Challenging Glass Conference Proceedings

First Steps Towards a Smart Laminated Safety Glass made of Thin Glass and Polycarbonate

Sebastián Andrés López — 2024-06-16

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 cross-section of laminated safety glass. In response to this specification, a composite panel made of thin glass and polycarbonate is proposed as an alternative to laminated safety glass. The multi-layer cross-section is designed to be lightweight with a slim nominal thickness for security glazing, and to possess advantageous structural-physical attributes. This paper presents a further possibility of the favourable combination of both materials. The results of a research project at the Chair of Building Structure at Universität Siegen indicate that the integration of smart layers in the cross-section of a laminated safety glass made of thin glass and polycarbonate is a promising approach for further investigation. This leads to the development of a switchable composite panel with improved luminous and solar characteristics. The smart element is laminated between two polycarbonate sheets using polyurethane interlayers during an autoclave process. It is essential that the composite panel passes climatic stress tests for durability at high temperature and in humidity, which are fundamental requirements for further research as laminated glass and laminated safety glass. This paper identifies the necessary materials for a minimal cross-section by means of experimental standard tests to fulfil the requirements of a laminated safety glass with adjustable luminous and solar characteristics.

Lightweight IGU

Jürgen Neugebauer — 2024-06-16

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 glass. For a given situation room-high IGUs with defined sizes and different boundary conditions such as curvatures for cold bent glass applications will be analysed. Based on building physics demands triple IGUs will be considered for a better thermal performance. In a parametric study flat and cylindrically shaped IGUs will be compared. The influence of the variation of different parameter on the internal loads the so-called climatic loads on the one side and the so-called coupling effect for external loads such as wind and barrier load on the other hand will be elaborated. With transient simulations of the pendulum impact the fail-limit state was examined in addition. Based on the prEN19100 a structural design was carried out. As the result of the study the minimum of the possible glass thicknesses depending on the geometry and the load is given.

Lightweight Insulating Glass Unit

Pascal Joos — 2024-06-16

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 physics and monument preservation constraints, as well as considering the radiation that is important for plant growth. The further development of glass refinement and the resulting improvement in glass properties play a decisive role in this. Lightweight and highly efficient chemically strengthened 0.7 mm thin glass and 4 mm thick low-E coated thermally toughened glass are combined in an insulating glass unit. A test concept was developed to test the load-bearing safety and personal safety of lightweight insulating glass and chemically strengthened glass. The strength, the influence of surface damage, the fracture pattern as a result of various loads and the residual load-bearing capacity were analysed. The results obtained fulfil the assumption that the impressive deformation capacity of the glass results in a high level of safety without being a safety risk. A hail resistance class 3 was achieved by firing a hail cannon. The radiation transmission of the entire lightweight insulating glass unit was measured using a spectrophotometer. A light transmission of 82% and UV transmission of 52% were achieved. Work has already begun on the refurbishment measures and the designed glass will be installed in the middle of this year.

Reducing Deflection of Thin Glass by Prestress

Austin Bensend — 2024-06-16

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 relies on a prestress pattern generated by cold-forming a double-curved surface into a flat pane. Unlike most cold-warping that starts with a flat sheet of glass deformed to a final warped surface, this approach begins with a hot-formed glass shape that is flattened elastically to a planar lite. The process results in a pattern of membrane prestress contained within the glass. As a result of the deformation, the center region of the glass is put into tension, which is balanced by regions of compression within the glass at the perimeter, adjacent to the frame. The membrane tension region that develops increases the glass stiffness for deflections out-of-plane, in a similar manner to the way tensioning a cable generates higher stiffness to resist applied lateral loads acting on it. Numerical models and test results from Enclos and AGC are presented in this study.

Thin Glass Installation

Marialena Toliopoulou — 2024-06-16

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 and electronics. In architecture, thin glass holds potential for creating complex, lightweight, and transparent architectural structures. This paper addresses the constraints of thin glass in construction and explores optimal bending techniques to maximize its potential through a detailed study of its properties. The current study establishes design guidelines and a computational approach for utilizing cold bent thin glass in the design process. The findings showcase a successful computational method providing tools, design principles, and guidelines for working with single curved cold bent thin glass panels. The paper also examines suitable connection types for thin glass projects, proposing a hinge clamp connection. A case study illustrates the proposed workflow, resulting in a prototype using a 3D-printed approach for the suggested connection design.

Light Forms

Catie Newell — 2024-06-16

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 scale is possible. Secondly, hollow voids created in the pressing process offer unique opportunities for prismatic effects, and controlling light transmission and privacy, in addition to creating an encapsulated air pocket while still maintaining thick walls. Next, the necessary adhesive joint to adhere the two halves together becomes an opportunity for deploying color shifts through dyed adhesive joints and considerations for reuse through reconfiguration and feasible furnace recycling. Lastly, the overall form of each modular unit is a decahedron designed in a manner that through the change of orientation tessellates into various patterns. Utilizing offset stacking, the patterns can also introduce angles and curvatures across an architectural wall while taking advantage of the compressive strength of glass. Light Forms investigates the correlation of geometry and structure as it also relates to optical performance and design opportunities.

More with Less

Jackson Jewett — 2024-06-16

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 of material. If tailored appropriately, TO can reduce component sizes and thereby diminish the total annealing time needed while intelligently placing material in the areas where it will be utilized effectively. For TO of glass to be successful, algorithms must properly capture glass’s intricate material behavior. This research proposes a suite of TO algorithmic frameworks that design specifically for structural glass. These algorithms are demonstrated in a 2D design space, and the resulting geometries are fabricated using cut float glass and tested for experimental comparison on a 4-point bending load case. The results of these experiments inform which TO strategies have most promise for future research in TO of cast glass structures.

Structural Design Optimization of Cast Glass Artwork via a Digital Design Solution

Omar Aloui — 2024-06-16

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 the risk of stress concentrations on the glass. In this context, Pae White’s sculpture, “Qwalala”, stands as a testament to both the possibilities and challenges in glass art. “Qwalala” pays tribute to the “Gualala” river depicting its meandering course through northern California. This glass sculpture represents a curving glass wall (0.7m to 2.5m
tall) extending over 78 m and contained within a 36m x 10.3m bounding area. The wall is comprised of over 1500 cast glass bricks with 26 different colors, meticulously crafted by Italian artisans and bonded together using only Structural Silicone. Originally, the sculpture was commissioned for the Venice Art Biennale in 2017 and was exhibited at the island of San Giorgio Maggiore in Venice. However,
in 2023, the “Qwalala” found a new permanent home at the Claremont Mckenna Campus in Claremont, California. The change in location prompted a careful reevaluation of the design as the loading conditions on the wall have changed due to the increase of seismic risk in Claremont. Additionally, the client required minimizing the Silicone bonding area to maximize the transmission of light between the bricks. To meet these requirements, a more detailed analysis of the silicone patches between the bricks has to be conducted. The irregular unwinding path of the wall further complicates the task as it results in non-uniform overlapping patches between the glass bricks where the bonding material can be deposited. In this paper, we describe a parametric design workflow combining Grasshopper and the Strand7 API, capable of capturing the geometry of each overlapping path and allowing a more accurate modelling of the silicone. This resulted in a 40% reduction in the total Silicone bonding area in the wall compared to the previous installation in Venice, despite the more demanding new loading conditions imposed on the “Qwalala” glass wall.

Surface and Finishing Quality Exploration of Complex Cast Glass Forms Produced on Disposable Moulds

Menandros Ioannidis — 2024-06-16

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, requiring considerable post-processing to yield a glossy, smooth surface. This in turn results in a compromised dimensional accuracy and on increased time and production costs. If the surface remains unprocessed, it can greatly affect not only the visual but also the mechanical properties of the cast glass element. Aim of this research is to improve the surface quality of complex glass components cast in disposable moulds, directly during demoulding, reducing in this way the need for post-processing. To achieve this the research focuses on exploring ways to pre-process disposable moulds. In specific, the research focuses on series of kiln-cast laboratory experiments at various maximum firing temperatures / annealing schedules involving the use of two different types of disposable moulds, 3D-printed sand moulds (3DPSM) and silica plaster moulds (Crystalcast®), and the application of refractory coatings, coating combinations and protective layers. The experimental work conducted thus far indicates that the best results are obtained at the lowest maximum temperature tested (870oC), with the combination offering the best finishing quality to be a synthetic (ceramic) sand mould coated with Crystalcast® and Zirkofluid® (6672, 1219). Scaling-up of the kiln-cast prototypes unveils a complex correlation between the maximum dwell time at the maximum firing temperature and the casting effectivity/ performance of mould materials and coatings.

Advanced Simulation for Thermal Stress Assessment

Andrea Zani — 2024-06-16

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, current standards lack uniformly defined procedures and often carry simplified assumptions that lead to over-conservative results. This paper presents an advanced simulation workflow to accurately assess the temperature and stress distribution in glass lites for complex curtain wall applications. First, a 2D steady-state heat-transfer analysis is completed, followed by a simplified 2D transient simulation considering typical year weather data to identify the high-risk boundary conditions. Lastly, a refined 2D–3D transient thermal model is created, whose outputs are translated into thermal stresses on the glass surface and edges through mechanical finite element modeling. This combined thermal–mechanical analysis allows for a more accurate temporal and spatial assessment of the temperature and stress distribution on each glass lite compared to linear approaches. This paper will present a case study to display the proposed workflow and prove how 2D steady state assessments and linear stress calculation tend to be more conservative by 60–80% when compared to 3D transient combined thermal–mechanical analysis.

Challenges in Phase-Field Modeling of Glass Fracture

Gergely Molnár — 2024-06-16

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 dynamic tensile fracture scenarios. The results demonstrated strong alignment with experimental observations, accurately capturing complex crack patterns and dynamic fracture behaviours. Key parameters like the critical energy release rate and internal length scale were shown to significantly influence fracture simulation outcomes. While the phase-field method shows promise in advancing glass fracture mechanics, challenges remain in parameter sensitivity and integrating more sophisticated material models. This study highlights the method's current capabilities and points to future research directions for enhancing its applicability and efficiency in glass fracture simulations.

Crack Segmentation for High-Speed Imaging: Detection of Fractures in Thermally Toughened Glass

Henrik Riedel — 2024-06-16

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 investigations, we propose a novel machine learning framework for crack segmentation in high-speed imaging that addresses the complexity of glass fracture and minimises the required labour costs. In this study, the crack propagation of a sample was recorded and analysed at 2,000,000 images per second. The results showcase accuracies surpassing 97% while requiring only two labeled images for training, thus streamlining practical implementation. Furthermore, we show the method's robustness to the extent that hyperparameter tuning becomes unnecessary. Instead, we offer guidelines for selecting the most crucial hyperparameters depending on the problem. Our method offers a promising approach for non-
linear temporal interpolation of noisy images, with implications for various applications extending beyond glass fracture analysis.

Design of a Numerical Sensor Concept as the Basis of a Hybrid Digital Twin for Monitoring Load-Bearing Glass Façades

Nathalie Nießer — 2024-06-16

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 developed. This involves both measurements of real load-bearing systems and simulations using numerical sensors. The two concepts will initially be developed independently, whereby the virtual model is approximated in a continuous process using measurements of the real structure. For this idea of the hybrid digital twin, a numerical sensor model is first presented in this article, which is also used for the evaluation of real sensors and thus serves as a basis for further investigation. The research project on the safety of glass façades in load-bearing structures is an important step towards improving the reliability and durability of such structures. The introduction of a hybrid digital twin will contribute to the development of an improved safety concept and the further establishment of these applications.

Digital Microscopy as a Tool to Understand Glass Fracture

Fred Veer — 2024-06-16

Microscopy has been an indispensable tool for science since the 17^th 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 internal defects and complicated 3D surface defects can be imaged. In the field of float glass this allows for the study of edge and surface defects pre-fracture and the damage visible post-fracture. In the field of cast glass this allows for studying the -often complex- network of defects in the bulk. The ability to view and study such internal defects supports research efforts towards the characterization and application of recycled glass. The paper will show the critical aspect of using the right lighting and lenses and the settings needed to obtain high quality images of complex 3D damage. This will be demonstrated based on the microscopic analysis of multiple float and cast glass specimens tested in 4 point bending at the TU Delft Glass lab. Using proper lighting and technique provides a new insight into the fracture processes of glass.

Experimental and Numerical Characterization of Input Forces in Glass Curtain Walls under Soft Body Impact

Nicola Cella — 2024-06-16

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 facade (and thus the expected effects), and its variations with impact characteristics (i.e., type of impactor, impact energy) or facade features (i.e., target region, etc.). The present study aims at overcoming these issues and possibly support a computationally efficient, but still refined, numerical analysis of glass curtain walls under soft body impact. A primary advantage is taken from a set of original experiments carried out on full-scale facade samples, under the effect of
twin-tyre or spheroconical bag impactors (with up to 160 impact configurations). Differing from earlier efforts, the experimental setup is characterized by the implementation of a set of pressure sensors that are used to track the evolution of impact surface and time history of impact force on glass. To further explore the experimental findings, a Finite Element numerical analysis is carried out in Abaqus. The presented results show in general a rather close agreement of displacement peaks – with an average scatter of about 10% for the twin-tyre and 25% for the spheroconical bag configurations – and confirm a high sensitivity to impact features. In addition, a satisfactory agreement is found between the measured time histories of impact force and the corresponding imprint surfaces on glass, especially for the twin-tyre impactor. Such a result can support the elaboration of even more efficient modelling strategies (i.e., 2-DOF approach) that could help optimizing further the analysis and design of glass curtain walls under soft body impact.

In-Process Breakage Analysis of Tempered Glass Based on Fluid-Structure Interaction Approach

Asier Iglesias — 2024-06-16

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 techniques, such as spray mist cooling, to gain traction. Additionally, glass is a very brittle and sensitive material to local stress concentrations. Thus, depending on how the tempering process is performed, an excessive and/or non-homogeneous cooling might result in local residual stresses, which may exceed the allowable strength and cause premature fracture of the material. To this end, a fluid-structure interaction approach is proposed to consider the local phenomena during the glass cooling process. The defined nozzle configuration is observed to play a significant role on the residual stress distribution of heat treated components. In addition, water mist cooling is able to temper thin glass but, at the same time, large tensile residual stresses might develop during the cooling down process. The obtained numerical results are in good agreement with previous experimental investigations available in the literature.

Influence of Design Variables on Seismic Performance of Unitized Curtain Walls

Simona Bianchi — 2024-06-16

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 a focus on unitized curtain walls, this paper provides insights into the influence of design variables on façade seismic response by means of an extensive experimental campaign and an associated parametric study to test alternative designs under both quasi-static and dynamic loading conditions. The variables considered included variations in unit dimensions, glass and joint aspect ratios, joint and framing detailing, and support conditions. This research delves into a statistical analysis of the experimental results, in order to define parameters such as glass and façade unit rotations, frame elongations and distortions, utilization factors at different intensity levels. The results provide insights that guide façade design decisions for achieving desired seismic performance levels.

Numerical Investigation of Laser Powder Bed Fusion of Glass

Kyriaki Corinna Datsiou — 2024-06-16

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 laser—glass powder bed interaction and the impact of processing parameters. Through this understanding, the research seeks to identify practical strategies that can be employed to improve the quality and properties of the built parts. Bulk solid and powder soda lime silica glass properties are used as input in the model, while the laser heat flux and scan strategy, conversion of powder feedstock to bulk solid glass and heat losses from convection and radiation effects are introduced in the model through Fortran coding. The study showed that effective powder consolidation, resulting in well-defined geometrical features, is achieved for temperatures near the glass melting point. Additionally, uniform consolidation depths and widths can be achieved by increasing laser power, elevating substrate temperature and reducing scan speed within certain limits, whilst ensuring hatch spacing is below the corresponding single scan track width for unidirectional adjacent laser trajectories.

Numerical Study of the In-Plane Bending Behaviour of a Novel Steel-Reinforced Glass Frame Prototype

Mirko Pejatovic — 2024-06-16

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 a focus on ensuring structural safety for both individual components and the overall system. This method improves transparency and preserves a seamless visual appearance of the statically indeterminate beam through the utilization of Cast-In-Place (CIP) bonding technology. CIP bonding technology permits on-site lamination, offering a solution for installing large laminated glass components in locations challenging to be reached and accommodating sizes that exceed the dimensions of standard production and transportation capabilities. This paper places particular emphasis on the numerical study of the in-plane behaviour of a novel steel reinforced glass frame prototype conceived to be (partly) constructed using UV-curable beam-column connections. For that purpose, a series of non-linear 3D Finite Element (FE) simulations is performed in Abaqus. Specified interlayer properties used in the simulations relate to SentryGlas®, which is used for beams and columns, whereas UV-curable resin is used for beam-column connections. Sensitivity analyses are performed assuming various stiffnesses of the UV-curable resin. The numerically simulated behaviour of the novel frame prototype is compared to the experimental results of an equivalent simply supported beam. The results indicate that the effect of the considered beam-column connections can significantly enhance the load-carrying capacity of the steel-reinforced glass frame system.

Online Stress Calculation in Tempering Process Based on Measured Process Data

Antti Aronen — 2024-06-16

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 fragmentation which are important values for safety glass that meets the standards. To solve the residual stresses of tempered glass, it is important to know the glass material and the thermal history of the glass. The thermal history of the glass can be solved based on the information measured from the process and use this data with a heat transfer model. Time-dependent temperature profile is therefore used with thermo-elastic models to solve the stresses. The physical models and the measured data for calculation are presented in this study. The calculation model is then compared to offline stress measurements to find the accuracy of the results. The possible source of errors is also discussed.

Phase Field Fracture Model for Assessing the Load Bearing Capacity of Fractured Glass

Mauro Corrado — 2024-06-16

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 of the present work is the development and testing of a robust numerical model that can naturally introduce the generated crack pattern into virtual specimens and manage the interaction among many fragments. The phase field fracture model is herein explored, by assigning the damage variable to fit the pre-existing crack pattern. Then, the specimen is loaded letting the phase field managing the fragments interaction. The dependence of the stress tensor with the damage variable is herein defined through the Cleavage-Deviatoric model, since it prevents fully damaged regions from transmitting tensile and shear stresses yet keeping their ability to bear compressive forces. Indeed, this model can asymptotically reproduce unilateral and frictionless contact conditions between the existing crack lips. Preliminary case studies are discussed to check the potentiality of the proposed approach.

Quality Control of Safety Glass and How it Can Reduce CO2 Emissions

Jorma Vitkala — 2024-06-16

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 roller wave, edge kink, anisotropy, white haze, scratches, flaws, coating defects and how to indicate them. Measuring glass output temperature from bottom surface is one key indicator to good quality especially on coated glass. The latest quality control systems and their new possibilities will be examined from different perspectives. I will do some practical test runs and show how changes in the different settings affect the final quality. It has been estimated that the various degrees of error at different stages of glass production are up to more than 15%. Removing faulty glass from production at an early stage will save large amounts of money.

Relation between edge stress, bending strength, surface stress and fracture pattern of thermally toughened glass

Lena Efferz — 2024-06-16

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 deduction of the edge stress and transfer to bending strength and fracture pattern could provide essential findings for assuring the safety requirements of tempered glass. In this experimental investigation, the surface and edge stress were measured on standardized format thermally toughened safety glass, with different edge processing and glass thicknesses from three different suppliers. Afterwards, the fracture pattern is controlled, or the bending strength is analyzed in a
destructive four-point bending test. Conclusively, the results from the photoelastic and destructive tests are compared to determine whether the photoelastic measurement methods used to measure surface and edge stress can be employed as quality control.

Structural Assessment of Translucent Walls Built with a Novel Type of Insulating Aerogel-Filled Glass Bricks

Vlad-Alexandru Silvestru — 2024-06-16

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 transparent glass areas, but to offer a translucent alternative for part of the otherwise opaque wall areas. This paper focuses on the structural behaviour of walls composed of such aerogel-filled glass bricks. The components of such a brick and their functions are described. Moreover, two prototype systems for supporting the bricks in translucent walls are introduced – one with interlocking connections and pre-stressed wires, the other with interlocking connections and edge clamping. Both systems are analysed in finite element simulations from a structural point of view under out-of-plane loading. The resulting global deformations as well as occurring stresses in different components are analysed. Based on the findings, advantages and limitations of the different systems are highlighted and suggestions for improved alternative systems for translucent walls with insulating aerogel-filled glass bricks are made.

Structural Topology Optimization for Abrasive Water-Jet Fabricated Glass

Kimhong Heng — 2024-06-16

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 process. Here, we consider a volume minimization problem in which global displacement and global maximum principal stress design criteria are considered. The optimization algorithm is developed based on a density method with a robust filtering method. The Method of Moving Asymptote (MMA) is used as the standard optimizer. The numerical examples are presented in both 2D and 3D design structures. We perform topology optimization with mechanical properties specifically obtained experimentally for water-jet cut glass. We find that customized topology optimization can minimize effectively the volume of the structures and improve structural performance.

Viscoelastic Fractional Model with a Non-Uniform Time Discretization for Laminated Glass: Experimental Validation

Lorenzo Santi — 2024-06-16

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 approximation via Prony series of the relaxation function and a uniform discretization of time for the numerical solution. The model is also validated through the comparison with experimental test. The novel approach based on fractional calculus presents two main advantages: 1) the definition of the model parameters from experimental data is simplified; and 2) the numerical implementation is easier and computationally more efficient. When a long observation time is considered, the use of a non-uniform time discretization presents the great advantage of not neglecting any part of the relaxation function. Use of traditional uniform time discretization requires the use of large time steps making it impossible to describe all the changes of the relaxation curve within the large time interval. Practical examples will be presented using viscoelastic models for Trosifol® Extra Stiff (PVB) and SentryGlas® interlayers. This methodology also shows potential to advance next generation standards for the design of structural laminated glass.

An Approach for a Passively Shaded Glazed Steel Façade Utilizing Digital Design Strategies

Julian Länge — 2024-06-16

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 while keeping views to the surrounding alpine landscape with only passive shading systems. Structurally the façade acts as a folded plate structure formed through a grid of hollow steel profiles that is glazed on site with hidden fixations, sealed and mechanically secured through local pressure plates. For design and execution, a 3D parametric geometry model was utilized that served as a basis for structural and energetic simulations. Local climate data were imported into the model and informed the geometry of the facade, the performance of which was investigated through solar radiation studies within the model. Furthermore, the adjacent serrated metal-clad facades were generated based of the glass facades’ geometry. Harvesting the potential of these design strategies, the highly performative façade is intertwined with the character of the building which blends into the landscape around it.

Case of study

Arnau Bover i Pagès — 2024-06-16

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 curvature capabilities of the glass manufacturer. The steel structure is made up of 3D curved tubular beams and reconstituted straight welded profiles, which were subjected to a strict dimensional analysis by means of 3D scanners to ensure the structure’s assembly. The connections between the profiles have been done using complex 5-axis machined structural nodes and hidden prestressed bolts. The glass façade is composed of double-curved fritted and tempered laminated insulating glass panels which are two sided supported by the primary 3D curved hollow sections and a bespoke stick curtain wall. The glass façade is crowned by a spherical glass supported on its entire periphery with natural ventilation around it provided by 13 motorized windows. The verification of the structure considered second order effects and global imperfections using a finite elements software where the joint stiffness played a vital role. Advanced finite element software was used to determine it and it was validated through experimental tests.

Design of a 5m Span All-Glass Walkway

Bert Van Lancker — 2024-06-16

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 balustrades and the structural glass beams using a transparent acrylic adhesive. The bonding process was executed entirely in situ. The end supports of the all-glass walkway take the form of discrete steel shoes with neoprene elements to avoid hard glass-steel contact. These supports are concealed behind a wooden cladding. The design process encompassed finite element modelling, implementing viscoelastic behaviour of the interlayers and hyperelastic behaviour of the transparent acrylic adhesive. The innovations introduced in this project come in several dimensions: only three glass components are used, which are bonded together to form a cohesive structural entity using a transparent acrylic adhesive, which maximises transparency by eliminating conventional steel connectors. This paper elucidates the design principles, the challenges encountered during installation and the intricacies of the in situ bonding. This project serves as a reference of all-glass applications using structural adhesive bonding, and therefore contributes to the advancement of structural glass engineering.

Glass Engineering beyond Buildings

Michele Andaloro — 2024-06-16

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 periscopes to generate novel views and perspectives from both above and below the footbridge where it is installed.

Glazed Curved Shell for Villers-Cotterêts Castle

Thiemo Fildhuth — 2024-06-16

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 glazed with 2m x 2m, diagonally curved insulating glass units. The shell geometry and tesselation have been form-found to be clad with single curved glass. The shallow rise of 1.3m combined with a low glass curvature of 25m, the structural node geometry, the irregular courtyard shape, the incapacity of the masonry to absorb horizontal forces, rainwater drainage and the building regulations were key challenges to be met. In the present contribution, the solution to these topics is discussed within the context of other quadrangulated glazed grid shells, such as the Academy Museum of Motion Pictures in Los Angeles or the roof of lightrailstation in The Hague. The comparison shows the necessity to develop individual glazing and construction solutions depending on the boundary conditions and complexity of each project.

Panoramic Perfection: Unveiling Technical Insights from “The Henderson” in Hong Kong

Andreas Komm — 2024-06-16

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 resilience. Engineered, manufactured and installed by seele, they serve as effective shields against solar radiation and glare, seamlessly complementing the organic architecture. Collaborative efforts focused on maximizing the transparency of the building envelope as interdisciplinary teams navigated challenges in structural engineering, design aesthetics and compliance with strict regulatory standards of the building authorities in Hong Kong. Thanks to targeted investigations, advancements in glass construction technology and engineering innovation, a procedure was developed that ensured optimum bearing of the panoramic glass panes. This project contributes to the safety and durability of high-rise glass structures to withstand extreme conditions and showcases the transformative potential of bold design concepts, rigorous testing, and international collaboration. The result is a visually stunning and structurally outstanding masterpiece.

Port of Montreal Tower - Glass Cage

Bethanie Cloutier — 2024-06-16

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 transparency of the glass elements, steel framing was eliminated and connection hardware was minimized by means of simplification of load paths while mobilizing the structural contributions of all glazing elements. The laminated heat-treated inner lites of the sidewall insulating glass units cantilever outward through the façade, anchored top and bottom to the tower structure by a combination of sliding and fixed pin connectors. Structural silicone adhesive bonds the roof, floor, and soffit panels to horizontal curtain wall members which, in conjunction with the pin connector anchors, provide lateral stiffness, stability and load resistance to the glass structure. While differential vertical movements are anticipated between the perimeter of the “glass cage” and the curtain wall, such lateral movements are precluded by the incorporation of horizontal bracing to the tower framing. The entire glass envelope was assembled and silicone bonded at a controlled environment workshop before being shipped to site, where a challenging and daring installation was successfully effected in winter conditions.

Predictability and Performance of High Strength Epoxy Glue Glass Asssemblies

Paul Covillault — 2024-06-16

‘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 structural predictability of isostatic structures typically used in glass design. Even minor deviations in this kind of structure can result in multiple different outcomes, with different load distributions leading to higher local stress concentrations. The details and assembly process are designed to reduce the sensitivity to these different outcomes. For that, all possible eccentricities, and imperfections due to either fabrication, manufacturing, or erection on site have had to be analysed, physically tested, and reduced to a minimum. Involving extensive testing and manufacturing knowledge, this paper will focus on the design methodology of the project, examining how predicted behaviour both in the setup of the calculations and in the design of the node was controlled. The aim is to share knowledge on how to stay within the necessary risk margins and avoid unpredicted outcomes for glued connections.

Restoring Hi-Tech Architecture

Peter Lenk — 2024-06-16

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 of suspended glass panes. After approximately 25 years of service Arup was called back to provide advice to the client following a glass breakage incident. This triggered a detailed condition survey which concluded that a project refurbishment was overdue. Arup then provided further studies to inform strategic options as to how to best refurbish the façade. This advice led to the appointment of Octatube to provide Pre-Construction Services Agreement (PCSA) support to assist the façade appraisal and to carry out design, material testing, calculation and to provide critical construction advice, and then lead to Ocatatube’s appointment to fully refurbish the iconic façade.

Structural Glass Design for External Glazed Walkways in Iceland

Augustin Jouy — 2024-06-16

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 frames, pinned to the concrete slab. The glass panels act as diaphragms to provide overall stability. Panels are silicone bonded to the frames to ensure an effective in plane load transfer. The silicone thickness has been determined to optimise the requirements for shear resistance of the silicone and the overall flexibility of the structure, in conformity with a H/250 limitation. Calculations were carried out using Strand7. Wind loads on the panels (out-of-plane) and bracing loads (in-plane) have been decoupled by adding a toggle fixing on the connection to the frames. This allows to maximise shear capacity of the silicone bonding. Roof panels to frame connections use the same hybrid fixing method. Roof-to-wall panel connections involve a glass-to-glass silicone bonding with a load bearing pad in between. Wall panels’ shoe connections and their connections to surrounding buildings also rely on silicone bonding to ensure an even distribution of bracing loads along the corridor’s length.

Additive Manufacturing of Interlocking Glass Masonry Units

Daniel Massimino — 2024-06-16

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 is capable of printing a maximum volume of 32.5 x 32.5 x 38 cm - suitable for producing full-size masonry units. As part of this work, we discuss how to adapt design guidelines for glass AM to produce interlocking units. To evaluate fabrication ease and structural performance, three fabrication methods, Fully Hollow, Print-Cast, and Fully Printed, are compared. To compare the accuracy, repeatability, and structural capacity of each masonry unit, geometric analysis, surface roughness, and mechanical testing is conducted. Results varied by fabrication method, with average strength ranging from 3.64-42.3 MPa for initial fracture and 64.0-118 MPa for ultimate strength. Accuracy in print dimensions were < 1 mm with a standard deviation of 0.14-1.6 mm. Results demonstrated that Fully Hollow masonry units provide a more immediate path to implementation, while Fully Printed units have the potential to provide an entirely glass, transparent, and circular building component fabrication method.

Advancing Sustainable 3D Printing: The Feasibility of Recycled Glass as a Building Material With Additive Manufacturing

Michael Stern — 2024-06-16

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 type during extrusion, contributing to a deeper understanding of their printing behavior. We discuss the potential applications of this work in various fields, such as recycled glass architecture and mass product customization. This study contextualizes the use of different glass sources for 3D printing and discusses some of the manufacturing challenges of utilizing post-consumer recycled glass. Our findings open new avenues for customized fabrication with recycled materials, paving the way for innovative and sustainable practices with a larger library of materials for 3D printing technology.

Design of Additive Manufactured Glass Components for Glass Point Fixings

Philipp Amir Chhadeh — 2024-06-16

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 flat glass elements. The innovative laser glass deposition printing process (LGD), developed by Laser Zentrum Hannover e.V., involves locally heating fused silica glass fibres with a CO2-laser, enabling precise deposition of viscose glass on substrates of the same material. In order to implement the LGD process in glass facades an examination of the component is required. This paper introduces a series of mechanical examination techniques, such as indentation and bending tests. The results derived from the testing are the foundation for a parameter study in order to develop a button shaped point fixing for glass facades.

Spray Printing Glass

Matthias Seel — 2024-06-16

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 the Glass Competence Center was investigating the parameters color, transparency, interface and residual strength. Color and transparency seemed to be influenced by temperature, velocity, granulate, base material and more. This paper presents a feasibility study of spray printed glass on flat glass and shows results regarding the practical realization, pore distribution of the novel glass connections and microscopy. The current samples achieved size of 190 mm by 30 mm for soda-lime silicate glass and 200 mm by 85 mm for borosilicate glass. Larger sizes are possible and ask for investments in heat chambers, robot arms and associating torches. The dimensions of the samples can be scaled up. Spray printed glass can be used for new elements, but also to strengthen reused glass panels e.g. by making ribs. That makes spray printing glass a revolutionary product that has favorable prospects in applications in several markets.

Calibration of a Hyperviscoelastic Material Model for Silicone Structural Glazing Joints in the Context of Earthquakes

Tom Reisewitz — 2024-06-16

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 concerning resistance and influence. The load-bearing capacity of the structural sealant might be reduced on the one-hand side, while the impact on the bond might be decreased on the other-hand side. A more thorough investigation of the structural performance of silicone within bonded glass structures under different loading scenarios is urgently required and an appropriate material model is essential. The calibration of this model is crucial to better understand the performance under dynamic loading. A hyperviscoelastic material model, which considers time-dependent properties and large deformations, seems promising. The aim is to identify the material parameters for this model based on dynamic mechanical thermal analysis and tensile tests.

Experimental Characterisation and Calibration of Hyperelastic Material Models for Finite Element Modelling of Timber-Glass Adhesive Connections under Shear and Tensile Loading

Tine Engelen — 2024-06-16

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. This, in turn, requires a strong structural bond between the timber and glass. Therefore, in this paper, experimental tensile and shear tests are performed on bonded timber-glass specimens with five different structural adhesives. Special attention is put on the failure behaviour of the adhesives, where both cohesive failure and loss of adhesion were identified. The nonlinear stress-strain behaviour of these adhesives is evaluated and used to asses different hyperelastic material models. Two calibration methods are used to determine the model parameters of the hyperelastic material models. Simulations have shown that the first method, assuming uniaxial tension, was not suitable for the performed tensile tests. However, with the second method, using an inverse parameter fitting method, a better approximation was obtained. The results from this work can be used to model bonded timber-glass connections in larger structures more accurately. The nonlinear stress-strain behaviour of the adhesives can be represented with hyperelastic material models. The experimental data is compared to existing hyperelastic material models where available. In case existing models are lacking, the experimental data is used to determine the model parameters. Finally, suitable stress and strain failure criteria are determined. The results from this work can be used to model bonded timber-glass connections in larger structures more accurately.

Experimental Investigations on the Cyclic Load-Bearing Behavior of Structural Glazing Joints under Seismic Load

Paul Müller — 2024-06-16

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 narrowed down to areas of practical relevance as part of a theoretical stress analysis.
On this basis, extensive experimental investigations of the low-cycle fatigue behavior of structural glazing joints are presented. Cyclic stress-strain curves are determined and compared with quasi-static reference tests to describe the basic low-cycle fatigue behavior. The influence of the previously determined parameters on the cyclic load-bearing behavior can thus be determined and presented. These investigations provide an important basis for describing the behavior under typical seismic random loading. In particular, the type of load application caused by the different construction types of glass and facade buildings can be mentioned as a decisive influencing factor in addition to the frequency of building construction. The results provide a first important contribution to the modeling and design of structural glazing joints against earthquake effects. Within the framework of the IGF project "RISIKO", further extensive scientific investigations will be carried out on this basis in order to develop a design model for structural glazing joints in disaster scenarios.

Experimental Work on Thick Epoxy Adhesive Bonds for Glass-Steel Joints in a Ship

Daniël Wium — 2024-06-16

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 tolerances on the linear bonding surfaces of the glass and steel substrates, and to reduce strains within the adhesive, the application of a relatively thick layer of adhesive is evaluated. However, as this thickness is significantly larger than the recommendation of the adhesive manufacturer for optimal strength, its consequences on the mechanical performance of the bond need to be investigated. Therefore, tensile tests are performed with standardised dumbbell specimens at various strain rates. Shear tests are also performed with glass-steel double-lap bonded joints, to evaluate the shear strength of the epoxy with a thick layer and various bonding surface preparation methods.

Holistic Review of the Permanent Shear Deformation Effects on Structural Silicone Joints in SSG Façade Systems

Jordi Alcaine — 2024-06-16

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 path within it. To conform with this new load path, shear deformation will occur in the SSG joints. The deformation in the SSG joint will be permanent unless the supporting main structure returns to its original position. The structural performance of SSG joints subjected to permanent shear deformation in combination with short term loads is not adequately covered by any guidance. The aim of this paper is to provide a better understanding of the effect of the permanent shear deformation on SSG joints. Experimental tensile and shear testing has been carried out by Sika on H-specimens (Sikasil® SG-500) while imposing prescribed levels of shear deformation in combination with different accelerated aging conditions. The testing procedure, results and main conclusions are explained and summarised.

Influence of Bonded Air- Versus Tin-side on the Shear Strength of Glass-to-Glass Joints of Transparent Epoxy Adhesive at Elevated Temperatures

Yasmina Boutar — 2024-06-16

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 (float and low-iron glass) were chosen to conduct experiments. The differences in surface wettability, between air and tin-sides were examined for both glass types. Results showed that water contact angle measurements on float glass sides were 39.25 % and 3.98 % higher than measurements for low-iron glass on air- and tin-sides respectively. Furthermore, tensile and shear tests were performed on bulk-cured adhesive samples and bonded glass-to-glass block shear specimens respectively, at room temperature (RT), 40 °C, and 80 °C. The results showed that tensile and shear strengths decreased with increasing temperatures. Furthermore, the shear strength was influenced by the surface properties of the glass sides. Indeed, results on air-side likewise tin-side of low-iron glass demonstrated higher resistance for all tested temperatures in comparison with the float glass.

Investigation of Glass-to-Concrete Adhesive Joints through Three-Point Bending Tests

Cas Maertens — 2024-06-16

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 and construction of bonded glass-concrete elements. These insights serve as the foundation for future studies, exploring innovative applications where structural considerations seamlessly merge with aesthetic, durability, and safety considerations. The ultimate objective is to evaluate the potential of glass bonded to concrete, aiming to not only excel in structural performance but also to meet multifaceted demands across diverse engineering applications.

Methods for Dimensioning an Adhesive Joint for Use in Fluid-Filled Façade Element

Alina Katzera — 2024-06-16

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 concept. Therefore, in recent years, a number of researchers have looked at different methods for the design of adhesive joints. Such methods are presented by the Fachverband Konstruktiver Glasbau e.V. in the Technical Note FKG 01/2021. A further approach is presented by Drass & Kraus (2020, 2021a, 2021b), who proposes an approximation to the semi-probabilistic safety concept and thus to the current Eurocode 0 design standard by determining a material safety factor. This paper is concerned with the design of a load-bearing adhesive joint for use in a fluid-filled insulating glass unit. A specific façade element is used as an example for the calculations. Three dimensioning methods are compared: the analytical method according to ETAG 002-1, a numerical method according to Technical Note FKG 01/2021 and the approximation of a semi-probabilistic safety concept according to Drass & Kraus (2020, 2021a, 2021b). The results show significant differences between the design methods in terms of utilisation.

Stress Distribution along the Structural Sealant Joint Length of a Cylindrically Curved Glazing Panel

Mihail Istratii — 2024-06-16

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 compression and shear forces within the joint, both occurring at the same time. This means that in the case of a structurally bonded curved panel, additionally to the shear caused by differential thermal expansion of elements or glass self-wight which is covered by ETAG 002 and EN 13022 the designer must also consider the shear stress induced due to the panel curvature. The magnitude and location of this additional shear stress and also of the tension/compression stress can be identified using Finite Element Analysis.

Structural Performance of Adhesively Bonded Glass-GFRP Sandwich Beams

Dinith Ranaweera — 2024-06-16

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 prior to being utilized in the industry. Consequently, this study focuses on the structural performance of slender composite beams comprising of two glass face sheets with a GFRP core adhesively bonded to the face sheets representing a section of a larger panel. In the first phase of this study two different beam configurations are tested comprising of two sizes of GFRP cores, with two distinct wall thicknesses which are then compared against non-composite beams. Whereas the second stage of the study comprises of the long-term behaviour of these beams when subjected to staged long-term loading. The surface strain data and midspan deflection of the beams will be obtained from the specimens.

The Minimal Wall

Stefan Trifonov — 2024-06-16

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 discussion focuses on structural sealant glazing and the composite behaviour of glass and frame to resist out of plane loads. The study promotes capitalizing on the inherent contribution of the adhesive connection towards the flexural stiffness of façades and proposes ways of enhancing it for further structural optimization. The impact of the adhesive connection is assessed through an experimental program consisting of extensive four-point bending tests of representative beam samples and corresponding numerical studies. The article provides an interpretation of the interim results and discusses the potential of the proposed solutions to contribute towards a holistic approach to reduce the global warming potential of building envelopes. Finally, directions for future research needed for practical applications of the proposals are presented and discussed.

Time-Dependent Design of Hyperelastic Bonded Joints in Structural Glass

Benjamin Schaaf — 2024-06-16

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 degradation of the adhesive. From a design perspective, it is necessary to consider the time dependency. On the one hand, the bonded joint must be able to withstand variable loads of different strain rates at any time during its service life, taking degradation into account. On the other hand, if the bonded joint is also under a permanent load due to dead load of the glazing, it must also be ensured that the failure time would only be attained at the end of the component's service life. This article presents a fully probabilistic method that considers the degradation of the adhesive as well as various statistical influencing quantities (such as wind effects, manufacturing tolerances or material scattering) and determines a modification coefficient 𝑘𝑚𝑜𝑑 for silicone adhesives under variable loads by calibrating to specified reliability indices. In addition, partial safety factors are determined in accordance with Eurocode 0, which are investigated as part of a sensitivity analysis.

Adhesion of Laminated Glass Interlayer in a Double Cantilever Beam Test

Paul Elziere — 2024-06-16

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. We focus in this study on the Double Cantilever Beam (DCB) test that models one of these configurations. We compared three different types of typical interlayers used in the building industry, a standard Poly Vinyl Butyral (PVB), a structural PVB and an ionomer interlayer. We conducted tests at different temperatures and loading speeds to screen a broad range of conditions seen by the interlayer in the field. We found that the nature of the interlayer has a dramatic impact on the measured adhesion to glass which is directly linked to its mechanical properties and to the experimental conditions. In the specific loading conditions of the DCB test, we have identified for each interlayer, a regime of low adhesion levels combined to a rapid propagation of the delamination front under certain temperatures and loading speeds.

Adhesion Properties of Polyvinyl-Butyral-Laminated Glass under High-Speed Loading

Zhifei Chen — 2024-06-16

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) PVB-laminated glass and three loading rates (i.e., 0.1m/s, 0.5m/s, and 5m/s) were considered in the tests. The delamination behaviour of PVB-laminated glass was modelled using a numerical cohesive zone model (CZM) to accurately calibrate the interfacial adhesion properties. It was found that BG-R15 PVB-laminated glass exhibits a progressive delamination behaviour under high-speed loading, which results in a stable but low post-cracking force, whereas the delamination was significantly constrained for BG-R20 PVB-laminated glass, which leads to a higher post-cracking force but very poor deformability. The deformability of high adhesion grade laminated glass increases with the crack number since more PVB participates into the stretching of cracked laminated glass. The interfacial adhesion property shows a significant rate effect, with the bonding strength and energy release rate of BG-R15 PVB-laminated glass increase by nearly 25% and 50%, respectively, as the loading rate increases from 0.1m/s to 5m/s. In general, the energy dissipation capacity of the BG-R15 PVB-laminated glass is much higher than that of the BG-R20 PVB-laminated glass. This study can provide a valuable reference for the design of laminated glass under blast or impact loads.

Freely Hanging Multi-Layer Laminated Glass Subjected to Near-Field Blast

Alžběta Kohoutová — 2024-06-16

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 TNT. The samples were suspended on wire rope slings to eliminate support influences and allow comparison with numerical models. Samples were incrementally loaded with explosive weights to estimate the minimum impact energy required for glass failure. The overpressure from the blast was recorded and the response of the panels in terms of the acceleration, as well as crack formation and propagation, was studied. Accelerometers were affixed to each panel, whereas the crack development was examined after each test. The experimental results were compared to a numerical model. The study explores cracks based on numerous parameters like number of blasts and glass configuration. It also shows how different parameters impact panel velocity under blast and how damage affects their natural frequency. Comparison with numerical models shows that the setup accurately replicates the absence of supports.

Imperfections in Laminated Safety Glass

Paul Müller — 2024-06-16

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 ("planarity deviations" or "roller waves") in the thermally toughened glass can lead to permanent tensile stress in the thickness direction of the laminate. This stress, especially under environmental conditions (humidity and temperature), has not been considered in current quality assurance measures or scientific studies on the structural performance of laminated safety glass. This paper analyzes the performance of PVB composite samples under tensile load in the thickness direction of the laminate. Two PVB products are considered under two environmental conditions. Based on quasi-static tensile tests to determine a primary strength, the influence of load duration is analyzed in creep tests at different load levels. On the one hand, a relevant correlation between load level and failure time could be determined. Firstly, a relevant correlation between load level and failure time was established. Secondly, a relationship between quasi-static strength and creep performance is observed and a model for predicting the failure time of such specimens is proposed.

Influence of a Multilayer Interlayer with a Stiff Core on the Performance of Laminated Glass

Elena Fleckenstein — 2024-06-16

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 behavior of glass panes during impact and after breakage when high tensile stresses occur in the interlayer. A film with higher stiffness, lower time and temperature dependence can be laminated between two layers of interlayer material to improve laminated glass behavior. Given the need to conserve resources and reduce weight, the question arises as to whether such an interlayer could also be used to meet the safety requirements for laminated glass made out of thin glass. In this study, the influence of a multilayer interlayer of EVA and a stiff core film of modified polyester (MPE) in glass laminates was examined. For this purpose, the material and composite behaviors were experimentally studied and evaluated. This article presents the test setup and the results. The focus is on comparing the properties of interlayers with and without MPE films. The results show that the impact strength of thin glass laminates is improved by the multilayer interlayer.

Investigations on the Finite Strain Behavior of PVB

Alexander Pauli — 2024-06-16

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 quasi-static loading. The results of experiments on single-layer Standard PVB are presented, and a model of finite nonlinear viscoelasticity is derived. In particular, the formulation of phenomenologically motivated viscosity functions is described. Subsequently, the model parameters are calibrated on the experimental results, and the uniaxial stress state is simulated.

Material Characterization of Three Liquid Interlayers for Laminated Glass Solutions

Julian Hänig — 2024-06-16

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 study essential material properties were investigated. The research focuses on the viscoelastic, tensile, and creep properties of the LOCA. Additionally, the study considers how the materials age under radiation, high temperature and high moisture in accordance with the product standard for laminated glass. All results are summarized to provide a wide-ranging data base for dimensioning laminated glass made with LOCA. Finally, the properties of the materials are compared with conventional interlayers and their potential for use in laminated glass applications is discussed.

Mechanical Enhancement of Fractured Laminated Glass considering Fragment Overlaps and Temperatures

Dongdong Xie — 2024-06-16

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) and the multiple offset-cracked tensile (MOCT), were conducted at 20, 50, and 80℃. Both PVB and SG were considered. Additionally, the influence of the overlap length of offset fragments and initial delamination on tension stiffening was investigated based on finite element models. The results show that the mechanical properties of the composite materials, which correspond to a local response in the post-fracture laminated glass, are strongly dependent on the fragment overlap, temperature, and interfacial delamination. Moreover, the influence of the fragment overlap on the mechanical enhancement becomes pronounced even at high temperatures, which should be taken into account for the evaluation of the post-fracture performance of laminated glass.

Mechanical Performance of Liquid Cold-Poured Interlayer Adhesives in Comparison to PVB, EVA and Ionomers

Dominik Offereins — 2024-06-16

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 liquid cold-poured interlayer adhesives are investigated for their mechanical material properties in an extensive test regime. To be able to classify the characteristic values of the adhesives within a correct framework, the materials currently holding the largest market share, including Polyvinyl Butyral (PVB), Ionomers, and Ethylenvinylacetate (EVA), are also subjected to the experimental program. The temperature dependence of the material behavior is explored through Dynamic Mechanical Thermal Analysis (DMTA) experiments. Furthermore, the time-dependent material behavior at large deformations is scrutinized using various methodologies, such as tensile tests at different strain rates, cyclic tests, creep tests, and relaxation tests, all conducted in uniaxial tension mode. The outcomes of all tests led to promising results for one of the adhesives with advantages over those of PVB and EVA.

Post-Failure Behavior of Point-Fixing Laminated Glass Plates under Out-of-Plane Uniform Pressure

Sicheng Zhou — 2024-06-16

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 plies broken, which was applicable for LG plates made by heat-strengthened glass. In the above four modes, the top ply is always subjected to compression while the bottom one is in tension. The different responses of each configuration (different glass types and damage modes) were discussed and compared in this study. In addition, numerical models were adopted to reproduce the experimental results. The influence of the hitting location and glass types on the mechanical behavior of LG plates was analyzed. The results showed that the contribution of the broken glass ply could not be disregarded in the evaluation of the global stiffness of partially damaged LG plates and their bearing capacity.

Predictive Analysis of Laminated Glass Performance Under Static and Dynamic Loading Conditions

Amit Kumar Gupta — 2024-06-16

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 (standard/non-standard) can be found in the literature to develop and screen the different interlayer materials. In the last several years, we have witnessed extensive growth in computational modeling of complex nonlinear behavior of laminated glass panels with viscoelastic interlayers. To evaluate the mechanical behavior of laterally-loaded interlayer in laminated safety glass, finite element (FE) modeling is widely used in industry. Recently, FE modeling techniques and methods helped to identify selection criterion for proposed materials to be used in the interlayer of laminated glass. The present study aims to develop a numerical model (Finite Element model) verified by experimental results/data given in literature and to utilize the model to examine the mechanical behavior of laterally-loaded interlayer films in laminated safety glass subjected to standard/non-standard tests (four-point bending test and Impact test) conditions. Also, parametric studies (effect of interlayer/glass thickness, impactor speed, soft/stiff interlayer material etc.) are performed through FE analysis to investigate the impact of these parameters on the behavior of the interlayer material.

Ten Years of Stiff PVB: An Overview of Developments and Current Status

Wim Stevels — 2024-06-16

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 structural design of laminated glass were less apparent. This was due to a lack of suitable standards and/or national approvals on one hand, and a lack of broader set of performance data on the other hand. Meanwhile, many of these gaps have been addressed, and performance data from various suppliers have been on a converging path, as progress in standardization was made and best-practices emerged. In addition, interest in the use of stiff interlayers in general has recently intensified, as they can improve carbon footprint of laminated glass and facades. This article aims to cover these developments, as well as providing complimentary information on some aspects. Eventually, stiff PVB’s have become a viable interlayer choice in suitable laminated glass applications, supported by a substantial amount of performance data from multiple suppliers. Drivers for the use of this material category have changed from merely economic to supporting sustainability targets through carbon footprint reduction.

Benefits of Revised German Code for Glass Design

Geralt Siebert — 2024-06-16

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 other glass design codes including future Eurocode for Glass (CEN/TS 19100) into account. The paper shows the developments like reduced safety level for selected applications with lower consequence class (which is revolutionary for Germany), simplified calculation of conical point fixings, revised concept of classification and newly developed flow charts for design of balustrades. Overall, the field of application covered by the code is widened, more economic glass structures can be designed within the code. Calculation examples show difference of old and revised German standard for different applications to complete the picture.

Glass Serviceability Limits

Mohammed Hassan — 2024-06-16

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 manufacturing limits but rather by the deflection (serviceability) limits. Despite objective criteria guiding serviceability limits, occupant acceptance of deformation remains unexplored, leading to conservative designs. This paper introduces a novel method for measuring occupant satisfaction with glass deformations, aiming to establish acceptance thresholds comparable to objective criteria. An experimental campaign was conducted to assess volunteers' levels of perception and acceptance of various glass deformations. The glass was deformed using an electro-pneumatic system at levels corresponding to below, above, and at the current serviceability limit. The results demonstrate the feasibility of measuring human responses to deformations in the glazing and provide essential data for setting serviceability limits. The experiments indicate that, based on occupant feedback, the current serviceability limit of L/50, may be relaxed, thereby presenting opportunities for material efficiency, such as the adoption of thinner glass in facades. The methodology effectively captures human responses, revealing heightened perception of glazing movement at night and a higher acceptance during the day. Changes in reflection were the primary reason for the perception of movement, with lower acceptability at night. Overall, participants felt safe regardless of their prior knowledge on glass properties, and providing this information to participants did not improve acceptance, which was already sufficiently high. The findings from this research fill an important knowledge gap in understanding occupant acceptance of glass deformations, crucial for comprehensive user satisfaction assessments and evidence-based reductions in glazing thickness.

Spontaneous Breaking of Thermally Toughened Safety Glass in Facades

Philippe Letocart — 2024-06-16

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 not to perform it at all, preferring to replace the glass should failure on a building occur. In this talk, we will show that, due to recent advances in microanalysis techniques, it is now possible to state after a failure on a building whether the heat soak test was correctly conducted according the EN standard or not.

Strength Lab AI

Michael Kraus — 2024-06-16

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 geometrically non-linear setting, are time-consuming and require significant expertise. This study develops a customized Mixture-of-Experts (MoE) neural network architecture to overcome current limitations. It calibrates it on synthetically generated stress and deformation data obtained via parametrized Finite-Element-Analysis (FEA) of glass and glass laminate structures under both geometrically linear and nonlinear conditions for several joint support and loading conditions. Our findings reveal that the MoE model outperforms baseline models in predicting laminate deflections and stresses, offering a substantial increase in computational efficiency, compared to traditional linear and non-linear FEA, at high accuracy. The MoE is integrated within a novel web-based glass design and verification tool called Strength Lab AI and provided to the engineering public for future use. These results have profound implications for advancing engineering practice, offering a robust tool for the intricate structural design and analysis of glass and glass laminate structures.

Structural Glass Design Manual

Richard Green — 2024-06-16

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 and Engineers to have an informed decision-making process for selecting levels of robustness, which may or may not be otherwise required by code. The document aims at developing consistent practices to facilitate confident design in glass while also addressing a number of technical challenges.

W-Glass : A Cloud-Based User-Friendly Software Platform for Simplified EN 16612 Compliance

Mehmet Burak Yilmaz — 2024-06-16

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 implementation dependency chain. Additionally, the absence of explicit load combination specifications has led to variations in practical applications. This study aims to clarify the complexities and variations involved in implementing EN 16612, with a focus on procedural nuances from the end-user’s perspective. It examines the architectural design of a cloud platform, W-Glass, which is specifically designed to streamline the application of this standard. The platform facilitates end-users in performing relevant calculations with ease. Among its various components, the study highlights the calculation service as a particularly crucial element. Employing state-of-the-art programming techniques, this service efficiently manages the structures required by the standard, ensuring a codebase that is not only clean and flexible but also maintainable for potential future enhancements of the standard.

Active Wind Load Sharing Optimization of Double Skin Glazed Façade Design

Guido Lori — 2024-06-16

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 condensation, holes or slots are provided in the framing to allow air entering. The cavity is pressure equalized with the external and the full pressure acts on the inner skin, making useless the stiffer glazing at the
exterior in terms of wind load sharing. Permasteelisa aims to apply an active design, which changes the equalization conditions when the wind load acts. Valves have been developed and this paper shows design and experimental testing validation. The designer can provide the ventilation under serviceability conditions, but, by closing the gaps when the wind gusts occur, he can share the wind
loading according to the relative skin stiffness in ultimate condition, making a holistic design and matching the sustainability demand. So, it is paramount that standards recommend experimental validation to proof the system effectiveness, in addition to statements given for safe design purpose.

Beneficial Effects of Dissipative Brackets on Glazed Façade Maximum Capacity under Blast Loading

Guido Lori — 2024-06-16

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 possible to supply a high degree of resilience also to buildings with less safety demand, but affected by significant blast risk (soft targets or indirect targets). The reduced incremental façade cost and the negligible impact on functionality and aesthetics, compared with the benefits in terms of financial loss reduction, have favoured a systematic approach in world areas affected by large terrorist threat. The deformable bracket patented by Permasteelisa has upgraded the dissipative effect, increasing the maximum blast the glazing can resist up to the failure and reducing the load transfer to the building, resulting in sustainable blast risk mitigation, not just for individual buildings, but as coordinated
strategy in urban areas. This paper describes measurable cost and environmental benefits, showing different design solutions and experimental test validations of the dissipative brackets.

Design and Stability of Laminated Glass Beams and Cantilevers with Continuous Lateral Silicone Restraint

Richard Green — 2024-06-16

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 and/or strength models that allow higher levels of stress. A review of equations for cantilevers results in a wider range of approaches with significant variance between the outcomes of various published steel and glass standards. AS1288 has been used as the default standard for stability of glass fins, however for cantilevers it appears to have a misprint which has existed for decades. This paper presents strategies for determining the moment capacity of beams and cantilevers made of laminated glass with continuous flexible buckling restraints, such as structural silicone, which have initial imperfections and a known design strength capacity. Where multiple wave lengths form, the warping stiffness may contribute and formulations for rectangles are presented. The accuracy and validity of the approach is also assessed by means of comparisons with the outcomes of Finite Element numerical analyses.

Design of Glass Handrails

Richard Green — 2024-06-16

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.

Experimental Behavior of a Prototype 3m-Span Modular Glass Pedestrian Bridge

Joseph Robert Yost — 2024-06-16

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 performance of the interface material necessary to transmit the high in-plane compression forces between neighboring HGUs. As well, the feasibility of the proposed modular system has also been demonstrated through the successful assembly and disassembly of a 3 m span prototype pedestrian bridge known as Tortuca. Tortuca is comprised of 13 individual interlocking HGUs assembled into a compression-dominant form supported on steel abutments. In the current research study, the physical performance of Tortuca is experimentally investigated under controlled laboratory testing and using an extensive assortment of displacement and strain sensors. Significant findings related to experimental testing of Tortuca will be reported.

Experimental Study on the Thermal Performance of Soda-Lime-Silica Glass by Radiant Panel Testing

Evelien Symoens — 2024-06-16

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. This paper presents an experimental campaign employing an electrical radiant panel as the heat source to investigate the heat transfer phenomena in glass. The radiant panel consists of 21 emitters capable of producing a uniform radiative heat flux on glass specimens of different thicknesses. The experimental results allow us to derive heat transfer ratios specific to the glass material. These ratios are essential for accurate fire simulations, understanding heat transfer through glass, and quantifying the transmitted radiation through the glass, which is important for the combustible materials on the unexposed side of the glass component exposed to fire.

Flaw Characteristics of Architectural Glass and Long-Term Strength Prediction Model

Siyi Yi — 2024-06-16

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 analysing the flaw and statistical characteristics in glass, especially the edge defects, proposing a Monte-Carlo based model to simulate the long-term mechanical behaviour of glass specimen with distributed edge defects and modifying the 𝑘𝑚𝑜𝑑. 3D laser confocal microscope was utilized to observe the defects. The Monte-Carlo based model is able to generate edge defects and conduct numerical experiments to expand the data pool. Based on stress corrosion theory, the crack resistances under two load conditions (constant stress and constant stress rate) were derived respectively. By analysing and quantifying the influences of temperature, humidity and stress rate on crack growth parameters, the crack resistances under two
load conditions are compared, and a modified 𝑘𝑚𝑜𝑑 is then proposed. The Monte-Carlo based model is verified by lifetime test from literature. The modified 𝑘𝑚𝑜𝑑 is validated with substantial dataset across various load durations and is compared with international standards, demonstrating the accuracy in predicting glass long-term strength.

Glass Edges in the Building Industry

Paulina Bukieda — 2024-06-16

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 previous scientific studies confirms a high scatter in the edge strengths of different manufacturers. However, there are no generally valid grinding process parameters that can be associated with a high edge strength. Consequently, general edge strength values have to be questioned, as they potentially lead to safety concerns. Thus, the processes have to be investigated individually. For this purpose, an examination method with fracture tests and a microscopic defect analysis for process optimisation is introduced. Based on the results of two different edge grinding machines, the formation of defects is presented and their potential of causing early breakage is discussed. In an overall evaluation, approaches are proposed on how the manufacturing of glass edges with high edge strength can be verified and included in the design.

Influence of Scratch on the Crack Pattern of Monolithic Glass under Flexural Loading

Zhufeng Pan — 2024-06-16

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 glass plates are tested consisting of intact and scratched specimens with two typical loading rates. Test results show that the loading rate will lead to the variation of material strength but will not significantly influence the crack pattern for both intact and scratched glass. To have a thorough understanding of the fracture process of scratched monolithic glass, numerical simulation of CDR test is performed based on the peridynamics (PD) theory. The scratch features in the model are simplified to improve the computational efficiency. Deflection Results obtained from the plate theory are used to validate the PD model. The initiation and propagation of radial cracks along the surface are captured. Such research findings can contribute to the fracture behaviour evaluation of scratched glass elements.

Structural Damping of Glazed Facades and Resulting Risk of Vibration under Along Wind Excitations

Guido Lori — 2024-06-16

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 avoid additional useless reinforcements and checks, other researchers have identified testing conditions for which vibrations occurred even for natural frequencies up to 14Hz. The authors start from the analysis undertaken in their previous work, identifying damping as the decisive parameter. Differently from what is reported in several literature studies, working conditions of glazed façades result often in equivalent structural damping larger than the minimum values assumed in numerical calculations. By means of other experimental data, it will be shown that an indiscriminate reduction of the 5Hz limit would be probably unsafe. Recommendations will be given in order to run specific experimental investigations to solve the inconsistent literature experiences and to the address the limit in future standards in dependency on specific combinations of wind and system dynamic properties.

Temperature Distribution and Stress Relaxation in Glass under High Temperature Exposition

Maximilian Möckel — 2024-06-16

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 laminated soda-lime silicate glass in different components. The test set-up was chosen in a way to create an inhomogeneous temperature distribution from the heat source through the glass in order to create a more realistic load case than an assumption of homogeneity. The results of the experimental examinations were used to develop a first numerical model that was used to visualise details (e.g. temperature and stress distribution). In addition, the paper presents results of experimental and numerical examinations to the determination of the temperature distribution in different glass components, which leads to stress relaxation during high temperature exposure and affects fracture pattern in thermally toughened glass plates. This will pave the way towards understand of glass structures exposed to heat and fire and, as a vision, will form the fundamentals of a design concept.

Verifying a Glass Pane Under Combined In-Plane Compression and Out-of-Plane Lateral Loads

Philipp Kießlich — 2024-06-16

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 experimentally by exposing extracted specimens to on-surface lateral loads and in-plane compressive loads simultaneously. Additionally, in-plane compressive loads were combined with soft-body impacts. This combination of static loads with short-term lateral loads is interesting in terms of stability and the residual load bearing capacity. The results show how compressive in-plane loads increase stress and deformation according to first and second order deformations and indicate that premature stability failure occurs due to soft-body impacting.

Contribution to the Development of Cold Bent Glass Applications

Maximilian Laurs — 2024-06-16

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 developed by elastically applying the curvature at ambient temperature. Nevertheless, the widespread use is still opposed by surmounted imponderables, like advanced calculation models utilizing FEAs and missing experience in the application of this method.
This paper gives an extensive overview of the state of the art, like realized structures, deformation criteria and cold bending associated stress development, while also prompting a new analytical approach for the calculation of stresses in cold bent glasses. Moreover, a time-dependent buckling phenomenon on laminated glasses is discussed. In conclusion, aspects of the upcoming informative annex of the prEN 19100 (Eurocode 10 to be) on cold bending are discussed.

Experimental Investigation of Post Failure Performance of Warm Bent Laminated Glass

Minxi Bao — 2024-06-16

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 laminated glass are scarce. The high bending stiffness of laminated glass introduced though the induced curvature is highly beneficial in structural glass applications, however, this could be compromised by the spring-back effect following fracture and could eventually trigger ultimate limit state limitations until their safe replacement. This paper experimentally investigates the post-fracture performance of warm bent laminated glass. A number of parameters are tested, taking into account the different laminate layouts, glass geometries and types. The laminated configurations are fractured in a controlled manner and the post-fracture spring-back are identified. These findings can provide useful insights for the post-fracture mechanical response of warm bent laminated glass, point out important considerations for future design and promote the safe use of warm bent laminated glass in load bearing applications.

Laser-Based Bending of Low-E Coated Flat Glass

Najoua Bolakhrif — 2024-06-16

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 bending process dependent on the side exposed to the laser. If the laser-based bending is focused on the uncoated side of low-emissivity glass, a faster bending process compared to the uncoated glass is observed while maintaining the same laser power. The reflective properties of low-emissivity glass are maintained after the bending process. The near infrared reflectance of low-emissivity glass remains about 50% higher than uncoated glass. This study presents the laser-based glass bending technology as fit for purpose and proves the applicability of coated bent glass for architectural purposes.

Mechanical Properties of Glass Plate During Anticlastic Cold Bending

Xiaohan Hao — 2024-06-16

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 various factors, including aspect ratio, scale and composition of the plates. Subsequently, an effective finite element model was established and validated by test results, which is used for further explore the cold bending controlling condition for better engineering practice. The failure modes are considered as instability and strength failure. For laminated glass, maximum stresses can be derived from monolithic glass based on equivalent thickness method. The instability is induced by the compression area in the middle surface of glass plate which is significantly influenced by the composition of the laminates. Consequently, thin glass laminates exhibit enhanced stability because a reduced glass to PVB thickness ratio changes the compression area from bi-directional to uni-directional.

New Generation of Bending Tempering Equipment

Joan Tarrús — 2024-06-16

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 glass with smooth surfaces. In the realm of flat glass, tempering has been the most efficient practice to increase the glass strength. However, when it comes to doubly curved glazing, the options are limited to slumped laminated configurations due to known constraints in load-bearing capacity. While architects continue to explore challenging geometries, and engineers search for technical solutions to meet the demands of each new project, the industry has come up with the daring project-based solutions to meet the most demanding requirements. New developments in the construction industry, such as The Henderson tower by Henderson Land in Hong Kong and the L'Oréal's Innovation Centre in Paris, are pushing the boundaries and verifying the new manufacturing possibilities. Double curved and spherical tempered glass design measuring up to 6.5 m x 3.6 m is now a reality.

Early-Detection of EVA Encapsulant Degradation in PV Modules Based on Vibration Frequency Analysis

Chiara Bedon — 2024-06-16

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 load-bearing capacity of the sandwich PV system. As a major effect of ageing, ambient conditions, non-uniform / cyclic thermal gradients, humidity and even extreme mechanical / thermal loads, the rigidity of these films can largely modify and decrease, thus possibly affecting the mechanical capacity of the PV module, and even exposing the solar cells to fault. Knowledge of the effective bonding level is an important step for diagnostic purposes. In this regard, the present study is based on a preliminary but extensive parametric Finite Element (FE) numerical investigation of full-scale commercial PV modules of typical use in buildings. The attention is given – for PV module arrangements of technical interest – to the effect of EVA stiffness in terms of vibration modes and especially frequency sensitivity. As shown, when compared to newly installed PV modules, any kind of stiffness decrease is associated to major frequency modifications for the composite system, and in the worst configuration, such a frequency scatter can decrease down to -40% the original condition. Such a marked stiffness decrease would be implicitly associated to a weak mechanical performance of the sandwich section, with major stress peaks and deflections in the PV system, even under ordinary loads. The presented results, in this sense, suggest that major consequences can be prevented and minimized by monitoring the vibration frequency of PV modules.

Electrophoretic Light Modulator (ELM) Dynamic Glass Technology: A Daylight and Energy Performance Study

Matthew Tee — 2024-06-16

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 buildings globally relates to the solar and light transmission properties being fixed. This implies that a static glazing solution, is often not working optimally for most of the year. Dynamic glass solutions can be pre-programed, operated according to sensors which respond to the environment, or switched manually by occupants of the building to balance energy and visual comfort demands. This paper aims to present the findings of a study on a specific dynamic glass technology, Electrophoretic Light Modulator (ELM) produced by eLstar Dynamics, showing how this compares from an energy and daylight perspective against a ‘static’ typical glass with high performance coating in the climate of Amsterdam, the Netherlands. Using the software package IDA ICE, simulations were performed showing the benefits of adopting the eLstar technology in reducing energy demand while also improving internal daylight conditions.

Environmental Impact of Passive Smart Window Technologies

Paolo Matricardi — 2024-06-16

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 (GWP). While current literature focuses on the advantages of these technologies in terms of operational energy savings, other critical environmental considerations are currently missing. This paper aims to bridge the existing gap by introducing a novel framework for evaluating the broader environmental impact of passive smart windows through a multi-category LCA method. By analysing the life cycle of these technologies, including production, usage, and disposal, the research seeks to provide a holistic understanding of their contribution to sustainability. The framework is based on systematic literature review on current state-of-art approaches and Interviews with key stakeholders in the dynamic glazing value chain. Literature review and interview results are presented, and then the framework is demonstrated through a case study of a thermochromic technologies for an office building in the Netherlands. Preliminary results show the critical areas where improvements on the methods or on the performance of the technology are required for the achievement of holistically sustainable high-performing glazing.

Photovoltaics in the Building Envelope

Barbara Siebert — 2024-06-16

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 materials, glued constructions - in some cases also point-glued in the form of backrails. With photovoltaic cells a laminated safety glass turns to simple laminated glass. There are also more and more applications that not only act as cladding, but are also installed as fall protection or "overhead". This paper begins with an overview of the different types of modules and their applications. It discusses building regulations including the necessary structural analysis and testing verifications. Another important aspect is the anchoring to the building. Until now most applications are standard applications with framed panels on roofs or installations on fields. More and more attractive applications from the architectural point of view are built or are under construction. Finally, some projects are presented.

The Preliminary Assessment of Visual Performance of Novel Switchable Glazing Assemblies for Glare Control in a Mediterranean Climate

Etienne Magri — 2024-06-16

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 intolerable glare, both with the view outwards, as well as on screen. This paper discusses a preliminary assessment of the visual performance of a novel glazing assembly comprising of two, independently switchable solar-PDLC (solar Polymer Dispersed Liquid Crystal) and SPD (Suspended Particle Device). These interlayers are intended to control the visible light transmittance into an indoor space. The outcome of this study shall be used to determine the order and assembly combination of a prototype IGU for eventual full-scale testing from both visual and thermal comfort perspectives. Using a scaled model to represent a typical indoor space with a high glazing ratio and a luminance photometer, the Daylight Glare Probability (DGP) provided by the different states and positioning of the switchable glazing are compared to that provided by conventional static glass under identical field test conditions. Comparisons of the visual appearance of the potential combinations of these technologies were also investigated, to assess the ability of switchable films to instantly convert transparent openings into opaque, wall-like elements. Results indicate that such a combined switchable glazing assembly does have the potential for reducing glare, and thus merits further investigation in a full-scale study.

Towards New Diagnostic Strategies and Monitoring Tools for Long-Term High-Performance Smart Facades

Mohammad Momeni — 2024-06-16

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 with continuous modifications that can alter the performance of glass components, and also minimize their capacity. It is thus of primary importance, in support of an optimal maintenance strategy for facade systems, to possibly track their response in time, and prevent major faults or performance losses, or even risk for customers. However, key performance indicators (and corresponding sensors) to monitor the response of these composite systems should be first properly detected, and supported by a robust assessment of tracked registrations towards properly established alert values. In this context, this study explores from an analytical and numerical point of view the performance of Double (DGU) and Triple (TGU) insulated glass units, when exposed to ordinary loading conditions. The goal of present analyses (preliminary to experiments) is to capture some important performance indicators, study their modification as a function of boundary / loading conditions, and define possible monitoring strategies to support the implementation of an efficient early warning system for smart facades.

A Portable Technology for Measuring Haze Levels in Thick Laminated Glass Panels

Guillermo Casas — 2024-06-16

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 when viewing a standard mask through the material under controlled diffuse lighting conditions. Unlike previous approaches, this technology can be employed on installed glasses without requiring exposed edges for double-sided measurements, making it suitable for on-site work. The experimental evidence provided indicates that its precision and robustness are adequate for quality control.

Luminance-Based Methodology for Assessment of Haze in Glazing

Alessandra Luna Navarro — 2024-06-16

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 methods for measuring haze are not appropriate for assessing large samples, either at manufacturing sites or in-situ. However, haze defects are often only exhibited and visible when glazing is produced in large samples or installed under real luminous conditions. This paper introduces a novel HDR-based method that measures haze by evaluating the halo around a light source that is observed through the defected glazing. The halo serves as a proxy for haze severity and it is quantified by using luminance-based measurements. In this work, the newly-proposed method is verified by comparing the ranking in haze severity of different samples as performed by means of a standard hazemeter and the newly proposed method. Additionally, the paper examines the dependence of this ranking on factors such as camera setup distance and light intensity. It was found that the proposed method was able to effectively ranks samples differing in haze intensity by more than 0.1 orders of magnitude. Positioning the camera closer to the glazing and using higher light intensity yielded more accurate results. However, for haze levels below 1% and differences smaller than 0.1 orders of magnitude, the accuracy is insufficient. To define the expected level of accuracy of methods for haze characterisation in-situ, the sensitivity of the human eye to haze under varying luminous environments and view content needs to be quantified.

Optical and Structural Developments in Air Traffic Control Tower Glazing

Louis Moreau — 2024-06-16

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 explain the newest technical solutions available. This paper can be used as a checklist or design guide if you need to conceive an ATCT or other structures, such as an indoor observation deck or high-end retail storefront, where vision is paramount. Special attention will be given to visual distortion in transmission, haze, anisotropy, double image, reflection management, electrochromic, and glass-to-glass connections.

Optical Anisotropy Effects in Laminated Tempered Glass

Lena Efferz — 2024-06-16

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 effect and to investigate the influence of the superposition of different orientated glass panes. An influence from the interlayer is not markedly evident. Aside from a few outliers, there are percentage deviations of less than 6% in the 95% quantile value. The influence of the retardation pattern of the individual sheets is significant; depending on their position in the furnace, the superposition of the individual glass sheets results in a dot-shaped or a strip-shaped pattern. The experiments have demonstrated that retardation can be cumulative or reduced depending on the azimuth angle of the individual retardation value. Finally, six glass panes were installed in an outdoor test rig to observe the optical appearance under various light condition and different viewing points. Here, a correlation of the findings from the previous retardation measurements is clearly revealed.

Optical Distortions in Architectural Glass

Thomas Henriksen — 2024-06-16

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 guidelines, with a proposal for future research directions. Based on the findings in this paper it is suggested that the best method to determine optical distortion is to measure the changes in milli diopters, based on the current methods utilized for monolithic glass when measured in transmission. However, this method would need to be expanded to laminated glass, IGUs and potentially to curved glass, as well as a method to measure optical distortion in reflection. These methods will have to be developed through further research to better understand the causes behind the different optical phenomena.

The Thermal Resistance of a Vacuum Insulated Glass Panel

Cenk Kocer — 2024-06-16

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 a concise and detailed description of the potential thermal resistance which a VIG design might provide. In this work a design framework is outlined. Through a well-defined process, the total thermal resistance of any VIG design can be determined with high accuracy. Various designs are examined as case studies, and measurements are conducted to assess the precision of the design process. Ultimately, such a framework would enhance the confidence of architects, engineers, and others, enabling them to make informed design choices and incorporate VIG products into building projects.

Case Study on the Re-use Potential of Insulated Glass Units

Marcel Reshamvala — 2024-06-16

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 raw material can be saved that otherwise would be consumed for the production of new glass. This way, the common principles of sustainability - sufficiency, efficiency and consistency - can be realized for the life cycle of flat building glass. The following case study estimates the potential of different scenarios for circular waste treatment of glass panes by applying the 9R Framework to insulating glass units (IGUs). The scenarios are defined and presented. A life cycle assessment (LCA) using identical system boundaries for these scenarios was executed and the results are compared to producing IGUs entirely with new glass. Finally, the feasibility of the strategies is evaluated and recommendations for the processing of glass in stock are derived.

Circularity of Existing Aluminium Unitised Curtain Wall Façades

Rianne Teeuwen — 2024-06-16

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 conclude that reuse is technically feasible, saves carbon, and that the proposed metric can help to incentivize building owners and project developers to choose circular reuse.

Glass a Scarce Commodity

Gertjan Peters — 2024-06-16

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, including structural integrity and energy performance considerations. Additionally, this article investigates the potential for glass reuse by analysing ongoing and future research, supply-demand dynamics, innovative building design, the concept of the future glass factory, and the re-evaluation and promotion of regulatory frameworks. To promote glass reuse, the article emphasizes customization over standardization. Considering the diverse dynamics of projects, from high-rise buildings to terraced houses, and varying regional construction requirements, solutions must be specific and adaptable, rather than standardized.

Glass Bottle Earth Brick for Structural Wall

Hoessein Alkisaei — 2024-06-16

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 investigates the potential of prefabricated earthcrete bricks that integrate glass container bottles for the construction of structural load-bearing walls for affordable housing in Brazil while at the same time reducing pollution, enhancing aesthetics, and promoting environmental friendliness. Initially, the mechanical behaviour of the container glass bottles in earth bricks is investigated through FEM modelling. Subsequently, prototypes are made and tested in the laboratory, revealing a compressive strength between 8.21 and 11.40 MPa. From these findings, it is concluded that reusing glass bottles for the construction of structural walls capable of supporting small-scale structures could be feasible.

Re-Glass: Product Development Pathways for Post-Consumer Glass

Sophie Pennetier — 2024-06-16

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 samples, to assess challenges arising from various production parameters including: glass types, processing methods, annealing temperatures and schedules, cullet sizes and distribution. These explorations offer high-level perspectives for developing post-consumer glass solutions driven by emissions and logistics primarily, and tectonics secondarily, exploring the cost-effective diversion of glass products from landfill to generate solutions staying within the built environment. The research examines performance aspects of recycled glass as emblematic of sustainability in design and underscores the role (and implications) of texture in architectural materiality. Performance and viability are weighted with considerations for the US market (hauling distances, energy grid emissivity across states, market culture, labor rates, incentives, or lack thereof). This exploration proposes innovative avenues for integrating distinctive, sustainable recycled glass as a hallmark into architectural frameworks.

Recycle Glass

Michael Elstner — 2024-06-16

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 cullet, pre- and post- consumer cullet. In order to be able to use cullet in float glass production, it must be of high quality. Since there are a large number of architectural glass products and glass types, it is essential to collect and sort in the most adequate way

Recycling Post-Consumer Glass: A Challenge and an Opportunity for the Flat Glass Industry

David Entwistle — 2024-06-16

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 background to the study and how the lessons learned are now being applied. The thesis examined the barriers to recovering end of life glass from commercial projects in London, and identified the drivers that will open pathways for glass to be recycled. Data was collected from 57 interviews with key stakeholders (clients, developers, main contractors, façade engineers, architects, demolition contractors, waste management companies and cost consultants). The nature and scale of an investigation such as this, had not been undertaken before. This paper will explain how the lessons learned are being realized into a new way of working by dealing directly with clients and equipping the existing deconstruction supply chain. This provides a ‘cost and time’ effective solution and guarantees that end of life glass is being recovered back to new building glass.

Remanucycling

Marco Zaccaria — 2024-06-16

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 glass product: the insulating glass unit, whereby the glass panes could be reused or recycled. Recently, an industrial machine capable of disassembling insulating glass units was developed. This innovation represents a crucial step for implementing circularity of transparent façades, but it is not the only step required for remanucycling to occur. Selective deconstruction must replace demolition, the material flow is to be diverted from landfill towards disassembly plants, from where additional new logistic routes are to be established. The glass transport will have to shift from a predominantly stock-size model to a cut-size model. Selective deconstruction and cut-size transport are more work-intensive than demolition and stock-size transport, respectively. This hints that one of the challenges for remanucycling to occur is to develop extremely effective practices that can keep the costs of operation below a break-even threshold. In order to reuse glass components, specific quality protocols are to be proposed, established, validated and eventually standardized. These protocol are to be specific by glass type. The environmental footprint of remanucycling is yet to be assessed, but its benefit mainly comes from scaling-up. This study introduces the concept of remanucycling and applies it specifically to the architectural flat glass industry. The transformation needed, along with the challenges and opportunities arising from this transformation are described. The purpose is to provide a holistic view of how the glass industry might shift towards a circular economy so that the changes needed can be identified and coordinated at industry and scientific level.

Reuse and Remanufacturing of Insulated Glass Units

Martien Teich — 2024-06-16

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 of how old insulating glass units can be re-manufactured to match the state of the art in terms of the energy efficiency. For this purpose, dismounted IGUs from the 1980s are used. After analyzing the remaining functionality, the double IGUs are disassembled. The single glass pane is cleaned, and the old edge sealing is removed. The old glass pane is combined it with a new coated low-e glass and a spacer system to form a new upgraded IGU with warm edge technology. This study demonstrates that remanufactured IGUs can achieve the performance of IGUs made from new glass.

Reuse Potential of Architectural Glass

Jagoda Cupac — 2024-06-16

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 is almost entirely unexplored. For aged glazing to be reused in construction, better knowledge of its surface quality and structural performance is needed. The main objective of this paper is to explore the effects of ageing and exposure to indoor and outdoor environment on the strength of glass. A comparative investigation is undertaken to evaluate the strength and surface quality of the internally, externally and cavity-facing glass surfaces of insulating glass units (IGUs) after 30 years of use in a building envelope in the Netherlands. The glass panes are separated from the IGU assembly and cut into specimens for microscopy and coaxial double ring tests. The study shows that the visual quality is best preserved on the cavity-facing surface, consequently exhibiting the highest bending strength. The internally and externally facing surfaces, with visibly more extensive damage, exhibited similarly lower strengths at low probabilities of failure. When compared to the design strength of new annealed glass acc. to EN 16612, all the surfaces showed a reuse potential, with considerable bending strength.

The Reuse Potential of Hundreds of Insulating Glass Units in Buildings

Esther Geboes — 2024-06-16

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 standalone glass thickness meter to verify non-standard cavity widths. The product age was obtained via the spacer code or general building information. A threshold of maximum 15 years was set as general indicator of a residual service life of 10 to 25 years. The results of the applied method show that just over 50% of the IGUs meet the required argon concentration. Furthermore, the combination of a maximum IGU product age of 15 years and a 90% nominal argon fill resulted in 24% of tested IGUs as potentially suitable for reuse. The results raise questions about the reuse of IGUs in practice, which are discussed in this paper.

Traceability

Angelica Rota — 2024-06-16

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 entire lifespan. The focus is on post-consumer glass, investigating the benefits of a glass panel code marking and its role in transitioning from an open to a closed material loop. By analysing recovery scenarios of post-consumer glass supported by a traceability system, this research outlines a framework for data collection and storage integrated within digital construction models. This study assesses the potential impact of code marking on post-consumer glass, emphasizing real-world integration possibilities. Insights gained enlightened opportunities for stakeholders involved in the glass recovery and remanufacturing process. The findings underscore the transformative potential of traceability in achieving a circular economy within the construction industry.

Up-cycling Glass Waste for Bioreceptive Applications by Foaming

Georgina Giassia — 2024-06-16

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 investigated, as the means to achieve a capillary-porosity (open pore) network that can incorporate large amounts of waste into the recipe. A total of 22 different samples were produced to study the parameters related to the mixture, foaming process, and potential biofilm formation. Microscopic analysis was conducted initially, followed by a series of preliminary experiments designed to inform subsequent sample iterations based on promising findings related to their hydraulic performance. All samples were assessed for their water absorption, evaporation rate and frosting resistance. The test results pinpointed two iterations showcasing superior performance: (1) contaminated soda-lime powder with 10wt% CaCO3 as foaming agent, formed at 840°C, (2) a mixture with a ratio of 1:1 with borosilicate and soda-lime glass powder with 0.33wt% Carbon black and 1.66wt% CaHPO4, formed at 790°C. The two selected formulations were further tested for moss-growth and compressive strength. Based on the findings regarding foaming for bioreceptivity, the study suggests that façade tiles represent one of the most promising market applications, offering a means to transform unexploited urban surfaces to green substrates for bio-growth.

Whole Life-cycle Carbon Assessment of Building Retrofits with Water-Filled Glass (WFG) Secondary Glazing

Giulio Cavana — 2024-06-16

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 strategies are to replace low performing elements, or to add secondary layers to the existing glass. This second strategy in particular is shown to present several benefits, however these are seldom considered and verified within a wider Life-Cycle Analysis (LCA). To this effect, this paper aims to quantify the savings achieved through the ERM of secondary layer addition to existing glazed facades, for a high WWR office building in cooling and heating dominated climate locations (Dubai, London, and New York). This is then evaluated against an LCA for each glazing ERM chosen, to assess how each retrofit affects the embodied carbon produced. Two base scenarios in each city have been simulated in TRNSYS (single and double glass cases), with three standard market options for layers addition (single, double, and water-filled glass). Water-filled Glass is introduced as a potential ERM for the first time, that utilizes a water layer to improve performance. The aim of this paper is to evaluate the holistic efficiency of different ERMs within the transparent building envelope.

Editorial

Christian Louter — 2024-06-16

Welcome at Challenging Glass!

At this 9^th 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 and go over the past years, but the importance of circular design is to stay! Therefore, on top of the regular technical sessions on the topic, we bring five speakers to the stage who will pitch their views on the circular use of glass and discuss it with each other and the audience. You are warmly invited to actively participate!

Furthermore, we are happy to welcome no less than five top-notch keynote speakers. The first keynote will focus on the Mirage project and will be delivered jointly by Dr Faidra Oikonomopoulou, Dr Telesilla Bristogianni and Mr Alexandros Cannas. The second keynote will be presented by Dr Peter Zoon, who will explain how glass plays an important role in crime scene investigations. It promises to be a criminal talk! Last but not least, Dr Corentin Fivet will share his work on new design paradigms for reuse during his closing plenary lecture.

During the conference you will be able to retrieve all abstracts and papers, but also presenter details and programme updates with our conference app. After the conference, all papers will be available online, either through our online proceedings platform or through the peer-reviewed journal Glass Structures & Engineering (SpringerNature).

We explicitly like to thank the continuous support of our sponsors, Scientific Committee members, authors and attendees.

Together with you and with our co-hosts James O’Callaghan, Mauro Overend and Fred Veer we are eager to kick off Challenging Glass 9!

Christian Louter, Freek Bos and Jan Belis

June 2024

Organisation and Committee

Challenging Glass — 2024-06-16

Conference Organisers

Prof. Christian Louter – Delft University of Technology
Dr Freek Bos – Technical University of Munich
Prof. Jan Belis – Ghent University

Conference Co-Hosts

Prof. James O'Callaghan – Delft University of Technology
Prof. Mauro Overend – Delft University of Technology
Dr Fred Veer – Delft University of Technology

Conference Support

Deborah Dekker – Delft University of Technology
Noor van Geffen – Delft University of Technology
Rens Hoekstra – Delft University of Technology
Lukas Huber – Delft University of Technology
Laura Jurić – Delft University of Technology
Hrishika Rastogi – Delft University of Technology
Sandra Schuchmann-Hagman – Delft University of Technology
Jacqueline van Unen-Bergenhenegouwen – Delft University of Technology
Iris Nederhof-van Woggelum – Delft University of Technology

Scientific Committee

Dr Chiara Bedon – Trieste University
Prof. Jan Belis – Ghent University
Prof. Lucio Blandini – University of Stuttgart
Dr Freek Bos – Technical University of Munich
Dr Telesilla Bristogianni – Delft University of Technology
Prof. Suwen Chen – Tongji University
Prof. Paulo Cruz – University of Minho
Dr Jagoda Cupać – Technische Universität Dresden
Dr Corinna Datsiou – University of Hertfordshire
Dr Martina Eliášová – Czech Technical University in Prague
Prof. Michael Engelmann – Technische Universität Dresden
Prof. Steffen Feirabend – Hochschule für Technik Stuttgart
Prof. Markus Feldmann – RWTH Aachen
Dr Laura Galuppi – University of Parma
Dr Rebecca Hartwell – Delft University of Technology
Prof. Christian Louter – Delft University of Technology
Dr Stephen Morse – Michigan Technological University
Prof. Jürgen Neugebauer – FH Joanneum
Dr Jens Henrik Nielsen – Technical University of Denmark
Prof. James O'Callaghan – Delft University of Technology
Dr Faidra Oikonomopoulou – Delft University of Technology
Prof. Mauro Overend – Delft University of Technology
Prof. Jens Schneider – Technische Universität Wien
Prof. Christian Schuler – Munich University of Applied Sciences
Dr Miriam Schuster – Technische Universität Darmstadt
Dr Vlad Silvestru – ETH Zurich
Dr Bert Van Lancker – Ghent University
Dr Fred Veer – Delft University of Technology

Keynote Speakers

Challenging Glass — 2024-06-16

Keynote Speakers

Dr Faidra Oikonomopoulou – Delft University of Technology
Dr Telesilla Bristogianni – Delft University of Technology
Alexandros Cannas, Dipl.-Ing. CEng MICE – Eckersley O'Callaghan
Dr Peter Zoon – Netherlands Forensic Institute
Prof. Corentin Fivet – Structural Xploration Lab - EPFL