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.
This paper reports on an investigation of glued joints in glass load-bearing structures, with reference to the effect of various substrates (glass, steel, stainless steel, aluminium) and their ...surface treatment (sandblasting for the glass surface) on the adhesion of selected adhesives. The thickness of the adhesive layer and the effect of artificial ageing – a simulation of 5 years of ageing in outdoor central-European conditions – are also discussed. Tensile and shear tests were carried out on three series of specimens with various adhesives and substrates – two series for tensile and shear tests, and one series for shear tests on specimens exposed to ageing. Our results show that sandblasting the glass surface can improve the adhesion, and thus the strength values, of an adhesive joint in cases where, with a smooth glass surface, cohesive failure is not reached. The thickness of the adhesive layer had a significant effect for a semi-rigid acrylate adhesive, where the joint achieved higher strength values with less thickness of the glue. The effect of ageing varied according to the adhesive. The most visible changes were observed for a two-component acrylate adhesive and for methacrylate UV-adhesives. One of the selected glues was marked as unsuitable for load-bearing connections due to significant worsening of its mechanical properties after ageing.
Taking advantage of two full-scale experimental tests carried out on square hollow glass columns under low velocity impacts, the paper aims to further assess via Finite Element models the structural ...performance of such structural systems. In them, the resisting cross-section consists of four adhesively bonded laminated glass panes. Adhesive joints are also used for the connection between glass columns and top/bottom restraints. As a result, careful consideration in the analysis and design of these innovative systems is required, to guarantee appropriate fail-safe design principles for a typically tensile brittle material, as well as to account for possible accidental or exceptional loading conditions.
Simplified but computationally efficient FE models are validated in the paper towards the available full-scale test results. Key aspects in the observed overall performances under low velocity impact are then emphasized, with careful consideration for several loading configurations, including variations in the release distance for the impacting mass as well as in the type of impact (hard/soft body). In conclusion, a FE sensitivity analysis is also carried out, giving preliminary evidence of the effects of some main input parameters on the overall performance of the examined systems, including possible localized damage in glass, as well as geometrical and mechanical features in the column restraints.
Looking at a current architecture, there are many examples of glass load bearing structures such as beams, panes, balustrades, columns or even stairs. These elements are mostly made of laminated ...glass panels. Panels are bonded together with polymer interlayer significantly influencing a shear forces transfer between them. There is still overall lack of knowledge in the task of shear forces transfer between these panels. It principally depends on the polymer stiffness, which is affected by an ambient temperature, humidity and load duration. Civil engineers currently tend to design laminated glass members on the safe side, generally not taking laminated panels interaction provided by the interlayer into account. This approach leads to uneconomical and robust glass bearing members significantly preventing the use of laminated glass more extensively. There are many polymer interlayers made for structural laminated glass applications available on a market. Most of them differ in stiffness and other important properties therefore these must be experimentally examined to design safer and more economical laminated glass members. This paper is focused on the shear modulus of PVB (polyvinyl-buthyral) and SentryGlasÒ (ionoplast) experimental investigations as a function of temperature and loading ratio. It is possible to find out these functions by static creep or relaxation tests as well as by dynamic mechanical thermal analysis-DMTA. A lot of DMTA experiments in shear with the aforementioned interlayers in various loading conditions have been performed in order to determine their shear stiffness. It also enables to identify their Prony parameters as a part of the next survey. Experimentally verified common polymer interlayer stiffness helps engineers to design safer and cheaper glass constructions. This is the way how to extend the use of laminated glass in a current architecture.
An accurate material representation of polymeric interlayers in laminated glass panes has proved fundamental for a reliable prediction of their response in both static and dynamic loading regimes. ...This issue is addressed in the present contribution by examining the time-temperature sensitivity of the shear stiffness of two widely used interlayers made of polyvinyl butyral (TROSIFOL BG R20) and ethylene-vinyl acetate (EVALAM 80-120). To that end, an experimental program has been executed to compare the applicability of two experimental techniques, (i) dynamic torsional tests and (ii) dynamic single-lap shear tests, in providing data needed in a subsequent calibration of a suitable material model. Herein, attention is limited to the identification of material parameters of the generalized Maxwell chain model through the combination of linear regression and the Nelder-Mead method. The choice of the viscoelastic material model has also been supported experimentally. The resulting model parameters confirmed a strong material variability of both interlayers with temperature and time. While higher initial shear stiffness was observed for the polyvinyl butyral interlayer in general, the ethylene-vinyl acetate interlayer exhibited a less pronounced decay of stiffness over time and a stiffer response in long-term loading.
Glass is increasingly used as a structural material in buildings, not only for enclosing spaces but also for bearing loads. To meet architect requirements for a uniform structure without appearance ...disturbance, adhesively bonded joints are preferred over mechanical fasteners. However, in the construction industry, most technical guidelines cover only soft structural silicone sealants, while stiffer adhesives like epoxy resins are not considered. Alternatively, the specific transparent epoxy adhesives offer a high potential for bonded glass assemblies, enabling thinner joints and a fully transparent junction. Indeed, under real service conditions, elevated temperatures are one of the worst factors affecting the mechanical properties of structural bonded joints. Therefore, in this paper, an experimental program was conducted to evaluate the performance of transparent bonded glass joints with epoxy resin over a wide range of temperatures. Tensile and shear tests were performed on bulk-cured adhesive samples and bonded glass-to-glass block shear specimens respectively, at room temperature (RT), 40, 60, and 80 °C. The differences in surface characteristics such as roughness, wettability, and surface free energy (SFE) between both glass sides were examined. The results showed that tensile and shear strengths decreased with increasing temperatures. Furthermore, the shear strength was influenced by the surface properties of the glass sides. At all tested temperatures, the rougher bonded glass side specimens revealed higher shear strength coupled with a mixed failure while a loss of adhesion characterised the smoother glass surfaces.
•Full-scale experimental assessment of the performance of glass columns under impact.•Various impact configurations are investigated, including soft or hard bodies.•Preliminary damaged column is also ...analysed, to assess the effects of imperfections.•The global performance of the examined full-scale columns is critically discussed.•Local effects, crack propagation and collapse mechanisms are further explored.
Glass is largely used in buildings as a novel construction material. Due to the intrinsic mechanical properties of such material, however, specific design recommendations are demanded in order to offer appropriate “fail-safe” requirements. This is especially true in the case of load-bearing structural glass elements where redundancy, stability and residual resistance should be guaranteed. In this regard, based also on a past research effort, the paper experimentally investigates the structural performance of full-scale square hollow glass columns, whose resisting cross-section consists of four adhesively joined laminated glass panes. Impact tests are carried out on in-plane compressed specimens, including both a reference undamaged column and a deliberately, preliminary broken specimen. The effects of multiple impact test configurations (inclusive of various release configurations for the impact mass as well as type of impact body) are hence emphasized, with critical discussion of the observed overall results and failure mechanisms.
Abstract
Adhesive connections are commonly used in many industries as automotive, aerospace, electronics and also in civil engineering. Adhesives in civil engineering are used for non-load bearing ...structures but nowadays are requirements for using adhesive also for load- bearing structures especially for glass structures. Silicones are mostly used adhesives in civil engineering, they have good resistance to external environment but their lower strength and lower stiffness does not meet requirements for many applications. For this reason, are better semi-rigid or rigid adhesives but there is a lack of information about them. The paper is focused on experimental testing of transparent adhesive connection glass to glass. Four epoxy adhesives were chosen for double lap shear joint. Specimen were exposed to shear test until failure. Shear force and displacement were measured during test. Shear stress, elongation at break, shear modulus and failure mode were obtained from the tests. Only one epoxy adhesive had low adhesion to glass. Specimen with this adhesive had the lowest shear strength. Other three adhesives showed good adhesion to glass and had shear strength 6.5 times higher. Failure mode of specimen with these adhesives was always breaking of the glass.
There are many examples of glass load bearing structures used in a contemporary architecture, such as panes, balustrades, and even stairs. For safety reasons, these structural elements are made of ...laminated glass which is a composition of glass plies bonded with polymeric interlayer. The distribution of stress in a perpendicularly loaded laminated glass panel depends on the shear stiffness of the used interlayer. There are various interlayers for laminated glass applications available on the market with wide variety of shear stiffness. To correctly evaluate the shear coupling provided by the interlayer, great research efforts have been made followed by appropriate national Standards and Codes for laminated glass in bending in recent years. Polymeric interlayers are viscoelastic materials and their stiffness is time and temperature dependent, which makes the reliable design of laminated glass panel in bending rather complicated. This paper is focused on experimental investigation of six polymeric interlayers (Trosifol® BG R20; Trosifol® Extra Strong; Evalam® 80/120; Evasafe®; SentryGlas® 5000; Krystalflex® PE399) loaded in displacement-controlled shear test in various temperatures and loading rates. The experiments showed nonlinear stress–strain dependence and confirmed the viscoelastic behaviour of presented interlayers. In addition, the values of their initial shear stiffness are listed and failure modes of testing specimens are presented. Results obtained in this study can be used for the estimation of the rate of glass plies interaction in short-term loaded laminated glass structures. All experiments were performed in Klokner Institute CTU.
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