A preliminary study of the nonlinearity of adhesive point-fixings in structural glass facades

Abstract

The recent demand for architectural transparency has drastically increased the use of glass material for structural purpose. However, connections between structural glass members represent one of the most critical aspects of glass engineering, due to the fragile behaviour of this material. In that respect, research activities on adhesive point-fixings are currently on-going. The mechanical behaviour of adhesive point-fixings is affected by large nonlinearities, which are usually investigated by nonlinear Finite Element Analysis (FEA). This paper focuses on the geometrical and the material nonlinearities of adhesive point-fixings for glass structures.Firstly, the nonlinear material behaviour of two selected adhesives are investigated by means of uniaxial tension and compression tests on the bulk material. The production of specimens, test methodology and displacement rate dependency are discussed. Secondly, the nonlinear stress distribution occurring in the adhesive and the joint stiffness is investigated by means of nonlinear FEA. The effects of several parameters on the mechanical behaviour of adhesive point-fixings, such as the connection dimensions and adhesive elastic properties, are studied.The adhesive stress-strain curves resulting from the experimental campaign show that the adhesives exhibit a large nonlinear behaviour. The results show that the stress and strain at failure reduce as the displacement rate is reduced. From the numerical investigations it is concluded that large nonlinearity involves the mechanical behaviour of adhesive point-fixing which cannot be neglected. The stress distribution within the adhesive deviates from uniform nominal stresses, even in case of simple load condition, with stress peaks up to four times higher than nominal stresses. List of notationα σ, max [-] ratio between the maximum principal stress and the nominal stress α σ, mis [-] ratio between the Von Mises stress and the nominal stress σ nom [MPa] nominal stress 86 J. Dispersyn et al. / A preliminary study of the nonlinearity of adhesive point-fixings in structural glass facades σ max [MPa] maximum principal stress σ mis [MPa] Von Mises stress η [-] stress triaxiality p [MPa] hydrostatic pressure σ [MPa] stress tensor σ [MPa] deviatoric part of the stress tensor E [MPa] Young's modulus of elasticity of the adhesive v [-] Poisson's ratio of the adhesive D [mm] diameter of the metal connector t [mm] adhesive's thickness ε zz [-] longitudinal strain ε yy [-] transversal strain ε peak [-] maximal strain ε peak [MPa] maximal stress ε fail [-] strain at failure σ fail [MPa] stress at failure

Transparency in Structural Glass Systems Via Mechanical, Adhesive, and Laminated Connections ‐ Existing Research and Developments

“…Examples of punctual adhesive connections. Reproduced from ref . under the terms of the CC‐BY‐X license, Copyright 2014, IOS Press.…”

“…Two components adhesives, because of the catalyzer part, are instead characterized by shorter curing time and more pronounced depth‐thickness ration are possible. Typical mechanical properties are reported in ref . UV‐cured polymers are characterized by very low viscosity and − compared to other adhesives − are usually applied in very thin layers.…”

“…Following this study, more specific research was further performed on adhesively bonded point‐fixing, with care for two materials only (MS polymer, i.e., modified silane − and epoxy adhesive), see Figure c. The study involved both experimental and numerical analysis of connections under different load conditions.…”

“…Limited experimental research efforts are indeed available in the literature for SG connections at different temperatures. In this regard, preliminary results of numerical parametrical analyses performed in refs . showed that the stress state distribution in SG laminated connections is rather complex and that the full three‐dimensional stress and strain tensor must be properly considered for an appropriate description of the adhesive stress state.…”

03.21: Structural glued connections with different metal substrates

“…Adhesive bonding is now an established method in automotive and aerospace industry assemblies but in civil engineering is still rarely used for structural applications. Nowadays, comprehensive research of glued connections for civil engineering usage, especially glass-metal joints [1,2], is carried out. Adhesive joints are very often used with brittle material mostly due their great benefit in possibility of stress accommodation along the whole connection in comparison with bolted joints.…”