Laminated Glass Elements Research Articles

Influence of embedded steel mesh inserts on post-breakage capacity of laminated glass

Glass, as a building material, has been known for a long time. The first glass uses were limited to filling window frames. However, in recent years, the popularity of glass in construction has increased significantly. All this is due to the growing trend to bring as much natural sunlight into the buildings as possible. The increasingly popular treatment of glass as a construction material requires using laminated glass, in which a film permanently joins together two or more glass panes. This unique behaviour is because the film between the glass sheets holds the glass fragments in place when they are fractured. In this way, avoiding the risk of injury to people in the vicinity is possible. As part of the ongoing project, “Innovative solution for point-fixed laminated glass with improved capacity after glass fracture” financed by the National Center for Research and Development (NCBR) within the LIDER XI Program, an idea of laminating a steel woven mesh to glass laminates is being investigated. The steel mesh insert is designed to increase the load-bearing capacity of the sample in the post-breakage phase, thus increasing the safety of building occupants. The article deals with the post-breakage capacity of laminated glass elements subjected to three types of loading: in-plane, out-of-plane and combined actions.

Multiscale beam model for simulating fracture in laminated glass structures

This paper presents a novel numerical model for the mechanical behavior of laminated glass structures. The numerical model is designed as the multiscale numerical approach capable of simulating the fracture of laminated glass elements. This approach combines the fine-scale multilayer model and the coarse-scale macro model to achieve accuracy with high computational efficiency. The multilayer model describes the real laminated glass cross-section and further provides the parameters for the macro model that has a monolithic cross-section and behaves according to the constitutive model derived from the fine-scale multilayer model. Thus, using fine-scale material parameters for glass and interlayer, a multiscale approach can increase computational efficiency. The proposed models are discretized using the embedded discontinuity finite element method (ED-FEM) and operator split computations. The discontinuity in the displacement field, typical of cracks as the dissipative mechanism for fracture, is represented with the embedded discontinuity approach. The heterogeneity of glass elements (regarding initial imperfections) is included using five different model setups. The comparison between numerical results and experimental tests (four-point bending tests on laminated glass elements) shows a very good agreement. In addition to these comparisons, simplified engineering approaches for deflection prediction are also tested in the numerical model and compared with experimental results.

Experimental Tests of Laminated Glass with Embedded Steel Mesh Subjected to In-Plane Loading

Abstract This article presents the issue of the in-plane post-breakage capacity of laminated glass elements. It presents the results of an ongoing research project that aims to develop novel reinforced, laminated glass elements with embedded steel woven mesh and increased post-breakage capacity. The research was focused on tensile strength tests in a custom-made experimental set-up. The tests were carried out on laminated glass samples consisting of two glass panes with 8, 10 and 12 mm thicknesses, bonded with an EVA Clear interlayer (3.04 mm thick). A total of 36 reference and reinforced samples were tested (6 series of 6 samples each). During the tests, an increase in load after glass breakage was observed for all samples, however, the samples reinforced with steel mesh showed much better strength in the post-breakage phase. It was found that the steel woven mesh embedded in laminated glass increases the post-breakage capacity by approximately 300% compared to the reference samples.

Review of the Main Mechanical Testing Methods for Interlayer Characterization in Laminated Glass

In the last decades, the use of structural glass has increased exponentially. The reliability of brittle structural glass elements is considerably improved if laminated glass elements are chosen because, in this case, a redistribution of internal forces is permitted once a limited breakage occurs. Thus, instead of monolithic glass, composite materials consisting of two or more glass plies bonded together using a polymeric film as an interlayer are used. In the event of glass failure, because of the chemical bond between the different materials, the adhesion to the interlayer prevents glass fragments from scattering. To design structural elements, the definition of the mechanical features of the interlayer is necessary. However, several standards and techniques can be applied, considering the characterization of either the interlayer itself or the laminated glass. The paper reviews the main existing methods and focuses on the standard suggested by the CEN/TS 19100:2021, analyzing in detail the effect of the different parameters involved. A numerical model is presented to account for the effect of the stress level, glass, and interlayer thickness. Although the standard leaves a certain degree of freedom in choosing those parameters, in some cases the results can differ.

Monotonic and Creep Studies on the Pull-Through Resistance of Laminated Glass with Locally Embedded Steel Mesh.

The paper deals with the phenomenon of post-breakage capacity in point-fixed laminated glass elements and reports the results of an ongoing research project aimed at developing a reinforced point-fixed laminated glass element with locally embedded steel mesh and increased post-breakage capacity. The work involved monotonic and creep studies on the pull-through resistance in a custom-made experimental setup. A total of 12 test series and 48 specimens were tested, including reference and reinforced samples. In the monotonic loading experiment, the load increase after the initial glass breakage was observed for all specimens. However, the reinforced specimens with embedded steel mesh showed significantly improved post-breakage capacity. It was found that the local reinforcement in the direct vicinity of the hole in the glass increased the post-breakage strength by 46.3%, 102.6%, and 156.2% for reinforcement diameters of 75 mm, 110 mm, and 150 mm, respectively. Moreover, the creep study found that the reinforcement significantly increased the time to failure.

Response of laminated glass elements subject to dynamic loadings using a monolithic model and a stress effective Young’s modulus

Due to the brittle nature of the glass, to study the response of glass elements subjected to dynamics loadings is of great interest, mainly when human injury resulting from glass breakage may occur. Laminated glass consists of two or more layers of monolithic glass and one or more viscoelastic interlayers. In this paper, a technique to predict the dynamic response (deflections and stresses) of laminated glass elements using a linear elastic monolithic model is proposed and validated. In a first step, the modal parameters and the dynamic response of a monolithic model are calculated using the modal superposition technique. Then, the modal parameters and the modal coordinates of the laminated glass element are estimated using the equations derived in this paper. Finally, the stresses in time and frequency domain are estimated using an effective stress Young’s modulus.

Layered Laminated Glass Elements with High Load‐Bearing Capacities

In contemporary structural glass applications, laminated glass plays a key role, as it enhances elements beyond the dimensional limits of monolithic glass and ensures the required redundancy. As the size and expectations of glass as primary load‐bearing element increase, so do laminated glass layer sizes, and along with them, the manufacturing and production possibilities. However, the design and application of layered laminated glass as primary load‐bearing element such as transparent columns or masonry structures is still in its early phases compared to other structural glass elements. As a result, the Institute of Building Construction at the Technische Universität Dresden, in cooperation with Finnglass and Kuraray, investigated horizontal and vertical layered laminated glass elements under compression tests. As the interlayer of laminated glass highly affects the load‐bearing behaviour and can cause early glass breakage due to induced tensile stresses, different interlayers (Standard‐PVB, SentryGlas® and PVB without plasticizer) were examined in two specimen scales. This paper presents the main insights and assesses the failure modes within the experiments of layered laminated glass under uniaxial compression. Based on the examinations, constructive recommendations of layered laminated glass elements are derived.

Enhanced effective thickness model for buckling of LG beams with different boundary conditions

Because of their characteristic high slenderness ratios, laminated glass elements are frequently subjected to buckling phenomena. Here, simple analytical formulae for the evaluation of the effective thickness for the compressive buckling verification of laminated glass beams are proposed, based on the Enhanced Effective Thickness model, widely used for the design of laminated glass. The model applies also to multilaminates. Tables for the calculation of the relevant coefficients in the most common cases have been added for ease of reference and to facilitate the practical use. Comparison with numerical results, performed by considered paradigmatic cases, confirm the accuracy of the proposed formulae.

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.

Bond characterization of monolithic and layered glass panels and ultrasonic tests to control glued surfaces

An experimental investigation is presented regarding the compressive and shear strength of monolithic and PVB laminated glass elements connected by acrylic glue. Ultrasonic tests were also used to control the efficiency of glued surfaces of glass panels.Twenty-four triplets composed of three float glass elements glued with acrylic adhesive were prepared to perform bond tests. Of these twelve triplets were made with monolithic glass elements with a nominal thickness of 20 mm, while twelve were made with layered glass elements 20 mm thick. Three single elements of monolithic glass and three of layered glass were tested for compressive strength. Ultrasonic tests were performed on a sample made by gluing two layered glass panels 200 × 300 × 20 mm in thickness in which defects in glued surfaces were generated artificially. Experimental stress-strain curves in compression for glass elements and shear stress-slippage curves from bond tests were also derived with crack patterns at rupture.

Cálculo simplificado de vidrio laminado: determinación de desplazamientos en vigas y placas ante cargas estáticas utilizando modelos monolíticos

In the calculation of laminated glass elements, glass layers are commonly considered as linear-elastic whereas the polymeric interlayers present viscoelastic behavior. Consequently, the mechanical behavior of laminated glass elements depends on time and temperature. Many finite elements are needed to calculate these elements because the thickness of the glass layers (and above all that of polymeric interlayers) are much smaller than the other two dimensions of the element (with and length). For this reason, the calculation of these elements is very high time consuming. Recently, several authors have proposed the effective stiffness concept (alternatively effective thickness or effective Young's modulus) for the simplified calculation of laminated glass elements. In this work, a methodology is proposed to predict the deflection of laminated beams and plates under static loadings using a linear elastic monolithic model (analytical or numerical) and the equations of the effective stiffness for the laminated glass. The equations proposed in this work have been validated by experimental tests carried out in simply-supported beams and in a plate supported at the four corners, the maximum error being less than 10%.

Mechanical characterization of polyvinil butyral from static and modal tests on laminated glass beams

Polyvinyl butyral (PVB) is the polymeric interlayer material most used in laminated glass elements. As other used interlayers, the PVB mechanical behavior is viscoelastic. Therefore, its mechanical characterization can be carried out by static (creep and relaxation) or dynamic tests in a dynamic mechanical analyser (DMA). However, the PVB layers constrained in laminated glass elements are subject to high temperature and pressure conditions in an autoclave during the manufacturing process, which can affect to the mechanical properties of the interlayer. In this paper, the mechanical properties of PVB constrained in laminated glass beams have been determined by static and dynamic tests on laminated glass beams with different boundary conditions and at different temperatures. The estimated curves are compared with those obtained by testing free PVB specimens in a DMA.

Study of the time-temperature-dependent behaviour of PVB: Application to laminated glass elements

The mechanical behaviour of laminated glass elements is governed by material properties of the interlayer, the Polyvinyl Butiral (PVB) being the most used interlayer material in these elements. PVB is a viscoelastic material whose mechanical properties (Young’s modulus, shear modulus, etc.) depend mainly on the load application time and the temperature. Thus an adequate mechanical characterization of the PVB must be performed in order to predict the response of laminated glass elements with a good accuracyIn this work, PVB specimens were subjected to static relaxation tests and to dynamic experimental tests (frequency domain) at different temperatures from −15oC to 50oC using a DMTA equipment. Then the curves at different temperatures were related using the William-Landel-Ferry (WLF) Time-Temperature Superposition (TTS) model to obtain the mastercurve of both the time and frequency domain Young’s moduli of the PVB. Finally, a viscoelastic Prony based model was fitted to the experimental data and used, afterwards, to simulate numerically the static and dynamic behaviour of different laminated glass elements at different temperatures. The numerical simulations were compared with the static and dynamic experimental results achieving a good accuracy in both the static deflections and the natural frequencies. With respect to the damping, the discrepancies are less than 22%.

Comparison of viscoelastic finite element models for laminated glass beams

Laminated glass elements, which consist of stiff elastic glass layers connected with a compliant viscoelastic polymer foil, exhibit geometrically non-linear and time/temperature-sensitive behavior. In computational modeling, the viscoelastic effects are often neglected or a detailed continuum formulation typically based on the volumetric-deviatoric elastic-viscoelastic split is used for the interlayer. Four layerwise beam theories are introduced in this paper, which differ in the non-linear beam formulation at the layer level (von Kármán/Reissner) and in constitutive assumptions for the interlayer (a viscoelastic solid with the time-independent bulk modulus/Poisson ratio). We perform detailed verification and validation studies at different temperatures and compare the accuracy of the selected formulation with simplified elastic solutions used in practice. We show that all the four formulations predict very similar responses. Therefore, our suggestion is to use the most straightforward formulation that combines the von Kármán model with the assumption of time-independent Poisson ratio. The simplified elastic model mostly provides response in satisfactory agreement with full viscoelastic solutions. However, it can lead to unsafe or inaccurate predictions for rapid changes of loading. These findings provide a suitable basis for extensions towards laminated plates and glass layer fracture, owing to the modular format of layerwise theories.

Calculation of displacements and stresses in laminated glass beams under dynamic loadings using an effective Young modulus

Laminated glass is a sandwich element that consists of two or more sheets of monolithic glass with one or more interlayers of a polymer that usually show viscoelastic behavior. In recent years, the concept of effective thickness has been proposed to calculate displacements and stresses in laminated glass elements subject to static loadings. The method consists of using a monolithic model with the same length and boundary conditions and subject to the same loading as the laminated glass model but with an effective thickness such that both models (the monolithic and the laminated one) provide the same displacements and stresses as the laminated glass beam. This technique allows to save time in the calculation of the laminated glass elements subject to dynamic loadings compared with the layered finite element models which are very high time consuming because many small 3D elements are needed to model accurately all the layers of the sandwich element and because the core usually shows a time and temperature dependent behavior. In this paper, a technique to estimate displacements and stresses in the frequency domain in laminated glass beams subject to dynamic loadings is proposed based on the effective Young modulus concept. Both the effective thickness and the effective Young modulus can be used interchangeably in laminated glass elements but the later is more attractive for being used in finite element models. The technique is validated by experimental tests carried out on laminated glass beams at different temperatures.

Comparative Study on Structural Performance of Different Laminated Glass Composites and Brick Wall

Laminated glass composites are structural glass members made by assembling thin laminated panels which are connected by structural adhesives called interlayer. Laminated glass composite is a safety and security glass which enables significant improvement in the post-breakage behaviour. The interlayer of laminated glass composites ensures the integrity of the glass by holding it together. In the field of modern and innovative architectural engineering, the applications of laminated glass composites are increasing due to its lighting, aesthetics and architectural advantages. This paper introduces the buckling and vibration characteristics of different laminated glass elements using ANSYS 16.2.

An effective thickness to estimate stresses in laminated glass beams under dynamic loadings

Finite element models for estimating stresses and displacements in laminated glass elements under dynamic loadings are very time-consuming because (1) many small 3D elements are needed to model accurately all the layers of the sandwich element and (2) the core usually shows a time and temperature dependent behaviour. In the last years, the concept of effective thickness using a quasi-elastic solution has got the attention of the research community because of its simplicity and reasonable level of accuracy achieved in the calculation of laminated glass elements under static loadings. In this paper, a dynamic effective thickness to estimate stresses in laminated glass beams under dynamic loadings in the frequency domain is derived using the correspondence principle. The analytical equations are validated by experimental tests carried out on simply supported and free–free laminated glass beams at different temperatures in the range 20–40 °C.

Cálculo de desplazamientos en placas de vidrio laminado sometidas a carga estática mediante el concepto de módulo de elasticidad efectivo

In recent years, the use of laminated glass as a structural element has increased considerably, mainly in facades, roofs, stairs or security windows. Laminated glass elements are sandwich structures which presents a complex behaviour due to the combination of the mechanical properties of glass layers (linear-elastic) with the properties of the polymeric interlayer (linear-viscoelastic). Recently several authors have proposed the concept of effective thickness in order to simplify the laminated-glass static calculations, using a monolithic model with an equivalent flexural stiffness equal to that of the laminated element. Due to the variations of the laminated glass properties with temperature, introduced by the viscoelastic polymeric interlayer, for each different temperature, a different effective thickness must be determined. This particularity implies a large number of assessments for each of the possible working situations. In this work, the Young's modulus concept is proposed as an efficient alternative to be used in finite elements models. The proposed methodology is validated by experimental tests on laminated glass plates under uniformly distributed load.

Glass - steel hybrid elements under four point bending test

Problems evolving from the brittleness of structural glass result in need of innovative solutions which will improve the post-breakage behaviour of the elements in the structure. As the need of the glass performance gets higher, the fully tempered glass gets in the focus and its usage becomes greater. But although this type of glass gives great performance with its tensile strength and deflection capaciy, it has no residual strength. Due to its breakage pattern into small pieces the collapse of the element may be instant even in laminated glass elements. Thus, increasing the post breakage behaviour is crucial in order to keep the integrity of the tempered glass element. This can be done either by changing the interlayer properties, or including kind of reinforcement in the element structure. This paper presents experimental testing of the performances of steel plate reinforced hybrid glass element under four point bending test. As a result, it shows the improvement in mechanical behaviour of the described hybrid structure concept compared to a monolithic glass element with same dimensions, by means of stress distribution and reinforcement capacity.

Flexural and Torsional Buckling Behavior of Eccentrically Compressed Laminated Glass Elements with a Viscoelastic PVB Interlayer

AbstractDue to their typical high slenderness ratios, glass structural elements can be often subjected to buckling phenomena. Major difficulties in a correct estimation of their effective buckling strength and load-carrying behavior are generally given by a combination of multiple mechanical and geometrical aspects, especially in presence of laminated cross sections or interacting applied loads. In this paper, buckling experiments are performed on laminated glass beam-columns eccentrically compressed. Extended numerical and analytical comparisons are performed with test results in terms of Euler’s critical loads or load-displacement paths. As shown, appropriate calibration of numerical and analytical models generally can provide good agreement between buckling predictions and experimental results. Viscoelastic numerical models, in particular, if well-calibrated in terms of mechanical [e.g., creep effects in polyvinyl butyral (PVB)-foils] and geometrical properties (e.g., initial imperfections, load eccent...