Laminated connections for structural glass components: a full-scale experimental study

The use of glass material for structural components has drastically increased in the last decade. Among others, a laminated connection is a type of adhesive joint that makes use of foil interlayer adhesive to transfer forces between glass and metal parts. In this work, the use of embedded laminated connections is studied as connection between glass beams. In particular, it is experimentally investigated the use of embedded connections laminated to make a moment joint between laminated glass beam segments. The mechanical behaviour of such glass beams with embedded laminated connections is studied under different loading scenario. Tests are performed under monotonic, creep and damage protocol. Different geometry and location of the embedded laminated connections are compared. The results of this work showed that embedded laminated connections represent an efficient means of load transfer between glass beams. It is observed that the choice of an appropriate geometry and location of the embedded connections can provide a substantial enhancement to the mechanical behaviour of the beam. In particular, a redundant and ductile structural behaviour of the moment connection can be achieved. Furthermore, results also showed that beams with embedded laminated connections are able to resist to severe damage scenarios and to sustain the applied load over time, even in the case of breakage of all glass panels.OLD Structural Desig

The mechanical behaviour of SentryGlas® ionomer and TSSA silicon bulk materials at different temperatures and strain rates under uniaxial tensile stress state

An innovative type of connections for glass components, called laminated connections, has been developed in the last years. Two materials have been used for laminated connections: the transparent ionomer SentryGlas® (SG) from Kuraray (former Dupont) and the Transparent Structural Silicon Adhesive (TSSA) from Dow Corning. In this paper, the mechanical behaviour of SG and TSSA bulk materials is studied under uniaxial tensile stress condition. The effects of strain rate and temperature variations are investigated. Particular attention is paid (i) to the study of these polymers in cured condition and (ii) to the computation of true stress and strain field during the tests. Firstly, it is observed that the mechanical behaviour of both SG and TSSA are temperature and strain rate dependent. These effects are quantitatively determined in the paper. Secondly, two additional phenomena are observed. For TSSA, it is observed that the material goes from fully transparent to white colour, exhibiting the so-called whitening phenomenon. For SG, instead, it is observed that the strain field distribution is dependent on the temperature. More specifically, the material exhibits a non-uniform strain field distribution due to the occurring of the necking phenomenon. Measurements along the specimens, using Digital Image Correlation techniques, showed that the localized strain propagates over the full specimen length, resulting in a cold-drawing phenomenon. Finally, it is also shown that engineering and true stress–strain definition exhibits large deviation indicating that the finite deformation theory should be used for the computation of the stress–strain curves to be implemented in numerical modelling.OLD Structural Desig

Laminated connections under tensile load at different temperatures and strain rates

In the last years, a novel typology of adhesive connections for structural glass application has emerged, known as laminated adhesive connections, which makes use of the transparent ionomer SentryGlas® (SG) from Kuraray and the Transparent Structural Silicon Adhesive (TSSA) from Dow Corning. Despite being used in several projects, limited information is available in literature on their mechanical behaviour and on the effects of strain rate and temperature. In this work the behaviour of laminated connections under tensile loading is studied by means of experimental, analytical and numerical analyses. The experimental investigations show that temperature and strain rate variations have important effects on the mechanical response of the connections. Two main interesting phenomena are also observed: the whitening phenomenon in TSSA and the development of bubble within the SG adhesive. The analytical studies of the stress state show that confinement state of the adhesive induces a non-uniform three-dimensional stress distribution in the adhesive with a dominant hydrostatic component of the stress tensor, which is observed to be in agreement with the experimental results. Three-dimensional finite numerical analyses show that the stress field deviates from the uniform distribution with a large gradient of hydrostatic and deviatoric stresses over the adhesive area. The output of the finite numerical model are then compared with the observations of the experimental campaigns. Herein, the full set of numerical results is synthetized by the definition of so-called stress factors. The latter allow to derive the three-dimensional stress state in the adhesive at different temperatures and to compute the stress peak in the non-linear stress field distribution. Finally, prediction models are proposed for the tensile resistance of TSSA and SG laminated connections. A logarithmic law is proposed for the strain rate effects for both TSSA and SG connections. Linear and inverse hyperbolic-tangent-based laws are instead proposed for the TSSA and SG temperature effects, respectively.Accepted Author ManuscriptOLD Structural Desig

Experimental and numerical analysis of thick embedded laminated glass connections

Laminated glass components are usually realized by bonding glass plates using interlayer polymers that develop adhesion forces during lamination. Recently, these adhesion forces have been used also to realize special adhesive connections for structural glass components and assemblies. The typical example of such a joining technique is conventionally known as “embedded laminated connection” where a metal insert is encapsulated in multi-ply laminated glass components. In this study, careful consideration is paid for the investigation of the mechanical behaviour of embedded laminated connections with thick metal insert. To this aim, small-scale laboratory tests, Finite Element (FE) numerical models and analytical considerations are presented. Firstly, the results of experimental investigations at different temperatures are discussed, giving evidence of the geometrical and mechanical parameter effects on the so observed performances. It is observed, in particular, that the temperature affects not only the maximum load carrying capacity but also the failure mode of the studied connection typology. Non-linear numerical simulations are then developed in ABAQUS on FE models, able to account for the geometrical and mechanical properties of the reference connection specimens. Further analytical considerations are also presented, in support of the observed experimental findings. It is shown, in particular, that as far as high temperatures are not attained, the mechanical performance and failure mode of the examined connections is strictly related to glass breakage. In addition, it is also observed that at high temperature, failure mode (i.e. bubble formation) and failure location are in line with the expectations. Rather close correlation can be also found for the same embedded connections between test results, FE numerical simulations and analytical assumptions.Accepted Author ManuscriptOLD Structural Desig

Edge-laminated Transparent Structural Silicone Adhesive (TSSA) Steel-to-Glass Connections

The connections between glass components are very critical aspects of structural glass design. Laminated steel-to-glass connections have recently been developed that combine high strength and transparency. This work focuses on the Transparent Structural Silicone Adhesive (TSSA), produced by Dow Corning. TSSA is typically used for the realization of circular point connections on the glass surface. An alternative approach of using TSSA is considered in this study, by laminating stainless steel connectors on the edge of the glass. These connections are experimentally and numerically investigated. The edge bonded specimens are tested in shear and the stress distribution of the adhesive is analyzed by means of a three-dimensional finite element model. The distribution of stresses in the adhesive is non-linear showing significant stress peaks towards the free edges of the adhesive. A parametric study is conducted to relate the magnitude of the shear stress peaks and bending stresses with the eccentricity of the applied load. The occurrence of failure at lower engineering stresses than the ones recorded for circular point connections is explained using the theory of bending-shear interaction laws. Based on these failure criteria, shear stress peaks that occur due to the eccentricity of the applied load have an important influence on the global resistance of the connection.OLD Structural Desig

Mechanical behaviour of Transparent Structural Silicone Adhesive (TSSA) steel-to-glass laminated connections under monotonic and cyclic loading

Steel-to-glass laminated connections, which have recently been developed, limit stress intensifications on the glass and combine strength and transparency. Transparent Structural Silicone Adhesive (TSSA) connections have been used in several projects worldwide; however, the hyperelastic and viscoelastic nature of the material has to date not been fully investigated. In this work, the first objective is to investigate the mechanical response of TSSA connections under static and cyclic loading by means of experimental tests. Firstly, the shear behaviour of TSSA circular connections is characterized by means of monotonic and cyclic loading tests. The adhesive exhibits significant stress-softening under repeated cycles that becomesSteel & Composite StructuresStructural Integrity & CompositesApplied MechanicsOLD Structural Desig