Structural Glazing Research Articles

Experimental investigations on the cyclic load-bearing behavior of structural glazing joints under seismic load

AbstractIn addition to static loads, structural glazing joints in glass and facade construction in many regions are subject to extraordinary effects such as earthquakes. Seismic actions are characterized by a randomly recurring and dynamic load that affects the structural behavior of the viscoelastic material. Publications on the load-bearing behavior and design of structural glazing joints against seismic loading have not systematically considered these effects. In this paper, relevant parameters influencing the seismic loading of structural glazing joints are determined, evaluated, and narrowed down to areas of practical relevance as part of a theoretical stress analysis. On this basis, extensive experimental investigations of the low-cycle fatigue behavior of structural glazing joints are presented. Cyclic stress–strain curves are determined and compared with quasi-static reference tests to describe the basic low-cycle fatigue behavior. The influence of the previously determined parameters on the cyclic load-bearing behavior can thus be determined and presented. These investigations provide an important basis for describing the behavior under typical seismic random loading. In particular, the type of load application caused by the different construction types of glass and facade buildings can be mentioned as a decisive influencing factor in addition to the frequency of building construction. The results provide a first important contribution to the modeling and design of structural glazing joints against earthquake effects. Further extensive scientific investigations will be carried out on this basis in order to develop a design model for structural glazing joints in disaster scenarios.

Investigations on the influence of manufacturing and curing effects on the properties of structural-glazing adhesives subjected to tensile stresses

AbstractDemand for structural glazing joints has increased considerably in recent years due to the ever-increasing loads resulting from growing dimensions, especially in spectacular glass structures. Within the scope of planning and production monitoring, existing influences are analyzed based on the standard H-sample from the current structural glazing guidelines. These guidelines do not define any specific methodology or guidance for manufacturing test specimens. For determining load-bearing properties, various parameters, such as specimen age and curing condition, have a relevant influence during and after manufacturing. This study aims to investigate the manufacturing process for H-specimens systematically to identify and minimize the interfering influences. On this basis, the influence of the curing of modified H-specimens was investigated in detail for specimens under tensile load. Next to curing at room temperature, tempering at 40 °C was investigated for two different H-joint geometries. Thereby, a relevant influence of specimen age and different curing conditions on the strength as well as stiffness properties could be determined. As one result of the study, the curing time can be shortened by tempering the specimens in relation to the specified 28 days by ETAG 002-1. For calculation methods used in practice, like the structural spring method, suggestions for statistically validated strength and stiffness parameters representing the load-bearing behavior are proposed, considering the adhesive’s curing state and the joint’s nominal stress.

On the Possibility of Using Adhesive–Sealants Based on MS-Polymers for Structural Glazing

On the Possibility of Using Adhesive–Sealants Based on MS-Polymers for Structural Glazing

In-Plane Behaviour of Unreinforced Masonry Strengthened with a Structural Glass Window: A Proof of Concept

Innovative solutions for seismic-retrofitting existing structures are currently required, as often traditional strategies are expensive, non-reversible, highly invasive, and/or fail to address both serviceability and ultimate limit states together. The present paper describes a preliminary experimental campaign performed at TU Delft to investigate an innovative structural glass window for strengthening masonry buildings. To this purpose, a prototype composed of a timber frame, a semi-rigid adhesive, and a 20 mm thick structural glazing layer was designed. The prototype aimed to improve the structure’s behavior against minor but more frequent service vibrations (SLS), as well as against ultimate ones (ULS). Specifically, an increase in the structure’s in-plane capacity and stiffness was targeted to reduce cracking at low drifts/displacements, while at larger drifts, the adhesive’s tearing and timber crushing were used to activate damping. To evaluate the prototype’s performance, a quasi-static, cyclic, in-plane test on a strengthened full-scale wall was performed and compared with available data on a similar, yet unstrengthened, wall. Although the benefits were not pronounced in terms of cracking and energy dissipation, the implementation of the proposed strategy provided an increase in terms of initial stiffness (18%), force capacity (8%, 36%), and ductility (220%, 135%). This outcome provides the ground for numerical studies that will help better delineate the proposed strategy and improve the current design.

Silicone structural glazing under blast loading

Silicone structural glazing under blast loading

A mesoscopic analysis of cavities in two components silicone adhesive with cylindrical butt joint specimens

In the construction industry, silicone adhesives were firstly used as sealant because of their elasticity and resistance towards environmental exposition. Nowadays, modern façades need to fulfil thermal efficiency, while keeping transparent design. Structural glazing façades satisfy these requirements due to silicone adhesives. However, because of the complex nonlinear material behaviour of silicone adhesives, only a conservative dimensioning with linear material law using high safety factors is proposed in the European guideline ETAG 002. This investigation aims to quantify cavities in cylindrical butt-bonded specimens on a mesoscopic scale in two-component silicone adhesive for layers at minimum ETAG 002 requirement (4 mm). As hydrostatic tensile stress accounts for cavities, the necking transversal to the load has been monitored with digital image processing during tensile tests. In the developed in-situ tensile aperture cavities have been quantified with an X-ray micro-computed tomography (Micro-CT) on a mesoscopic scale at defined strain. With scanning electron microscopy (SEM) footprints of cavities on the fracture surface can be observed. As main conclusion cavities have been visualised in-situ under tensile load and quantified to volumes ranging from 0.0055 mm³ to 0.194 mm³.

Sound Insulation of Façade Element with Triple IGU

Sound insulation design for structural glazed façade is an important task in environmental noise control, as increased continuously repeated noise is a significant factor impacting on people’s well-being and is associated with a negative impact on their health. For façades, in addition to sound insulation, requirements for safe use and high energy efficiency are also usually raised, which partly determine the composition of the glazing: triple insulating glass unit (IGU) with inner safety laminated glass sheet. Therefore, the aim of the research was to investigate the structural sealed façade structure with triple IGU and to determine the effect of the thickness of ordinary and laminated glasses, their position in the IGU, the thickness of the gas cavities, and the mass of the structural frame on the sound insulation level of structural glazing. Experimental measurements of the sound insulation index of the investigated façade elements with IGU of various constructions were performed in an acoustic reverberation chamber according to standard procedures. The result of the study indicated that the use of the second laminated glass in a triple IGU is inefficient, the highest sound insulation indicators are achieved by increasing the thicknesses of the external glass sheet and the gas cavity; increasing the mass of the frame also has only little effect on the sound insulation of the structural glazing.

Investigation of the Resistance to Operational Impacts of Sets for Structural Glazing of Facades

Investigation of the Resistance to Operational Impacts of Sets for Structural Glazing of Facades

Bonded Glass Tubes as Translucent Jacket of the Museum of Fine Arts in Houston – Design, Engineering and Testing

The “Nancy and Rich Kinder Building” is one of three new buildings being constructed as part of the redevelopment of the Museum of Fine Arts in Houston Campus. From the outside, the building is almost completely wrapped in translucent hot‐bent semicircular tubes made of laminated glass (“Cool Jacket”). The glass tubes not only serve as a design element, they also regulate the incidence of daylight and reduce the energy entry into the building. An almost invisible fixing was realized by the use of special structural glazing profiles on the inside of the glass tubes. Both the glass tubes, which are exposed to high thermal stresses, and the adhesive joints, which have to withstand high wind loads, required detailed finite element calculations as well as experimental investigations. The article describes and evaluates the calculations and experiments as well as the design and installation.

Derivation of Kinematic Equations Based on Full-Scale Racking Tests for Seismic Performance Evaluation of Unitized Four-Sided Structural Sealant Glazing Curtain Wall Systems

Curtain wall glazing systems are a major part of a building due to the multiple roles they have, including occupant protection against environmental effects and the transfer of loads to the structural system. From a structural perspective, limited analytical guidelines and methods exist to aid designers in their determination of the curtain wall performance without extensive simulation or laboratory testing. This study takes experimental data from full-scale, “unitized”, four-sided structural sealant glazing (4SSG) curtain wall system mockups featuring a re-entrant corner subjected to cyclic racking displacements in accordance with the American Architectural Manufacturers Association AAMA 501.6 protocol to derive and establish equations that predict the relative displacements of the glass relative to the glazing frame, based on the amount of inter-story drift. Through derivation and testing, sealant cohesive failure and glass cracking were identified as limit states and corresponding drift levels were determined to control many of the equations. Displacements from the newly derived equations were correlated to the effective shear strain value experienced by the structural silicone in the mockup concurrently with the curtain wall’s drift capacity. This paper provides detailed derivation of the kinematic equations for possible use by glazing design professionals. Such equations can help designers to more easily predict the drifts that cause damage to such systems by manual calculations without the need for expensive mockup testing or time-intensive computer models.

Silicone bonded steel-glass joints under high temperature

Abstract The use of structural adhesive for the bonding of steel-to-glass elements increased along with the structural and aesthetic requirements of high-performance transparent building skins, providing better performance of the steel-glass assembly reducing the stress concentration in the glass ply. However, the behavior of bonded joints subjected to high temperatures and the alteration of their mechanical characteristics after a heating process are fields that need to be deepened. The present paper aims at providing an innovative contribution to the gap in the knowledge of the behavior of bonded joints at ambient temperatures up to 300 °C. A detailed overview of the test set-up followed by the results of the mechanical tests will be provided. The tests are composed of two main steps that are namely the heating at different temperatures of the joint specimens and the definition of the residual capacity of the joint, under tear or shear load. A comparison of the mechanical behavior will be provided for different structural adhesives: commonly used adhesive DC993, SG20, SG500, and SIKA265 characterized by a soft elastic modulus, and TSSA, a high strength structural glazing silicone film adhesive. The test allows proposing residual resistance criteria that, even if they are obtained for a specific type of steel-glass joint, provide useful information about the choice of the adhesive in cases in which high temperatures are expected. Finally, a finite model is calibrated on the basis of the experimental results, supplying information about the possible modeling choices and the influence of the specific geometry adopted in tests on the results.

Novel Studies on Thermo-Mechanical Properties of Structural Glass with and without Lamination

The attractiveness of glass is something that occupied the world market with a unique claim. It has many applications that go beyond the provision of visual aesthetics, which includes a view of the inside and out. Due to extreme levels of clarity, structural glazing may be so transparent that it may go unnoticed by design or make a strong visual impact such as the focal point of a building. This paper focused on structural glass with various laminated/laminated conditions that were used to investigate the Dynamic Mechanical Properties. The storage modulus (G'), loss modulus (G'') and damping factor (tan delta) were determined at various levels, ranging from room temperature to elevated temperatures (250 °C) to understand the behavior of glass structure with and without laminated glass over a range of temperatures. The G' & G'' were tested to understand the effect of bonding, fracture behavior between the pure glass and laminated glass to observe the response with respect to temperature. Results are found that G' and G'' improve over a range of temperatures for laminated glass with enlightening fracture behavior. Laminated glass also has a major influence on the damping factor, but it also depends on the laminated thickness and materials. Thermo-Mechanical Properties of laminated glass are more improved, without affecting the transferability of glass.

Stress-strain state of Insulated Glass Unit in structural glazing systems

Stress-strain state of Insulated Glass Unit in structural glazing systems

Engineering exterior translucent coatings with the use of profile glass and composite materials

The paper raises certain questions concerning the use of structural glass (glazing) in external vertical enclosures of modern construction systems, pointing to the need for combining composite materials, especially composite foam, in translucent enclosures, which helps dramatically reduce the weight of external panels while improving their heat and sound insulation performance. It also emphasizes the relevance of energy efficiency at the building operation and building construction stages, as energy efficiency is not only the heat saving performance during building operation, but also a high effectiveness of the construction technology.The novelty of the study lies in engineering a wall panel possibly combining two materials — profiled glass and composite foam. The paper not only details the panel design, but also describes the manufacturing technology and the envelope arranging processes with two wall panel attachment methods and related joint assemblies. Based on a number of scientific publications, the handling mechanisms are discussed suitable for different ways of coupling the structural elements — wall panel and floor slab. Focusing on box-type structural glazing, the authors stress the need for further study involving other types of structural glass (channel shaped, ribbed, trimmed) to create multicomponent wall panels for a variety of regional climate conditions.

Laser surface modification of structural glass for anti-slip applications

The use of soda-lime silicate glass as a structural element has become frequent in modern buildings. The load-bearing applications of glass in floors, footbridges, terraces, or stairs require an optimal combination of non-slippery properties of the surface, element weight, and strength, and structural glazing can be compromised by the incorporation of laser surface patterned ornamental motifs. Laser surface modification has significant advantages for selective surface area modification; nevertheless, the mechanical performance of the processed glass remains unknown, which precludes reliable structural calculations and employment in construction. In this study, we investigated the surface modification of annealed and heat-strengthened glass via CO2 laser scanning for the production of rough anti-slip surfaces. The surface roughness and the reduction of the bearing load strength were quantified. Slip resistance-enhanced surfaces with roughness values (Rz) above 20 μm and characteristic bending strength preservation up to 74% were obtained. The results pave the way for the use of laser surface-modified plates in laminated glass elements with optimized strength calculation and weight reduction.

Member moment capacity of complex-shaped aluminium mullions under wind suction loading

Unitized curtain wall systems made of aluminium frame infilled glass panes are commonly used to form the building envelopes in many buildings. The vertical framing members of such systems known as mullions are extruded aluminium sections with complex geometries. These mullions must transfer the wind load acting on the building envelope to the main structural system. This paper presents a detailed numerical study on the member moment capacities of long span mullion sections subject to wind suction loading. Validated finite element models of the mullions developed to predict their section moment capacities were extended to predict the member moment capacities. The procedures adopted in developing the finite element models and the analysis results are given in this paper. Mullions of different cross-section geometries with varying member slenderness used in both the captive and structural glazing systems were considered. In addition, the performance of open and hollow mullion sections was investigated. Lateral restraints provided by the glass panels to the mullions were simulated in the models while the effect of providing lateral restraint at the mid-span of the mullion through bracing was also investigated. The finite element analysis results were compared with the predicted capacities of Aluminium Association Design Manual and Eurocode 9 Part 1-1 design rules and suitable recommendations were made in relation to their applicability for mullion sections. Improved mullion sections reinforced with cold-formed steel stiffeners were proposed and their potential use in real world applications was discussed.

Nonlinear elastic finite fracture mechanics: Modeling mixed-mode crack nucleation in structural glazing silicone sealants

Requiring both stress and energy conditions to be met simultaneously proved key to modeling brittle crack formation at singular and nonsingular stress concentrations in linear elastic materials. The present work extends this so-called coupled stress and energy criterion to brittle crack nucleation in hyperelastic media using the example of silicone adhesives. For this purpose, we provide a comprehensive constitutive as well as fracture mechanical characterization of the structural silicone adhesive DOWSIL™ 993 using a large set of experiments and propose a mixed-mode failure model for crack initiation in nonlinear elastic materials. Characterized in independent experiments, the model is used to determine critical loads of hyperelastic adhesive bonds in both shear and tension dominated configurations. For any of the examined adhesive joint configurations the model predicts and explains size effects and agrees well with experimental findings. We study stable and unstable crack propagation observed in video recordings of our experiments. It is shown that crack initiation, crack growth and crack arrest are caused by nonmonotonic energy release rates and can be predicted. Effects of excess energy available after crack nucleation and initial unstable crack growth are discussed.

МЕТОДИКА КОМПЛЕКСНОЙ УСКОРЕННОЙ ОЦЕНКИ ДОЛГОВЕЧНОСТИ ЭЛЕМЕНТОВ СВЕТОПРОЗРАЧНЫХ ОГРАЖДАЮЩИХ КОНСТРУКЦИЙ ДЛЯ СОВРЕМЕННЫХ ФАСАДНЫХ СИСТЕМ ПОД ДЕЙСТВИЕМ КЛИМАТИЧЕСКИХ ФАКТОРОВ В УСЛОВИЯХ КЛИМАТА ДАЛЬНЕГО ВОСТОКА

Taking into account features of climate of the Far East and the capitals of the Khabarovsk and Seaside regions - the cities of Khabarovsk and of Vladivostok the technique of the complex accelerated assessment of a durability of elements of the translucent protecting designs (TPD), such as, aluminum shapes, double-glazed windows of structural appointment, sealants and sealing laying for structural glazing of the modern front systems is offered. Two new modes of integrated accelerated tests under the influence of climatic factors for double-glazed windows, sealants and sealing laying (mode 1) and aluminum shapes (mode 2) allowing to carry out at the same time tests of elements of TPD with use of a unique test equipments are developed. The short state-of-the-art review of high-rise construction in Khabarovsk and Vladivostok is given. As artificial climatic factors at the accelerated laboratory tests cyclic influences of positive and negative temperatures, humidities, transitions through 0 ° C, ultra-violet radiation, the slaboagressivnykh of chemical environments (solutions), the salt fog are accepted (for aluminum shapes). Requirements to assessment of test data on each characteristic indicator of elements of TPD are provided. On the basis of the developed technique NIISF RAASN standard is developed.

Shear behaviour of structural silicone adhesively bonded steel-glass orthogonal lap joints

This paper outlines an experimental study on the shear behaviour of structural silicone adhesively bonded steel-glass orthogonal lap joints. In the combination of steel plate and glass panel to form a hybrid structural glazing system, bonded joints with structural silicones can provide certain flexibility which relieves stress peaks at critical points of glass panel. The cohesive failure and its related fracture pattern of test joints with varied geometries of adhesives are examined experimentally. It is shown that the presence of two failure modes as discrete voids and macro cracks is closely related to the adhesive thickness. The effects of geometric parameters of adhesives on the joint shear strength are examined. It is demonstrated that the joint shear strengths are increased with increased individual overlap length, reduced adhesive thickness or increased adhesive width while the shear deformation corresponding to maximum shear force is mostly influenced by adhesive thickness. Mechanical contributions for those effects are analyzed accordingly. Finally, an analytical formula allowing for the equilibrium of strain and force on the adhesive and adherend is proposed for the analysis of shear strength. It is demonstrated that calculated normalized shear force ratios predicted by proposed formula agree well with those from experimental results.

A newly developed silicone technology to improve thermal performance of curtain walls

ABSTRACTArchitectural trends in modern commercial façades tend towards larger glass surfaces and slimmer frame designs like structural glazing, which result in increased transparency of the design. Design should however take into consideration energy efficiency requirements. Energy regulations and climate policy targets set up strict requirements for future buildings. According to the Energy Performance of Buildings Directive, by 2020 all new buildings in EU will have to be built as “Nearly Zero‐Energy Buildings”. All public buildings have to meet that target two years earlier, at the end of 2018. These targets dictate high demand on building envelope performance and pose challenges in building design. Respecting these targets brings along an increased comfort for the building's occupants: higher internal surface temperatures reduce condensation risk and prevent mould growth while improving the indoor climate. Current solutions reduce the energy loss of curtain walls by using insulating glass units, thermally broken framing systems, low‐emission coatings and warm edge spacers. However, these technologies are reaching their maximal efficiency as they have been on the market for several decades, hence new materials and technologies are required. Since all the major elements of the façade have already been optimized, it becomes critical to ensure that the design of details is not neglected. There is a strong relationship between material characteristics at the detail level and the resulting impact on performance and durability of a façade. Unfortunately, further energy optimization of curtain walls often comes at a price, since the obtained performance improvements are limited whilst adding significant complexity and costs. The challenge today is therefore to develop solutions providing a better performance at a reasonable cost and low complexity to ensure easy adoption of the market and consequently, a significant impact on the improvement of the building stock. This paper introduces a brand‐new silicone technology and illustrates design integration and performance within different structurally glazed façade systems such as unitized and toggle designs. Looking at façades requiring curtain wall U‐values (UCW) below 1.2 W/m2K, the improvements in terms of surface temperatures, psi‐value, but also overall Ucw‐value can be remarkable at efficient cost. A comparison to existing conventional technologies is shown with regards to the overall level of impact on the entire curtain wall energy efficiency performance.