Challenging Glass Conference Proceedings <p><strong>Challenging Glass Conference Proceedings</strong> collects the conference articles presented at the international bi-annual Challenging Glass Conference and focuses on the Architectural and Structural Application of Glass.</p> TU Delft Open en-US Challenging Glass Conference Proceedings 2589-8000 Glass design in Switzerland <p>In the past glass design in Switzerland was based on foreign standards and regulations. Questions raised whether the application of these standards is suitable, as they do not comply with the Swiss Standard SIA 260 – Basis of design. The most used standards are the German technical regulations for the use of glazing with linear supports (TRLV) and the DIN 18008. The Swiss society of engineers and architects (SIA) initiated a structural glass standard committee with the task to develop a Swiss glass design standard. The new Swiss glass design standard is based on the same concept as the Eurocode10 "Design of Structural Glass", which is currently in preparation. In future, this standard will be the basis of the Swiss national annex of the Eurocode. An important issue in glass design practice is the shear coupling effect in laminated glass. The standard allows taking into the shear coupling effects and thus will lead to more economic pane thickness. A new concept was developed to meet post failure requirements without time-consuming and costly tests. A new approach for the determination of temperatures in IGU was established to determine the climate loads of insulated glazing units (IGU).</p> Thomas Wüest Andreas Luible Copyright (c) 2020 Thomas Wüest, Andreas Luible 2020-09-04 2020-09-04 7 10.7480/cgc.7.4610 Investigation of Wind and Temperature Dependence for Dimensioning of Laminated Inserts <p>This study proposes a review of different design approaches allowing to dimension a laminated insert connection. It focuses on façade assemblies, where the critical load is due to wind, and where the stiffness relies on a highly viscoelastic material SentryGlas®. The high variability of material stiffness is considered using three different approaches. The first approach determines critical wind speeds and temperature values using a site-specific probabilistic analysis. The second approach uses the First Order Reliability Method to perform a probabilistic design. The final approach suggests a method for evaluating the wind and temperature dependence. This method is based on the Monte-Carlo simulation method and shows potential for optimizing the dimensioning of such façade connections.</p> Matthieu Thésé Jorge Hidalgo Copyright (c) 2020 Matthieu Thésé, Jorge Hidalgo 2020-09-04 2020-09-04 7 10.7480/cgc.7.4477 Structural Behaviour of Glass Panels Under Soft-body Impact <p>Glass is a commonly used material in modern architecture not only for building enclosures but also for glazed barriers preventing building occupants from falling out of balconies or different levels inside buildings. The paper reports some results of an on-going research project involving testing of glass balustrades and infill panels mounted with different fixing methods, such as linear clamps, local clamp fixings, and point fixings through holes in glass. A reduced numerical model for prediction of strength of glass under soft body impact is also presented. In the experimental study toughened and heat-strengthened glass, as well as two interlayer materials of different stiffness, were used.</p> Marcin Kozłowski Kent Persson Dániel Honfi Natalie Williams Portal Copyright (c) 2020 Marcin Kozłowski, Kent Persson, Dániel Honfi, Natalie Williams Portal 2020-09-04 2020-09-04 7 10.7480/cgc.7.4479 Structural Glass in Superyacht Applications: Overcoming Challenges, Design Standards and Analysis Methods <p class="CGCAbstract"><span lang="EN-US">Structural glass has become a popular material in marine applications. It has been used to enhance the transparency not only in luxury yachts but also in passenger vessels like cruise-ships. Yacht designers being inspired by all-glass facades and structural glass pavilions are trying to adopt these achievements and promote the glass design and engineering technology in the shipbuilding industry. However, designing glass elements in a marine environment involves more challenges comparing to civil applications. Glass engineers should not only consider in their calculations the wind loads and the movements of the support structure, but also the significantly higher wave loads and accelerations due to the ship movement. In addition, the watertightness of the windows is particularly important for the integrity of the vessel and the safety of the passengers. Finally, the thickness and weight of the glass can influence significantly not only the cost but also the stability of the whole vessel. The aim of this paper is to describe the typical requirements a glass window in superyacht applications needs to fulfil, possible challenges a glass engineer will meet and methods to overcome these challenges. In addition, we will present the most important design standards and compare them with relevant standards from the building industry. We will then explore the most common analysis methods and their impact on the accuracy of the results and glass build-up optimization. Adhesive connections of the glass elements to the main structure will also be described as these are the main mechanism to accommodate the hogging, sagging and torsional deformations of a hull in case of a stormy sea. </span></p> Kosmas Moupagitsoglou Copyright (c) 2020 Kosmas Moupagitsoglou 2020-09-04 2020-09-04 7 10.7480/cgc.7.4609 Sharing of general loading in double glazed units. The BAM analytical approach <p>Double Glazed Units (DGUs) consist of two glass panes held together by structural edge seals. Calculation methods for DGUs consider that actions applied on one pane develop effects in all the panes, due to the coupling from the entrapped gas. Various methods have been proposed in standards to evaluate this <em>load sharing</em>, which depends upon the stiffness of the glass panes, the thicknesses of spacer and the size of the DGU. A comprehensive analytical formulation, the Betti’s Analytical Method (BAM), has been recently proposed to calculate the load sharing in DGUs of any shape, composed by glass panes of arbitrary thickness, with various support conditions at the borders and various types of external actions, including concentrated and line loads. Simple expressions can determine the gas pressure as a function of a universal shape function, which coincides with the deformed surface of a simply supported plate, of the same shape of the DGU, under uniformly distributed load. Here, comparisons are made with numerical analyses, performed by implementing an <em>ad hoc</em> routine in the software Straus7, developed by Maffeis Engineering, where the deflection of the glass panels is iteratively calculated, until the volume enclosed reaches a value compatible with the pressure exerted by the gas. The numerical routine, that is part of an integrated parametric approach to the façades design, allows precise calculations for any kind of build-up, panel shapes and load conditions.</p> Laura Galuppi Gianni Furio Mario Royer-Carfagni luca barbieri Massimo Maffeis Copyright (c) 2020 Laura Galuppi, Gianni Furio Mario Royer-Carfagni, luca barbieri, Massimo Maffeis 2020-09-04 2020-09-04 7 10.7480/cgc.7.4484 Simulation Tool for the Analysis of Simple Flat and Cylindrical Insulated Glass Units <p>A simulation tool for simple flat and cylindrical insulated glass units (IGUs) has been developed using VBA code included on Excel and RF-COM, the programmable COM Interface for the RFEM of Dlubal. The software allows the non-linear computational analysis of rectangular flat panels and cylindrical IGUs considering the monolithic equivalent thickness of the inner and outer glass panel. The sealant silicone elastic properties can be defined by the users, including, if necessary, the rotational stiffness. Climatic load and superficial uniform loads (typically wind loads) can be defined.</p> <p>The tool automatically generates the inner and outer glass panels with shell elements and the boundary conditions in RFEM. Both panels are connected all along the perimeter by means of spring elements with the equivalent stiffness of the silicone. The internal pressure due to climatic loads and the distribution of the superficial uniform loads are automatically calculated by means of an iterative method. This method, published for other authors in the recent past, considers the bending stiffness of both glass panels and the silicone for the definition of the resultant load.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br> <br> The results of the simulations have been successfully correlated with the commercial software SJ-MEPLA for flat panels and ANSYS Workbench 19.0 for flat and cylindrical panels, in this case, modelling the air cavity with a 3D hydrostatic fluid element (HSFLD242). The simulation tool provides an accurate definition of the internal pressure, deflection and stress on glass panels and forces through the sealant silicone with a reduced pre-post and calculation time, being ideal for parametric studies.</p> Tomàs Colldecarrera Copyright (c) 2020 Tomàs Colldecarrera 2020-09-04 2020-09-04 7 10.7480/cgc.7.4505 GS&E journal > Mechanical analysis and characterization of IGUs with different silicone sealed spacer connections - Part 1: experiments <p>Due to several advantages, insulated glass units (IGUs) are largely used in buildings to realize curtain walls, vertical partitions but also roofs or pedestrian systems. The typical IGU consists of two glass layers, either monolithic and/or laminated sections, that can mechanically interact via an hermetically-sealed air (or gas) cavity between them. As known, load sharing phenomena have a crucial effect on the actual mechanical response of a given IGU. Accordingly, simplified analytical methods are available in the literature to account for these load sharing effects. The existing approaches, however, assume that the spacers providing the mechanical connection along the edges of glass panels are infinitely rigid. In this paper, original experimental tests are proposed for IGU specimens characterized by the presence of different types of spacer connections, as obtained from on a selection of configurations of technical interest. The actual mechanical contribution of spacer components is then investigated, giving evidence of major findings from small-scale shear and IGU four-point bending tests. Based on comparative test observations, the edge connection efficiency is then assessed for the investigated configurations.</p> Chiara Bedon Claudio Amadio Copyright (c) 2020 Chiara Bedon, Claudio Amadio 2020-09-04 2020-09-04 7 GS&E journal > Mechanical analysis and characterization of IGUs with different silicone sealed spacer connections - Part 2: modelling <p>Insulated Glass Units (IGUs) typically consist of two glass layers, either monolithic and/or laminated sections, that mechanically interact via an hermetically-sealed air (or gas) cavity, and a series of linear spacer connections along their edges. In this paper, based on the experimental tests for small-scale IGU joints under pure shear and IGU prototypes in bending discussed in “Part I”, a special care is spent for the Finite Element (FE) numerical characterization and analysis of these composite systems, with a focus on the actual mechanical properties and load-bearing mechanism for the involved components. Major advantage is taken from the full 3D solid geometrical description of the connection components and the gas cavity infill. The actual role of both primary and secondary sealant layers is first assessed. Further support is derived from analytical calculations for the connection efficiency assessment, based on the adaptation of simplified formulations of literature. Finally, a calculation example is proposed to assess the magnitude of load sharing phenomena, based on FE numerical and analytical calculations for selected configurations.</p> Chiara Bedon Claudio Amadio Copyright (c) 2020 Chiara Bedon, Claudio Amadio 2020-08-28 2020-08-28 7 GS&E journal > Slumped IGU’s with large airspaces: engineering challenges and solutions <p>Aside from external cladding pressure loads that are always considered in IGU design, a variety of unique factors must also be addressed when analyzing the structural performance of a slumped IGU with a large air cavity. These factors include the volume of air within the cavity, the stiffness and strength of the outer and inner lites of glass, elevation changes between the glass fabrication facility and the building site, temperature changes over time, fluctuations in barometric pressure, and increased stress on the secondary structural perimeter seal. Appropriate deflection limits for mullions or other elements supporting the IGU must also be established due to the increased stiffness of the IGU resulting from the slumped glass geometry. Engineering challenges related to the design of slumped IGU’s will be highlighted and explained using Nike’s new retail flagship store in New York City, Nike House of Innovation 000, as a case study for a dynamic facade featuring custom carved and slumped insulating glass units. Principal analysis methods, testing procedures, and a summary of the various software tools used to evaluate the slumped IGU’s will be provided. The solutions shown will illustrate how the fundamental design and engineering approach taken for Nike can be successfully applied to other projects that incorporate slumped IGU’s into their facades.</p> David Bott Copyright (c) 2020 David Bott 2020-09-04 2020-09-04 7 Numerical and Experimental Investigations on the Inherent Stress State of Cold-bent Glass <p>In today’s architecture the bending of glass plays an important role in achieving free forms in modern façades. In addition to the usual procedure of hot bending glass sheets into the desired shape, the option of cold bending is being used more and more frequently. In this process a glass pane is bent into the desired shape and fastened to a substructure without prior heating and at low cost. This inherent bending state comes along with different beneficial but also with some unfavourable perks that have to be considered in the engineering process. The resulting influences on the strength of the glass and stiffness of the overall system are investigated in a German research project. In large-scale tests, special attention is paid to the established shape of the pane during the bending process and the resulting load on the steel substructure.</p> Maximilian Laurs Copyright (c) 2020 Maximilian Laurs 2020-09-04 2020-09-04 7 10.7480/cgc.7.4503 Thin glass as a tool for architectural design <p>Glass with a thickness of less than 2.0 mm can be defined as a thin glass or with a thickness of less than 0.5 mm even as ultra-light. Thin glass requires for curved surfaces in order to gain structural stiffness in static use. The geometry is based on the known theory of developable surfaces. Such Façades may therefore be created from cold bent or curved laminated thin glass layers. In the past semester a seminar with architectural students were held and three projects of this seminar are worth to be presented to the public for demonstration of possibilities for use of thin glass. The definition of a seminar project for students was a connection of a big housing area with the nearby stop of the local tram which is separated by a railway line. Two possibilities for the pedestrian are given to pass the railroad. The first one is a passage underground below the railroad and the second one is a bridge above the railway line. This paper contents a study of architectural design made by students. Two projects which will be presented in this paper focuses on the design of the entrance building of a passage underground and the third project is a design of a pedestrian bridge above the railroad. Beside the architectural design a structural analysis was done to support the design process such as with ranges of possible bending radii for the curved thin glass elements and to guarantee the feasibility of the design</p> Jürgen Neugebauer Irma Kasumovic Ivo Blazevic Nicolas Auer Christiana Rath Katharina Baumhackl Copyright (c) 2020 Jürgen Neugebauer, Irma Kasumovic, Ivo Blazevic, Nicolas Auer, Christiana Rath, Katharina Baumhackl 2020-09-04 2020-09-04 7 10.7480/cgc.7.4693 Beyond Materiality, Towards Craftsmanship <p>This paper describes the design process UNStudio undertook in the redevelopment of the C&amp;A Building on 18 Septemberplein in Eindhoven, the Netherlands. The design brief primarily called for the rebranding of the building while maintaining the building’s façade historic value and aesthetic. Secondarily, the design is meant to activate the urban context where the building is located without competing with the neighboring landmarks. UNStudio saw an opportunity to rethink the transparent layer – the glass window – of the building as a tool to enhance its identity minimizing the aesthetic impact on its historic facade.</p> <p>This case study outlines opportunities to innovate while designing with glass through two often polarized perspectives: contemporary architecture and historic preservation. Architects constantly negotiate the value of private versus public space, transparency versus opacity, and building energy performance in our built environment through the use of glass. Emerging integrated technologies such as LED, photovoltaic, lamination, and touch sensitive layer are enabling new ways of rethinking the roles and applications of glass: as an architectural element, an information layering surface, and an agent for light and transparency. New opportunities are thus arising for glass in digital media facades and parametric façade design. On the other hand, architects’ role in historic preservation requires a diligent approach to glass application due to the constraints of local zoning and aesthetic regulations (governed in the Netherlands by the Welstandscommissie) that seek to protect certain historic values in existing buildings. The objective of this paper is to apply UNStudio’s design thinking sensibilities towards – and understanding of – glass as a system, to contemporary themes of community, social branding, and the environmental impact of architects’ interventions on the built environment.</p> Ben van Berkel Gerard Loozekoot Filippo Lodi Sitou Akolly Atira Ariffin Copyright (c) 2020 Ben van Berkel, Gerard Loozekoot, Filippo Lodi, Sitou Akolly, Atira Ariffin 2020-09-04 2020-09-04 7 10.7480/cgc.7.4608 Rethinking the Cast Glass Mould. <p>This paper explores two alternative mould fabrication technologies that allow for the casting of (solid) glass components with a great degree of freedom in shape and size and/or of a customized design, in a cost-efficient way. In specific, the paper discusses the research, design and experimental work conducted at TU Delft on 3D-printed sand moulds and adjustable, high-precision steel moulds. 3D-printed sand moulds can provide a high-accuracy, cost-effective solution for solid glass components of complex geometry and/or of customized design. Although this mould technique is already used for metal castings, it remains still unexplored in the field of glass casting. Accordingly, this paper presents the first experimental findings at TU Delft of this mould technology: mould samples using different binders and treated with various coatings for surface finishing are tested in the high temperatures anticipated in glass (kiln-)casting. Following, 3D-printed moulds are prepared for a given glass geometry and physical glass prototypes are made by kiln-casting. Adjustable metal moulds are another mould technique that offers a degree of freedom in the modulus of a structure. Essentially, components of different sizes and, to an extent, shapes can be generated by the same mould. Accordingly, the design principles and engineering of such a mould and the potential applications and limitations of this technology are discussed. As a proof of concept, an adjustable mould is made using 3D-printed PLA and laser-cut MDF. The mould is used for the generation of wax models of variable forms, which are used to kiln-cast glass prototypes by the lost-wax technique. Based on the findings on both presented mould technologies, guidelines are given on their suitability according to the production volume, the level of accuracy required and the complexity and variation of forms involved.&nbsp;</p> Faidra Oikonomopoulou Ivneet Singh Bhatia Wilfried Damen Felix Van Der Weijst Telesilla Bristogianni Copyright (c) 2020 Faidra Oikonomopoulou, Ivneet Singh Bhatia, Wilfried Damen, Felix Van Der Weijst, Telesilla Bristogianni 2020-09-04 2020-09-04 7 10.7480/cgc.7.4662 Ageing of annealed and chemically strengthened glass <p>Eight 45-year-old naturally aged windows collected from two buildings in two different locations revealed surface characteristic bending strengths in the range of 38-54 MPa. An artificial ageing method by sandfall was developed to reproduce the weakest failure stresses among the naturally aged samples. When this method was applied to chemically strengthened glass, the results varied depending on the glass composition and the strengthening cycle. To achieve the characteristic bending strength of 150 MPa specified by EN 12337, after the artificial ageing, soda-lime silicate glass needed routine strengthening cycle of 24 hours, whereas the newly developed Falcon® glass performed well after a shorter 8-hour strengthening cycle, with characteristic bending strength still above 300 MPa after artificial ageing. This study also includes a comparison with other studies in the literature regarding natural ageing and the application of sandfall artificial ageing to annealed glass and chemically strengthened glass.</p> Xavier Gillon Copyright (c) 2020 Xavier Gillon 2020-09-04 2020-09-04 7 10.7480/cgc.7.5225 Comparison of the Residual Stresses at the Edge and Surface of Thermally Toughened Glass <p>The strength of thermally toughened glass is regulated in EN 12150-1 for fully tempered glass (FTG) and EN 1863-1 for heat-strengthened glass (HSG). The manufacturer has to prove the strength by four-point bending tests based on EN 1288-<br>3. A measurement of the residual stresses of thermally toughened glass is not demanded. Consequently, the determination of the strength is containing the amount of residual stresses. As residual stress is depending on the manufacturing process, the amount and distribution can change within one glass pane and between different glass panes. A research project determined the residual stresses at the surfaces and the edges of HSG and FTG with varying glass thicknesses using photoelastic measurements. Thereby, FTG showed lower values of the residual stresses at the edge compared to the surface. Looking at HSG, the results of the residual stresses at the edge and surface were nearly the same. To analyse the edge strength, four-point bending tests were conducted. Thereby, the load was introduced into the strong axis of the specimens to implement constant tensile stresses along the glass edge. The comparison of the edge strengths showed that the edge strength of FTG is in the same range than HSG. Therefore, the lower residual stress at the edge of FTG reflects in significantly lower edge strengths. The paper includes a detailed presentation of the photoelastic measurements at the edge and the surface as well as the determined residual stresses of more than 80 specimens. In addition, the conducted four-point bending tests are described and the obtained edge strengths are correlated to the measured residual stresses. Based on that, the paper contains a discussion of the standardisations, the process of thermally prestressing and the consequences for the final glass strengths.</p> Katharina Lohr Paulina Bukieda Bernhard Weller Copyright (c) 2020 Katharina Lohr, Paulina Bukieda, Bernhard Weller 2020-09-04 2020-09-04 7 10.7480/cgc.7.5226 Construction of Full Residual Stress Depth Profile in Glass Using the Knowledge of Surface Stress <p class="CGCKeywords" style="margin: 24.0pt 42.55pt .0001pt 42.55pt;"><span lang="EN-US">This paper presents the development of a simple method to determine the full residual stress depth profile in architectural (i.e. construction sector) glass. The proposed model requires only the knowledge of the surface residual stress of glass, which can be known from the glass manufacturer or can be measured using a Scattered-Light-Polariscope (SCALP), as input. The requirement of through-thickness force equilibrium and the knowledge of parabolic shape of the residual stress depth profile are used to uniquely determine the residual stress depth profile in any given glass panel. Unlike the complex models reported in the literature, the proposed technique does not require modelling the complex multi-physics phenomenon of the generation of residual stress or the use of complex computational models. The residual stress predictions from the proposed model were validated against experimental results. The paper also presents a sensitivity analysis in order to justify the accuracy of the proposed model even after the possible errors/inaccuracies in the only input data (i.e. surface stress) of the model was incorporated in the analyses.</span></p> Mithila Achintha Copyright (c) 2020 Mithila Achintha 2020-09-04 2020-09-04 7 10.7480/cgc.7.4504 Experimental Investigation into SLS Glass Surface Modification Using KrF Excimer Laser <p class="CGCAbstract">Glass is a brittle material and any damage or modification of its surface may have a profound impact on the strength. To modify the glass surface, the precision of the instrument is determining for achieving the most reliable results. Nowadays, laser technology as a non-contact tool is employed as a glass cutting, drilling and holing tool in many applications such as sensors and optical communications. Along with high speed, flexibility, and scalability, lasers with short pulse duration can break the interatomic bonds before perturbing the lattice. Among lasers, excimer micromachining lasers have some advantages in terms of surface morphology, including depth control, edge quality, and minimizing peripheral thermal damage as the ablation process is more likely to be material-removing instead of heating. This article aims to examine the interaction of krypton fluoride (KrF) excimer laser with the soda-lime silica (SLS) glass by fabricating grooves and microholes.</p> Shahryar Nategh Pieter Vijverman Jeroen Missinne Jan Belis Copyright (c) 2020 Shahryar Nategh, Pieter Vijverman, Jeroen Missinne, Jan Belis 2020-09-04 2020-09-04 7 10.7480/cgc.7.4485 Experimental investigation on the structural performance of square hollow glass columns under axial compression <p>This paper presents an experimental study into the global behavior of glass columns with square hollow cross-section under axial compression. In the research, totally 6 specimens were tested. All specimens were of the same geometry (length 750 mm, width 150 mm and 10 mm) but had different composition. Half of them were made of monolithic glass, with the other half made of laminated glass. The adopted interlayer material is PVB which is widely used in practice. During the test, vertical displacement, lateral deflection and normal stresses at mid-span were measured. For all specimens, local failure mechanism at the top or bottom due to progressive cracking was found, without any damage occurred at the glued joint. However, there is significant difference between the specimens made of monolithic glass and those made of laminated glass. Laminated glass columns had a sufficient residual capacity, able to carry compressive load in the post-crack stage, while monolithic glass columns collapsed quickly after the appearance of the first crack. Subsequently, the influence of the initial geometrical imperfection was studied in detail. Based on the results of experiment, the current findings could be further extended to various glass columns typologies (e.g. different cross-sections) in order to build appropriate practical design rules.</p> Suinan Zhao Suwen Chen Copyright (c) 2020 Suinan Zhao, Suwen Chen 2020-09-04 2020-09-04 7 10.7480/cgc.7.4473 Load-bearing Behaviour of Laminated Tempered Glass with Reground Edges <p>Designers use exposed glass edges to reach maximum transparency, for example within glass steps, glass beams or glass columns. These applications require mechanical finishing to achieve high optical quality and to compensate for the edge notch that results from the manufacturing process of safety glass. Regrinding of annealed glass is allowed without restrictions. In the case of glass with load bearing functions, tempered glass, heat-strengthened glass or fully tempered glass, is required. However, a risk of premature failure occurs when regrinding tempered glass because of a reduction of the compression zone at the edge.</p> <p>A research project at the Institute of Building Construction, Technische Universität Dresden, examined the impact of regrinding tempered glass on the load-bearing capacity of the glass edge. The study showed the load-bearing capacity decreased depending on the regrinding depth. Specifically, the study revealed a significant difference between the weakening of heat-strengthened glass and fully tempered glass due to the different inherent stress conditions of the different types of glass. Accordingly, regrinding heat-strengthened glass is possible up to a certain limit without critical weakening.</p> <p>To extend the previous studies, the project team conducted component tests on laminated glass beams manufactured from fully tempered glass and heat-strengthened glass with and without reground edges. The examination included tensile bending tests. The experimental results show the influence of regrinding on the load-bearing capacity of the glass components. This paper focusses on the evaluation of the component tests as well as the structural design. Moreover, the results of the pre-tests with single pane glass beams are presented and compared with the component tests. The research results will allow the utilization of structural glass elements with the highest optical quality in the future.</p> Maximilian Möckel Katharina Lohr Bernhard Weller Copyright (c) 2020 Maximilian Möckel, Katharina Lohr, Bernhard Weller 2020-09-04 2020-09-04 7 10.7480/cgc.7.4433 Non-destructive testing of the strength of glass by a non-linear ultrasonic method <p class="CGCAbstract"><span lang="EN-GB">The paper presents basis and experimental results of a non-destructive method aimed at determination of the presence of large surface cracks in glass samples by measurements with NAW® technology (Nonlinear Acoustic Wave). The method is based on a transmitted ultrasonic wave in the material from which the non-linear content of the signal can be analysed. A sample containing defects presents nonlinearities in the form of distortions, such as, higher order harmonics that are detected. Nonlinearities in the signal are primarily formed at crack-tips and the number of nonlinearities is proportional to the amount of damage, or defects, in the sample that is investigated. The result of the measurement and evaluation, that only takes a few seconds, is a damage value that is easy to understand and to use for immediate application. A number of preliminary test results and comparisons with destructive testing for various test setups, as well as a recent test strategy including fabricated defects with a nanoindenter will be discussed. </span></p> Kent Persson Kristian Haller Stefan Karlsson Marcin Kozłowski Copyright (c) 2020 Kent Persson, Kristian Haller, Stefan Karlsson, Marcin Kozłowski 2020-09-04 2020-09-04 7 10.7480/cgc.7.4498 GS&E journal > Study on the optical quality and strength of glass edges after the grinding and polishing process <p>Glass edges result from cutting glass sheets and a further optional finishing. The mechanical interference into the brittle material glass causes flaws and cracks at the edge surface. Those defects have an influence on the strength of the whole glazing. Within the scope of a research project at the Institute of Building Construction from the Technische Universität Dresden, the grinding and polishing process is examined in terms of characteristic visible effects on the glass edge and the edge strength. Thereby a special focus of the research project is the impact of various polishing cup wheels for the chamfer surface of annealed glass. The article presents some basics about the processing steps of glass edges surfaces, introduces the considered grinding and polishing cup wheels and gives an overview of the performed experimental examinations. A microscopic analysis enables a characterisation of typical defects at the surfaces. Furthermore, four-point bending tests are performed to determine the bending tensile stresses at failure. The combination of both methods enables an analysis of the fracture-causing defect before destruction and a correlation between the optical surface quality and the bending tensile stresses. Additionally, the microscopy could be used to support the adjustment of a grinding machine and control reproducible edge qualities. The evaluation shows that a special development of polishing cup wheels for the chamfer can improve the surface quality and consequently increases the edge strength.</p> Paulina Bukieda Katharina Lohr Jens Meiberg Bernhard Weller Copyright (c) 2020 Paulina Bukieda, Katharina Lohr, Jens Meiberg, Bernhard Weller 2020-09-04 2020-09-04 7 GS&E journal > Semantic Segmentation with Deep Learning: Detection of Cracks at the Cut Edge of Glass <p>In this paper, artificial intelligence (AI) will be applied for the first time in the context of glass processing. The goal is to use an algorithm based on artificial intelligence to detect the fractured edge of a cut glass in order to generate a so-called mask image by AI. In the context of AI, this is a classical problem of semantic segmentation, in which objects (here the cut-edge of the cut glass) are automatically surrounded by the power of AI or detected and drawn. An original image of a cut glass edge is implemented into a deep neural net and processed in such a way that a mask image, i.e. an image of the cut edge, is automatically generated. Currently, this is only possible by manual tracing the cut-edge due to the fact that the crack contour of glass can sometimes only be recognized roughly. After manually marking the crack using an image processing program, the contour is then automatically evaluated further. AI and deep learning may provide the potential to automate the step of manual detection of the cut-edge of cut glass to great extent. In addition to the enormous time savings, the objectivity and reproducibility of detection is an important aspect, which will be addressed in this paper.</p> Michael Drass Hagen Berthold Michael Anton Kraus Steffen Müller-Braun Copyright (c) 2020 Michael Drass, Hagen Berthold, Michael Anton Kraus, Steffen Müller-Braun 2020-09-04 2020-09-04 7 GS&E journal > Investigating the flexural strength of recycled cast glass <p>Currently, tons of&nbsp; high quality commercial glass are down-cycled or landfilled due to contaminants that prevent close-loop recycling. Yet, this glass is potentially a valuable resource for casting robust and aesthetically unique building components. Exploring the potential of this idea, different types of non-recyclable silicate glasses are kiln-cast into 30*30*240mm beams, at relatively low temperatures (820 oC - 1120 oC). The defects occurring in the glass specimens due to cullet contamination and the high viscosity of the glass melt, are documented and correlated to the casting parameters. Then, the kiln-cast specimens and industrially manufactured reference beams are tested in four-point bending, obtaining a flexural strength range of 9-72MPa. The results are analysed according to the role of the chemical composition, level of contamination and followed casting parameters, in determining the flexural strength, the Young’s modulus and the prevailing strength-limiting flaw. Chemical compositions of favourable performance are highlighted, so as critical flaws responsible for a dramatic decrease in strength, up to 75%. The defects situated in the glass bulk, however, are tolerated by the glass network and have minor impact on flexural strength and Young’s modulus. The prerequisites for good quality recycled cast glass building components are identified and an outline for future research is provided.</p> Telesilla Bristogianni Faidra Oikonomopoulou Rong Yu Fred A. Veer Rob Nijsse Copyright (c) 2020 Telesilla Bristogianni, Faidra Oikonomopoulou, Rong Yu, Fred A. Veer, Rob Nijsse 2020-09-04 2020-09-04 7 GS&E journal > Double ring bending tests on heat pretreated soda–lime silicate glass <p>The strength of glass plays an important role in the dimensioning of glass components in the building industry. Here, not only parameters such as support conditions, loading rate, relative humidity etc. play an important role, but the damage by means of scratches also determines the fracture strength of glass. A heat treatment after damaging may have an influence on the resulting glass strength. The correlation between heat treatment temperature, and in particular elevated temperatures up to the glass transition temperature, and fracture stress has been studied by different researchers with several approaches of pre-treatment of specimens and test setups. This paper methodically presents various preliminary investigations which were carried out within the framework of the pre-treatment of the samples in order to investigate the influence of heat treatment of the pre-damaged samples on the fracture stress. For this purpose, double ring bending tests were performed at room temperature on pre-damaged, heat-treated soda–lime silicate glass specimens. The aim of the investigations is to obtain estimates of the extent to which a heat treatment prior to the strength test influences the fracture strength of soda–lime silicate glass. Parameters like the heat treatment temperature, the dwell time of the samples inside the furnace and the furnace design were considered. The results show that the heat treatment can increase the fracture stress of soda–lime silicate glass as float glass significant due to an assumed healing of the pre-damage during heat treatment.</p> Gregor Schwind Fabian von Blücher Michael Drass Jens Schneider Copyright (c) 2020 Gregor Schwind, Fabian von Blücher, Michael Drass, Jens Schneider 2020-09-04 2020-09-04 7 An experimental study on thermoplastic interlayers in laminated glass using fiber optic strain sensors <p>The method of fiber optic strain measurement based on Rayleigh signal analysis enables the detection of the deformation behaviour of glass laminates for the purpose of modelling its load-bearing characteristics. With distributed fiber optic sensors, which consist of a diameter of 0.16 mm, it is possible to determine strain patterns on both glass surfaces and its interlayers. The sensors used in tensile and bending tests on monolithic as well as laminated glass supplement the deformation measurements taken with strain gauges and inductive displacement sensors. The study describes the results of the principal applicability of fiber optic strain sensors to evaluate the structural behaviour of laminated glass and provides the basis to define a model for the material characteristics of viscoelastic interlayers.</p> Thorsten Weimar Christian Hammer Copyright (c) 2020 Thorsten Weimar, Christian Hammer 2020-09-04 2020-09-04 7 10.7480/cgc.7.4602 Determination and Verification of PVB Interlayer Modulus Properties <p>Interlayer modulus properties are important for the calculation of the load resistance of laminated glass configurations. The determination of interlayer properties can be made on the interlayer material directly, or indirectly through measurements on laminated glass test specimens. One challenge relates to the four-decade range of modulus values that interlayer materials go through with variations of temperatures and duration that are relevant to building elements. Furthermore, in determination of properties directly on the interlayer, e.g. by dynamic mechanical analysis, methodological choices and data treatment play an important role, apart from experimental and material variation. To some extent, this also holds true for modulus determination on laminated glass specimens, with the added challenge that the properties of a relatively soft material are derived from the response of a rigid assembly. In this contribution, three material models are provided for of all major PVB interlayer formulations (conventional, structural, acoustic trilayer), as determined by dynamic mechanical analysis and compared to modulus values obtained in four-point bending experiments. The validated material models can provide modulus data relevant for glass design for a wide range of load scenarios in a concise format.</p> Wim Stevels Pol D'Haene Copyright (c) 2020 Wim Stevels, Pol D'Haene 2020-09-04 2020-09-04 7 10.7480/cgc.7.4440 Effects of Humidity and the Presence of Moisture at the Bond-line on the Interfacial Separation of Laminated Glass for Flat Glass Re-use <p>The built environment is under scrutiny to address environmental design challenges by considering a whole-life holistic approach that seeks reductions in operational emissions whilst simultaneously pursuing reductions in embodied emissions. Reduced embodied emissions can be found through the responsible sourcing of resources and re-use of materials in their highest obtainable value. Laminated glass is used widely within the building industry for improving security and for reducing the risk of human injury from glass fracture. At present, few options exist for the re-use and high-value re-cycling of laminated glass; it is most commonly disposed of in landfill or <em>down-cycled</em> into aggregate material due to its low perceived value at end-of-life. Whilst some efforts have been made to separate the poly-vinyl butyral (PVB) interlayer from glass in the automotive industry, such processes typically involve destructive crushing of the glass sheets and residual glass that is not at a high enough purity to be considered for re-cycling as cullet for visual glass applications. A more effective removal of the PVB-interlayer through severing of the PVB-glass interfacial bonds, would allow flat glass from existing laminated glass panels to be re-conditioned to fulfil the latest functional requirements in architectural glass. Whilst the temperature and strain rate dependency of the PVB-interlayer material itself has been well-researched, the fundamental nature of the interfacial bonding between glass and PVB, governed by initial processing, is not well-understood.&nbsp; This paper presents findings from the latest experimental research that explores methods of separating 2.9 mm x 100 mm x 150 mm flat glass sheets from a 0.38mm PVB-interlayer for flat glass re-use and/or re-cycling of glass sheets at their highest obtainable value at end-of-life. A bespoke standardised test has been developed by the authors inspired by the compressive shear test, to evaluate methods for achieving separation between the interlayer and glass on a small-scale. Tests were conducted at room temperature to evaluate the effects of varying displacement rate (0.125mm/min, 0.5mm/min and 1.0mm/min), humidity exposure and the influence of water infiltration along the bond line.&nbsp; It was found that the influence of humidity-ageing and water infiltration along the glass-interlayer interface during separation led to a greater proportion of delaminated area compared to the un-aged samples. The greater proportion of delaminated area was found to be a result of a mixture of the effects of a change in the bulk material properties of the interlayer and the intrinsic value of interfacial adhesion.</p> Rebecca Hartwell Mauro Overend Copyright (c) 2020 Rebecca Hartwell, Mauro Overend 2020-09-04 2020-09-04 7 10.7480/cgc.7.4727 Four-point bending tests of PVB double laminated glass panels – experiments and numerical analysis <p>Current architecture uses glass even for load bearing structural elements. Typical example is perpendicularly loaded laminated glass panel as a part of balustrade, staircase, or canopy. Laminated glass is a composition of two or more glass plies bonded by polymeric interlayer which enables the shear transfer between the individual plies in a laminated panel. The shear transfer depends on the shear stiffness of a certain interlayer as a time and temperature dependent parameter. Shear stiffness in time and temperature domain can be numerically described by a discrete Maxwell model whose Prony parameters may be obtained by Dynamic mechanical thermal analysis (DMTA) of a particular interlayer. There are various techniques of DMTA as well as various Prony parameters fitting methods. As soon as shear stiffness given by Maxwell model is quantified, it is desirable to verify its credibility by experiment. This paper compares the experimental data from displacement-controlled four-point bending tests in various loading rates and from four point bending longterm creep experiment of double laminated glass panels with PVB interlayer Trosifol BG-R20® to the numerical analysis performed in ANSYS® 18.0. The interlayer was modelled as a viscoelastic material by two discrete Maxwell models. Prony parameters of the first Maxwell model were based on DMTA results performed on small scale specimens in single lap shear mode and Prony parameters of the second Maxwell model were based on DMTA results performed on small scale specimens in single lap shear mode and torsion mode. Results show that Maxwell model based only on single lap shear tests enabled to describe the long-term response of a panel while that based on single lap shear and torsion tests was more precise in task of displacement-controlled test. All experiments and analyses were performed at CTU in Prague.</p> Tomáš Hána Miroslav Vokáč Martina Eliášová Zdeněk Sokol Klára V Machalická Copyright (c) 2020 Tomáš Hána, Miroslav Vokáč, Martina Eliášová, Zdeněk Sokol, Klára V Machalická 2020-09-04 2020-09-04 7 10.7480/cgc.7.4460 Linear Calculation Methods of Composite Panels <p>Innovative glazing, which combines polycarbonate and thin glass to composite panels, ensures a slighter alternative to glass laminates with a high resistance against manual attack. Due to experimental studies, these thin glass-polycarbonate composite panels are classified as laminated safety glass and security glazing. The study describes analytical models to analyse their structural behaviour for static short time loads. In accordance to the geometrical boundary conditions of the four-point bending test, the composite panel can be described by the beam theory. A multi-layered system is calculated with the sandwich beam theory with a bending and shear deformation. Additionally, an extended approximate solution based on Wölfel is compared to the classical theory of sandwich elements as well as with experimental results.</p> Sebastián Andrés López Thorsten Weimar Copyright (c) 2020 Sebastián Andrés López, Thorsten Weimar 2020-09-04 2020-09-04 7 10.7480/cgc.7.4517 On the Low-Velocity Impact Response of Laminated Glass with Different Types of Glass and Interlayers <p>An adequate understanding of the response of laminated glass structures to impact loading becomes essential to rationalise their design, which has been proven by several studies that appeared in the last years. Our study focuses on the behaviour of three-layer laminated glass plates subjected to the low-velocity impact of a steel impactor. Using combined experimental and computational analysis, we study the influence of the laminated glass composition on the response of laminated glass, crack initiation and the final fracture pattern. A polyvinyl butyral or ethylene-vinyl acetate interlayer merges annealed or heat-strengthened soda-lime-silica glass panes together so that the tested panels have the same cross-section layout. As the boundary conditions of the plate largely influence the impact performance of glass panels, the samples were suspended on thin steel ropes to avoid the effect of supports on the laminated glass response. The finite element model of this contact-impact problem, accounting for the time/temperature-dependent behaviour of two polymer interlayers, is presented and validated. Finally, we discuss the effect of the glass and foil type on the contact force and response of laminated glass plates.</p> Alena Zemanová Petr Hála Petr Konrád Jaroslav Schmidt Radoslav Sovják Michal Šejnoha Copyright (c) 2020 Alena Zemanová, Petr Hála, Petr Konrád, Jaroslav Schmidt, Radoslav Sovják, Michal Šejnoha 2020-09-04 2020-09-04 7 10.7480/cgc.7.4483 Three-point bending test of laminated glass with PVB and EVA interlayers at elevated temperature <p>This paper presents the experimental results of a three-point bending test conducted on laminated glass at elevated temperature in an environmental chamber. The focus of the present research was on bending stiffness degradation of the laminated glass in correspondence to elevated temperature. The tested specimens were made of two fully tempered glass plates bonded with EVA and PVB interlayers. For each type of laminated glass and set temperature, we prepared and tested 5 specimens. Each of the specimen was preconditioned to a set temperature before the experiment conducted in an environmental chamber. The tests were conducted at 23°C, 35°C and 60°C after the specimens had reached the defined contact temperature. During the experiment, the midspan deflection, longitudinal midspan deformation and the force at midspan were recorded. In the end, the behaviour of two different types of laminated glass plates was compared based on measured midspan deflection, deformations and stiffness degradation. Based on the results it can be seen that the laminated glass with EVA interlayer behaves stiffer and that the stiffness degradation is almost linear and slower in comparison to the specimens with PVB interlayer.</p> David Antolinc Copyright (c) 2020 David Antolinc 2020-09-04 2020-09-04 7 10.7480/cgc.7.4491 GS&E journal: Investigations on the execution and evaluation of the Pummel test for polyvinyl butyral based interlayers <p>Laminated safety glass (LSG) is increasingly used as structural element in buildings. Of central importance for safety are the adhesion and the residual load-bearing capacity in the post fractured state. In literature a large number of tests to assess adhesion is mentioned. These include, e.g. peel tests, through-cracked-tensile/-bending tests, VW-pull tests and compressive shear tests. However, especially in industry, the Pummel test is widespread for determining the quality of adhesion in LSG with polyvinyl butyral based interlayers. This test method proves to be simple and quick to carry out: The laminate is stored at − 18&nbsp;°C and then completely destroyed at room temperature with hammer blows. The adhesion level (0–10) is determined by visually comparing the adhering glass fragments with reference pictures or with the help of diagrams and tables which indicate the Pummel value as a function of the free film surface. Pummel value 0 is to be interpreted as no adhesion and Pummel value 10 as very high adhesion. Due to the lack of standardization, the execution and evaluation is very much dependent on the test institution and executive person. This paper shows different Pummel classifications that can currently be found on the market. Subsequently, approaches to the automatization and standardization of the execution and especially the evaluation of the Pummel test are shown. Three image evaluation methods in Matlab are presented, discussed and compared: (1) analysis of binary images, (2) statistical evaluation of the greyscale images and (3) texture analysis using co-occurrence matrices.</p> Miriam Schuster Jens Schneider Tuong An Nguyen Copyright (c) 2020 Miriam Schuster, Jens Schneider, Tuong An Nguyen 2020-09-04 2020-09-04 7 GS&E journal > Adhesion Rupture in Laminated Glass: Influence of Interfacial Adhesion on the Energy Dissipation Mechanisms <p>In laminated glass under impact, most of the energy dissipation occurs in the coupled delamination and deformation of the polymer interlayer. The strong dependency of these mechanisms on interlayer nature, on loading rate and on temperature is known: however, the effect of the interfacial adhesion is unexplored. In this work, a surface modification technique is proposed, along with a mechanical characterization of the debonding with the Through Crack Tensile Test. We show that changing adhesion mostly affects dissipation close to the delamination front, while dissipation in the volume of the PVB interlayer seems unaffected, which we attribute to the competition between the changes in both strain and strain rate in the viscoelastic interlayer. Finally, we discuss the experimental observation of the limits of the steady-state debonding regime, related to the competition between adhesive crack propagation and cohesive failure in the interlayer.</p> Paul Fourton Keyvan Piroird Matteo Ciccotti Etienne Barthel Copyright (c) 2020 Paul Fourton, Keyvan Piroird, Matteo Ciccotti, Etienne Barthel 2020-09-04 2020-09-04 7 Application of a mobile measuring device for the planar evaluation of the current in-situ stress condition in glass <p>The load-bearing capacity of glass as a structural material as well as sustainability and resistance of a built-in glass against appearing loads and forces is assuming an ever-greater importance. Next to analytical and numerical calculations of maximum load-bearing capacity and the ultimate limit state, there is no generally accepted standardized non-destructive inspection method available, with which it is possible to estimate the prevalent load situation and predominant stress conditions, particularly in relation to mechanical or adhered connections. Within the research project “BiGla”, a measuring instrument based on photoelasticity was developed, which enables to measure and monitor occurring load states during the installation process, as well as the utilization of glass components subjected to significant load changes during their life cycle. Based on the combined examination of photoelasticity and its synergism with the finite element analysis it becomes possible to transfer qualitative measurement results into quantitative evaluations of predominant stress conditions. Achieved results, gained during experimental investigations under laboratory conditions, as well as during extensive field tests, are presented in this publication.</p> Marcus Glaser Benjamin Schaaf Mascha Baitinger Barbara Siebert Copyright (c) 2020 Marcus Glaser, Benjamin Schaaf, Mascha Baitinger, Barbara Siebert 2020-09-04 2020-09-04 7 10.7480/cgc.7.4487 Behaviour of Different Glass Elements subjected to Elevated Temperatures – State of the Art <p>Glass has become an indispensable construction material. However, in extreme events such as fire, the behaviour of glass elements is still relatively unknown. The susceptibility of glass to thermal shock and its changeable material properties when subjected to high temperatures make predicting the behaviour of glass elements during fire complex. Practical applications of fire-resistant glazing, however, already exist as infill panels and frameless glass walls/doors, and are commonly used. They are highly effective to maintain compartmentation, providing temporary protection of the unexposed side against the passage of flames and smoke and, depending on the classification, they also provide thermal insulation. This paper gives an overview of experimental research performed on glazing subjected to fire loading. Outcomes of temperature-dependent properties, monolithic glazing and multi-glazed products are summarised to create an insight in the thermal behaviour. The current shortcomings to determine the fire resistance of glazing are identified and promising numerical software developments are summarised.</p> Evelien Symoens Ruben Van Coile Jan Belis Copyright (c) 2020 Evelien Symoens, Ruben Van Coile, Jan Belis 2020-09-04 2020-09-04 7 10.7480/cgc.7.4489 Combined Voronoi-FDEM approach for modelling post-fracture response of laminated tempered glass <p class="CGCAbstract"><span lang="EN-US">In this work, a combined Voronoi and finite-discrete element method (FDEM) approach for reconstructing the post-fracture model of laminated glass (LG) was proposed. The fracture morphology was determined via introducing Voronoi tessellation with statistical distribution parameters such as the fragment face numbers, volume and sphericity. The residual interaction between glass fragments was described with cohesive zone model. One fractured LG block under uniaxial tension, which was taken from a triple layered LG beam with ionoplast interlayers, was modelled and validated with experimentally recorded data. Through iteration analysis, the key cohesive parameters were determined for the most applicable model. It is followed by investigating the influence due to the fragments interaction property. The results show that the cohesion and frictional property can be combined to well describe the residual interaction behaviour between fragments. The frictional property has a remarkable effect on the post-fracture resistance whereas the associated effect on the stiffness is not evident. Compared to other cohesive parameters, the cohesive stiffness factors present predominant effect on both the post-fracture stiffness and resistance. </span></p> Xing-er Wang Jian Yang Zhufeng Pan Yuhan Zhu Copyright (c) 2020 Xing-er Wang, Jian Yang, Zhufeng Pan, Yuhan Zhu 2020-09-04 2020-09-04 7 10.7480/cgc.7.4737 Dynamic Behavior of Laminated Glass Plates <p>This paper dealt with the theoretical and experimental dynamic behaviour of laminated glass. The developments are based on the contrasted plate model (Boutin and Viverge 2016) that accounts for the high contrast of mechanical properties between the glass layers and the soft viscoelastic interlayer through the additional kinematic variable describing the sliding between the glass layers. This yields an analytic tri-Laplacian representation that encompasses (i) the shear related to the sliding within the PVB, (ii) the local bending of each glass layer, and (iii) global bending of the whole laminate. In dynamics it is shown that three types of bending waves exist, two being evanescent and one being propagating. This enables the determination of the modes of laminated glass plates submitted to different boundary conditions. The energy balance enables to assess the local dissipation of the PVB, which results in the damping of the modes. This approach is compared to vibration tests performed at temperatures ranging from 30 to 50°C. The influence of the PVB on the eigen frequencies and on the damping is clearly evidenced. A good qualitative correspondence with the theory is obtained.</p> Claude Boutin Kevin Viverge Copyright (c) 2020 Claude Boutin, Kevin Viverge 2021-02-23 2021-02-23 7 10.7480/cgc.7.4713 Investigating the origin of breakage of panes subjected to blast loading by acoustic emission testing <p class="CGCAbstract"><span lang="EN-US">The Fraunhofer EMI shock-tube facility “Blast-STAR” is used to simulate blast loadings from high explosive detonations similar to realistic conditions. Mainly tests on explosion-resistant safety glazing and façades are carried out. Due to the extreme conditions during the test, it is not trivial to accurately analyze the specimen reaction and in particular to determine the start of breakage of the glass pane. Usually high-speed footage is used for this purpose. Since the size of tested elements is increasing, the determination of place and time of breakage becomes more challenging. Monk and Clubley successfully used piezo transducers in an alternative approach to measure the shock wave originating from glass breakage for detecting the point of initial cracking. They used long-duration blasts, characterized by small peak pressures and a long positive phase duration. In contrast, the blast waves generated with the “Blast-STAR” are characterized by higher peak pressures and a considerable shorter positive phase. The presented work examines the applicability of the approach for the “Blast-STAR” experiments and the accuracy compared to video recordings. Within the paper five shock tube tests are described and evaluated. The results and the experimental set-up are discussed and an outlook for further research is given.</span></p> Jan Dirk van der Woerd Copyright (c) 2020 Jan Dirk van der Woerd 2020-09-04 2020-09-04 7 10.7480/cgc.7.4512 Nonlinear Calculation Methods for Polymeric Materials in Structural Glass Construction - an Overview <p>Since time began there has been a strong fascination in foreseeing the behavior of buildings and constructions. &nbsp;Now In order to predict this behavior, we use experimental, and increasingly more time- and cost-effective, computational simulations. Finite Element Analysis (FEA) is a method that has become increasingly prevalent and has become firmly established in aviation and vehicle construction for decades. In recent years, there has been a marked growth in the use of numerical simulations for the verification of adhesive bonds, particularly in façade development where polymeric materials such as sealants or thermoplastic spacers are becoming increasingly important. This is partly driven by their expansion stress behavior, which differs greatly from the classic linear behavior of established materials such as aluminum, steel or glass. The present work uses non-linear material laws for FEA and exhibits the behavior of the sealant joint in various load scenarios on several projects. The presented case studies show that the developed calculation methods can be used to describe polymeric materials very precisely and thus simulate a wide variety of load scenarios on glued components in time and money saving manner.</p> Christian Scherer Thomas Scherer Thomas Schwarz Wolfgang Wittwer Ernst Semar Copyright (c) 2020 Christian Scherer, Thomas Scherer, Thomas Schwarz, Wolfgang Wittwer, Ernst Semar 2020-09-04 2020-09-04 7 10.7480/cgc.7.4492 Ongoing Research into the Failure of Glass at High Strain-Rates <p>The failure of glass has been studied extensively by many researchers. However, the focus has previously been on the static to quasi-static, rate-independent behaviour. It is commonly accepted that the strength of glass is sensitive to the applied loading time, however, the amount of research in the field of loading rate dependency seems very limited. Consequently, the effect of loading rates on the strength is sparingly described in the available literature despite its relevance when designing for impact and blast loads. The present paper presents an ongoing research project considering the failure of glass at high strain-rates. It provides a brief review of existing studies showing a strength increase with loading rates relevant for e.g. blast loads. Based on existing experimental work, a numerical model considering different failure models is presented. The different considered failure models are then compared and discussed for their applicability. The paper also includes an outlook of the project, briefly explaining a novel concept for a high strain-rate test setup planned to be built during the summer of 2020.</p> Martin Jensen Meyland Jens Henrik Nielsen Copyright (c) 2020 Martin Jensen Meyland, Jens Henrik Nielsen 2020-09-04 2020-09-04 7 10.7480/cgc.7.4428 The Application of Waste Float Glass, Recycled in Structural Beams made with the Glass Casting Method <p class="CGCAbstract"><span lang="EN-US">It is not obvious to talk about glass recycling when we realize that a mature recycling procedure for glass bottles is already working well. However, apart from glass bottles, unfortunately, that a large amount of glass will disappear into landfills. This large quantity of unrecycled glass indicates that there is a large potential in upgrading the glass recycling process. In the field of architecture, we see a fast-growing interest in using glass, also for structures. The glass bricks of Crystal Houses in Amsterdam are a good illustration. Aiming at maximizing the recyclability of glass, this paper focuses on the structural use of the glass components made from recycled glass through kiln casting method. An overview of the existing glass recycling industry is given at the beginning, followed by a discussion of glass type to be recycled. After this the experimental process of the glass recycling is introduced, which uses coated float glass with tints as the basic material to be recycled. Following this, a further exploration in three structural properties of the recycled products is conducted, namely: Young’s modulus, coefficient of thermal expansion and the fracture strength, with mechanical experiments. Finally, the test results are analyzed together with the chemical composition of the recycled products, which is derived from X-ray fluorescence (XRF) analysis. The result contains the value of mechanical properties and it evaluates the possibility of the structural use as a recycled-float-glass beam. In the end of this paper, the future possibility and feasibility in structural application of recycling waste float glass are discussed. </span></p> Rong Yu Copyright (c) 2020 Rong Yu 2020-09-04 2020-09-04 7 10.7480/cgc.7.4775 100% transparant floating glass boxes <p><sup>b </sup>Si-X, the Netherlands</p> <p>The C&amp;A building in Eindhoven will be modernised and therefore UNStudio designed several glass structures for the building. One of these glass structures are four glass boxes of 5,5 meters wide and 7 meters high, which are floating in front of the existing façade. In addition, each glass box contains a work of light art designed by Arnout Meijer. LED strips illuminate the box from the inside, while the reflective film on the glass creates an unusual and striking effect. To optimize this effect no metal connections were allowed in the design.</p> <p>The size of 5,5 by 7 meters was exceeding every international standard format in the glass industry. ABT designed an ‘Origami’ glass box with glass panels glued together. This geometry solved the problem of the limited size of the panels and also made a more economic structural form.</p> <p>The glass panels are connected seamless with different type of glues. ABT made an extensive research for the right type of glues in cooperation with the university of Leuven.</p> <p>The glued connections are combined with glass notches; a new type of connection, inspired by timber connections and earlier research of stacked glass columns. FEM DIANA models showed that this is a promising way to connect glass structures.</p> <p>Sober thinking of the engineers about mechanical schemes solved the demand of UNStudio, seamless floating glass boxes. The result can be seen at the 18 September plein in Eindhoven.</p> Diana de Krom Erwin ten Brincke Corné Hagen Wout Hoogendoorn Copyright (c) 2020 Diana de Krom, Erwin ten Brincke, Corné Hagen, Wout Hoogendoorn 2020-09-04 2020-09-04 7 10.7480/cgc.7.4546 Adjustable point supported glass floor in the renewed building of the National Museum in Prague <p>The building of the National Museum in Prague is a part of the historical heritage of the Czech Republic. Very huge reconstruction and maintenance of whole building was ongoing during the last decade. Special emphasis was devoted to every detail of the interior as well as the facade elements to keep the historical value of the building adding modern architectural elements like transport glass flooring and balustrades. This paper deals with the project of the glass flooring in total area about 200m2 placed directly in the main tower of the building as a representative place with nice view to a historical parts of the city. The tower is a part of the main Pantheon with historical coloured glass elements visible from the inside of the building, therefore, glass flooring was the only possible solution to open this area for people by keeping the daylight from the top of the Pantheon.</p> Michal Netušil Martin Boček Copyright (c) 2020 Michal Netušil, Martin Boček 2020-09-04 2020-09-04 7 10.7480/cgc.7.4490 An Adjustable Mould for the Casting of Glass Voussoirs for the Construction of Fully Transparent Shell Structures <p>Compared to flat sheets of float glass, cast glass components have a thicker geometry and thus a high buckling resistance. This buckling resistance in combination with the high compressive strength of glass make cast glass components suitable for the construction of fully transparent shell structures that are mainly subjected to compressive stresses. Shell structures often have the shape of surfaces with varying Gaussian curvature. When constructing such a shell structure out of cast glass components, components of varying geometries are needed. An adjustable mould was developed that can be used for the casting of glass components (i.e. voussoirs) of varying geometries. The possible voussoir geometries that can be cast in the adjustable mould are limited to voussoirs with planar, convex, polygonal intrados and extrados. These voussoirs can be used to construct fully transparent shell structures. The voussoirs are dry-assembled with a rubber interlayer in between. Tongue and groove shaped interfaces ensure an interlocking connection. By tessellating a shell structure, the shell structure is divided into a discrete number of voussoirs that can be cast in the adjustable mould. Several aspects have to be taken into account when optimizing the tessellation pattern including planarity, interior angle size, face size and alignment to the flow of forces. A design was made of a shell structure that covers the courtyard of the Armamentarium in Delft. This shell structure served as a case study used to demonstrate the tessellating process and the use of the mould developed during this research.</p> Felix van der Weijst Faidra Oikonomopoulou Marcel Bilow Copyright (c) 2020 Felix van der Weijst, Faidra Oikonomopoulou, Marcel Bilow 2020-09-04 2020-09-04 7 10.7480/cgc.7.4472 Capital C, geometric optimization of a free-form steel gridshell towards planar quadrilateral glass units <p>The former Diamond-exchange building in Amsterdam, now called Capital C, is restored to its former glory and currently undergoing a major renovation. This listed building has been returned to its original design and topped with a spatial gridshell roof structure of glass and steel, designed by renowned architect office ZJA Zwarts &amp; Jansma Architects. This paper focuses on the geometric optimization of the free-form gridshell towards planar quad glass units.</p> <p>&nbsp;</p> <p>The final shape of the gridshell is determined by a parametric computer model. With a by ZJA in-house written program, the boundary conditions were defined, where after the software searches the ideal shape. In the case of Capital C, the ideal shape was a geometrical free-form shape but with planar or minimal curved quadrilateral glass. This to represent the faceted aesthetics of the diamond, representing the building’s heritage. In addition to the look, optimizing to planar glass panes also increased the feasibility and cost-efficiency of the design. During this process Octatube, as a specialist Design and Build contractor, was approached and challenged to realize this innovative and complex design.</p> <p>&nbsp;</p> <p>In principle the gridshell has one repetitive structural steel connection. However due to its shape every connection is unique and itself composed of many unique parts. In the final design, approximately 1000 different steel elements and 200 different glass units are applied. With a traditional design method, where all elements are modelled one by one, a minor change to the geometric shape of the shell would lead to a large amount of labour. A time-consuming and error-prone job. Therefore the design is automated, by means of an in-house developed parametric tool by Octatube, which converts the complex basic geometry into a FEM-model and detailed production model.</p> <p>&nbsp;</p> <p>The applied methods of parametric design and engineering allowed the team to not only optimize the glass-design until late in the engineering phase, incorporating a file-to-factory workflow, it also allowed for fast and very precise pre-fabrication. Not unimportant when installing a free-form glass and steel gridshell on top of a listed building in the heart of Amsterdam.</p> Koos Fritzsche Wouter van der Sluis Erik Smits Jack Bakker Copyright (c) 2020 Koos Fritzsche, Wouter van der Sluis, Erik Smits, Jack Bakker 2020-09-04 2020-09-04 7 10.7480/cgc.7.4493 Complex Curved Storefront: The Looking Glass <p class="CGCKeywords"><span lang="EN-US">A bespoke structural glass storefront is designed for the P.C. Hooftstraat 138. Developer Warenar Real Estate assembled a design team with UNStudio, Arup and Octatube. The façade features twisted geometries with precisely detailed glass connections and custom non-orthogonal steel and glass doors. At ground floor level the facade starts flush with adjacent buildings but rising up it also leans and cantilevers outwards to become more visible from a distance. For optimal quality and minimalistic detailing, a scheme was designed in which most elements could be pre-assembled in the factory into three large 2m x 8,5m high units. Connections between curved glass elements are all glued in combination with stainless steel elements for edge protection and emphasis on the curved geometry. Risk of thermal breakage of annealed curved elements that are partially inside and partially outside is minimized by gluing stainless steel plates to the glass elements that act as cooling ribs. Frequent collaboration throughout the whole project between all parties resulted in successful delivery with no glass breakage during the construction phase. It took years to design, months to assemble in factory, but only 2 days to construct on site.</span></p> Chris Noteboom Peter Lenk Iris Rombouts Erik van der Thiel Copyright (c) 2020 Chris Noteboom, Peter Lenk, Iris Rombouts, Erik van der Thiel 2020-09-04 2020-09-04 7 10.7480/cgc.7.4607 Design & Engineering of the iconic spherical shell of the Academy Museum of Motion Pictures, LA <p>Renzo Piano Building Workshop designed a 290,000 sf museum celebrating the artistry and technology of film, becoming the world’s first museum and event space devoted to the Motion Picture. The 388 Mio USD project consist of a six story tall renovated existing building and a dome-shaped iconic new building housing a 1,000-seat theater. Both buildings are linked by several – partially suspended – bridges. The 150 ft diameter dome is a steel grid shell with cable bracing and flat, shingled glass panels on a secondary layer. The single-layered curved structural steel tubes have a diameter of 4 inches only. With an airy and weightless quality, the globe’s structure seems to dissolve into the background. The construction of the steel glass structure was completed in autumn 2019; grand opening of the museum is planned for summer 2020. Knippers Helbig was responsible for design and engineering of the structure and glazing system of spherical glazed gridshell structure from concept stage until signed and sealed drawings and calculations and was responsible for design and engineering of the bridges during Design Development.</p> Roman Schieber Florian Meier Copyright (c) 2020 Roman Schieber, Florian Meier 2020-09-04 2020-09-04 7 10.7480/cgc.7.4429 Erin Mills Town Centre Globe Structure <p>Erin Mills Town Centre is a shopping mall in Mississauga, Canada owned by Cushman &amp; Wakefield in Toronto. The revitalization project was designed by MMC International Architects Ltd. and features a 27.4m diameter glass and steel globe at its Centre Court. The structural glass for this globe structure is created with laminated double curved glass panels patch supported by a steel structure. Some challenges arose during construction due to the frit on the glass panel and the thermal stress created between the inner and outer lites of the laminated assembly. Testing was used to establish a workable solution for replacement glass in order to correct the in-situ issue that was discovered</p> John Kooymans Copyright (c) 2020 John Kooymans 2020-09-04 2020-09-04 7 10.7480/cgc.7.4765 Façade becomes structure <p>The Green Village at the TU Delft is a living lab for sustainable innovations. The Co Creation Centre will be their new meeting centre. This centre is getting a climate tower and to get the isolation standards, triple glass was necessary. Unfortunately, the original design for the centre was too expensive. The triple glass was one of the big cost items.</p> <p>Then the team got the ingenious idea to use the façade as the bearing and stabilising structure. This idea made the project feasible in costs.</p> <p>The aim was to design a façade with as few as possible modifications compared to a standard façade. In the future Triple glass will become more and more standard. The Triple glass is structurally oversized and therefore the material is not used optimally, which makes triple glass less sustainable in using raw materials. Triple glass can be made more sustainable if we utilize this overcapacity for the structure.</p> <p>Using glass panels for stabilising a structure has been done before. But often it becomes a complex façade in assembly. In this façade silicone joints are used to initiate all the forces and the normal way of mounting is followed.</p> <p>And the team even went one step further. In the original design the building had both columns for the roof load and glass fins to take the wind loads from the façade panels. The glass fins are an expensive part of the façade. Since glass is good in compression, why not use the fins as columns? Of course the buckling of the fins is an important risk since these fins are 5.2 meters high. By clamping the fins between the glass panels the buckling risk is reduced significantly. ABT made FEM calculations using the DIANA software to find the critical parameters for this structure. It was found that the spring stiffness of the horizontal support by the façade is the most critical element.</p> <p>To verify the DIANA calculations two glass fins were tested at the TU Delft at the end of September 2019.</p> <p>By utilising the materials better the use of raw materials and the costs are significantly reduced. With that a more sustainable design was achieved. The aim is to develop this into an innovative standard system.</p> Diana de Krom Fred Veer Kris Riemens Wout Hoogendoorn Copyright (c) 2020 Diana de Krom, Fred Veer, Kris Riemens, Wout Hoogendoorn 2020-09-04 2020-09-04 7 10.7480/cgc.7.4545 Redundancy tests on glass fins <p>Since 2010, Octatube has adopted glass fins as structural components in at least 20 different projects, both in facades and roofs (the van Gogh Museum, the Tottenham Experience, Canal House Amsterdam are some relevant examples). Glass is widely known as a fragile material and it usually breaks in a brittle fashion, whereas a metal like steel typically fails plastically. The post-breakage behavior of glass beams is not easy to predict, therefore Octatube performed a range of tests on different glass fins varying the test setup. All tests were performed in house, at Octatube’s factory/test area in Delft, the Netherlands. In this paper two case studies are discussed. For the brand-new Spartherm Headquarters in Melle (Germany) laminated glass fins are adopted to support large insulated glazing units. Due to the round shape of the building the glass fins spanning for a maximum of 5,3 meters, are also curved on one side. The glass fins were tested both in un-cracked and cracked conditions to assess the overall safety of the design. For the refurbishment of the National Gallery of Ireland in Dublin, a new glass roof, over the old Sculpture Courtyard, was designed by Heneghan Peng Architects. With glass beams up to 8,3 m, and 3x10mm fully tempered PVB laminated panes were adopted. In cooperation with T/E/S/S engineering, the second support system was designed for post breakage behavior. In case of total failure of a glass fin, the safety was is ensured by catenary action in combination with a stiff frame of glass beam. This was tested in a true size, 6,0 meter, mock up. The residual capacity in the glass beam is ensured provided that the global structural system and detailing are carefully designed.</p> Peter van de Rotten Michele Arinze Akilo Wouter van der Sluis Copyright (c) 2020 Peter van de Rotten, Michele Arinze Akilo, Wouter van der Sluis 2020-09-04 2020-09-04 7 10.7480/cgc.7.4605 Square One Rotunda Fin Wall <p>Square One Shopping Centre is owned by Oxford Properties in Toronto, Canada, and was designed by MMC International Architects Ltd. The shopping centre went through a recent expansion and features a large glass and steel rotunda for its feature entrance into the new expansion. The feature glass wall is oval in plan and is 18m tall utilizing a custom splicing detail to minimize the use of steel at the connections. The fin wall was analysed and tested to ensure the connection detail behaved as predicted. This paper will visit the design of the fin wall and review the findings of the physical testing performed on the connection detail.</p> John Kooymans Copyright (c) 2020 John Kooymans 2020-09-04 2020-09-04 7 10.7480/cgc.7.4766 The development and testing of large sandwich panels <p>The TU Delft glass group designed, developed and build three glass sandwich panels for the Glasstec 2018 in collaboration with ARUP. These were composed of heat strengthened laminated float glass with Schott glass tubes as the core. Initial small scale tests were used to determine the parameters for the digital design by ARUP. Based on these results form-finding was used to determine the optimum configuration of the glass tubes in the panel. This was verified by further scale model experiments which led to more refinements in the form finding algorithm. The small scale tests were extend to full scale prototypes which were proof tested at TU delft using a static and dynamic load of standing or dancing students. The full scale panels were then exhibited at the Glasstec 2018 where they were walked over by thousands of people. Finally one of the panels was tested to destruction. It was found to be very resilient and failed in a safe way. The test results are compared with FEM models. The important lessons learned from this for the design and production are explained.</p> Fred Veer Copyright (c) 2020 Fred Veer 2020-09-04 2020-09-04 7 10.7480/cgc.7.4488 Thin Glass in Architecture - Possible Applications and Challenges <p>Thin glass offers a promising prospect for lightweight façades with reduced use of raw materials, also opening up entirely new perspectives for architectural expression with its excellent optical quality as well as its high flexibility. The realisation of projects featuring thin glass as a structural element is so far limited due to several challenges led by structural issues mainly induced by the product's low stiffness. This paper attempts to bypass this issue by exploring the possibilities of the structural application of thin glass as a membrane element using examples of all-glass projects from the past as well as researches conducted in the present. The use of thin glass as a compressive member is impractical since the risk of buckling poses a greater threat than stress exceedance. As an alternative, its application as a tensile member is proposed, supported by examples from academic and industrial researches. In this context, a new type of glass support is introduced, enabling a moment-free load transfer into the glass.</p> Özhan Topcu Vladimir Marinov Copyright (c) 2020 Özhan Topcu, Vladimir Marinov 2020-09-04 2020-09-04 7 10.7480/cgc.7.4547 GS&E journal > Skylight of the hotel RITZ: case study <p>The five-star luxury Hotel Ritz in Madrid is currently under refurbishment. The works include the construction of a new large skylight above the main hall inspired on the original design. This paper focus on the design and construction of this skylight which consist of 2 different parts, the Hall Bajo with a vault shape, and the Hall Alto which is a trapezoidal dome crowned by a pyramid roof. The structure consists in slender steel welded T profiles and small rectangular plates which connects the main beams. The connections between the structural members are welded in order to obtain a rigid connection. The perimeter consists in a welded RHS beam which creates a stiff tension ring which is completed by a visible cable. The pyramid roof performs as a compression ring for the in-plane loads and as a Vierendeel beam for the vertical loads. The cladding is composed of flat and cylindrical insulating glass panes. A geometric study is carried out in order to define the cylindrical surface that better fits a spherical frame. Some panes are structural, providing stability to the slender profiles. To guarantee the tight geometric tolerances required the structure is divided into modules, which also facilitates the transport.</p> Arnau Bover Jordi Torres Carles-Hug Bitlloch Jordi Vilà Copyright (c) 2020 Arnau Bover, Jordi Torres, Carles-Hug Bitlloch, Jordi Vilà 2020-09-04 2020-09-04 7 GS&E journal > Artificial Intelligence for Structural Glass Engineering Applications - Overview, Case Studies and Future Potentials <p>'Big data' and the use of 'Artificial Intelligence' (AI) is currently advancing due to the increasing and even cheaper data collection and processing capabilities. Social and economical change is predicted by numerous company leaders, politicians and researchers. Machine and Deep Learning (ML/DL) are sub-types of AI, which are gaining high interest within the community of data scientists and engineers worldwide. Obviously, this global trend does not stop at structural glass engineering, so that, the first part of the present paper is concerned with introducing the basic theoretical frame of AI and its sub-classes of ML and DL while the specific needs and requirements for the application in a structural engineering context are highlighted. Then this paper explores potential applications of AI for different subjects within the design, verification and monitoring of façades and glass structures. Finally, the current status of research as well as successfully conducted industry projects by the authors are presented. The discussion of specific problems ranges from supervised ML in case of the material parameter identification of polymeric interlayers used in laminated glass or the prediction of cut-edge strength based on the process parameters of a glass cutting machine and prediction of fracture patterns of tempered glass to the application of computer vision DL methods to image classification of the Pummel test and the use of semantic segmentation for the detection of cracks at the cut edge of glass. In the summary and conclusion section, the main findings for the applicability and impact of AI for the presented structural glass research and industry problems are compiled. It<br>can be seen that in many cases AI, data, software and computing resources are already available today to successfully implement AI projects in the glass industry, which is demonstrated by the many current examples mentioned. Future research<br>directories however will need to concentrate on how to introduce further glass-specific theoretical and human expert knowledge in the AI training process on the one hand and on the other hand more pronunciation has to be laid on the thorough digitization of workflows associated with the structural glass problem at hand in order to foster the further use of AI within this domain in both research and industry.</p> Michael Anton Kraus Michael Drass Copyright (c) 2020 Michael Anton Kraus, Michael Drass 2020-09-04 2020-09-04 7 GS&E journal > Conceptual design and FEM structural response of a suspended glass sphere made of reinforced curved polygonal panels <p>The paper introduces a novel concept for structural glass shells that is based on the mechanical coupling of double curved heat-bent glass panels and a wire frame mesh, which constitutes a grid of unbonded edge-reinforcement. Additionally, this grid has the purpose of providing redundancy. The panels have load-bearing function, they are clamped at the vertices and dry-assembled. The main novelty lies in the use of polygonal curved panels with a nodal force transfer mechanism. This concept has been validated on an illustrative design case of a 6 m-diameter suspended glass sphere, in which regular pentagonal and hexagonal spherical panels are employed. The good strength and stiffness achieved for this structure is demonstrated by means of local and global FE models. Another fundamental feature of the concept is that the reinforcement grid provides residual strength in the extreme scenarios in which all panels are completely failed. A quantitative measure of redundancy is obtained by comparing this scenario with the ULS.</p> Maurizio Froli Francesco Laccone Copyright (c) 2020 Maurizio Froli, Francesco Laccone 2020-09-04 2020-09-04 7 GS&E journal > Large Deflection Glass Facade in Typhoon Area: Taikoo Place 2 Podium Wall <p>The case study presented is a 195 meters tall office tower with a raised podium made of full height glass panels, up to 15 meters high. The panels are only restrained by prestressed high-strength stainless-steel rods, lying entirely in the glass panel build-up, composed by four 12 mm thick plies, laminated with 1.52 mm thick sheets of ionoplast interlayer, with an overall thickness of approx. 52 mm. Due to the facade geometry and the high wind expected, movement joints between rods are introduced, allowing for differential movements to avoid peak stresses in the glass panels. Also, smooth transition between rod rectangular section at the interface with the glass panels to circular section at anchor points need to be ensured by CNC machining to avoid failure of the rod anchors due to fatigue. Sophisticated non-linear 3D FEM models had to be analyzed to predict glass stresses, differential movements to be accommodated by the joints and geometrical transition between rod sections. The main innovation of this facade was the use of prestressed rods in conjunction with jumbo size glass panels. As tension structures experience large movements, it was crucial to understand the effect of these deformations imposed by the rods onto the full height glass panels, analyzing steel and glass members together as a single facade entity. Furthermore, in contrast to typical cable wall facade where the prestressed elements (cables) are offset from the glass line, here the rods are located in the plane of the glass panels and completely flush with them, ensuring the thinnest possible build-up in relation to the large facade span. A rocking portal frame, moving together with the rods to avoid excessive warping in the glass panels, has been used as a solution to deal with the required opening in the facade. An additional complication was given by the high wind load (typhoon) applied on the facade which required rods&amp;rsquo; prestress in the order of 1000 Kilonewton in order to limit glass stresses and deflections.</p> Giovanni De Mari Copyright (c) 2020 Giovanni De Mari 2020-09-04 2020-09-04 7 GS&E journal > Repositioning Messeturm – Maximum Transparency <p>The Messeturm (“Trade Fair Tower”) in Frankfurt/Main is currently adjusted to the requirements of a modern office building. The lobby area has been enlarged by a highly transparent façade consisting of oversized insulating glass (IG) units. The IG units are curved and have a size of up to 17 m x 2.8 m. To obtain a perfectly curved façade, the IG units were fabricated with laminated cold-bended glass panes. Horizontally the IG units are supported by tapered stainless steel fins. Inclined steel beams connect the top of the façade fins with the tower structure creating a rounded roof. The vertical façade with its glass roof allows maximum transparency for people inside the lobby as well as for people passing by outside to the nearby trade fair grounds. The glass was fabricated by sedak. The façade was installed by seele on behalf of the owner OFFICEFIRST, the asset-management of Blackstone.</p> Steffen Feirabend Florian Straz Roland Bechmann Stefan Kloker Peter Eckardt Copyright (c) 2020 Steffen Feirabend, Florian Straz, Roland Bechmann, Stefan Kloker, Peter Eckardt 2020-09-04 2020-09-04 7 GS&E journal > Stone-Glass Curtain Wall – Designing an Outstanding Facade in NYC <p>The new World Trade Center complex in New York City rose up into the heights during the last decade. Nine new buildings including 1776 ft tall One WTC and Calatrava’s sculptural Oculus Station cover the 60,000 m 2 area in the world’s most outstanding construction site. One spot is still under construction and will host “The Ronald O. Perelman Performing Arts Center” – a new kind of multidisciplinary venue with an astonishing smooth facade made from exceptional stone-glass. The cube-shaped building is 49 m x 49 m wide and 42 m tall. A steel roof cantilevers from the inner core and holds hot-rolled steel mullions to carry the curtail wall. The total span is 36 m with one intermediate support only. This encloses a large area interior room for public events, arts and theatre performances. As a special feature, the whole building is covered with stone, in particular 4800 stoneglass insulating glass units grouped in aluminum cassettes carrying four glass panes each. The intention is to present a white four-sided landmark structure with distinguished black veining during the day and a glowing amber-like appearance at night when the interior of the building is illuminated.<br>Stone-glass units have never been used in this scale. Standard PVB interlayers were not an option for the product as it cannot be laminated properly. Therefore, Josef Gartner accepted the challenge to design and build using alternative materials. The paper presents the project and its facade design. Numerous additional experimental assessments were conducted – from small scale quasi-static air pressure tests of the glass to full scale performance mock-up tests. Finally, a design process was developed that covers all critical demands of an incomparable project.</p> Michael Engelmann Andreas Kübler Franz Hirsch Copyright (c) 2020 Michael Engelmann, Andreas Kübler, Franz Hirsch 2020-09-04 2020-09-04 7 Experimental Analysis of Laminated Embedded Steel Insert in Load Bearing Connections <p>Use of glass as a load bearing structural elements has increased significantly in last years. The glass is brittle material, which behaves elastically until brittle failure which occurs suddenly without any warning. Therefore, special emphasis shell be devoted to the connections with load bearing role. Their inappropriate design can lead to local peaks of stress or eccentricity of the connections and the generation of additional moments, resulting in a reduction of the load-bearing capacity. Currently, mechanical (clamped, friction-grip and bolted connections) or adhesive joints are commonly used, the latter being characterized by a more uniformly distributed stress along the connection and the undisturbed surface of the glass panels. The disadvantage of polymeric adhesives is however the sensitivity of the load-bearing capacity to the ageing, technology of the production - the proper cleaning of the surfaces as well as the application of adhesive, UV stability during the lifetime etc. Although, there is still a lack of information about all aspects of the adhesive behaviour in the load bearing joint, their use in structural applications is considered very promising. In the last years, a novel typology of enhanced adhesive connections, known as laminated adhesive connection, has been developed. These connections are formed during the lamination process of the laminated glass fabrication and they are characterized by transparency and high aesthetic appearance especially when the size of the laminated metal insert is limited. Paper is focused on the experimental investigation of novel embedded laminated connection with thick steel plate and built-in internal thread pre-prepared for common bolts, used to assembly glass element to another one, or directly to the steel or concrete substructure. Mechanical behaviour of this connection is main goal of the research. Small scale test specimens were tested to obtain mechanical behaviour of the connection. Embedded stainless steel plate in laminated glass is in vertical position and enables connection between the glass cantilever beam and supporting structure. The specimens were loaded until maximum strength of connection was reached.</p> Josef Bajtek Copyright (c) 2020 Josef Bajtek 2020-09-04 2020-09-04 7 10.7480/cgc.7.4476 Experimental and numerical investigation into the mechanical behavior of embedded laminated connections <p>Embedded laminated connection (ELC) is a novel type of connection in structural glass and its application increases the transparency and surface flatness of structural glass elements. In this study, laboratory tests have been conducted to investigate the mechanical behavior of embedded laminated connections. Two groups of ELC, i.e. ELC laminated with triple annealed glass layers (TA-ELC), ELC laminated with double outmost tempered glass layers and one mid annealed glass layer (DT-ELC). The data of the pull-out force and displacement of the ELC under the pull-out load was collected and analyzed. The experimental results reveal that the TA-ELC group exhibits brittle failure, whereas DT-ELC group significantly improves the maximum loading capacity. Compared to TA-ELC group, the outmost tempered glass layers in DT-ELC group can render greater ductility. The study also indicates that the crack initiation as well as the final failure of the TA-ELC are both induced in the outmost glass layers. The crack initiation of the DT-ELC is firstly observed in the mid glass layer and the final cracking at failure is generated in the outmost glass layers. A numerical study was also performed to simulate the entire failure process. It is then found that materials in TA-ELC group keeps behaving in an elastic manner before the crack initiation. In DT-ELC, the stable stage of the pull-out force is caused by the yielding of SG layers.</p> Chenjun Zhao Jian Yang Xing-er Wang Iftikhar Azim Copyright (c) 2020 Chenjun Zhao, Jian Yang, Xing-er Wang, Iftikhar Azim 2020-09-04 2020-09-04 7 10.7480/cgc.7.4551 Influence of adhesive layer thickness and temperature on mechanical properties of two-part acrylate adhesive <p>In recent years, architects, as well as customers, have been increasingly interested in glass structures. Glass is used except facades also for canopies above building entrances, bannisters, staircases or load-bearing structural elements such as beams or columns. Glass is a brittle material with elastic behaviour until brittle failure so particular attention should be paid to details and connections of glass with glass or glass with other material. This article is focused on double-lap shear glass-metal joint using a two-component acrylic adhesive. In addition to glass, two different materials were included in the experimental programme, Zn-electroplated steel and aluminium. Totally four sets of specimens were tested. Three sets of specimens are differing in adhesive thickness layer. The last set of specimens was tested at elevated temperature.</p> Markéta Zikmundová Martina Eliášová Zdeněk Sokol Copyright (c) 2020 Markéta Zikmundová, Martina Eliášová, Zdeněk Sokol 2020-09-04 2020-09-04 7 10.7480/cgc.7.4478 Structural Silicone Glazing - Design & Modelling <p class="CGCAbstract"><span lang="EN-US">The use of Structural silicone glazing (SSG) systems in large commercial glazed facades is well established in current practice, mainly due to the architectural aspiration of&nbsp;having a continuous smooth glass surface across the building elevation.&nbsp;Enhanced thermal and security (blast) performance are typically listed as an advantage for this particular type of systems. SSG façade systems are structurally complex due to the fact that multiple load-paths can be identified within the system. It is accepted as good practice to detail façade panels so that the dead load of the glass is not carried through the structural silicone. But can this be achieved in reality? The aim of this paper is to identify and discuss challenges with the assumption that the SSG is isolated from the glass self weight and provide a better understanding on the complexity of SSG systems. The influence of stress/strain and creep due to the&nbsp;long-term load on the system capacity will be investigated. Some degree of long term loads are usually&nbsp;present due to detailing and real system behaviour. Real project examples will be used to identify opportunities for improvement and findings will be summarised at the end of the paper.</span></p> Jordi Alcaine Peter Lenk Ed Forwood Copyright (c) 2020 Jordi Alcaine, Peter Lenk, Ed Forwood 2020-09-04 2020-09-04 7 10.7480/cgc.7.4548 Tests of the embedded laminated glass connection under short-term tensile and eccentric shear loads <p>The embedded laminated glass connection belongs to the group of the most widely used ways of the glass components connecting. As it becomes common to use glass as a material for load-bearing elements, the connection must be able to bear stresses arising during the lifetime period. To find out the load capacity of the connection under different loads, experiments have to be performed. Within the ongoing research at the Faculty of Civil Engineering of Czech Technical University in Prague, two series of experiments of the embedded laminated glass connection have been performed. There were two sets of identical samples. Both sets included several combinations of glass panes and types of foils. The first series of tests was focused on the characteristics of this type of connection under the short-term tensile loads. The second one was dealing with the characteristics under the short-term eccentric shear loads. <br> Due to using the identical samples for both series of tests, it was possible to compare the obtained results. The experiments show that the tensile load capacity of the connection is much higher than its eccentric shear load capacity. It also reveals reaching the tensile resistance limit of the weakened glass pane as a dominant mode of failure. However, further research consisting of numerical modelling and additional experiments is in progress.</p> Michaela Zdražilová Zdeněk Sokol Martina Eliášová Copyright (c) 2020 Michaela Zdražilová, Zdeněk Sokol, Martina Eliášová 2020-09-04 2020-09-04 7 10.7480/cgc.7.4471 The Production and Performance of Heat Bonded Glass Connections <p class="CGCAbstract"><span lang="EN-US">Connecting glass with heat bonds is a way to create all-transparent glass structures. Two methods have been researched in theory and practice, glass welding, through local heating, and glass fusion through global heating. Both methods have been applied to produce 10 mm thick T-sections of soda lime glass while preventing thermal shock failure and minimizing residual stress. These specimen, and specimen with an adhesive joint, have been tested destructively. It is concluded that it is possible to connect 10 mm thick soda lime glass by welding, if the glass is preheated and the surrounding temperature remains elevated during the welding process. Additionally, glass fusion of a similar product through global heating is possible for the applied temperature schedule. The mould has a paramount influence on the quality of the product. For both production methods, the annealing schedule was adequate to reduce residual stress. The average strength of the fused specimen was 44% larger. The standard deviation of the welded specimen was smaller: the standard deviation relative to the mean value was 9% for the welded specimen and 60% for the fused specimen. However, the amount of tested specimen is little. This research is a proof of concept for heat bonding soda lime glass of a structurally relevant thickness. </span></p> Anna Eskes Diana de Krom Telesilla Bristogianni Fred Veer Lisa Rammig Rob Nijsse Copyright (c) 2020 Anna Eskes, Diana de Krom, Telesilla Bristogianni, Fred Veer, Lisa Rammig, Rob Nijsse 2020-09-04 2020-09-04 7 10.7480/cgc.7.4458 GS&E journal > Dimensioning of silicone adhesive joints: Eurocode-compliant, mesh-independent approach using the FEM <p>This paper deals with the application of the semi-probabilistic design concept (level I, DIN EN 1990) to structural silicone adhesives in order to calibrate partial material safety factors for a stretch-based limit state equation. Based on the current legal situation for the application of structural sealants in façades, a new Eurocode-compliant design concept is introduced and compared to existing design codes (ETAG&nbsp;002). This is followed by some background information on semi-probabilistic reliability modeling and the general framework of the Eurocode for the derivation of partial material safety factors at Level I. Within this paper, a specific partial material safety factor is derived for DOWSIL&nbsp;993 silicone on the basis of experimental data. The data were then further evaluated under a stretch-based limit state function to obtain a partial material safety factor for that specific limit state function. This safety factor is then extended to the application in finite element calculation programs in such a way that it is possible for the first time to perform mesh-independent static calculations of silicone adhesive joints. This procedure thus allows for great optimization of structural sealant design with potentially high economical as well as sustainability benefits. An example for the static verification of a bonded façade construction by means of finite element calculation shows (i) the application of EC&nbsp;0 to silicone adhesives and (ii) the transfer of the EC&nbsp;0 method to the finite element method with the result that mesh-independent ultimate loads can be determined.</p> Michael Drass Michael Kraus Copyright (c) 2020 Michael Drass, Michael Kraus 2020-09-04 2020-09-04 7 Automated design and analysis of reinforced and post-tensioned glass shells <p class="CGCAbstract">Shells made of structural glass are beautiful objects from both the aesthetics and the engineering point of view. However, they pose two significant challenges. The first one is to assure adequate safety and redundancy concerning possible global collapse. Being single-layered, in a shell made of structural glass, the brittle cracking of a single pane can lead to a sudden propagation of failure, up to instability. The second one is to guarantee cheap replacing possibilities for potentially collapsed components. This research explores a novel concept to address both requirements, where glass is both post-tensioned and reinforced and develops the research on TVT post-tensioned glass beams. Following the Fail-Safe Design (FSD) principles, a steel reinforcement relieves glass deficiencies (i.e. brittleness and low tensile strength). Following the Damage Avoidance Design (DAD) principles, glass segmentation and post-tensioning avoid the propagation of cracks. Up to now, glass-steel systems were limited to mono-dimensional elements (such as beams and columns) or simple bi-dimensional elements (arches, domes, barrel vaults). Instead, massive structures are usually realized as grid shells, where glass is used as simple cladding. This research investigates piecewise triangulated glass shells to enable the creation of 3D free-form glass-steel systems, where glass is load-bearing material. Hence, laminated glass panels are mechanically coupled with a filigree steel truss, whose elements are placed at the edges of the panel and act as an unbonded reinforcement. In a performance-based perspective, these steel trusses can be sized to bear at least the weight of all panels in the occurrence of simultaneous cracks (worst-case scenario). The panels are post-tensioned using a set of edge-aligned cables that add beneficial compressive stress on glass to prevent crack initiation. The cable placement and accompanying pre-loads are derived with an optimization strategy that minimizes the tensile stress acting on the shell. This optimization procedure also considers the practical constraints involved in the process. The results obtained through this automated procedure are later investigated using nonlinear FE analyses. The resulting structures optimize the total material usage providing contemporarily both transparency and load-bearing capabilities. Post-tensioned shells excel in static performances, achieving high stiffness and good redundancy for the worst-case scenario, and improve the structural lightness and the visual impact with respect to state-of-the-art competitors.</p> Francesco Laccone Luigi Malomo Nico Pietroni Maurizio Froli Paolo Cignoni Copyright (c) 2020 Francesco Laccone, Luigi Malomo, Nico Pietroni, Maurizio Froli, Paolo Cignoni 2020-09-04 2020-09-04 7 10.7480/cgc.7.4496 The Numerical analysis and experimental verification on the thermal performance of hybrid Cross-Laminated Timber (CLT)-glass facade elements <p class="CGCAbstract"><span lang="EN-US">Structural solutions involving the mechanical interaction of timber and glass load-bearing members showed a progressive increase in the last decade. Among others, a multipurpose hybrid facade element composed of Cross-Laminated Timber (CLT) members and glass panels interacting by frictional contact mechanisms only was proposed ion the framework of the VETROLIGNUM project. While demonstrating enhanced load-bearing and deformation capacity performances under seismic loads, facade elements are known to represent a building component with multiple performance parameters to satisfy. These include energy efficiency, durability, lightening comfort and optimal thermal performance. In this paper, a special focus is dedicated to the thermal performance assessment of CLT-glass facade modules under ordinary operational conditions. Based on the thermal-chamber analysis of small-scale prototypes, reliable Finite Element numerical models are developed and applied to full-scale VETROLIGNUM solution. Sensitivity analyses are hence carried out to explore the actual thermal performance of these novel hybrid systems. </span></p> Vlatka Rajčić Chiara Bedon Jure Barbalic Nikola Perkovic Copyright (c) 2020 Vlatka Rajčić, Chiara Bedon, Jure Barbalic, Nikola Perkovic 2020-09-04 2020-09-04 7 10.7480/cgc.7.4459 Ultra Thin Composite Panel – An Exploratory Study on the Durability and Stiffness of a Composite Panel of Thin Glass and 3D printed Recycled PET <p>This paper investigates the stiffness and the durability of a composite panel that consists of thin glass as outer layers and a 3D printed core element from recycled PET. Thin alumino-silicate glass, mostly used for displays in computers, tablets and smartphones, is known for its flexibility, durability and high bending strength. However, for building applications, the high flexibility of thin glass may cause serviceability issues. Therefore, to stiffen thin glass, a composite concept of thin glass with a 3D printed core is developed. &nbsp;The core element of this panel consists of 3D printed recycled PET. The use of recycled PET has been taken into account, due to the increase of plastic waste for the next 30 years. A combination of both materials allows for a much stiffer composite panel and reduction in weight of 71,9 % compared to a normal double glazed window panel. This paper presents an overview of the durability of the composite panel. The durability aspects for this exploratory study are UV radiation, elevated temperature and fire. The UV radiation tests showed that the applied acrylic adhesive &nbsp;ensures for a good adhesion, which allows reaching high load bearing capacity. Also, these tests showed that recycled PET changes into a yellowish color and becomes more brittle. The temperature tests showed that at an elevated temperature of 80 ⁰C, recycled PET loses its stiffness and strength and cannot sufficiently take up forces when loaded. The fire experiments showed that the recycled PET core melted fully during the fire exposition.</p> Charbel Miled Nohra Saleh Christian Louter Michela Turrin Copyright (c) 2020 Charbel Miled Nohra Saleh, Christian Louter, Michela Turrin 2020-09-04 2020-09-04 7 10.7480/cgc.7.5051 GS&E journal > A Novel Concept for a Reinforced Glass Beam Carrying Long Term Loads <p>This paper presents a novel concept for improving the long-term load-bearing&nbsp; performance of reinforced glass beams (hybrid beams). The concept of reinforcing glass beams using steel or other (ductile) materials have been investigated over the last couple of decades utilising the fracture pattern of annealed glass to ensure a ductile behaviour. However, it is well known that the long-term strength of annealed glass is rather low due to so-called static fatigue leading to a relatively poor<br>performance for most hybrid-beams. As an example will a hybrid beam based on annealed glass exposed to 26 MPa permanent load fail in less than a day according to a European code. The novel concept suggested here utilises a combination of<br>annealed and fully tempered glass in an arrangement where the tempered glass carries the long-term loading whereas short-term loading is carried by the reinforced annealed glass. The concept is based on the relaxation of shear stresses in the PVB (polyvinyl butyral) interlayer, material properties of PVB from different authors have been compared, and a set of average parameters have been suggested. The main purpose of the paper is to introduce the concepts and mechanisms of such beams and provide a basis for further optimisation.</p> Jens H. Nielsen Bjarni G. Jónsson Chiara Bedon Copyright (c) 2020 Jens H. Nielsen, Bjarni G. Jónsson, Chiara Bedon 2020-09-04 2020-09-04 7 Editorial <p>The 7<sup>th</sup> edition of <em>Challenging </em><em>Glass</em> is unlike any of the previous events in the 12-year history of the conference. Due to the ongoing corona pandemic, the on-location event has been replaced by an online webinar, featuring a keynote by Chikara Inamura and a small selection of short paper presentations. &nbsp;&nbsp;</p> <p>We are proud to, nevertheless, be able to present to you these <em>Challenging Glass Conference 7 Proceedings</em>, which &nbsp;are published <em>Open Access</em> in collaboration with TU Delft Open. The proceedings contain more than 50 papers, by glass experts from around the world, while another 20 papers are published in collaboration with the Springer journal <em>Glass Structures &amp; Engineering</em>. We appreciate the efforts by all authors in these extraordinary times immensely.</p> <p>Organising this webinar and editing the conference proceedings has once again been an enjoyable experience, albeit different from previous ones. We would like to acknowledge all authors for their contributions, all scientific committee members for their valuable reviews, our esteemed keynote speaker for his inspiring presentation and of course all webinar participants for their interest in this event.</p> <p>We are grateful to our Platinum Sponsors Saint-Gobain and Eastman, as well as our Gold and Silver Sponsors for making this event possible. In addition, we would like to thank our hosting institution, Ghent University, particularly Shahryar Nategh for his support in compiling the conference proceedings.</p> <p>We wish you an enjoyable webinar and we trust you will encounter inspiring publications in these proceedings.</p> <p>&nbsp;</p> <p>Jan Belis, Freek Bos &amp; Christian Louter</p> <p><em>Conference Organisers</em></p> <p>September 2020</p> Jan Belis Freek Bos Christian Louter Copyright (c) 2020 Jan Belis, Freek Bos, Christian Louter 2020-09-04 2020-09-04 7 10.7480/cgc.7.5126 Sponsors <p>The Challenging Glass 7 proceedings and webinar are sponsored by:</p> <p>Platinum Sponsors:</p> <ul> <li><a href="" target="_blank">Saint-Gobain</a></li> <li><a href="" target="_blank">Eastman</a></li> </ul> <p>Gold Sponsors:</p> <ul> <li><a href="" target="_blank">Bellapart</a></li> <li><a href="" target="_blank">Dow</a></li> <li><a href="" target="_blank">SEEN</a></li> <li><a href="">Trosifol</a></li> </ul> <p>Silver Sponsors:</p> <ul> <li><a href="" target="_blank">Ayrox</a></li> <li><a href="" target="_blank">Octatube</a></li> <li><a href="" target="_blank">Permasteelisa</a></li> <li><a href="" target="_blank">Vitroplena</a></li> </ul> <p>&nbsp;</p> Challenging Glass Copyright (c) 2020 Challenging Glass 2020-09-04 2020-09-04 7 10.7480/cgc.7.5211 Conceptual Design of Timber-Wood Concrete-Glass façades <p>Within several research projects and with the aim to optimize structural performance, energy efficiency and ecological characteristics of structural building components the Department of Structural Design and Timber Engineering (ITI) at the Vienna University of Technology (TU Wien) developed several wood-based composite systems combining timber and wood concrete as well as structural glass components. Certain advantages in the application of these individual composite systems could be shown within the described former research activities. Due to a suitable combination of the named materials, a structural optimized construction with increased resource efficiency on component level as well as on the overall construction level can be achieved. For the assessment of this opportunity, different types of timber-wood concrete-glass façades with a special focus on varying glass components are developed and compared to conventional wall structures. The comparison is carried out regarding to the materialization on component level, as well as to the overall construction level, whereby a scale-independent assessment of the examined constructions types can be reached. This assessment shall be enabled by a broad spectrum of computations ranging from static and dynamic thermal simulations for annual heating and overheating periods up to various thereof resulting ecological impact calculations.</p> Alireza Fadai Daniel Stephan Copyright (c) 2020 Alireza Fadai, Daniel Stephan 2020-09-04 2020-09-04 7 10.7480/cgc.7.4481 Recycled glass mixtures as cast glass components for structural applications, towards sustainability <p>The problem of sustainability represents one of the most important issues that the world has to face nowadays, not only in terms of energy consumption and of the consequent CO<sub>2</sub> emissions, but also in terms of material waste streams that end in landfill. 38 million tons of glass waste are produced every year in the European Union and new targets have been set for 2020 towards a more sustainable management of such wastes. Nowadays, only the container glass industry has reached a considerable recycling rate, while for all the other sectors we are still witnessing downgrading processes. Looking at the world of construction, glass has been more and more employed as a structural material thanks to its high transparency and compression strength. Although the use of glass can be attractive under multiple aspects and its production is continuously increasing, once employed as a construction element, it is rarely reused or recycled due to the high-quality requirement demanded to the industry of production. Nevertheless, besides its main applications as a 2-dimensional element, the new technology of cast glass has been recognised as a potential mean of glass recycling. Here, glass is designed and used under the form of repetitive 3-dimensional units assembled in a whole geometrical shape. In fact, thanks to its higher load-bearing capacity under monolithic shapes, this glass can admit less restrictions and potentially incorporate different types of waste. For this reason, the aim of this experimental work is to find a possible combination between glass families, specifically soda-lime, borosilicate and lead-crystal glass, to be recycled as cast glass components. Each type of glass was powdered or grinded under the form of cullet and different mixtures were prepared to be melted at temperatures of 970°C, 1120°C and 1200°C through the kiln-cast tecnique. Finally, an experimental splitting test was performed to define a force trend and a fracture behaviour for each sample. Some preliminary results have been achieved drawing the guidelines for a further investigation. Soda-lime-silica glass and lead-crystal glass mixture revealed to be the most compliant glass recipe with the required physical and mechanical properties, when reheated at 1120°C. The decrease in the melting temperature of the compound and the higher transparency given by the addition of lead glass revealed the potential benefit, in terms of sustainability, for future projects.</p> Giulia Maria Anagni Telesilla Bristogianni Enrico Sergio Mazzucchelli Copyright (c) 2020 Giulia Maria Anagni, Telesilla Bristogianni, Enrico Sergio Mazzucchelli 2020-09-04 2020-09-04 7 10.7480/cgc.7.4482