. What if the float glass production process ceases to exist due to energy resource depletion, raw material scarcity, or carbon budget constraints? In such a context, glass reuse will be crucial. This article discusses the design, logistics and quality related challenges of reusing float glass,...
Brazil has a low percentage of recycled container glass due to multiple factors, such as inadequate waste collection and recycling infrastructure, low public awareness about recycling's significance, and insufficient laws to promote it. In addition, the country faces high levels of homelessness and inadequate housing. As a result, an increasing number of builders are exploring repurposing glass bottles as a construction material for walls, occasionally incorporating them into traditional earthen building techniques. Therefore, this paper...
Our research examines the viability of recycling soda lime glass from post-consumer Insulated Glass Units (IGU), mixing various types of architectural glass cullet and fusing them into flat plates by using electric kilns. Those kilns operate at lower temperatures than standard float glass production, which significantly reduces manufacturing emissions. The research outcomes suggest the potential for near-site operations, reducing transportation logistics, costs, and emissions. Strength and emissivity tests were performed on the recycled glass...
Increasing the circularity of flat glass does not only mean to collect glass cullet from internal and pre- consumer processes. It also means to use glass cullet from the post- consumer applications, such as residential or commercial buildings. The flat glass industry is currently in a transformation phase to reduce its CO2 emissions. To produce Low Carbon Glass with reduced carbon emissions generated during the production of float glass, a holistic approach is applied. Among these, one of the pillars is the increased use of cullet. Cullet comes from different sources: internal...
Closed loop recycling of end of life building glass rarely happens, with most glass manufacturers declaring less than 1% post-consumer content in their new glass. Instead, it follows a linear process and is often crushed together with other building materials and put into landfills or recovered to low grade fill applications. Could this be the most important challenge for the glass industry, as we consider strategies for combatting embodied emissions and creating a circular economy? This paper will utilise the findings from the author’s MSc Façade Engineering thesis and explain both the...
Remanucycling is the process of disassembling a product at its end-of-life into its constituent parts and materials with the purpose of maximizing their reclamation potential. The components which are still in good working conditions can be used as constituent for remanufacturing new products, those that cannot be used for remanufacturing can then be recycled and eventually downcycled, whilst the landfill path is to be banned. For remanucycling to occur products must be disassemblable and the resulting components fit for the purpose. This applies to the most widespread architectural...
Many office and residential buildings in Europe need to be renovated in the near future to meet current energy efficiency requirements. This often comes down to updating the insulation performance of the building envelope including the windows. Most “old” windows consist of a frame and a double insulated glass unit (IGU) or even monolithic glass panes – typically without any low-e coating. These non-coated double glazings have an Ug-value of 2.7 W/m²K (single glazing even 5.2 W/m²K). Modern coated triple glazed IGUs provide Ug-values of up to 0.5 W/m²K. This paper deals with the question...
Glass is a highly durable and infinitely recyclable material, yet in practice only a small portion of architectural glass products re-enters the value chain after its first use. An increasing rate of energy retrofits of the EU building stock will result in replacement of 85% of existing windows in near future; in the current linear glass supply chain, this will generate large amounts of glass waste. Despite high recycling rates of container glass in Europe, window glazing is very rarely recycled into new glazing, and reuse...
Reuse of entire insulating glas units (IGUs) in façades is a high-level circular strategy to decrease material and energy use and CO2 emissions. Yet, how many post-consumer IGUs are fit for such a direct reapplication and comply to building regulations having a 90% nominal argon filling and a sufficient residual lifetime? To address this question, almost one thousand IGUs in more than 40 different buildings in The Netherlands were studied. The glass and cavity width and the argon concentration were measured with the Sparklike Laser Portable. Then, each IGU was double-checked with a...
Achieving a circular business model for recovering building materials needs multi-level actions within the construction chain and strengthen the stakeholder engagement. One actual trade back in the reclamation of building materials is the lack of comprehensive data and information regarding their history and features. One way to deal with this problem could be the use of a material passport, which can be easily integrated in the building information model (BIM). This research explores strategies to close the life cycle of building materials, emphasizing traceability throughout their...
This research discusses the potential of upcycling glass for bioreceptive applications in the urban environment, proposing a paradigm shift in design philosophy to address escalating linear glass waste streams and mitigate challenges posed by extreme weather phenomena and air pollution. By harnessing the benefits of bioreceptivity as an alternative to conventional green living wall systems, a novel idea of exploiting unutilised glass waste is explored, through engineering the optimum microporosity to enhance water retention from the surrounding environment. The method of glass foaming is...
The existing building stock possesses a proportionally high impact on greenhouse gas emissions due to its low operational energy performance; retrofitting is a prominent strategy in many countries to help solve this, and as such is considered important to achieve a carbon neutral society. Among the energy retrofitting measures (ERMs), those impacting the performance of building envelopes are of primary relevance, especially ones that possess high Window-to-Wall Ratios (WWR) over 50%; these are predominantly found in office buildings built after 1960s. Here, the two dominant ERM...
Traditionally, curved façade geometries can be achieved by the means of hot bending glass or tessellation of the underlying geometry into plane parts, or even combinations of aforementioned. While the first method is not cost, nor energy efficient, for it relies on a heating process and requires bending moulds for every geometry, the second requires a vast amount of opaque substructure, opposing the aim of translucent façade structures. Contrary to these methods, the cold bending of glass omits those detrimental side effects of modern façade design. So, a promising technique was...
Increasing trends and demands for curvilinear glass forms in the architectural, automotive and marine industries have inspired the research and development of alternative glass bending methods. Warm bent lamination, also known as cold bent lamination, has emerged as a promising method for introducing curvature in laminated glass. Research on warm bent glass to date has mostly focused on the initial spring-back effect after the removal of the temporary mechanical supports and the long-term relaxation action over time. However, studies on the post fracture performance of warm bent...
The bending of glass allows architectural freedom of design and at the same time to offer ecological and economical sustainable advantages through material-appropriate design. Coated low-emissivity and uncoated glass were treated using our innovative laser-induced bending technique. The microstructure and spectral properties of coated low-emissivity and uncoated glass were analysed by scanning electron microscopy and spectrophotometry. Due to the anisotropy of coated glass, the reflective property significantly impacts the...
Anticlastic glass surfaces play a significant role in free-form glass facades. For realizing anticlastic surface, cold bending by loading at the corner of the plate is more adaptive and more economic than traditional hot bending method. Previous research on anticlastic cold bending mainly focuses on the description of instability phenomenon and qualitative analysis of parameters. However, the failure mechanisms of glass plates during cold bending and the influence of lamination remains unclear. In this paper, the anticlastic cold bending test was conducted to explore the influence of...
This paper reveals the new manufacturing possibilities for spherical and some organic geometries, taking advantage of state-of-the-art equipment for tempering and heat strengthening. Free forms in architecture have become increasingly prevalent with the advancement of computer-aided design. Glass is an essential building material and we have seen it used in outstanding structures, façades, skylights and other applications. On some occasions, desired geometries have been achieved by projecting flat triangular complex layouts while in other cases, the design team may have pushed for curved...
In recent years, the desire for increased performance, transparency and visual flatness of glazing elements in curtain walls has generated renewed interest in thermally induced fractures. They typically occur under climatic conditions that induce a large temperature difference across the glass. During design, approximate tools are available to assess the expected temperature gradients that the glazing might be exposed to, however, they sometimes fail to adequately evaluate the actual induced thermal stresses. Additionally,...
This paper investigates the challenges and potentials of phase-field modelling in simulating glass fracture. The phase-field method, a variational approach to fracture modelling, treats cracks as diffused interfaces, thus eliminating the need for explicit crack tracking. This study explores its application to glass, a material with unique fracture characteristics due to its amorphous structure and brittleness. We implemented the AT1 phase-field model using Abaqus and validated it against various experimental setups, including micro-cantilever and micro-pillar tests, L-shaped samples, and...
Fracture morphology characterization in broken glass panes is crucial for designing laminated safety glass (LSG) in civil engineering. Verifying completely broken LSG systems requires destructive sampling, increasing costs and hindering development. Therefore, to determine the residual load-bearing capacity, the link between the pre-fracture characteristics and the fracture morphology must be
known. However, when the crack propagation needs to be directly captured with high-speed imaging, conventional methods are no longer sufficient for detecting cracks. To enable such...
Recently, increased efforts have been made to explore the possibility of using glass panes as structural components, such as shear stiffeners. However, there are obstacles to the widespread use of these panes, even though they have proven their load-bearing capacity in structural systems (Haese 2013). The sudden failure of individual glass panes is a major concern because it can affect the overall structural safety. To better understand the causes of this unpredictable behaviour of glass façades, a numerical and physical sensor concept in the form of a hybrid digital twin will be...
Microscopy has been an indispensable tool for science since the 17th century. It has been used to study glass fractures for decades. The main problem with conventional microscopy is that you can only see a complete image if all aspects of the image are in the same geometrical plane of focus. Digital microscopy is a critical advance since it can combine information in different geometrical planes into a single image. With a transparent material such as glass this opens up new perspectives in that by using the right combination of transmission and reflective lighting both...
For structural design purposes, complex full-scale mock-ups and experiments are often required to assess the dynamic performance of glass curtain walls and facades under soft body impact. The test protocol (based on the use of twin-tyre or spheroconical bag impactor types) represents a key design step to satisfy, to ensure the protection of building occupants. Besides, soft body impact effects commonly need to be verified with the support of cost-time consuming experimental procedures. The major intrinsic uncertainty is the description of the force-time input function for the target...
In recent decades, there has been a perceptible transformation in how glass is perceived, evolving from being used for its aesthetic appeal to being acknowledged for its structural capabilities. Structural glass components are most often heat treated to increase their ultimate strength. For this purpose, the tempering process is applied. In this context, air is the quintessential cooling technique employed to rapidly cool and fortify the material due to its associated low cost. Nevertheless, it may encounter certain limitations when quenching low thickness components, making other...
Creating safer and more resilient building facades has become a primary concern in contemporary design, particularly in earthquake-prone regions, where there is a potentially high impact on financial, social and environmental losses. Glazed curtain wall systems are widely used in modern architecture. Yet, despite decades of research efforts aimed at enhancing the understanding of their seismic
behaviour, it is not clear how design choices affect the response of glazed facades. This is crucial given the wide range of glass, framing and joint variations that are at our disposal. With...
Additive manufacturing of glass using laser powder bed fusion has been recently developed, demonstrating its potential to be applied in small scale applications such as flow reactors for the chemical engineering and pharmaceutical manufacturing industries. While previous research demonstrated that complex 3-dimensional shapes can be manufactured, built parts are often brittle, exhibit high porosity and lack transparency. This study employs a transient, heat transfer finite element analysis to shed light on the thermal response of...
In contemporary architecture, there is a growing emphasis on structural transparency, often leading to the consideration of design solutions that incorporate complete structural systems made from materials such as structural glass. While glass is typically fragile and exhibits elastic deformations under normal loads during its service life, unforeseen events can cause glass breakage. Load redistribution requirements at the member and system level can be crucial in preventing potential structural collapse. A new method for connecting beam components was developed in (Martens, 2018), with...
Optical stress measurement in tempered glass has its challenges. Stresses can be measured optically based on the optical anisotropy behavior of the glass. For example, the stress profile can be measured only offline, or stresses can be measured online at the edge. However, with an online stress calculation in the tempering line based on measured process data, the stress profile can be solved, and more information about tempered glass can thus be obtained. This information about stress level is important for glass processors because it provides information about glass strength and...
The use of glass as structural material has highlighted the need for more reliable numerical approaches to analyze its mechanical behavior, especially in the accidental eventuality of fracture. Modelling the behavior of fractured laminated glass, in fact, is fundamental to assess the Post-Fracture load-bearing capacity. However, this is a highly challenging task because of the many interplaying factors, such as the viscoelastic and thermal-dependent behavior of the interlayer, the presence of a highly complex and variable crack pattern and the interaction among fragments. The objective...
The presentation will focus on the quality monitoring of the different stages of the safety glass processing. Defects in processed glass are extremely expensive, causing unnecessary work, energy costs and increasing CO2 emissions. Quality monitoring can be carried out at many different stages of production. This presentation will mainly focus on the problems of the tempering process and how to avoid different quality problems. I will also explain what causes defects and how and by what changes in settings defects can be avoided. Defects will focus on tempering process problems such as...
Thermally toughened safety glass must meet safety requirements in the building industry. Here, destructive tests are defined in the product standards, which must be carried out on small, standardized format (360 mm x 1100 mm) glass elements to determine the fracture pattern and bending strength. This is costly and not in the interests of sustainability. As part of the quality control of optical anisotropy effects in tempered glass, isochromatic scans that can provide information on the edge stress are acquired. The evaluation of the isochromatics and retardations at the edge with...
Among a multitude of functions, the façade is responsible for providing sufficient thermal insulation and supplying the building interior with enough natural light. For the latter, transparent glazed areas are essential. However, compromises in terms of the glass-to-wall ratio are often necessary since large glazed areas lead to overheating in summer and heat loss in winter. A novel type of highly insulating translucent glass brick made from annealed glass and filled with aerogel granulate was developed recently as an alternative in this regard. The bricks are not supposed to replace the...
The application of structural topology optimization to glass may enable the design of architectural and lightweight glass structures. There is still a lack of specific topology optimization tools for such a brittle material. This work establishes a topology optimization computational method for the design of glass structures fabricated via abrasive water-jet cutting. This allows to obtain load-bearing glass components which can have a high strength-to-weight ratio while accounting for changes in mechanical properties induced by the fabrication...
We discuss a novel approach, based on fractional calculus with a non-uniform time discretization, to numerically simulate interlayer viscoelastic behaviour and associated time-dependent deformation of laminated glass. Reference is made to the classic example of a simply supported laminated glass beam under long-duration loads. The fractional model is compared with some results obtained using the widely used finite element software ABAQUS 2021, which for the viscoelastic properties of the polymeric interlayer, utilizes the more traditional approach based on the Wiechert model and...
Laminated glass is a key safety element in modern building with glass façades. Tuning the adhesion between the interlayer and the glass as well as the mechanical properties of the interlayer are essentials to both the quality of the laminated glass manufacturing and to the final performance, especially regarding their wind-load and impact resistance. Adhesion tests conducted on laminated glass include pure shear and tensile loading tests. However, certain assembly geometry and framing systems lead to more complex loadings being applied on the...
Laminated glass has been widely used as safety glass for decades owing to its remarkable post-breakage load-bearing capacity. The post-breakage behaviour of laminated glass is mainly affected by several key factors such as the interlayer property, the adhesion property of the glass-interlayer interface, and the size of glass fragments. In this study, the adhesion properties of polyvinyl butyral (PVB) laminated glass under high-speed uniaxial tension were studied by through-cracked tensile (TCT) tests. Two adhesion grades (i.e., BG-R15 medium adhesion grade and BG-R20 high adhesion grade)...
Laminated glass holds promise as a resilient building material with the potential for successful application under explosive conditions. This study investigates the dynamic response of freely hanging laminated glass to near-field blast loading. Experimental trials were conducted, examining two laminated glass configurations: a 5-layer setup and a 7-layer setup. Panels were designed using the sacrificial glass ply concept, comprising alternating layers of glass panels and polyvinyl butyral interlayers. The experimental methodology involved two types of explosives: Semtex 1A and granulated...
With the continuing architectural trend toward transparent structures, the use of glass in the construction industry has increased significantly in recent years. The characteristic brittle failure behavior of glass is counteracted by the use of Laminated Safety Glass (LSG) in order to meet the safety-related requirements for breakage, post-breakage, and residual load-bearing capacity. For LSG, at least two panes of glass are laminated to form a monolithic composite with a polymer interlayer. During the manufacturing process, geometric imperfections...
Laminated safety glass is an important component of modern façade structures and is used when higher safety requirements are demanded. The interlayer increases the stiffness due to the available shear action, ensures the residual load-bearing capacity of the structure in the event of failure and holds broken pieces of glass in place. However, the stiffness and tensile strength of conventional interlayers such as EVA or PVB are known to strongly depend on time and temperature. This phenomenon is particularly critical for the...
The numerical simulation of the residual load-bearing capacity of laminated glass (LG) is one of the most relevant topics of current research in structural glass engineering. The mechanical description of the behavior of the interlayer plays a crucial role. Several approaches and models already exist in automotive engineering and structural protection. Structural glass design assuming quasi-static loads misses a detailed model so far. The aim of this work is the mechanical description of the time-dependent behavior of Polyvinylbutyral (PVB) under large deformations considering...
The demand for versatile and visually appealing glazed structures has been increasing in recent years. To meet contemporary architectural needs, a wider range of functionalities is required, including smart, bendable and thin laminated glazing. In particular, cold poured liquid interlayers are gaining prominence for complex curved cold bending and smart interlayers, where conventional interlayer films impose limitations. This paper presents research on several liquid optically clear adhesives (LOCA) for application as interlayers in laminated glass. Within a comprehensive experimental...
The post-fracture performance of laminated glass is becoming a significant focus due to the growing breakage incidents of tempered glass and its long-term replacement. However, the influence of tension stiffening due to the adhesion of glass fragments to polymeric interlayers, one of the main factors affecting the structural capacity of the post-fracture laminated glass, is still unclear, especially when considering different fragment overlaps and temperatures. In this work, two types of uniaxial tensile tests with predefined cracks, including the multiple through-cracked tensile (MTCT)...
Currently, liquid cold-poured adhesives are infrequently used as interlayers of laminated or laminated safety glass in structural glass applications, despite their inherent benefits. The potential advantages of these materials are characterized by easy handling, rapid curing devoid of elevated temperature or pressure requirements, and consequently, a comparatively low energy demand. Despite the prolonged availability of certain products in the market, comprehensive scientific inquiry into their mechanical and thermal material characteristics remains limited. In this paper, two specific...
This paper presents the results of an experimental and numerical investigation of the mechanical response of undamaged and damaged 2-ply laminated glass plates. Two types of glass plies, thermally toughened and heat-strengthened, coupled with SentryGlas (SG) were considered. Laminated glass plates supported with articulated point fixing bolt under out-of-plane uniform pressure were investigated under four different damage configurations: (i) undamaged; (ii) partially damaged, with the bottom ply broken; (iii) partially damaged, over-flipping the specimen of mode II; (iv) both two glass...
Laminated safety glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Glass laminate films, the plastic film called an interlayer that is adhered between sheets of glass, are an important component of many glass applications. In an event that causes breakage of the glass, it is held in place by an interlayer, between its two or more layers of glass. The interlayer keeps the glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. Various physical tests...
Around ten years ago, reduced plasticizer content poly(vinyl butyral) (PVB) interlayer types were introduced to the laminated glass market for use in general construction. The main purpose of these interlayers is to reduce the glass thickness or enable larger glazing spans. In these stiff PVB types, the plasticizer level is reduced to around 17 weight %, as compared to around 27 weight % for conventional PVB types. Although it was known at the time that these formulations can meet safety requirements for laminated glass, the options for use in...
Increasing security concerns and a trend towards larger glass panels are driving the adoption of thicker laminate glass panels in prominent architectural works worldwide. However, the polymeric materials used in these laminates can lead to haze, a detrimental optical defect that impairs transparency perception, particularly when used in thick, multi-layer laminates. This work presents a novel technology capable of accurately and robustly measuring haze in glass laminates of arbitrary thickness, based on using computer-vision to measure changes in contrast...
Visual defects, in particular haze, in glass and façade technologies can significantly impact the aesthetic quality and human experience of daylight and views in buildings. The glass and façade industry increasingly requires methods that can objectively predict and measure the subjective user experience of haze. This is required to appropriately inform the manufacturing process, ensuring optimal functionality and performance, and avoiding material waste and economic losses due to the replacement of defective glazing. Existing...
With about 4,500 medium and large airports around the world, Air Traffic Control Towers (ATCT) are essential elements of our transport infrastructure. Safely orchestrating air traffic requires a perfect visibility of aircraft in all weather and lighting conditions. Aviation being a conservative field, towers are built or renovated using decades-old technologies, with disappointing results. Design parameters can be grouped in five categories: structural, blemishes, insulation, photometric and optical. Transcending country borders and traditions, we will detail each of these groups and...
Minor fluctuations in the tempering process of architectural glass could lead to residual stress differences resulting in birefringence and undesired optical iridescence, also known as anisotropy effects. The control of anisotropies, which are quantified as optical retardation, is limited to monolithic glass. In modern architecture, laminated glass panes consisting of an interlayer of polyvinyl butyral (PVB) or ionomer (SentryGlas®) are frequently applied. In this paper, photoelastic studies are performed on laminated glass panes before and after the lamination process to evaluate their...
This paper is a review of methods to determine optical distortion in architectural glass, with a focus on the methods described in the current available standards and guidelines. References from building projects are used as reference points in the review of the methods. In addition to the review initials measurement studies are performed in a laboratory to determine the physical phenomena behind the optical distortion. The paper concludes on the different types of optical distortion seen, the methods which were used for the survey and how it corresponds to the current standards and...
The role of energy use in our dwellings is a critical part of any policy which aims to mitigate climate change. A significant proportion of this is the uncontrolled loss of energy through the windows, which in some buildings is a large area of the envelope. Vacuum Insulated Glass (VIG) is the next-generation technology, where transparent windows will be as thermally insulating as the opaque wall. More importantly, at the potential high thermal resistance that could be reached, buildings would provide a net surplus of energy. Nevertheless, the current available literature has not provided...
Resembling the harsh surfaces of the nearby alpine mountains, the geometry of the glazed steel façades of the new Dynafit Headquarters in Kiefersfelden is based on energy driven design principles. Built with a vertical and horizontal tilt the valleys of the serrated glass façades are oriented along the solar inclination during summertime. Triangular shading panels that are fitted into the valleys and oriented perpendicularly to the solar inclination in combination with solar control coatings on a triple-insulation glazing minimize solar heat gains...
The world’s largest cosmetic company, L’Oréal, has renovated its headquarters located in Paris. During this renovation, a cutting-edge glass façade was built in the building’s courtyard, consisting of a meshed lamellar-type conical tower topped by a spherical dome. The total height of the glass façade is 25.0 m from the ground floor level and the width is approximately 9.0 × 12.8 m. The steel frame is a lamella type structure composed of quadrilaterals and triangles. The geometry was managed through a 3D parametric model with Rhino and Grasshopper that was adjusted for the double...
For a residential building in the French Alps, Vitroplena designed and installed an all-glass walkway. The structure connects the upper platform of the stairwell and the master bedroom spanning a distance of 5.28 m. The width of the bridge is approximately 1 m. The structural performance of the walkway relies on a 101010.4(TTG,sPVB) floor plate supported by 200 mm high 101010.4(TTG,sPVB) structural glass beams. The accompanying 1010.4(TTG,sPVB) balustrades are laminated to these structural glass beams. A key feature of this design is the adhesive bonding of the floor plate to the...
At the core of facade design is the concept of interdisciplinarity, a bridge between concept and materialization apt to relay a built form effectively responding to a wide and diverse spectrum of parameters and aspirations. This paper presents a case study where a facade design approach has been successfully applied to the design and development of a highly complex artwork constituted of structural glass elements. C-010106 by Sarah Oppenheimer—commissioned by the University of Texas’ public art program, Landmarks—is comprised of two structural glass systems acting like...
After several years of renovation, the Renaissance castle of Villers-Cotterêts, hosting the “Cité internationale de la langue française” desired by the French president and developed by Olivier Weets Architecte, has been opened to the public in October 2023. Centerpiece and emblematic symbol of the castle is the fully glazed, double curved grid shell covering the interior courtyard, which has been developed and engineered by the authors throughout all construction stages. The cushion-shaped, 16m x 36m roof consists of a rhombic grid structure of slender, custom-welded steel profiles...
The organic design and seamlessly reflective surface of “The Henderson” establish it as a landmark in Hong Kong. With its all-glass façade and a height of 210 m, the skyscraper designed by Zaha Hadid Architects offers spectacular panoramic views. Particularly noteworthy is the “Banquet Hall” on the top floor, distinguished by its fully glazed roof and engineered by Eckersley O’Callaghan. Large-format, coated and curved glass panes with the best possible technical specification in terms of thickness and minimal dimensional tolerances counterbalance architectural aesthetics and structural...
The Port of Montreal Tower is a uniquely shaped observation tower situated at the south end of the Alexandra Quay Maritime Terminal pier, offering a breathtaking 360° view of the city and the surrounding area. Its top floor gives access to a “glass cage” measuring 2.5 m wide x 3.6 m high that projects 1.5 m beyond the face of the tower wall. This paper describes the challenges presented in the design and construction of this unique all-glass volume that is anchored through the curtain wall directly to the Tower’s steel structure at a height of 55 m above ground. In order to maximize the...
‘Reflexions’ is a 12m high, 4.6m deep, and 4.6m wide, sculpture conceived as a 3D glass scaffolding. Its ambition is to be modular and be easily assembled and dismantled, with connections that are designed to be fixed on-site. The scaffold consists of 1195 laminated glass bars each capped with an annealed epoxy embedded stainless steel connector, to marry to 313 star shaped nodes. This paper describes the cutting-edge epoxy bond and the process of the assessment of its capacity, through calculations and testing. The fully assembled structure has high redundancy and challenges the...
In this paper we will discuss a challenging, iconic, heritage, refurbishment project – Channel 4’s headquarters building located in London, England. The building was originally designed by Richard Rogers and Partners in collaboration with Arup, RFR and was executed in 1994 by Eiffel under a sub-contract package with Permasteelisa. We will methodically outline the procedures that were followed to assess and restore this ageing, iconic cable net façade where, in an almost unprecedented way, the face glass is used structurally to support the dead load of the panels below to create a chain...
The brief was for external full glazed walkway corridors for a private lodge in East Iceland for a private client. The walkways act as both interconnecting links between buildings spread over the site and offer panoramic views of the valley beyond. They are designed to withstand extreme weather conditions such as high winds up to 2.5kPa and heavy snow loads up to 6.7kN/m². The walkways have dimensions of 1.6m large, 2.3m high and can extend up to 17m in length. Walls and roofs are formed by glass panels of up to 4.0m. The structure is composed of a series of stainless-steel portal...
In engineering applications, the frequency analysis represents a first and practical step to collect relevant parameters for structural and mechanical diagnostics. Any possible material / component degradation and deterioration can be prematurely detected by frequency modifications that exceed a certain alert value. In this paper, the attention is given to the dynamic mechanical analysis of commercial photovoltaic (PV) modules, in which the solar cells are typically encapsulated in thin viscoelastic interlayers made of Ethylene-Vinyl Acetate (EVA), which are primarily responsible for the...
Mechanical heating and cooling are often required to balance the energy flows in and out of a space to maintain comfortable temperatures. There is significant pressure in many countries to reduce the energy consumption of buildings and one way to achieve this is to reduce the area of glazing. However, this conflicts with providing natural daylight which is critical to the visual comfort, health, and wellbeing of occupants. The typical approach currently used to improve glass performance is to use coatings applied to the build-up; the major limitation with glass coatings affecting most...
This paper draws attention to the environmental impact of passive smart windows, a novel high-performance glazing technologies that can change their solar transmittance to control the amount of solar gain, thus reducing cooling energy demand. Despite the large influence of building envelope technologies on overall embodied carbon in buildings, the environmental impact of passive smart windows has been inadequately addressed, with a dearth of numerical data on various impact categories beyond energy consumption and Global Warming Potential...
Photovoltaics in façades are currently enjoying great popularity, also as a way of contributing to renewable energy production. There are various subsidy programmes to promote the installation of photovoltaics. Two "worlds" meet here, the world of electricity and the world of construction. In case photovoltaic modules are CE-labelled, the basis for this is not the European Construction Products Regulation but a low-voltage directive. Taking a closer look at the set-up of these modules, one very often finds unregulated construction products: Thin glass, no PVB as an interlayer but other...
The control of glare in office environments is often retrospectively improvised using shading devices, typically internal blinds. This also involves blocking the view, with an unwarranted artificial lighting load during broad daylight. Today’s glazing technology, particularly that of the IGU (insulated glazing unit) delivers much of the expected performance in terms of better U-values, g-values, and the VLT (visible light transmittance). However, despite the leap towards energy efficiency goals, visual comfort is still being compromised in climates with high solar insolation resulting in...
Glass facades are complex systems in which glass panes are required to interact with many other load-bearing and secondary components. As a matter of fact, they represent a physical barrier expected to offer long-term structural safety, functionality and durability. On the other side, many influencing parameters make them possibly vulnerable (especially glass) and thus eventually reduce their load-baring capacity, or functionality. The effect of different mechanical and thermal boundaries and loading conditions, ambient and long-term effects, affect especially insulated glass components...
Glazed façade design is governed by several requirements; often one of them is dominant on a component, so holistic optimization is difficult to apply. Moreover, standards are not in line with system state of the art, but they are still a reference for the players. An example is the wind load sharing in multiple skin facades. All glazed facades have double skin areas, also when they are considered single skins. Indeed, in front of the slab, the closure has two skins, an opaque outer glazing and a metal internal sheet. The cavity is ventilated to mitigate the temperature and avoid...
During the early 2000s, facade blast enhancement was characterized by heavy design, tempered thick glazing, rigid framing and massive connections to the building structure. The research undertaken in more recent years has shown that most part of the reinforcements was not required to match the protection targets. On the contrary, a dissipative strategy was incorporated, to analyse the façade element post-elastic behaviour, in order to use as much as possible their inherent energy absorbing properties and developing dynamic calculations with reduced conservative assumptions. It has been...
The stability of monolithic glass beams is reasonably well defined; as an elastic material it behaves in a similar manner to other elastic materials such as steel, for which there are many equations of different forms which give similar results. Special care is required for continuous restraint to the tension flange. Equations presented in Australian Standard AS1288 Glass in Buildings – Selection and Installation have been used successfully for many years for monolithic fins when used with the strength model of AS1288 but require a more comprehensive approach when using laminated fins...
Glass handrail loading and design in the United States lags behind best practice in other parts of the world. Improvements are possible for the design load, residual capacity and damage-event loading, each of which could be based on occupancy. Neither static loading nor impactor testing accounts for the dynamic effects of sustained loading to handrails during crowd load events. Alternate configurations for improved robustness at similar size and cost are presented.
This research is related to the structural performance of a shell-type system made of hollow glass units (HGU) that utilizes glass as the primary structural material. The efficient structural function of the proposed shell-type system is designed using Polyhedral Graphic Statics to achieve a system geometry that maximizes in-plane compression and limits the presence of tension. The large-scale shell structure is constructed using a modular assembly of individual hollow glass units. To date, the research team has completed studies on individual HGU strength and stiffness, and the...
Assessing the fire performance of structural materials is crucial for ensuring the safety and integrity of buildings and structures. Traditionally, this assessment involves expensive and time-consuming physical fire tests. However, an alternative cost-effective approach is numerical modelling, which requires a deep understanding of heat transfer mechanisms specific to the material of interest. While numerous models exist for opaque materials, modelling glass in fire conditions presents additional complexities due to its transparency and wavelength-dependent heat transfer characteristics....
Architectural glass has been widely used in modern buildings due to its aesthetics and functionality. The growing use of glass in load-bearing structures raises concerns about its long-term strength due to the existence of the flaws and subcritical crack propagation. Better understanding of flaw characteristics is crucial for evaluating the mechanical properties. However, existing knowledge on
flaw characteristics is limited, and the load duration factor 𝑘𝑚𝑜𝑑 specified by standards doesn't consider different stress histories. This paper aims to fill these gaps by observing and...
In the building industry, different types of glass edges are used depending on their application and function. A widespread assumption is that the edge strength increases with the degree of optical finishing. This corresponds with the European standardisation, which targets an adjustment of the bending strength in form of edge finishing factors. Thereby the highest edge strength is set with polished edges. This article presents research which shows that the recommended edge finishing factors of annealed glass can be insufficient, particularly for the polished edge. Comparison with...
Scratch-induced surface damage of aged glass elements can lead to strength degradation of glass material and thus threatens the safety of architectural glass. It is of significance to evaluate the mechanical performance of scratched glass elements. In this study, deep close-to-reality scratch is introduced at the centre of the annealed glass plate by a diamond indenter. Coaxial double ring (CDR) test is conducted to evaluate the flexural performance of scratched glass. The test setup is based on EN 1288-5 standard and the specimens are square size for convenience. A total number of 40...
The authors investigate the dynamic factor dependency on the major wind excitation parameters, including mean wind velocity, turbulence factor and system dynamic properties, by means of the Single Degree of Freedom (SDOF) simplification. The reason of the research is the controversial limit stated in the EN1991-1-4:2005, set to 5Hz, which represents the minimum value of the system first natural frequency allowing to ignore dynamic amplification factors to incorporate into the equivalent static approach. While the largest part of the scientific community aims at reducing this value, to...
High temperatures, especially non-uniform temperatures distributions, on glass structures can induce stress relaxation, viscous material behaviour and glass fracture. Temperature exposure of toughened glass to 290°C and above can result in a partial reduction in strength of the glass component and, in case of fracture, a change in the fracture pattern due to stress relaxation. To achieve a better understanding of the heat transfer in monolithic and laminated glass, test series in an electric furnace on different glass specimens were carried out. The specimens were made of monolithic and...
Using glass elements as designated members of the structural design of buildings does not only require conscientious planning of structural redundancies, but also proof of safety for single components. In reality, random loads act in an unknown combination on a component, which is not directly resembled by the modelling process a priori. Hence, understanding the mechanical behaviour of glass components under probabilistic combination of static and dynamic loads is required. To serve this understanding best, the most critically loaded component of a glass shelter was examined...
The German code for design of glass structures DIN 18008 was first published in final version 2010 and 2013; as several major changes were suggested, the periodical revision took longer than expected. Part 1 and 2 (basis of design and linear supported glazing) are published in final version in 2020, recently a draft of revised part 3 (point fixed glazing), part 4 (balustrade glazing) and part 5 (walk-on glazing) were published with date November 2023. Revision is based on experience from its practical application, implements recently finished research activities and takes development of...
The performance of the building envelope of a building is crucial for minimizing operational carbon emissions and maintaining indoor comfort. Contemporary building envelopes, such as highly engineered glazed façades, achieve high performance levels but also add a significant amount of embodied carbon. For example a 1mm reduction in glass thickness could save 3 kgCO2eq/m2. There is therefore an incentive to reduce the thickness of the glass panels, but the minimum thickness possible is often not governed by strength or...
Spontaneous glass breakage of thermally toughened glass due to NiS inclusions can be largely prevented by a Heat Soak Test (HST)1. This well-established test has been incorporated into the European standard EN 14179-1:2005. However, according to literature (Yousfi 2010b), there might be a theoretical probability, that a potentially dangerous inclusion could lead to a breakage after a well-conducted HST. Glass processors may neglect to conduct the test for a variety of reasons (sometimes furnaces are not calibrated, are overloaded, a wrong temperature profile is run etc.), even advising...
The demand for transparent building envelopes, particularly glass facades, is rising in modern architecture. These facades are expected to meet multiple objectives, including aesthetic appeal, durability, quick installation, transparency, and both economic and ecological efficiency. At the heart of facade design, particularly for structural glass elements, lies the assurance of structural integrity for ultimate and serviceability limit states with a requisite level of reliability. However, current structural engineering assessments for glass and glass laminate designs, especially in the...
Other than limited special cases, there is a lack of standards providing guidance on the design of structural glass in the United States and much of the world. This has resulted in an ad-hoc approach by cities (authorities having jurisdiction), architects, and engineers. This paper outlines the key aspects of designing with glass in a manner that has reliability and robustness consistent with other structural materials while recognizing the unique aspects of glass. This voluntary design manual is aimed at providing 4 consistent levels of risk in applications that allow Architects, Owners...
Published in 2019, EN 16612 represents a significant advancement in window glass standards, surpassing its predecessor, prEN13474. It introduces new methodologies for calculating triple-glazed insulating glass units, a detailed approach to determining the shear transfer coefficient, and refined formulations for design strength and cavity pressure variations. These enhancements, however, add complexity to the procedural application of EN 16612. In particular, the variable shear transfer coefficient, depending on loading conditions, influences multiple calculation steps, creating a complex...
Glass remains a popular material in architectural and engineering applications for the building envelope. However, meeting the increasing demands on façade elements while implementing all requests is an unrealisable challenge for monolithic glass. Therefore, laminated safety glass, which is a combination of at least two glass panes and an interlayer, can be a solution for more and more applications in the building sector with enhanced requirements on safety, such as splitter bonding in the broken state. Furthermore, the European standards permit the use of glazing plastic material in the...
The topic of climate change has arrived in the everyday thinking. There is an ongoing discussion about how the man-made environmental impact can be reduced. Several strategies can be observed. One is the increasing of recycling and reuse potential on the one side, and another is reduction of built mass on the other side. In this case the built glass mass can be reduced with the usage of thin glass in the design process of insulated glass units - IGUs. This paper is a discussion about concepts to minimize the glass thickness as much as possible for a usage of thin glass for insulated...
With the inscription "The Materials are Iron and Glass", the medal from the 1851 World's Exhibition also aptly describes the Crystal Palace and the botanical gardens of the University of Bern, which were built around 1860. The filigree steel structure, which is protected as a historic monument, must be preserved. In order to ensure the load-bearing safety of this structure with as few reinforcement measures as possible, the weight of the roof glazing is reduced to an absolute minimum. A variant study of possible insulating glass units is carried out within the framework of the building...
Enclos has identified a novel technique to substantially stiffen glass via prestress. Significant reductions in deflection of thin glass have been demonstrated numerically and on prototype mockups using this technique. The potential integration of this technology with glass such as AGC’s Falcon Glass presents opportunities for performance improvement and material optimization. This study examines prestressed glass specimens which are 0.5mm, 1.1mm, and 2.1mm thick in comparison to glass of the same thicknesses that has not been enhanced by the novel stiffening method. The technology...
The architectural prominence of glass structures, driven by ongoing innovations in manufacturing and post-processing techniques, reveals the material's remarkable structural potential. Aluminosilicate glass, distinguished by superior strength and flexibility, particularly in comparison to soda lime glass, facilitates the production of ultra-thin glass with thicknesses as low as 25 μm. This has led to the emergence of "thin glass," defined as any glass below 2 mm in thickness. Thin glass, celebrated for its unique attributes, has found diverse applications in industries like automotive...
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