Challenging Glass Conference Proceedings

Robotic Reconfigurable Sand Molding for Doubly Curved Float Glass

Rena Giesecke, Benjamin Dillenburger — Fri, 27 Jan 2023 00:00:00 +0100

The presented research investigates loose sand forming as a reconfigurable molding strategy for custom glass parts. Doubly curved glass parts usually require the labor-intense fabrication of individual ceramic or steel molds. Reconfigurable molds for glass are limited to specific modular geometries and require costly heat-resistant actuation mechanisms. Three-dimensionally (3D) printed sand molds for glass slumping require binders and cannot be reused. The objective of this research is to facilitate a waste-free fabrication of doubly curved glass elements and a facile, fast, low-cost mold-making process for the hot bending of glass. The molding system employs granular loose sand material, which is heat resistant and can be quickly reformed. In combination with novel digital tools and robotic fabrication, the technique provides a flexible molding system for the transformation of industry-ready float glass. This research presents the first results, including possible granular material systems for loose granular molding, robotic setup and placement strategies for granular materials, and volumetric material formation considering robotic process parameters. Furthermore, it investigates mold stability during slumping and the geometric precision of mold and resulting glass elements. The resulting glass elements are fully transparent with no contamination caused. The presented approach allows for smooth curvatures, easy mold removal, and complete mold recycling without further processing. The method was applied in several mid-scale experiments, including investigations into which family of forms can be produced. The geometric freedom and limitations of the proposed fabrication method are discussed. Reconfigurable sand molding for glass could enable the geometric customization of glass elements and allow for novel optical, structural, or decorative properties in glass facades and windows.

Topologically Optimized Cast Glass: A New Design Approach for Loadbearing Monolithic Glass Components of Reduced Annealing Time

Wilfried Damen, Faidra Oikonomopoulou, Telesilla Bristogianni, Michela Turrin — Mon, 06 Jun 2022 00:00:00 +0200

Up to now, fabricating cast glass components of substantial mass and/or thickness involves a lengthy and perplex annealing process. This has limited the use of this glass manufacturing method in the built environment to simple objects up to the size of regular building bricks, which can be annealed within a few hours. For the first time, structural topological optimization (TO) is investigated as an approach to design monolithic loadbearing cast-glass elements of substantial mass and dimensions, with significantly reduced annealing times. The research is two-fold. First, a numerical exploration is performed. The potential of reducing mass while maintaining satisfactory stiffness of a structural component is done through a case-study, in which a cast-glass grid shell node is designed and optimised. To achieve this, several design criteria in respect to glass as a material, casting as the manufacturing process and TO as a design method, are formulated and applied in the optimisation. It is concluded that a TO approach fully suited for three-dimensional glass design is as of yet not available. For this research, strain- or compliance based TO is selected for the optimization of the three-dimensional, cast glass grid shell node; in our case, we consider that a strain based TO allows for a better exploration of the thickness reduction, which, in turn, has a major influence on the annealing time of cast glass. In comparison, in a stress-based optimization, the considerably lower tensile strength of glass would become the main restrain, leaving underutilized the higher compressive strength. Furthermore, it is determined that a single, unchanging and dominant load-case is most suited for TO optimisation. Using ANSYS Workbench, mass reductions of up to 69% compared to an initial, unoptimized geometry are achieved, reducing annealing times by an estimated 90%. Following this, the feasibility of manufacturing the resulting complex-shaped glass components is investigated though physical prototypes. Two manufacturing techniques are explored: lost-wax casting using 3D-printed wax geometries, and kiln-casting using 3D-printed disposable sand moulds. Several glass prototypes were successfully cast and annealed. From this, several conclusions are drawn regarding the applicability and limitations of TO for cast glass components and the potential of alternative manufacturing methods for making such complex-shaped glass components.

Three-dimensionally (3D) Printed Sand Molds for Custom Glass Parts

Rena Giesecke, Benjamin Dillenburger — Thu, 30 Jun 2022 00:00:00 +0200

The presented research investigates a digital fabrication method for custom glass building elements based on three-dimensionally (3D) printed molds. Custom glass parts with specific geometries usually require several steps of manufacturing, highly specialized craft, or machinery. Computer Numerical Control (CNC) milled steel molds are only suitable for large lot sizes due to their high cost and limited geometric freedom. Lost-wax casting requires several steps of manufacturing and post-processing. This paper investigates an accessible, low-cost process for shaping glass artifacts using 3D printed molds to close the gap between mass-produced and custom-crafted glass elements. Previous research has demonstrated the potential of using binder jetting with inorganic binders for glass casting. This paper investigates a range of traditional manufacturing methods besides glass casting that can be combined with 3D printed molds, including foundry and kiln casting, blow molding, and slumping. The aim is to extend the manufacturing possibilities and provide a range of approaches for three-dimensional glass. The goal is to simplify the process from design to production of three-dimensional solid, hollow, or doubly curved sheet glass elements with high precision. This paper presents investigations of binder jetting techniques and material considerations, their heat resistance, compatibility with different glass-making processes, and coatings for mold treatment. Furthermore, the precision of the resulting glass parts is evaluated, and design guidelines for glass typologies are defined. Glass bricks or sheets for facades with geometric features enabled by the presented fabrication method could allow for novel optical, structural, or decorative properties in building elements.

The Chronology of Historical Glass Constructions

Mon, 20 Jun 2022 00:00:00 +0200

Glass surfaces are characteristic elements of façades and make a significant contribution to the authenticity of architectural monuments. Glass as a material is considered an important testimony of its time. Depending on the manufacturing process, it differs both in surface and material composition. The period of high modernism (ca. 1880-1970) overlapped with the technical developments of the industrial revolution, which led from manual production to industrial production. The further development of manufacturing processes as well as the dimensions and qualities of the glass thus shaped the development of glass constructions, which had to be made increasingly slimmer over time in order to guarantee a high degree of transparency. Today, historical windows are often replaced by new glazing made of float glass, which can cause the authentic character of buildings to be lost. A team working on the research project at the Technical University of Dresden and the University of Bamberg has therefore set itself the goal of examining in detail the glass and its construction in the period from around 1880 to around 1970. The aim is to define the living character of industrially manufactured glass from the time before the introduction of float glass as an authentic and style-defining feature of the period. The present work focuses on the chronological presentation of the development of glass designs. Furthermore, the development and use of refined flat glass is analysed and presented. This includes wired glass, laminated glass, thermally toughened glass, insulating glass and curved glass. The significance of historical glass constructions for engineers and planners can be derived from the results and the evaluation.

Glass Façade and Structure Movements

Raul Corrales — Mon, 20 Jun 2022 00:00:00 +0200

For designing and constructing a glazing façade the analysis of the foreseeing structural movements must be considered from the first steps of the project. This basic assessment could become quite complicate for those projects where large displacement are expected or just for projects where the design intent would not allow to use standard solutions. Frequently, when working with large glass units, the movement issue must be analysed in detail. The purpose of the presentation would be introducing different approaches to be considered when developing a glass façade concept. Which are the most important live loads, how it would be possible to set out the façade elements for anticipating structural movements, how to create sliding supports or how to introduce customed expansion joints in grazed façades. Real projects would be presented as example of different possible situations, the aim is introducing the basic concept but focusing in real cases studies, this would be interesting to fix the ideas. At the same time those examples show that dealing with this issue could also be quite complicate with a standard project or with quite small glazing units.

Microscale Discrete Element Model for Simulating Bridging Behavior of Fractured Glass Laminates

Xing-er Wang, Jian Yang, Shennan Peng, Yige Wang, Xiaonan Hou — Thu, 30 Jun 2022 00:00:00 +0200

The bridging behavior between fragments is one vital factor in the post-fracture stage of glass laminates. A particle-based discrete element model was developed in this work to simulate the bridging behavior of fractured glass laminates. The model was based on the calibration of hyperelastic PVB material properties using soft-bond model and further validated with the experimental data as well as the observations from through-crack-tensile tests. In order to investigate the bridging performance of fractured glass laminates with multiple fragments under uniaxial tension, three factors encompassing the crack aligning, fragment number and adhesion conditions were considered to perform a parametric study. The results give an exploratory application of the developed discrete element models in the estimation of the post-fracture behaviors. It is found that the smaller fragment size can diminish the tension-stiffening effect in the non-aligned case which might generate an enhancing ratio of initial modulus up to nearly 3.6. The non-aligned cracks can also lead to a very high strength if the adhesion ability can be guaranteed. However, the delamination of fragments is expected to control the post-fracture strength of fractured glass laminates with PVB interlayer.

Evaluation Methods for Surface Compression Stress Measurements with Unknown Principle Stress Directions

Kerstin Thiele, Steffen Müller-Braun, Jens Schneider — Mon, 01 Aug 2022 00:00:00 +0200

The birefringent properties of glass can be well utilized for non-destructive testing of thermally tempered glass. The surface compression stress as well as the compression zone depth of thermally tempered glass is commonly measured with a scattered light polariscope. The measurement with scattered light polariscope provides information about stresses acting perpendicular to the measurement direction. Therefore, the measurement depends on the direction. In order to make a statement about the rough level of the prestress, a measurement in one direction can be sufficient, assuming an isotropic stress state and a relatively homogeneous distribution of the surface compression stress. However, in order to be able to make a more detailed statement about a non-isotropic stress state, measurements in up to four directions are necessary. Information about the direction of principal stresses and differences of principal stresses can then be evaluated. In the present work, it is investigated which deviations can be expected by measurements performed in only one direction or by measurements using up to four directions. For this purpose, five methods are introduced, which deviate in the assumptions made for the current stress state. The methods are compared using measurements on thermally tempered glass in a four-point bending test and on thermally tempered glass specimens without any external load.

Numerical Study on Post-Fracture Behavior of a Two-Sided Reinforced Laminated Glass Beam-Column Connection Prototype

Mirko Pejatovic, Robby Caspeele, Jan Belis — Thu, 04 Aug 2022 00:00:00 +0200

The well-known concept of stainless steel reinforced laminated glass enables to achieve post-fracture capacity and ductility in transparent members. It has been experimentally demonstrated before that this hybrid concept satisfies safety criteria for statically determinate structural elements, as well as statically indeterminate beam systems. However, research on two-dimensional structural frame systems still lacks in literature. Exploiting the post-fracture behavior of such systems requires joints complying with the resistance of its connecting members. This paper presents a numerical and analytical study aiming at investigating the mechanical behavior of a two-sided reinforced laminated glass beam-column joint in the post-fracture domain and at failure. Comparative numerical studies are performed by means of Non-Linear Finite Element Analysis (NLFEA) in which glass is modelled by applying (a) the Reducing Element Approach (REA) and (b) the Brittle Cracking Model (BCM), respectively. Moment-rotation curves and crack patterns at failure are presented outlining main particularities associated with both models. The results suggest that the joint prototype has a significant post-fracture capacity due to the presence of continuous reinforcement that prevents failure upon fractures in glass. The glass-glass and glass-steel bond conditions were found to have significant influence on the rotational characteristics and the ultimate load. From the point of view of application in practice, the sufficiently refined REA model provides a good estimation of the rotational behavior of such a joint. An analytical model for prediction of the failure load was derived based on equilibrium conditions and specified material strength parameters. It distinguishes between two failure modes: brittle failure of the core and plastic failure of the critical adjoining sections. The analytical interpretation of the numerical results suggest that only a fraction (30-40%) of the total glass thickness in the core contributes to the resistance in the brittle failure mode.

Case Studies on the Thermally Induced Stresses in Insulating Glass Units via Numerical Calculation

Gregor Schwind, Franz Paschke, Jens Schneider — Mon, 25 Jul 2022 00:00:00 +0200

In the structural design of facade glazing, various types of loads such as dead weight, wind and climatic loads (pressure differences) must be taken into account. In practice, however, there are many cases of damage that can be attributed to direct solar radiation. In these cases, a so-called thermally induced fracture takes place, which can occur as a result of large in-plane temperature differences within the glass. Due to the increasing complexity of glazing constructions, this load type should be taken into account in future glass design. For this reason, thermal-mechanical investigations, were conducted. Commercially used double and triple insulating glass units were considered as vertical glazing and the solar direct absorptance per glass pane was varied. For numerical calculations, measured temperature data from the German Weather Service and free available Clear Sky model data were used as meteorological input. The results show that solar irradiance, along with temperature, is the driving influence on the thermally induced stress in insulating glass units. The investigations indicate that the inner pane becomes relevant on colder days and the outer pane on warmer days. Results also show, that the level of the outside temperature plays a negligible role for the thermally induced stresses of the middle pane.

Pilot Experiments for Multi-Criteria Human Comfort-Driven Structural Glass Design Assessment

Chiara Bedon — Mon, 20 Jun 2022 00:00:00 +0200

Civil engineering design and industry are continuously evolving with the support of advancements in technology. Digital tools are able to assist designers in solving several issues with more accuracy and minimized efforts. In parallel, maximization of human comfort is a target for various design procedures, where mathematical models and standardized protocols are conventionally used to optimize well-being of customers. Major challenges and troubles can indeed derive, structurally speaking, from human reactions, which are related to a multitude of aspects, and may further enforced by slender / transparent glass components. The so-called “emotional architecture” and its nervous feelings are intrinsic part of the issue, and hence the mutual interaction of objective and subjective parameters can make complex the building design optimization. This paper presents some recent studies in which human comfort for glass structures occupants is quantitatively measured, both with the support of remote digital technologies based on facial micro-expression analysis and in-field experiments able to capture kinematic and biometric parameters for customers moving in glass environments.

Numerical Study on Failure of Laminated Glass Subjected to Low-Velocity Impact

Petr Hála, Alena Zemanová, Jan Zeman, Michal Šejnoha — Mon, 20 Jun 2022 00:00:00 +0200

Laminated glass has been introduced to improve the mechanical performance, in particular impact resistance, of float glass while maintaining its transparency. However, its rate-dependent behaviour has not been sufficiently understood and various methods have been used to model it. This study compares the response of three material models commonly used to model glass cracking implemented in industry-standard LS-DYNA software: a smeared fixed crack model with the Rankine failure criterion, the nonlocal failure criterion by Pyttel et al. and the Johnson-Holmquist model. The input parameters are taken from several published studies, so each model was tested in multiple validated settings. The response of the models is compared with values measured during an earlier experimental campaign. The reference experiments involved freely hanging full-scale samples, which eliminated the effect of structural supports and allowed more accurate validation of the numerical models. The response of two types of glass, i.e. annealed or heat-strengthened, and two types of interlayer, i.e., polyvinyl butyral or ethylene–vinyl acetate, was tested and is simulated herein. The time evolution of the contact force, specimen accelerations, and fracture patterns are discussed, demonstrating the main shortcomings of the three models in simulating destructive tests on laminated glass samples under low-velocity impact.

Experimental Investigation of a Transparent Interface Material for Glass Compression Members

Mon, 20 Jun 2022 00:00:00 +0200

In this experimental research a transparent thermoplastic manufactured by the DOW Corporation and known as Surlyn is investigated for use as an interface material in fabrication of an all-glass pedestrian bridge. The bridge is modular in construction and fabricated from a series of interlocking hollow glass units (HGU) that are geometrically arranged to form a compression dominant structural system. Surlyn is used as a friction-based interface between neighbouring HGUs preventing direct glass-to-glass contact. An experimental program consisting of axial loading of short glass columns (SGC) sandwiched between Surlyn sheets is used to quantify the bearing capacity at which glass fracture occurs at the glass-Surlyn interface location. Applied load cases include 100,000 cycles of cyclic load followed by 12 hours of sustained load followed by monotonic load to cracking, and monotonic loading to cracking with no previous load history. Test results show that Surlyn functions as an effective interface material with glass fracture occurring at bearing stress levels in excess of the column-action capacity of an individual HGU. Furthermore, load cycling and creep loading had no effect on the glass fracture capacity. However, the load history had a nominal effect on Surlyn, increasing stiffness and reducing deformation.

Joint Research Project (in progress): Draft Standard for Determining the Thermal Stress of Glass and Glass-Glass PV Modules (BIPV) in the Construction Industry

Mon, 20 Jun 2022 00:00:00 +0200

For the design of façade and roof glazing, loads due to dead weight, climatic loads (IGU - pressure differences), wind and snow are well investigated and are considered in engineering practice. However, glass constructions are also ex-posed to thermally induced stresses due to direct solar irradiation. The standards and guidelines available so far, both nationally and at the European level, are partly outdated or contain only simplified instructions and specifications for calculating thermally induced stresses of façade and roof glazing. Within the research project, a variety of façade glazing configurations and additionally building-integrated (BIPV) glass-glass photovoltaic modules, for example as a façade cladding rear ventilated, are being investigated by means of numerical simulation and subsequent experimental validation with up-to-date German meteorological data. The purpose of the project is to reduce or prevent the occurrence of thermally induced glass breakage (thermal breakage) through European standardization. In this way, economic damage can be avoided. The present paper provides an insight into the two-years lasting joint research project, including the current status of science and technology, goals, structure and process, and descriptions of work packages. Results, such as the collection of the various influencing factors, meteorological data, and results from numerical simulations, will be presented after the project has finished at the end of September 2022.

Potentials and Limits of Simplified Models for Linearly Restrained Glass Balustrades under Static Loads and Impact

Emanuele Rizzi, Chiara Bedon, Alessia Bez, Claudio Amadio — Mon, 20 Jun 2022 00:00:00 +0200

Glass balustrades are designed to prevent large deflections and high stress peaks under conventional lateral loads. In practice, linear restraints are generally described in the form of ideal linear clamps for glass, to replace the actual geometrical and mechanical properties of restraint components. This means that strong simplifications are introduced in place of multiple details and components expected to offer local flexibility and prevent premature stress peaks in glass. In this paper, attention is given to linear restraints that are commonly described in terms of “clamp” boundaries for glass panels under lateral loads. The use of simplified mechanical models to characterize the actual stiffness and linear restraints and components is addressed, with the support of refined Finite Element numerical models and literature experimental data for balustrades under twin-tyre impact.

Editorial

Jan Belis, Freek Bos, Christian Louter — Mon, 20 Jun 2022 00:00:00 +0200

Welcome at Challenging Glass 8!

We gradually emerge from two difficult years of the covid-19 pandemic raging through the world in waves of constantly changing intensities. The associated uncertainties really put the ‘challenging’ into Challenging Glass this time. Still, some of our peers are not able to join us in Ghent, and they will be sorely missed. Nevertheless, we are happy to be able to return this year to the ‘real thing’: a live event which allows the international glass community to finally meet again in person. An excellent opportunity, especially within the UN-declared International Year of Glass 2022. We look forward to reconnect with international colleagues and old friends, but we also want to extend a particularly warm welcome to new and young peers who perhaps have not yet had many opportunities to build their professional network.

Dedicated as we are to the high standards of the Challenging Glass Conferences, we are once again proud to present a very promising programme. No less than five keynote speakers will share their original insights on glass with us: Stéphany Le Rhun on glass and circularity; Julian Jones on glass and bio-based materials; Markus Feldmann on the oncoming Eurocode on the Design of Glass Structures; and finally Robert Capel and Iris Rombouts on their latest glass projects. In addition, over 70 papers will be presented by experts from around the world, showcasing the latest findings in academia, practice and industry. Moreover, a special session on adhesive bonding in glass construction is organised by the European COST Action CertBond CA18120 - Reliable roadmap for certification of bonded primary structures.

All papers have been peer reviewed by our scientific committee and are published Open Access in Volume 8 of the online Challenging Glass Conference Proceedings. A selection of papers has been subjected to a separate double-blind peer-review process and is published in the special Challenging Glass issue of the Glass Structures & Engineering journal (SpringerNature).

Many thanks go to our sponsors, Scientific Committee members, authors and attendees to make it happen.
Let’s enjoy together!

Jan Belis, Freek Bos & Christian Louter
Conference Organisers
June 2022

Keynote Speakers

Challenging Glass — Mon, 20 Jun 2022 00:00:00 +0200

Keynote Speakers at Challenging Glass Conference 8:

Stéphany Le Rhun – Eckersley O’Callaghan
Prof. Julian Jones – Imperial College London
Prof. Markus Feldmann – RWTH Aachen
Robert Capel – Octatube
Iris Rombouts – Octatube

The Clamp Bender: A New Testing Equipment for Thin Glass

Fri, 29 Jul 2022 00:00:00 +0200

The bending strength of flat glass panels including the effects of their edges, is commonly determined by means of the four-point bending test method. This is an established and reliable method. However, when testing glass thinner than 3 mm, large deformation may occur. This means that the calculated stresses might not correspond to the actual, as the hypothesis behind the small deformation theory does no longer hold. Furthermore, it might occur that the specimen slips out of the supports, compelling the testing impossible. An alternative method, suitable for thin glass, consists of inducing an increasing curvature from flat until fracture. The curvature is to be constant along the length of the specimen at any time. The stress at fracture is calculated by knowing the
corresponding radius or the applied bending moment. The equipment capable of performing this test is the clamp bender whereby the glass is held by two clamps at the specimen’s ends. Rotational and translational movement combine to uniaxially bend
the glass as desired. This paper explores the validity of the clamp bender for testing thin glass by comparing the results generated by three different test setups developed at TU Darmstadt, TU Dresden and AGC. The three individually developed clamp bender setups follow the same principle, but present a few differences in actuation. Using these three clamp bender test setups, identical series of thin glass specimens were tested. The results showed that the glass fracture strength data coming from different setups match quite
well one another. This paper discusses the different test setups and compares the obtained glass strength data. It contributes to the development of a universally applicable, simple and reliable test method for thin glass.

Hail Resistance of Greenhouse Coverings

Jürgen Neugebauer, Georg P. Kneringer — Mon, 20 Jun 2022 00:00:00 +0200

Due to climate change, there will be more extreme weather in the future, such as storms, heavy rain events in combination with hail, and the associated damage to various structural areas of our life such as hail damage to greenhouse envelopes. For this reason, it is important to deal with topics which range from the origin of the hail to the damage caused by hailstorms. The so-called hail resistance classes can be determined in a laboratory using suitable testing equipment and in this case these tests were carried out in the laboratory of the University of Applied Sciences FH Joanneum Graz. The results of the classification of hail resistance classes for different materials for greenhouse enclosures are presented in this paper.

Experimental Strength Characterisation of Thin Chemically Pre-Stressed Glass Based on Laser-Induced Flaws

Shahryar Nategh, Marco Zaccaria, Jeroen Missinne, Jan Belis — Wed, 12 Oct 2022 00:00:00 +0200

The strength of chemically pre-stressed glass depends on the depth of surface flaws and the value of the pre-stress. So far, some research has been conducted on this topic; however, there were always uncertainties regarding the flaw depth and the pre-stress profile. Consequently, this research characterises the pre-stress profile using experimental methods. The latter include measuring the depth of layer (DoL) and the surface compressive pre-stress (C_S) with FSM-7000 h and verifying the achieved DoL with the Na⁺ and K⁺ distribution through the thickness obtained from the SEM/EDS analysis. Results demonstrate that the amount of K decreases parabolically (second-order) to a certain value and then remains constant. Based on this observation and some boundary conditions, the equation of the pre-stress profile was obtained for thin chemically pre-stressed aluminosilicate glass (Falcon^®) with 8 h and 24 h processing durations in molten salt at 460 °C. A non-strengthened glass (NSG) was also used as a reference for comparison. Then, three artificial laser-induced flaws with accurately controlled depths is tested by means of a clamp bender. The results of the strength tests demonstrated very low deviations in the failure stress. It was shown that even when the depth of the flaw is higher than the DoL, which means that the flaw tip enters the zone with the pre-tensile stress, there is still considerable resistance from the surrounding intact area. Furthermore, it was confirmed that the pre-stress strain energy for 24 h processing is larger than for 8 h, leading to more fragmentation after failure under a similar loading condition. Finally, it was found that the fracture toughness is not constant through the pre-stressed glass thickness, and it is dependent on the pre-stress profile with the peak value at the glass surface.

The Jardin d’Hiver in Paris, a Structural Glass Case Study

Jorge Hidalgo, Matthieu Thésé, Matt King, Victor Racodon — Tue, 12 Jul 2022 00:00:00 +0200

The 30 Avenue Montaigne in Paris, historical headquarters of Christian Dior on the Avenue Montaigne in Paris is currently undergoing a major refurbishment to be finished by early 2022. The centrepiece of the project is the Jardin d’Hiver , a new contemporary glazed element covering an existing terrace, creating a exceptional space in the project. The Jardin d’Hiver is a 10m high x 17m long x 8m wide box with four glazed faces: the roof, the two short sides and one long side. The other long side is the existing façade of the historical building. It is composed of 24 structural DGU panels (9 on the roof and the long side and 3 on each short side), 8 laminated glass beams and 8 duplex stainless-steel columns. The two end walls, formed by 3 DGU panels up to 3200 kg each, act as load bearing and bracing walls without any intermediate structure. Several challenges linked to the use of structural glazing were resolved during the design process such as the structural connections between glazed elements, robustness and post-fracture behaviour, differential thermal expansion of the materials and interaction with the main concrete and stone building structure. Nonlinear FE analysis and a full-scale test were performed to prove the design intent concept. The paper sets out the design process for the development of the glazed structure and it explores the balance required between the transparency of the structure, the reliability of the system and the constraints of an existing structure.

Apple Marina Bay Sands: Utmost Transparency

Graham Coult, Alexandros Cannas, Sam Gregson, Lorenzo Santelli — Tue, 27 Sep 2022 00:00:00 +0200

This study aims to describe the engineering challenges and decision making encountered during the design of the hybrid steel and glass structure of the Apple Store at Marina Bay Sands in Singapore. The structural scheme, which was developed to fulfil the architectural ambition for the utmost transparency, is documented and assessed alongside early-stage alternative solutions. Particular attention is then given to the innovative use of large glass panels as bracing for the steel superstructure. System robustness and post-breakage behaviour of the glass envelope are analysed, especially focusing on the challenges related to installing and replacing large conical glass panels on a small reinforced concrete island just off the shore of Marina Bay. This paper also explores the complexity of the envelope and all the lessons learned during the entire process from concept to construction including all the parallel design paths and tests that helped successfully progress the design thorough to completion.

Extreme Cold-Bending: Geometric Considerations and Shape Prediction with Machine Learning

Keyan Rahimzadeh, Evan Levelle, John Douglas — Mon, 20 Jun 2022 00:00:00 +0200

Cold-bent glass is seeing increasing adoption in construction projects with non-planar geometries. This paper presents work undergone for a set of four high-rise towers, featuring 11,136 unique cold-bent panels, hundreds of which are pushed beyond 250mm. The panels are all unique, non-rectangular, and in some cases, slightly curved. The challenging geometry complicates the prediction of the final panel shape, which is an essential step for producing fabrication drawings of a panel’s flat shape prior to bending. While Machine Learning is still a nascent technology in the AEC industry, prediction is a class of problems for which many Machine Learning techniques are ideal, especially when dealing with a large quantity of data, or in this case, panels. The paper discusses the geometric characteristics of highly bent glass, a methodology for the shape prediction of the panels, and the use of Machine Learning in its implementation. The methodology was deployed for over 3,500 pieces of installed architectural glass, and was shown to reduce geometric deviations as much as 75%, down to sub-millimetre tolerances.

The New Slumped Glass Facade at Tiffany's Flagship Store

Chenyu Pu, Jason Wang, David Bott, Daniel Vos — Tue, 12 Jul 2022 00:00:00 +0200

This paper presents a case study for the new slumped glass façade at Tiffany’s flagship store in New York City. The undulating façade of slumped IGU’s encloses a new, three-story addition that sits atop the existing Tiffany & Company building. Taken as a whole, the new façade appears as though it were a semi-transparent and flexible curtain of wave fold drapes, suspended from the roof of the new addition and wrapping its north and west elevations. The IGU’s, many as tall as 5.2 meters, consist of slumped glass outer lites and flat glass inner lites, which are glazed onto steel-reinforced aluminum curtain wall frames. Each slumped glass lite is formed into a series of four, wave-like arcs of differing lengths and radii, with the glass periodically rotated 180 degrees to create a more complex and seemingly random wave pattern despite the similar underlying geometry. As with all slumped IGU’s, their successful performance was contingent on solving a series of engineering challenges unique to their design. The volume of air within the slumped IGU cavity is much larger than that of a traditional flat IGU, leading to increased stress on the glass due to changes in temperature and atmospheric pressure. Because the slumped geometry of the outer lite substantially increases its stiffness, changes in air cavity pressure can lead to substantial deflection of the flat inner lite. Therefore, the size of the airspace and thickness of the inner lite were designed to prevent contact with the outer lite. As the stiffness of the vertically oriented slumped glass waves will distribute more wind pressure to the top and bottom of the IGU’s, the width of the secondary structural seal was modified accordingly. Finally, because the slumped glass did not allow for heat treatment, it remains annealed, and the potential for thermal stress breakage was thoroughly investigated.

Planning Phases of Glass Projects

Peter Lenk — Mon, 20 Jun 2022 00:00:00 +0200

This paper showcases the challenges in design, fabrication, and installation of glass projects. The modus operandi of an engineer working with glass is presented and the rationale behind the decisions explained. The first section discusses the motivations in several projects. The life cycle phases of the projects are outlined. The second chapter introduces the importance of conceptual design and generation of options on an all-glass staircase project example. Communication of the design intent is outlined in the third chapter, supported with graphical communication extracted from our recent project of a feature wall and glass elevator. The paper concludes with a brief discussion on procurement and construction phases with primary focus on the recently finished Coal Drops Yard in London. Final remarks on the structural glass design experience are presented in the conclusions.

The Story Behind Sky Pool

Graham Coult, Sam Gregson — Wed, 15 Sep 2021 00:00:00 +0200

The contribution will look at the decisions taken during the materials selection of the Skypool and the consequential complexities of working with an unusual structural material as acrylic. The early analytical solutions will be reviewed and judged on their merits. The criteria will look not only consider the typical engineering principles of strength and stiffness but also delve further into exploring the architectural requirements that are necessary for exposed structures where transparency is key. It will also consider aspects such as robustness, maintenance, replacement and embodied carbon and material circularity. In such simple landmark projects, the simplicity is often achieved with great difficulty and hard-won gains. This contribution will open the process to show the joy, excitement and collaboration that is an inherent part. It will consider the lessons learned on how the knowledge and construction methods of different materials need to be well understood to successfully progress such projects.

Design of a Curved Duplex Façade for a 67 m High Residential Tower at the Belgian Coast

Bert Van Lancker, Kenny Martens — Mon, 20 Jun 2022 00:00:00 +0200

Designed by Neutelings & Riedijk and Bureau Bouwtechniek, the Heldentoren (Eng. Hero tower) is a 67 m high residential tower situated in Knokke-Heist at the Belgian coast. On floor level +2, +7, +12 and +17, the curtain wall façade spans two floors and is partially curved with a bending radius of 2.3 m for which 88.2(ANG, PVB)/15(Ar)/88.2(ANG, PVB) hot bent insulated glass units are used. Considering viscoelastic material behaviour of the interlayers, implementing the curved shape of the glazing and performing geometrically nonlinear analyses, however, will structurally result in more economical glass compositions. The structural design of this duplex façade faced some challenges: high aesthetical requirements by using slim profiles, the curvature resulting in horizontal in-plane reaction forces on the anchors and anchorages combined with large eccentricities, and the impossibility to apply traditional curtain wall design principles leading to the need of structural calculations on system level taking into account the stiffness of the connections between mullions and transoms. The node stiffness was obtained by designing stainless steel stiffeners. Glass bearers transferring the glazing’s self-weight directly to the mullions avoided torsion in the curved transoms. The adopted design method led to a reduction with a factor 4.2 for the bending moments and deflections of the mullions compared to traditional design principles. A mock-up of the duplex façade allowed the identification and solution of technical issues and installation-related difficulties by the façade builder. Potential consequences of these interventions with respect to the structural performance of the façade could be revised as well.

Funicular Glass Bridge Prototype: Design Optimization, Fabrication, and Assembly Challenges

Thu, 09 Jun 2022 00:00:00 +0200

Polyhedral Graphic Statics (PGS) is an effective tool for form-finding and constructing complex yet efficient spatial funicular structures. The intrinsic planarity of polyhedral geometries can be leveraged for efficient fabrication and construction using flat sheet materials, such as glass. Our previous research used PGS for the form-finding of a 3 m-span, modular glass bridge prototype to be built with thirteen unique hollow glass units (HGUs) in a compression-only configuration. This paper reports its design optimization, fabrication, and subsequent modular assembly process. The computational modeling of the geometries is facilitated with the efficient half-face data structure provided by PolyFrame, a software that implements PGS. Regular float glass and acrylic are selected as the main structural materials, and they are fabricated using 5-axis water jet cutting and CNC milling techniques. With the help of 3 M™ Very High Bond tape, the glass parts and acrylic parts are bonded as HGUs, which serve as the basic structural and assembly modules. Surlyn sheets are used as interface material to prevent glass-to-glass direct contact between HGUs. The digital model is also simulated using ANSYS to ensure the effectiveness of the design. Due to the lightweight of the HGUs, the assembly of the bridge can be done by one person without the requirement of any heavy construction machinery.

Design Base for a Frameless Glass Structure Using Structural PVB Interlayers and Stainless-Steel Fittings

Wim Stevels, Thiemo Fildhuth, Thomas Wüest, Matthias Haller, Roman Schieber — Mon, 20 Jun 2022 00:00:00 +0200

Minimizing metallic primary structures in directly glazed grid shells is key to increasing transparency. Complete renunciation to a substructure results in the glass itself bearing the loads, with thin glass shells, for example, that support loads mainly via membrane forces. A 4.20 m tall, double-curved, frame-less modular glass shell with stainless steel fittings laminated into the thin interstice of two-ply laminated safety glass has been developed and built as a demonstrator to validate the concept. The fittings used to structurally join the glass modules transfer all translation loads and provide a certain rotational stiffness. They are geometrically designed to reduce stress peaks inside the laminate and feature a laminated contact surface at the edge of the glass. For lamination, an interlayer stack was applied comprising exterior layers of structural PVB to bond the fitting with the glass and translucent PVB as interior core layer for aesthetic reasons. The design of this structure initially relied on generic values for designing and finite element modelling of the fitting-interlayer bond, particularly in tensile “pull-out” mode. The present paper undertakes a review of basic interlayer stack data with regards to viscoelastic properties and adhesion, and the engineering hypotheses using recent preliminary fitting test results for various loading schemes (bending, shear, tensile).

Determination of the Linear Viscoelastic Material Behaviour of Interlayers with Semi-Crystalline Structures

Miriam Schuster — Mon, 01 Aug 2022 00:00:00 +0200

The temperature dependent linear viscoelastic material behaviour of the most commonly used interlayer PVB is typically determined by means of Dynamic-Mechanical-Thermal-Analysis (DMTA). By horizontally shifting the isothermal modulus curves, a mastercurve is created at a certain reference temperature, which can then be mathematically approximated with a Prony series. A time-temperature superposition principle can be derived from the shift factors. In contrast to PVB, EVA and ionomer (or ionoplastic) interlayers have semi-crystalline structures that melt when the melting temperature is reached and form again when the sample is cooled below the crystallization temperature. The exact structure and number of crystallites depend e.g. on the cooling rate and the physical age (or thermal prehistory) of the sample. These factors must be taken into account in the experimental determination of the material parameters with DMTA. Using the example of SentryGlas®, this article shows that the stiffness of semi-crystalline interlayers is affected by the crystallinity. Mastercurves from DMTA with different temperature programs are created. The degrees of crystallisation for the different temperature programs are determined with Differential Scanning Calorimetry (DSC). A time-temperature superposition principle, which applies to the purely amorphous material, and a time-crystallinity superposition principle are derived, which enable the determination of the material parameters for different temperatures and degrees of crystallization.

Determination and Evaluation of the Interlaminar Shear Modulus of Polyvinyl Butyral with Fibre Optic Sensors

Thorsten Weimar, Christian Hammer — Mon, 03 Oct 2022 00:00:00 +0200

The method of fibre optic strain measurement based on Rayleigh signal analysis enables the detection of the deformation behaviour of laminated glass and the modelling of its load-bearing characteristics. The measurement system is already calibrated for glass surfaces by studies of Chair of Building Structure at Universität Siegen. In addition to discretely measuring systems, such as strain gauges, the distributed measurement system is particularly suitable for the determination of the interlaminar shear modulus. The sensors used in bending tests on laminated glass supplement the deformation measurements taken with strain gauges and inductive displacement sensors. The study describes the results of the shear modulus of viscoelastic interlayers made of polyvinyl butyral and provides the basis to define and evaluate a model for the finite element analysis.

UV Transmission in Laminated glass: Effects on Plant Growth and Development

Esther Meinen, Björn Sandén, Anja Dieleman, Silke Hemming — Mon, 20 Jun 2022 00:00:00 +0200

When glass is laminated for safety reasons, it usually blocks UV radiation partially or even completely when UV blocking materials are used. In the last decade, there has been an increasing interest in interlayers with high UV transmission, especially in relation to greenhouse applications. In this paper, we present an overview of the effects of UV transmittance on plant growth and development, in order to advice on the use of the high transmission interlayers versus the standard interlayers. Using UV transmitting films instead of UV blocking films has opportunities to alter plant growth and morphology. In general, plants grow more compact with increased UV transmittance, growth and biomass are reduced, flowering is stimulated (although the effects are species dependent), concentrations of secondary metabolites which are positive from nutritional perspective are stimulated and flower appearance (color) can be positively influenced. Pollination by bees is improved when UV is present and plant resilience to pests and diseases is improved. These results show that UV transmitting materials can have potential to be used in for example botanical gardens, office centers and garden markets, where producing biomass might even be unfavorable. On the contrary, the increased ornamental value by improved shape and flower color will be appreciated. Therefore, these aspects of transmitting UV to plants can have potential for markets where plant production is not the main goal.

Thermal Rheological Behavior of Composite Interlayer in Laminated Glass

Dongdong Xie, Jian Yang, Xinger Wang, Chenjun Zhao, Xianfang Jiang, Gang Li — Mon, 20 Jun 2022 00:00:00 +0200

Laminated glass is growing its application in structural entities. The thermoplastic polymeric interlayer plays an important role in transferring force and achieving the composite action in laminated glass, which reveals evident temperature-dependent behavior. In this study, a novel composite interlayer (SGE®) was devised to improve the resistance of laminated glass against environmental actions and to enhance the post-fracture performance. It is comprised of modified ethylene-vinyl-acetate (PVE®) and polycarbonate (PC). Through dynamic mechanical thermal analysis, the temperature-dependent characteristics of SGE, PVE, and PC materials were investigated in detail. The results show that the thermal rheological behavior of SGE is similar to that of PVE. The temperature ranges of glass transition and crystal melting of SGE material are -35°C ~ -25°C and 45°C ~ 75°C, respectively. The corresponding ranges are -35°C ~ -15°C and 35°C ~ 65°C for PVE material. And temperature ranges of the main transition are influenced by imposed frequency. Besides, the relationship between time and temperature for PVE, PC, and SGE material is extensively complicated and the complexity depends on the investigated mechanical property, temperature range, and time range. And the simple thermal rheological behavior emerges in the storage modulus of polymers, but loss modulus and loss factor conform to the complex thermal rheological behavior at the temperature range of -50°C ~ 120°C under the frequency range of 0.1 Hz ~ 10 Hz.

Reducing Carbon Footprint of Laminated Glass Through the Use of Structural Interlayers

Björn Sandén, Jorge Hidalgo — Mon, 20 Jun 2022 00:00:00 +0200

Structural interlayers in laminated glass have allowed engineers and specifiers to extend and improve the use of glazing solutions in the construction industry. With the availability of embodied carbon values for these interlayers, it is now possible to assess more accurately the reduction in environmental footprint of laminated glass for construction projects. The Tour Montparnasse tower refurbishment project in Paris was selected as a case study to make a comparison between PVB and structural ionomers in terms of embodied carbon. A 15 % embodied carbon reduction could be achieved using the structural interlayer.

Development and Behavior of a Thin Fitting Connection for Lamination with Structural PVB

Thiemo Fildhuth, Pascal Joos, Thomas Wüest, Matthias Haller, Wim Stevels — Fri, 07 Oct 2022 00:00:00 +0200

Intended for the construction of a double curved, frameless modular glass shell demonstrator, a stainless steel fitting connection with a trapezoidal, thin sheet laminated into the interstice of two-ply safety glass has been developed. For the bonding within the glass laminate, structural PVB interlayer is used. Various interlayer plies of different PVB types can be stacked depending on the necessary interstice thickness and the intended esthetical appearance. The fitting is designed to mainly transfer translational forces, but it also provides some bending stiffness via a crossbar supported against the glass edge. Various tests, including tension, shear and bending load application, have been performed at the Lucerne University of Applied Sciences and Arts (HSLU) to explore the structural behavior and the load bearing capacity of the fitting connection. In addition, parameter studies using finite element models were made to explore the influence of the fitting geometry, dimensions, interlayer properties and loading type on the structural behavior of this type of connection. These parameter studies and test results allow to identify further shape optimization and application possibilities of such thin, laminated fittings for load bearing glass structures.

The Conjugate Beam Effective Thickness Method

Laura Galuppi, Adam J. Nizich, Andrea M. La Greca — Mon, 20 Jun 2022 00:00:00 +0200

The structural performance of laminated glass is strongly dependent on the shear coupling offered by the interlayer between the bounding layered and monolithic limits of the glass plies. The most common simplified design approach consists of defining the effective thickness, i.e., the thickness of a monolithic section with equivalent flexural section properties. The Enhanced Effective Thickness (EET) method has been verified to estimate deflection in laminated glass for a range of load and boundary conditions for two-, three-, and multi-ply beams; however, for some static schemes, the EET method is less accurate for predicting stress. The recently proposed Conjugate Beam Effective Thickness (CBET) method, initially developed for cantilevered laminated glass balustrade applications, accounts for the relative displacement of glass plies across the interlayer for a range of loads and statically determinate boundary conditions. In this paper, the CBET method is extended to the evaluation of two-ply simply supported beams under concentrated, uniformly, and tapered distributed out-of-plane loads. Predicted deflection- and stress-effective thickness obtained from effective thickness methods is compared with finite element model results in illustrative examples, demonstrating improved accuracy. Closed-form formulas are summarized in tables to facilitate the practical application of the CBET method in the design practice.

Prediction of Moisture Diffusion and Failure in Glass/Steel Adhesive Joints

Ioannis Katsivalis, Stefanie Feih — Thu, 04 Aug 2022 00:00:00 +0200

Glass/steel adhesive joints are being used increasingly in the construction industry as they offer significant structural advantages over conventional mechanical fastener approaches. However, adhesive joints are also known to be sensitive to moisture diffusion into the bondline, which reduces the interfacial bonding strength for hybrid glass/steel substrates. The effect of moisture on the performance degradation of glass/steel adhesive joints has been successfully predicted assuming adhesive property degradation but requires experimental determination of the affected moisture ingress zone. This study utilizes a multi-physics numerical approach implemented via the commercial finite element code Abaqus 2020, which firstly simulates moisture ingress into the adhesive/glass interface and subsequently couples the diffusion effects with a cohesive zone modelling approach for damage initiation and propagation. The numerical predictions are calibrated against experimental data on glass/steel Double Cantilever Beam (DCB) specimens, which are bonded with a ductile methacrylate adhesive (Araldite 2047-1). The modelling approach is then validated against the experimental response of large double lap shear joints of a significantly different bondline geometry. It is demonstrated that the numerical model successfully predicts the critical exposure time for partial to complete joint degradation enabling the development of engineering guidelines for life-time prediction of various joint geometries.

Examination of the Load-Bearing Behavior of a Bonded Edge Seal for Fluid-Filled Insulating Glass Units

Alina Joachim, Felix Nicklisch, Alexander Freund, Bernhard Weller — Mon, 20 Jun 2022 00:00:00 +0200

This paper presents a study on the development of a bonded edge seal for fluid-filled insulating glass units. Such novel façade elements enable multifunctional building envelopes and an improved energy efficiency of buildings. The bonded edge seal of a fluid-filled glazing is highly stressed due to the hydrostatic pressure that acts in addition to typical loads on façades. The permanent exposure to the fluid may also cause severe aging effects. Therefore, the edge seal is designed in such a way that the chemical and physical stress splits on two functional zones. The first functional zone serves as a protective seal and separates the fluid from the second, load-bearing functional zone. The adhesives for both functional zones were selected using an extensive test program. Once the materials have been selected, the novel façade elements are tested in large scale component tests. The mock-ups are built on a scale of 1:2 compared to the original size of the intended façade elements. Since the study focuses on the performance of the adhesively bonded edge, the edge detail is realized in original size while the glass size is smaller. The glass thickness is modified to achieve rotations in the edge zone that correspond to façade elements in original size. The tests are performed in a test rig for curtain walls, which allows the simultaneous loading of the element by cyclic wind pressure and constant water pressure. The adhesive bond carries all the loads except the deadweight of the glass panes. The test results are compared with the numerical calculations and an estimate of the load-bearing behaviour is made.

Adhesive Solutions for Cast Glass Assemblies: Ground Rules Emerging from Built Case Studies on Adhesive Selection and Experimental Validation

Faidra Oikonomopoulou, Telesilla Bristogianni — Fri, 10 Jun 2022 00:00:00 +0200

Cast glass is a promising, three-dimensional expression of the material for architectural and structural applications, particularly for the creation of all-transparent, self-supporting structures and envelopes. Typically applied in the form of solid blocks, cast glass components can be used as repetitive units to comprise fully-transparent, cast glass masonry walls. To maximize transparency and ensure an even load distribution, the glass blocks are bonded together by a colourless adhesive. Currently, there is a lack of standardized structural specifications, strength data and building guidelines for such adhesively-bonded cast glass-block systems. As a result, any new application is accompanied by experimental testing to select the adhesive and certify the adhesively bonded system. Since the choice of adhesive is highly dependent on the prerequisites set for each case-study -such as the structural and visual performance, available budget, the structure’s geometry and climate conditions- the preselection of the most prominent adhesive family at an early project stage can prevent an excessive budget and construction complications. This paper, therefore, aims to shed light on the selection process of adhesives for cast glass assemblies by first providing an overview of the most suitable bonding media families for such systems; these include stiff adhesives, flexible adhesives and cement-based mortars. Following, the paper reviews the research & development process of the adhesively-bonded glass-block systems in three distinct built projects, in which the TU Delft team has been involved: The Crystal Houses façade (NL), the LightVault, a robotically assembled glass vault (UK) and the Qaammat pavilion in the arctic circle (GL). The adhesive requirements for each of the three case studies are discussed in terms of structural and visual performance and ease-of-assembly (constructability). These criteria are decisive in pointing out the most promising bonding media family per case-study. The final shortlist of adhesive candidates within that bonding media family is subject to the full list of performance criteria, but also to market availability. The shortlist of adhesive candidates are typically experimentally evaluated, first via application testing and then via strength tests in order to choose the most suitable candidate. Based on the above, the review concludes in proposing guidelines for the effective selection, design and experimental verification of adhesively-bonded cast glass assemblies.

Pre- and Post-Failure Experimental Bending Analysis of Glass Elements Coated by Aged Anti-Shatter Safety Films

Silvana Mattei, Luca Cozzarini, Chiara Bedon — Mon, 20 Jun 2022 00:00:00 +0200

The main goal of Anti-Shatter Films (ASFs) applications for structural glass is to create a barrier able to keep together fragments and minimize risk after any impulsive or static load that could lead glass to cracking. The influence of ASF properties on the flexural strength of coated glass elements is thus a relevant topic for safe design purposes, but still little investigated. To this aim, an experimental material investigation is presented in this paper, in order to achieve a good knowledge of common ASFs from a chemical point of view. Moreover, the deterioration of mechanical and adhesion characteristics for ASF samples subjected to different environmental conditions and accelerated ageing is also investigated, so as to simulate the effects of long-term exposure to high humidity (HU) or high temperature (HT). An experimental campaign carried out on 20 small scale ASF-coated glass specimens is finally presented, based on a three-point bending (3PB) test setup. The out-of-plane bending response of unaged or aged samples is performed by taking into account two different displacement-rate levels, to assess their performance and bending capacity under steady-static or impulsive loads. In both cases, the attention is given to the characterization of elastic and post-failure performances. Finally, support for the interpretation of experimental outcomes is derived from a simplified theoretical model of composite beam with partial connection, in order to estimate the shear stiffness of ASF adhesive components in the elastic stage.

Integrated Connections for Glass–Plastic-Composite Panels: An Experimental Study under Tensile Loading at +23, +40 and +60 °C and Different Glass Build-ups

Julian Hänig, Bernhard Weller — Tue, 07 Jun 2022 00:00:00 +0200

The desire of builders and architects of maximum transparency and homogeneous surfaces in glass façades and glass structures extends to interior all-glass applications such as glass partitions or all-glass doors. In conventional glass systems the interconnections are performed by eye-catching fittings and clamping details that reduce the transparency and disturb the aesthetics. Novel glass–plastic-composite panels show a significantly reduced self-weight by composition of a polymer polymethylmethacrylate (PMMA) interlayer core and cover layers of thin glass. The innovative composites show high structural performance with optical properties of conventional glass. The panels allow for a direct connection into the thick PMMA interlayer core with the supporting structure or other panels. Such an integrated connection design reduces stress concentrations and allows for the development of small and unobtrusive fittings. Different integrated connections for the glass–plastic-composite panels have been designed and investigated. This article presents an experimental study on different connections, such as mechanically fastened and adhesively integrated, tested under tensile loading. Based on video analyses, crack progressions and failure mechanisms are evaluated and discussed in detail. The tests investigate temperature effects as well as the influence of the interlayer core thickness and glass type of the cover layers in varying build-ups. The comprehensive evaluation includes a description of the mechanical load-bearing behaviour in form of load versus displacement graphs as well as an investigation of crack progression and failure mechanisms for the final assessment. The results from this experimental study elucidate the structural characteristics of integrated connections in glass–plastic-composite panels under tensile loading and represent a basis for the ongoing development of real application fittings.

Comparison of Behaviour of Laminated Banister Panels with Embedded Connections

Michaela Zdražilová, Zdeněk Sokol, Martina Eliášová — Mon, 20 Jun 2022 00:00:00 +0200

Glass became a very popular building material in recent decades. Modern architecture often works with glass facades, roofs, banisters or columns. However, using glass elements in structures may be problematic due to glass elements connections. The connection must bear all stresses arising during the lifetime period and meet high aesthetical standards at the same time. Various bolted and adhesive connections were developed in order to achieve as transparent look as possible. The embedded laminated connection combines mechanical and adhesive fixing systems. The ongoing research at the Faculty of Civil Engineering of the CTU in Prague is focused on the characteristics of this type of connection. Within this research, two sets of real-scale laminated banister panels with the embedded connection were tested. The first set included the samples consisting of two 8 mm glass plies bonded with two layers of an EVA foil. The second set of samples consisted of one 10 mm glass ply and one 6 mm glass ply also bonded with two layers of an EVA foil. There was one pair of embedded steel countersunk bolts with HDPE liners in each of the lower corners. A short-term vertical load was applied on the samples. During the experiment, stresses and deflections in several points were measured. The experiments showed the collapse mode and a short-term resistance of a laminated glass panel with two sets of embedded point connections under a vertical load. It also allowed comparing the behaviour and resistance of two panels of identical total thickness differing in glass ply compositions.

Influence of Elevated Temperature on the Mechanical Properties of Transparent Adhesive Glass-Glass Joints

Markéta Zikmundová, Martina Eliášová — Mon, 20 Jun 2022 00:00:00 +0200

Glass is an attractive, transparent but brittle material which is increasingly popular in civil engineering. Not only small and secondary glass structures such as canopies or railings, but also load-bearing structures or structural elements such as stairways, beams, facades, etc. are commonly designed today. The wider use of glass places demands on the connections of glass-to-glass or glass-to-other materials. Mechanical connections are commonly used owing to their known mechanical properties but there is pressure to use adhesives for their considerable advantages. Unfortunately, there is not enough information about the mechanical properties of adhesives exposed to environmental effects and elevated temperature. The paper is focused on experimental testing of glass-to-glass connection using transparent adhesives. The specimens were prepared as double-lap shear joints with 1 mm adhesive joint thickness. In the study, three two-component epoxy adhesives were selected, one rigid adhesive and two semi-rigid adhesives. Specimens were tested at room temperature (reference set) and at elevated temperature (80 °C), six sets of specimens were prepared in total. The test was controlled by displacement with continuous loading until the specimen’s collapse. The cross-head speed was 0.05 mm/min. Shear strength at failure rapidly decreased for specimens exposed to elevated temperature and each specimen failed due to loss of adhesion between adhesive and glass.

Prototyping of Digitally Manufactured Thin Glass Composite Façade Panels

Daniel Pfarr, Christian Louter — Mon, 20 Jun 2022 00:00:00 +0200

The use of thin glass promises to enable a variety of construction industry pursuits. In addition to the ecological benefits of more efficient use of resources, architects can anticipate new design freedoms with thin glass. Based on the sandwich theory, the flexible thin glass can be combined with a 3D-printed open-cell polymer core to form a very rigid yet lightweight composite element. This paper presents an exploratory attempt on the digital manufacturing of thin glass composite façade panels with an industrial robot. It explains the idea of a digital “file-to-factory”-workflow which includes Computer-Aided Design (CAD), Engineering (CAE) and Manufacturing (CAM). The research shows a parametric design process to enable the seamless integration of digital analytic tools. Furthermore, this process shows the potentials and challenges of the digital manufacturing of a thin glass composite panel. Here, partial production steps executed by an industrial robot arm, such as large-format additive manufacturing, mechanical surface preparation, bonding and assembly process are explained. Finally, a first insight into mechanical properties of the composite panel are experimentally and numerically investigated and evaluated under surface load. The general concept of the digital design and manufacturing workflow as well as the results of the experimental study provide the background for the integration of further form-finding and analysis methods as well as the implementation of extensive mechanical investigations in future research.

Curtain of Glass – Textured by Stone

Michael Engelmann, Klaus Reuschle, Salvatore Muscatello, Thomas Sperandio — Mon, 20 Jun 2022 00:00:00 +0200

The new World Trade Center site was rebuilt after 9/11 comprising seven mayor skyscrapers around the memorial site and the 9/11 museum. Between WTC 2 and WTC 3, Santiago Calatrava’s Oculus Station spans its wings in the NY air while finally, the complex is completed by the “The Ronald O. Perelman Performing Arts Center”. This building sets a one-in-a-kind visual appearance to the area. Its four-sided, 42 m tall, even facade is made from 4736 equal-sized insulated glass panes. More specifically, the architectural vision is to create a marble stone front covered with glass which results in a stone-glass laminate as a part of an insulated glass unit. The marble shows a distinguished white face with crisp black veining. Each of the four elevations of the building impresses with a perfect symmetry and veins touching at the vertical center line. So, the design team at Josef Gartner was challenged to set-up a logistics chain from quarry in Portugal where the stone panels were cut and catalogued to glass production of laminated glass in France and IGUs in Germany and assembly of curtain wall mega-panels at Gartner in Germany up to the site in Lower Manhattan. Our in-house logistics concept, customized for this project, guarantees that each individual piece of stone finds its correct and unique spot defined by the architect on the 7,000 m² surface – a large-scale game of “Matching Pairs”.
The steel base building provides a cantilevering roof that holds 128 hot-rolled steel mullions. Each 36 m in length with one intermediate lateral support only. This allows the visitor to experience a clear and unobstructed view along the transom-free facade elements that carry the translucent stone-wall. During the day, it appears white from the outside and shines with an amber-glow during the night when the interior space is illuminated. We show the use of a novel stone-glass product that is exposed to a variety of requirements. The logistics chain is described from quarry to site making sure that the architectural and economical demand is met along the whole process. Finally, the team connects all branches in facade design using stone, aluminum, glass and architectural exposed structural steel assembled in one landmark project.

Application of an Iron-Based Shape Memory Alloy for Post-Tensioning Glass Elements

Tue, 12 Jul 2022 00:00:00 +0200

Previous research has evidenced that by adding a ductile reinforcement on the tension side of a glass beam, for instance by adhesive bonding, its post-cracking behaviour and redundancy were improved, while an additional pre-stressing of this reinforcement further helped to increase the initial cracking resistance. Past investigations used steel tendons or stainless steel strips, which required rather complex setups and procedures for mechanical pre-stressing. This study aims to introduce an easier-to-apply procedure with strips made of an iron-based shape memory alloy (Fe-SMA), which has the property of remembering its initial shape after a phase transformation from austenite to martensite. The Fe-SMA strips can be anchored to a parent structure as pre-strained strips, in case of a glass substrate by adhesive bonding. After activation of the Fe-SMA through a heating and cooling process, a tensile stress is generated in the strip, which applies a compressive stress field into the parent structure. This work discusses the results from first feasibility investigations dealing with the choice of adhesive and identifying a suitable activation procedure for Fe-SMA strips adhesively bonded to glass elements. The effective bond length, which needs to be considered when defining the anchorage length, was determined for two structural adhesives. While for the high-strength, brittle 2c-epoxy adhesive SikaPower®-1277, shorter bond lengths of a little more than 120 mm were sufficient, for the more ductile 2c-methacrylate adhesive Araldite® 2047-1, longer bond lengths were necessary for the same load level (more than 240 mm). Furthermore, an activation procedure by electrical resistive heating was applied, which (i) allowed sufficient heating of the Fe-SMA for activation, (ii) avoided too high instant temperature changes in the glass and (iii) did not affect the required anchorage bond length.

Design, Engineering and Experimental Testing of Tubular Glass Columns

Rozemarijn Veenstra, Chris Noteboom, Faidra Oikonomopoulou, Mauro Overend — Mon, 20 Jun 2022 00:00:00 +0200

This research revolves around the design, fabrication and testing of tubular glass columns, with particular focus on their redundancy and fire-safety mechanisms; moreover, addressing aspects such as: the column shape; cleaning and maintenance; end connections; geometric tolerances in the glass and demountability. Two alternative circular hollow (tube) column designs are initially developed and engineered to address these aspects, namely: the MLA (Multi Layered with Air) and the SLW (Single Layered with water). In both concepts the main load-bearing structure consists of two concentric laminated glass tubes. Thus, in order to explore the manufacturing challenges and structural potential of these concepts, the prototyping and experimental work focuses on six 300 mm long samples with 115 mm outer diameter that are laminated and fitted into customized, engineered steel end-connections. Particular attention in terms of manufacturing is paid to the lamination process and associated bubble formation, the possible fracture of the glass by internal resin-curing stresses and the interface between the glass tube and the steel end-connections. All samples are laminated with Ködistruct LG 2-PU component. Three samples are assembled using DURAN® (annealed) glass and the other three are using DURATAN® (heat-strengthened) glass. Subsequently, the six samples are tested in compression until failure to investigate the behaviour of the interlayer material, the post-fracture behaviour of the designs, the differences between annealed and heat-strengthened samples, the capacity of the glass tubes and the performance of the end connections. Initial cracks appeared between 95-160 kN (compression strength of 30-50 MPa) in the DURAN® samples and between 120-160 kN (compression strength of 37-50 MPa) in the DURATAN® samples. These loads are lower than the ones estimated by calculations; in specific, the first cracks occurred at 34-64% of the calculated load. Nevertheless, the samples are found to be robust, with a considerable load-bearing capacity beyond the first cracks, leading to a maximum nominal compression strength capacity of up to 152 MPa for the DURATAN® samples and up to 233 MPa for the DURAN® samples.

Silicone Structural Glazing Under Blast Loading

Valérie Hayez, Jon Kimberlain, Jie Feng, Sigurd Sitte, Mark Mirgon — Mon, 20 Jun 2022 00:00:00 +0200

Silicone sealants have a long history of successful use in high performance windows and curtainwalls, such as structural glazing (bonding) systems which can contribute to bomb blast mitigating window designs. Previous experimental work illustrated the increase in strength and elongation for silicone sealants at the typically higher strain rates of blast loading. These values have been used as design values for joint dimensioning. With the advent of more sophisticated analysis methods using finite element analysis software and the desire to optimize geometries of structural joints in high performance designs with extreme blast loads, there is a need to provide better material behavior models for silicones able to reproduce the typical loading during blast events. In a first step, small scale testing of various joint configurations at increased speeds was used to determine suitable material models. Next, the material model was validated using experimental test results of blast loaded adhesively bonded assemblies. Based on the obtained results, criteria for failure prediction are identified and suitable design strength values as well as joint dimensioning guidelines for engineering bonded systems are provided.

High-Temperature Behavior of Silicone Sealants

Valérie Hayez, Georg Scheutz — Mon, 20 Jun 2022 00:00:00 +0200

Since the early 2000s, an increasing number of globally reported fires in tall buildings, which have spread quickly, have been attributed to the façade. These dramatic events have raised concerns regarding the fire risk posed by materials used in façades and inside the building. Improved performance in both reaction to fire and fire resistance is a necessary requirement for construction materials. Silicone is used in many locations of the façade and buildings, such as sealing of linear joints or firestopping of penetrants in fire-rated walls and floors. Standardized testing enables the evaluation of the fire resistance of such linear and penetration seals in terms of integrity (avoiding the passage of hot smoke and flames) and insulation (limiting the rise of temperature on the non-exposed side). Silicone can also be used to assemble glass-to-metal frames in bonding applications such as smoke barriers. In these applications, retention of bonding and the mechanical properties of the silicone are a cause for concern when exposed to smoke and high temperature. This paper reviews the high-temperature behavior of a selected range of silicones used for sealing and bonding in construction.

Performance of Glass to Iron-based Shape Memory Alloy Adhesive Shear Joints with Different Geometry

Mon, 20 Jun 2022 00:00:00 +0200

Previous research has shown that glass beams with external, mechanical post-tensioning along their edges show better structural performance than glass beams without any such reinforcement. The initial and post-fracture load-bearing capacity of glass beams can be increased by reinforcing them with stainless steel or fiber-reinforced plastic (FRP) tendons that are post-tensioned and connected to the beam edges. However, post-tensioning of stainless steel or FRP bars or strips is complex and challenging because it often requires special setups, such as hydraulic jacks. Iron-based shape memory alloys (Fe-SMAs) are promising post-tensioning materials due to their efficient activation procedure and good mechanical properties. The target prestress level can be introduced by heating the Fe-SMA to a specific temperature followed by cooling down naturally to ambient temperature. As a contribution to assessing the feasibility of strengthening glass elements with adhesively bonded Fe-SMA strips, this paper focuses on the bond behavior of glass-to-Fe-SMA lap-shear joints based on numerical investigations. A finite element model is developed to evaluate the effect of adhesive thickness, Fe-SMA strip thickness and bond length on the structural behavior of glass to Fe-SMA lap-shear joints.

A Novel Technique for Enhancing Stress Concentration Features in Glass

Mithila Achintha — Mon, 20 Jun 2022 00:00:00 +0200

The brittle material behaviour of glass means that stress concentration features, such as geometric discontinuities (e.g., drilled holes) and mechanical connectors can weaken the structural efficiency of some glass structures. The poor structural efficiency due to the stress concentrations usually makes annealed glass unsuitable in applications where stress concentrations present, such as glass–bolted joints. Laminated and tempered glass are preferred in building construction industry due to their high strength and safe failure behaviour, respectively. However, laminated and tempered glasses are expensive compared to annealed glass. Moreover, laminated and tempered glasses offer limited design and construction flexibility, since the tempering and the laminating processes cannot be done at construction sites. This paper shows that bonding a small strip of Glass Fibre Reinforced Polymer (GFRP) on the surfaces of glass around stress concentration features in annealed glass can enhance the load capacity and ensure post-peak load resistance. The results suggest that the bonded GFRP strips retarded the propagation of a few major cracks causing complete fracture of the glass, thereby ensured higher load capacity and post-peak load resistance compared to unreinforced annealed glass. Since GFRP strips of small size are required in the proposed strengthening technique, the negative visual impact due to the translucent GFRPs are often negligible in most practical applications.

The Performance of Vacuum Insulating Glazing Units Subjected to a Soft Body Impact

Isabell Schulz, Cenk Kocer, Franz Paschke, Jens Schneider — Mon, 20 Jun 2022 00:00:00 +0200

The Vacuum Insulated Glazing is a highly thermally insulating structure consisting of two (or more) glass sheets, separated by an evacuated gap, and sealed hermetically at the glass edges. An array of support pillars maintains the separation of the panes under the constant load of atmospheric pressure. The performance and durability of the VIG, in terms of thermal loads and atmospheric pressure, has been well studied and ISO Standards have recently been published (ISO 19916-1:2018 and 19916-3:2021). However, the mechanical performance of the VIG, especially when exposed to dynamic loads, has not been dealt with in the scientific literature. The goal of this work is to investigate the mechanical performance of VIG’s subjected to soft body impact and gain insight into the failure mechanisms of the VIG when exposed to dynamic loads. Measurements of the surface stress on the glass were performed, when the VIG is subjected to the twin-tire pendulum impact test, as outlined in the Standard DIN EN 12600:2002. Two VIG units and one laminated VIG unit were tested and the results were compared to numerical data of a monolithic glass pane. It was found that the VIG failed at drop heights much lower than that prescribed in the Standard. An examination of the glass fracture patterns highlighted an origin of fracture caused by the contact of pillar-to-glass.

Investigations on the Cold Bending Behaviour of a Double Glazing Unit with a Rigid Edge-Spacer Frame

Tim van Driel, Chris Noteboom, Mauro Overend — Mon, 20 Jun 2022 00:00:00 +0200

Free-form façades with bent glass are becoming increasingly popular. As bending glass provides it with a better resistance to out-of-plane loads, it can result in thinner glass. A promising new technique is to cold bend thin glass plates with a stiff structural edge into a hyperbolic paraboloid (hypar), and to subsequently lock the corners to create a self-contained, self-stressed system. In this study, the bending process of specially-fabricated double glazing units (‘panels’) is investigated with a focus on a local instability phenomenon. The hypothesis that this instability is affected by edge stiffness of the plate, is tested by using 30x30 mm GFRP profiles as spacers along the perimeter of the glass. These were bonded to the glass using Dow 993 silicone adhesive. Four 1.5x1.5 m panels were produced in total, three with 4mm fully toughened (FT) glass, and one with 1.1 mm chemically toughened (CT) glass. The panels were cold bent in a series of laboratory experiments. A numerical model was developed to provide further insight on the mechanical response and to predict the outcome of the experiments. With the sizes of panels used it was not possible to form a hypar. Due to the small thickness of the glass, one the diagonals would always straighten when cold-bent. The 4 mm FT panels failed when the bottom plate fractured at a corner displacement of around 150 mm and a total load of 2.6 kN. The bottom plate of the CT 1.1 mm was also the first to fracture, at a corner displacement of 120 mm and a total load of 1.4 kN. The top and bottom plates came into contact in the centre of the plate when the corner displacement was around 50 mm for the FT 4 mm panels, and around 30 mm for the CT 1.1 mm panel. The numerical model predicted this contact and the overall behaviour of the panel up to a corner displacement of 60 mm. It was concluded that the glass was too thin to create a hypar with this panel size. The experimental data generated along with the numerical model are useful for future research and developments.

Design and Durability of Cold-Bent Insulating Glass Units

Pietro Demontis, Julia Endress, Viviana Nardini, Arnaud Vernier — Mon, 20 Jun 2022 00:00:00 +0200

Curved and free-form glass façades represent a clear trend in architectural design. Hot bending is the most common technique used to produce curved Insulating Glass Units (IGU). Although its effectiveness has been proved in many projects, it is well known that it can also be very expensive due to the big number of moulds usually required to build up a free-form façade. As alternative to the ‘hot-bending’ technique, the increasingly used ‘cold-bending’ method is investigated in this paper being less expensive as well as more sustainable. Such method consists in imposing an out-of-plane displacement to flat insulating glass units and generally requires forces of limited magnitude applied on site during installation. Cold-bending introduces permanent loads into the glass panes, the glass interlayers, the secondary sealing as well as the primary sealing, the latter one responsible for the gas retention and the resistance to moisture penetration in the IGU cavity. The paper presents the results of FEM analysis as well as tests performed on double glazed units including Sikasil® IG-25 secondary sealing joints and SikaGlaze® IG-5 PIB as primary seal and investigates their behavior due to cold-bending and exposure to climate conditions in accordance with EN1279-2. The results show that appropriate FE analysis can well predict the behaviour of the cold-bent system and that the amount of out-of-plane displacement introduced in the IGUs does not affect their integrity and durability. As example, the cold-bent limit identified is applied for shaping a cold-bent IGUs façade in a high-rise building.

Numerical Analysis of TGU Windows Under Blast – GLASS-SHARD Outlook

Chiara Bedon, Martin Larcher, Alessia Bez, Claudio Amadio — Mon, 20 Jun 2022 00:00:00 +0200

The analysis of load-bearing capacity and the determination of blast protection levels for ordinary glass windows and façade components in buildings is known to represent a design and research issue of crucial importance. In the same way, reliable methods to address this issue are mostly based on cost and management expensive experimental investigations on full-size samples. According to the tendency of recent years, this paper presents some of major outcomes of Finite Element (FE) numerical methods and simulations that have been explored in the framework of the GLASS-SHARD research project for glass windows and facades under explosion or soft-body impact. The attention is focused on the analysis of a Triple Glass Unit (TGU), so as to address the blast performance of a rather ordinary glass window for buildings characterized by the presence of multiple laminated glass (LG) layers, on one side, and by the presence of two interposed gas cavities. The TGU blast performance is investigated in terms of load-bearing capacity of single components, with respect to variations in the input blast loads (stand-off distance R, charge W, etc).

High-transparency Clear Glass Windows with Large PV Energy Outputs

Dieter Moor, Victor Rosenberg, Mikhail Vasiliev — Mon, 20 Jun 2022 00:00:00 +0200

Multiple modern glass and window products based on novel glazing designs, metal-dielectric coatings, and proprietary interlayer types have been developed recently. Advanced windows of today can control properties such as thermal emissivity, heat gain, colour, and transparency. In more recent and more novel glass products, solar energy harvesting through PV integration is also featured. Typically, semitransparent and also highly-transparent PV windows are purpose-designed, to include luminescent materials, special microstructures, and customized electric circuitry. Recently, significant progress has been demonstrated in building integrated highly-transparent solar windows (VLT up to 70%, with P_max ~ 30-33 W_p/m², eg Clearvue PV Solar Windows); these are expected to add momentum towards the development of smart cities. These Clearvue window systems are, at present in 2021, the only type of high-transparency and clear construction materials capable of providing significant energy savings in buildings, simultaneously with renewable energy generation. The technology has already been deployed and tested in both commercial property applications and in R&D greenhousing. Of special interest is the combination of properties provided by Clearvue solar window products, which includes significant power conversion efficiency (~3.3%), which is achieved in windows of colour rendering index of 99%, simultaneously featuring high PV Yield in multi-oriented building-integrated PV (BIPV) installations.

Coatings Sensitivity to the Quench Marks

Davide Maccariello, Romain Hivet — Mon, 20 Jun 2022 00:00:00 +0200

During tempering process, the non-homogenous heating or rapid cooling can induce localized strain in the glass leading to birefringence (or optical anisotropy) phenomenon, a result of the photoelastic effect. Since transmission and reflection coefficients of interfaces at high angles can be quite different with the polarization, inhomogeneous birefringence may manifest as peculiar geometric patterns of bright or darkish shadows or iridescence effects in given polarized observation conditions. The patterns appearance may be at the origin of dispute between the client and the glass manufacturer. Each party may have a different perception, how strong the anisotropies are and what is permissible. With the use of an in-line scanner for the optical retardation, it is possible to control and optimise the tempering process homogeneity and thus reduce the visibility of the patterns. However, the presence of low emissivity coatings on the façades windows can alter the visibility of the quench marks: depending on the coating nature, the quench pattern visibility can be magnified or reduced. Here, we show the calculation of σQM, as a parameter representing the coating sensitivity to quench marks, i.e., the capability of a coating to reveal or hinder the iridescence pattern of tempered glass. Thanks to the angular measurements of the transmission and reflection in s and p polarization we compute the quench mark sensitivity by estimating a color contrast gradient with regard to the phase delay.

Shaping Glass for Acoustic Performance

Catie Newell, Zackery Belanger, Wes McGee — Thu, 23 Jun 2022 00:00:00 +0200

Long Range is an experimental acoustic surface comprising 64 hexagonal, slumped glass panes, arranged in two layers of 32 panels each. It exhibits gradients of acoustic behaviors including reflection, diffusion, absorption, and transmission, accessed via modification of the form of glass panes at a variety of scales. Moving from flat panels at one end to increasingly slumped and perforated forms and culminating in deeply curved panels with porous openings, the components of Long Range aggregate into an acoustic and visual system of versatile behavior. The flat end primarily exhibits acoustic reflection, the center diffusion, and the severe end absorption and transmission, though all parts of the surface exhibit all four behaviors to some extent. Specific lines of research within the development of Long Range include controlled slumping of glass through cut auxetic patterns, the coalescing of visual and acoustic design, and formal and acoustic effects through wave-based simulation techniques. Lab testing demonstrates a correlation between the complexity of form, the presence of openings, and the severity of acoustic absorption.

Color Depth

Catie Newell, Ryan Craney — Mon, 20 Jun 2022 00:00:00 +0200

Color Depth is a material-based research project investigating the optical and structural properties of thick glass. The research is driven by an interest in optical gradients of transparency and color, which are designed through a manipulation of geometric form and composition. These qualities can be attributed to the interrelated optical effects created through reflection, refraction, and volume color, in direct correlation to the geometry of individual glass pieces and overall glass assemblies. An example of this can be seen in viewing a monolithic volume of glass that would appear to change color by varying the depths of its form. This concept was originally discussed in Josef Albers’ Interaction of Colour, and applied more specifically to glass in recent essays by Heike Brachlow. Color Depth utilizes this phenomenon of perceived color variation to construct and analyze architectural glass forms in both physical prototypes and design speculation. To evaluate architectural design opportunities, a multi-objective optimization workflow simulates and evaluates varying glass colors, forms, and compositions to achieve a desired visual effect. Additionally, the digital optimization process reveals patterns and visual effects that further the understanding of optical gradients when applied in an architectural context with various seasonal and diurnal environments. Keying into the geometry of glass– to deploy changes in color, darkness, or translucency—Color Depth ties together the physical attributes of a material system with its surrounding light.

Insights into Emissivity Changes During Tempering Processes and Potential for Utilization

Jorma Vitkala, Markus Klein, Daniel Schmidt, Senthil Vinodh — Mon, 20 Jun 2022 00:00:00 +0200

This contribution addresses the impact of tempering processes on the emissivity of LowE glass. The current status of a measurement series conducted at various tempering sites on different types of LowE glass is presented. Emissivity measurements using inductive eddy current sensors have been made on glass before and after tempering. The obtained data shows an improvement by factor 2 in emissivity depending on coating type. Effects from tempering recipes and the resulting emissivity homogeneity have been analyzed. Measurements also show significant worsening of the emissivity by the use of wrong tempering settings where too little convection occurs during heating that cause glass bending leading to the well-known white marks in the center of the glass along with significant loss in emissivity. Assessment of the glass emissivity properties as well as the negative effects of poor furnace recipe optimization on coatings were measured by eddy current systems, which rely on inductive methods for contact or non-contact real-time emissivity assessment. Comparison to thermographic images are shown and discussed. Finally, the status of measurement and analysis are summarized and the potentials to use of these phenomena are discussed.

Glass Up-Casting: A Review on the Current Challenges in Glass Recycling and a Novel Approach for Recycling “As-Is” Glass Waste into Volumetric Glass Components

Telesilla Bristogianni, Faidra Oikonomopoulou — Mon, 20 Jun 2022 00:00:00 +0200

This paper presents the casting of volumetric glass components from glass waste as an alternative glass-recycling approach. The approach is characterized by its flexibility to accommodate a variety of compositions and ability to yield volumetric (solid or thick-walled) glass products that can tolerate higher contamination rates without a significant compromise to their properties. The novelty of the proposed glass-to-glass recycling method lies in the “as-received” recycling of glass waste, using relatively low forming temperatures (750–1200 °C). This reduces both the need for expensive, labour-intensive and logistically complex purifying, segregation and treatment (e.g. removal of coatings) techniques, and the required energy and CO₂ emissions for product forming. Aim of this paper is to provide an overview of the potential but also of the technical and supply-chain challenges and limitations that still need to be tackled, in order to introduce this recycling approach to the market. Addressing the supply-chain barriers of glass recycling, the principal challenges linked to the collection and separation of glass waste and the established quality standards for the prevailing glass production technologies are identified, in order to argue upon the potential of this new recycling approach. In continuation, addressing the technical challenges that are mainly linked to contamination, an overview is provided of the main experimental findings on the influence of cullet contaminants and casting parameters on the generation of defects, and how these affect the mechanical properties. The experiments study a broad variety of glass compositions, including soda-lime, borosilicate, aluminosilicate and lead/barium glasses, and different levels of cullet contamination, of embedded (e.g. frit, wire) or external (e.g. stones, glass ceramics) character. Based on the cullet characteristics and imposed firing schedules, different glass quality grades arise and critical defects are highlighted. Thereafter, the most promising glass waste sources that can be recycled via this novel recycling approach are distinguished and directions for future research are highlighted.

Considerations for the Integration of Glass in Superyacht Structures

Daniël Wium, Evert Lataire, Jan Belis — Mon, 20 Jun 2022 00:00:00 +0200

In recent years, it has become popular for superyacht designs to incorporate large uninterrupted glazed areas in the superstructure. Larger windows increase the amount of natural light that enters the yacht and add to the yacht’s aesthetic appeal and exclusivity. Cruise vessels and other types of passenger ships have seen similar trends. However, window panes are currently isolated from the structural loads within a vessel and their dimensions are restricted by the presence of a frame as a conventional load-bearing structural component. The use of load-bearing glass components presents a solution to this problem as it can also add to the strength of a ship’s structure, thereby reducing the extent of conventional structural materials such as steel or aluminium profiles. Major challenges exist for the use of glass as a load bearing component in a ships’ structure. Even though a solid scientific background has been established for the structural use of glass in structures on land, a lack in knowledge exists of how the challenges in the marine environment can be addressed. This paper gives an overview of the requirements of a ship structure, and more specifically yacht structures, and describes the challenges associated with using glass as a fully integrated structural component. Further implications for the integration of structural glass in a superyacht structure are also discussed and suggestions for a possible design approach is presented.

MICA (Monitoring Internal Comfort Application):

Mon, 20 Jun 2022 00:00:00 +0200

Façades are one of the main elements that affect indoor environmental quality (IEQ) in buildings and building performance. Given the increasing development of sensor technology, the collection of building monitoring data is useful to understand whether the building and in particular the façade system performs as designed. The increasing use of Technical Building Management (TBM) as well as Building Automatic and Control System (BACs) has been demonstrated to be a promising method to decrease the energy consumption and increase the indoor comfort in new and existing buildings. This project aims to develop a tool showing and processing the monitoring data in a BIM environment using an IFC model. The application has been developed thinking about a BIM approach in the building management. Nowadays IFC models are the most used exchange file format in a BIM process. An IFC file can be loaded into a common data environment (CDE) reachable from stakeholders, sharing information and management strategies. The developed tool is a stand-alone application written in C# which is called MICA (Monitoring Internal Comfort Application). MICA can properly display the monitoring data of building sensors, sharing information between different building actors using the IFC format. It is a platform to visualize, manage and identify the IEQ aspects of building based on real monitored data.

Exploratory Study on the Load-Bearing Behaviour of Laminated Glass Beams Exposed to Fire

Maximilian Möckel, Katharina Lohr, Christian Louter — Mon, 20 Jun 2022 00:00:00 +0200

All-glass structures have become increasingly popular with architects and builders in recent years. Glass surfaces are becoming larger and more impressive, while connections are being decreased to obtain maximum transparency. The supporting structure of glass facades, glass roofs or walk-on glazing is mostly made of metal. One of the reasons for this are the fire protection requirements. To increase the overall transparency load-bearing glass structures have recently been given more attention. However, their use is currently still limited due to the concerns about glass performance in case of fire. Within a research study at TU Dresden load-bearing tests in a furnace were carried out to examine the load-bearing behaviour of glass beams exposed to fire. Different glass types and interlayer materials were tested with varying loads. This study provides a closer look at fire performance of glass beams and proposes further examinations to increase the load-bearing capacity in case of fire.

IN BETWEEN: An Interlayer Material Study for Interlocking Cast Glass Blocks

Maria Dimas, Faidra Oikonomopoulou, Marcel Bilow — Mon, 22 Aug 2022 00:00:00 +0200

Interlocking cast glass assemblies are a promising solution for architectural cast-glass applications aiming for high transparency and a reversible structure that allows the reuse of the glass components (Oikonomopoulou et al.,2018; Oikonomopoulou,2019b). In such a system, an interlayer material between the glass elements is essential, to assist the homogenous stress distribution and account for the surface microasperities of the glass elements. Towards circularity, this material should be dry (and not an adhesive), allowing for the eventual disassembly of the system. Previous experimental work by (Aurik at al.,2018; Oikonomopoulou at al.,2019b) has focused on the use of PU and PVC interlayers as suitable candidates; the focus in those studies has been solely placed on the mechanical performance of the interlayer material. This research provides a review of potential material candidates suitable for interlayers of an interlocking cast glass assembly based on a set of revised design and performance criteria that are divided into primary and secondary. Furthermore, the impact their unique material properties have on the potential application of the interlocking system is examined. The whole process, from fabrication to construction of the entire assembly, based on an assumed building scenario, is presented in a chain reaction manner, whose starting point is the interlayer itself. After defining the design criteria the interlayer should adhere to, the proposed candidates are: PETG sheets (Vivak®), Neoprene, Aluminum, Laminated Polyurethane (PU) and a Soft-core aluminum interlayer. The unique properties and fabrication challenges of all five proposed interlayers are considered, as well as their properties in relation to assembly, which leads to the development of two distinct assembly sequences. The main distinction concerns the interlayers that risk creeping and those that do not. The research concludes with a comparison between the interlocking assembly and the other glass block assemblies currently applied.

Rapid Safety Assement and Experimental Derivation of Damage Indexes for In-Service Glass Slabs

Chiara Bedon, Salvatore Noè — Mon, 20 Jun 2022 00:00:00 +0200

The mechanical performance of pedestrian structures attracts the attention of several studies, especially with respect to unfavourable operational conditions or possible damage scenarios. In terms of vibrations, for example, specific customer comfort levels must be satisfied, depending on the class of use, the structural typology, the involved materials, in addition to basic safety requirements. A special consideration should be given to in-service systems that are possibly affected by degradation or even damage, and thus potentially unsafe for pedestrians. In this regard, the availability of standardized non-destructive protocols for a reliable and rapid structural safety assessment may result in efficient support for diagnostic analyses. In this paper, 3 different laminated glass (LG) modular units belonging to 2 different indoor in-service pedestrian systems located in Italy are investigated. Operational Modal Analysis (OMA) procedures and dynamic identification techniques are used to quantify the residual capacity of the examined systems, including damage and material degradation, based on a single triaxial Micro Electro-Mechanical System (MEMS) accelerometer. The experimentally derived performance indicators and calibrated mechanical parameters for the examined structural system are assessed towards traditional design procedures, and further quantified with the support of Finite Element (FE) numerical model updating. A comparative analysis is carried out to explore the structural performance and safety levels of in-service LG slabs in regards to vibration comfort, deflection control and stress analysis.

How to Exploit the Glass Mass for Damping a Building?

Mon, 20 Jun 2022 00:00:00 +0200

The worlds spectacular skylines host tall and slender buildings to create a maximum of office, residential and commercial space on a minimized footprint. These structures need to cope with increasing wind forces at height and are additionally affected by wind-induced vibration due to their lower natural frequencies. The resulting vibrations make users uncomfortable. Therefore, heavy tuned mass dampers are installed in structures and occupy valuable space especially in the costliest top-floors. As an example, Taipei 101’s steel damper is located between the 87^th and 91^st floor and weights astonishing 660 metric tons. This raises the need for additional reinforcement which increases cost and carbon footprint.Most buildings in expensive metropolises are cladded with remarkable glass facades. Therefore, we asked the question if it was possible to use the existing mass – more specifically the glass mass in a Double‑Skin Facade – to dampen the building’s movement, create a comfortable space for the user, exploit more floor area for the investor and finally to minimize the amount of building material to reduce carbon footprint for society. The idea was realized in a collaborative research effort of TU Berlin, BTU Cottbus-Senftenberg and Josef Gartner GmbH that resulted in a full-scale mock-up of a Double‑Skin Facade. Its outer skin can move laterally on a guide rail system. As the building starts to move, the facade's inner skin remains fixed to the base structure while the outer skin follows the building’s movement in a delayed manner due to its mass inertia. The fixed inner skin and the moveable outer skin are connected by a spring system that is tuned to the first natural frequency of the base structure. During the motion of the facade’s outer skin, the spring system redirects the relative movement and generates a stabilizing force for the base structure in the opposite direction. Additionally, an electrical machine is placed in between to provide an adjustable damping effect for semi-active and passive control. It also serves the purpose of a generator to study the opportunity to harvest energy. The paper shows the structural design options for the novel facade concept in the context of a project review of Double-Skin and Closed-Cavity Facades. The function of a full-scale mock-up, its fabrication and installation are described to show feasibility and ongoing challenges. First test results reveal a close match between theoretical assumptions and the applied testing. This engineering-driven and experimentally validated design opens a new field of architectural options in sustainable facade design which is focused on tuning physical parameters that affect the damping properties of the global structure.

A Simple Numerical Tool for Superimposition of Climatic Load and Wind Load in Closed Cavity Facades: Importance of a Coupled PE-Thermal-Mechanical Model

Sat, 15 Oct 2022 00:00:00 +0200

This paper is the first in a series on the behavior of Closed Cavity Facades (CCF) under thermo-mechanical loading excitations. CCF are a novel trend for high performance double skin façade solutions, supplying high performances in terms of thermal and acoustic insulation and providing valuable benefits in terms of maintenance cost reduction. However, existing calculation methods adopted for double skin façade glazing verification under wind and climatic loads do not seem accurate to capture the particular behaviour of the CCF. In particular, the permeability of a CCF air cavity is several orders of magnitude less than the permeability of a ventilated double skin façade and current standards, such as EN1991-1-4, do not comprise any guideline for the optimized design of impermeable double skins. Both skins are recommended to be designed based on the full net pressure, or only discounting the internal pressure portion, without any provision for the load sharing effect. Moreover, climatic loads are conservatively applied ignoring permeability effects, overestimating in several cases the safety and serviceability behaviour under the daily and yearly temperature cycles. It is clear that the absence of a validated calculation approach enforces the demand for extremely safe assumptions, giving a paradox that a high performance façade is currently designed by a non-optimised calculation approach. In order to solve the shortcoming at hand, a comprehensive coupled pressure equalization-thermal-mechanical model has been developed and validated by means of experimental measurements. In this paper, the analytical basis of the model is described, starting from the scenario of a completely impermeable cavity and comparing the model outcomes with a reference software for the analysis of insulating glazing units. It will then be shown that the model can be extended to permeable cavities by accounting for a proper pressure equalization scheme through the openings. Finally, a sensitivity analysis of the major façade geometry variables was conducted with the numerical model, considering a wide range of possible applicative scenarios in term of permeability and skin stiffness.

Experimental and Numerical Assessment of Permeability Functions in Closed Cavity Facades

Fri, 14 Oct 2022 00:00:00 +0200

This paper is the second in a series on the behavior of closed cavity façades (CCF) under thermo-mechanical loading excitations. CCF are a novel trend for sustainable high quality double skin façade solutions, characterized by a minimal maintenance demand. The air cavity is designed according to stringent air tightness requirements, provided with a small dry air flow that preserves the relative humidity, minimizing the risk for condensation and dust ingress. This extremely reduced permeability, with respect to typical double skin design, gives a scenario in conflict with the general prescriptions for the structural calculations of double skins under wind and climatic loading. This paper is the second of a series of three documents that aim to identify the structural shortcomings in the current codes and to propose efficient calculation methods and modifications to the current calculation strategies. This will overcome a critical design paradox in double skin and in particular CCF aim to reach the highest sustainability performance, by means of outstanding thermal and acoustic insulation efficiency and providing the cavity with a clean and dry environment, suitable for a significant upgrade of the façade life expectancy. On the other hand, an overly conservative calculation approach is generally against the optimization of the sustainability performance indices, determining an excessive use of materials and then impacting the overall life cycle cost under several perspectives. In particular, the objective of this second paper is to describe in a measurable way the permeability behavior of a CCF, defining statistical variability and nonlinearity effects measured during dedicated experimental testing. The permeability functions represent a fundamental input for the proposed assessment tool introduced by the first paper and it will be seen that an accurate quality control during the manufacturing can ensure the robustness of an optimized calculation approach, based on the load sharing mechanism between the skins. In the third paper it will be shown that the proposed tool, fed by the experimental permeability functions, appears adequate to predict the façade structural behavior under the superimposition of thermal loading, wind loading and dry air flow effects, when compared with measurements collected during outdoor testing on a façade specimen.

Experimental Validation of a Numerical model for Closed Cavity Façade Glass Structural Calculation under Dynamic Cavity Temperature, Dry Air Flow and Wind Loads Effects

Sun, 16 Oct 2022 00:00:00 +0200

Closed Cavity Facades (CCF) are a novel trend for high performance double skin façades, providing a valuable benefit in terms of maintenance cost reduction. Current structural codes contain incomplete and conservative assumptions about the wind load sharing design for this type of multiple skin. In addition, in most codes glazing skins are investigated as separated structural glass elements, while it would be more appropriate to consider the structural interaction between the two skins. Indeed, the the CCF structural behaviour key is the air cavity response to wind loads and the way the cavity air supply is regulated in order to preserve low relative humidity. An optimal design of the outer and inner glass skin should take in account the superposition of the actions of wind and dynamic temperature and therefore the variable mass within the cavity. During the last years Ghent University and Permasteelisa have conducted a theoretical investigation and developed an assessment tool for the double skin structural design. The tool has been validated by means of an extensive experimental campaign. Several CCF elements have been exposed to on-site wind loads, solar thermal imposed loads and controlled laboratory quasi static and cyclic loading pressures. As such, the response to the natural climatic loading has been collected as representative of the CCF working conditions during its entire life. This paper is the last of a series of three documents that summarizes the outcomes about the research on the CCF panels. In the first paper the basics of the pressure-equalization model has been discussed and verified, describing in particular the extreme case of a fully closed cavity. In the second paper the permeability functions of the CCF have been derived as fundamental input for the dynamic simulations under variable cavity temperature conditions, which are the major objective of this third and last work. The experimental results and the numerical simulations are demonstrating the need for an improvement of the current codes. In particular, the simulations allow to account for a reliable load-sharing between inner and outer panes, leading to thinner glass panes. Note that this depends strongly on the airtightness levels of inside and outside, and manufacturing airtightness scatter should be accounted for ensuring a robust calculation approach.

Slim Skins: Towards a New Glazed Façade System

Mon, 20 Jun 2022 00:00:00 +0200

From early 20th century architects have envisioned transparent buildings such as Mies van der Rohe’s “skin and bones” concept and his 1921 proposal for the Friedrichstrasse Skyscraper competition in Berlin. One hundred years on, there is a much better understanding of the energy consumption implications of highly glazed buildings, yet architects, developers and users are still attracted to fully transparent facades. This paper sheds some light on the challenges to build with high performing glazing façade systems (originally called curtain wall systems) while efficiently utilising resources and reducing its manufacturing embodied carbon. This can be achieved by omitting the typical frame (mullions and transoms) and making the glass work structurally. Built examples by Octatube are Triodos Bank (Netherlands) and Echo Building (TU Delft- Netherlands). A further option that will focus on sustainable unitised systems is currently being explored by Octatube and TU Delft Building Technology graduation student. This is based on an optimised unitised frame integrated in between glazed units. These different systems will be assessed and compared against each other regarding its end-of-life recovery potential, embodied carbon and visual impact.

Experimental Investigation into the Effect of Elevated Temperatures on the Fracture Strength of Soda-Lime-Silica Glass

Evelien Symoens, Ruben Van Coile, Jan Belis — Thu, 22 Sep 2022 00:00:00 +0200

A comprehensive understanding of the fire performance of construction products is necessary to achieve fire safety of buildings. However, the behaviour of structural soda-lime-silica glass in elevated temperatures and fires is still relatively unknown. Soda-lime-silica glass is susceptible to thermal shock and its changing material properties when subjected to high temperatures makes predicting its behaviour in fire complex. This paper investigates the fracture behaviour and fracture strength of soda-lime-silica glass at elevated temperatures in a range which is relevant for e.g. early fire stages. An experimental co-axial double ring (CDR) setup was designed according to ASTM C1499-19. This setup was installed in an environmental chamber on a universal testing machine to control the temperature during the tests. First, multiple CDR tests at a controlled temperature of 25 °C were performed to get an experimental strength distribution at ambient temperatures. Second, CDR tests were performed at a controlled elevated temperature (i.e. a uniform temperature of 275 °C) to attain a distribution of the corresponding strength. A slight increase in average fracture strength was observed when increasing the temperature from 25 to 275 °C. Additionally, numerical simulations are performed to predict the behaviour of elevated temperatures on soda-lime-silica glass. These simulations are compared to the experimental results and some points of attention are raised.

Impact of Cutting Process Parameters on the Mechanical Quality of Processed Glass Edges

Paulina Bukieda, Bernhard Weller — Mon, 20 Jun 2022 00:00:00 +0200

The inspection of glass edges is gaining in importance in research, as the strength of a glass edge has been found to be highly dependent on its processing. Glass edges are produced by cutting. Depending on their type, they may be additionally seamed, ground or polished in the grinding process. Cutting and grinding processes create mechanical interference in the brittle material, leaving flaws and cracks in the edge surfaces. The current state of the art presents cutting process parameters which correlate with minor flaws and a high glass edge strength. Research at the Technische Universität Dresden aims to understand the impact of grinding processes and to develop parameters for processing glass edges with a defined and reproducible optical and mechanical quality. To isolate observations of the grinding process from the cutting process, this paper examines the impact of cutting process parameters on further processed glass edges. Several different cutting parameter-sets formed the basis of various test series that were performed on specimens whose glass edges were processed by the same manufacturer. This paper presents an optical and mechanical examination of the specimens. The results show that higher optical and mechanical qualities of the cut edge and arrised edge can be obtained by adjusting the cutting process parameters. It had no major impacts on smooth ground and polished edges.

Effects of Composition on the Durability and Weathering of Flat Glass

Sat, 21 May 2022 00:00:00 +0200

Among the environmental factors affecting glass weathering are humidity, exposure time, temperature, and the presence of pollutants in the atmosphere. Notwithstanding that the weathering produced depends on numerous factors, the important weathering effect of high humidity may be specifically mitigated by using a good chemical composition for the glass. To evaluate this relationship, flat glass samples from three suppliers were studied. The chemical composition of the samples was determined and the variability in compositions was evaluated to verify to what extent these small differences can affect their chemical durability. The chemical durability of the samples was evaluated by determining the hydrolytic resistance of crushed glass powder and using a visual appearance evaluation of bulk samples. The results demonstrate that when the samples are frequently washed, the compositional differences found between the suppliers can cause a significant difference in durability. The samples possessing the highest molar concentrations of Al₂O₃, and alkaline earth oxides (MgO + CaO) exhibited the highest hydrolytic resistance and the least visual deterioration. Differences encountered for the weathering products of glasses of comparable bulk compositions highlight that the process parameters play a major role in the alteration of the surface compositions of the glasses. For the unwashed samples, no consistent correlation was found between hydrolytic resistance and visual deterioration.

Edge Strength of Annealed Float Glass: Influence and Optimization of Cutting Process Parameters

Mon, 20 Jun 2022 00:00:00 +0200

The desire to apply annealed float glass with their economic and optical advantages is limited by the reduced edge strength due to the cutting process. The edge strength of annealed float glass is a decisive factor especially for insulating glazing due to temperature stress. In standards (e. g. DIN EN 18008), the edge strengths are reduced compared to the surface strength of annealed glass. This is mainly a result of the applied cutting process with the corresponding parameters and the glass handling after cutting. The type of cutting process and the cutting parameters (cutting wheels, etc.) have an effect on the development of micro cracks and thus also on edge strength. A defined cutting process allows reproducible and enhanced edge strength. This paper presents results of destructive and non-destructive investigations with regard to the edge strength. For the investigations, glass panes were cut on an industrial cutting machine with various process settings. Among other things, the following cutting parameters were varied: type of cutting wheel, cutting pressure, cutting speed and cutting fluid. In addition to the process parameters, different basic glasses, glass thicknesses and the cut process on the tin side were also investigated. The samples were examined with the aim to determine the correlations between the cutting process / glass parameters, the edge strength and the micro crack geometry and optimize the parameters. The destructive tests were carried out primarily with a modified four point bending test, but also with the standard four point bending test according to DIN EN 1288-3.

Non-Contact 3D Characterization System of Scratch-Induced Surface Damage on Monolithic Glass Panel

Zhufeng Pan, Jian Yang, Xing-er Wang, Yige Wang, Gang Li, Xianfang Jiang — Mon, 20 Jun 2022 00:00:00 +0200

Glass material has been widely used in modern architecture. Scratch-induced surface damage of aged monolithic glass panel leads to the strength degradation of material and thus threatens the glass safety. Therefore, in order to accurately evaluate the strength of aged glass elements, it is crucial to extract key damage features including the damage location and depth in a precise way. This study aims to develop a non-contact stage-wise scanning method to extract 3D damage characteristics on glass surface, which can further facilitate the investigation into the associated influences on the flexural strength of glass. Coaxial double ring tests on annealed glass specimens under various magnitudes of applied loads were performed, which aimed to explore the influence of the surface damage on the flexural strength. Monocular microscope equipped with an industrial camera was used to detect damage area throughout the glass panel in the first stage rapidly. It was then followed by a chromatic confocal scanner to precisely measure the damage depth within local damage area. The results via confocal microscope scanning were considered as the reference values. It shows that the proposed method can be a potentially alternative solution instead of confocal microscope for damage quantification.

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Experimental Investigation into the Effect of Elevated Temperatures on the Fracture Strength of Soda-Lime-Silica Glass

Impact of Cutting Process Parameters on the Mechanical Quality of Processed Glass Edges

Effects of Composition on the Durability and Weathering of Flat Glass

Edge Strength of Annealed Float Glass: Influence and Optimization of Cutting Process Parameters

Non-Contact 3D Characterization System of Scratch-Induced Surface Damage on Monolithic Glass Panel