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

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.

Experimental and numerical investigations of metal-to-glass embedded connections with thin stainless steel plate

Pieter Christian Louter, Manuel Santarsiero

The recent demand for architectural transparency has drastically increased the use of glass material also 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. This work presents the experimental and numerical investigations of embedded metal-to-glass connections realized by embedding a thin metal plate within an ionomer interlayer usually used for laminating glass panels. The tested specimens consist of small rectangular glass panels combined with rectangular stainless-steel plates, laminated with a transparent ionomer polymer. The experimental investigations are performed by pulling out the metal plate from the laminated glass panel, at constant displacement rate. Tests at different temperatures are carried out, because of the temperature sensitivity of the interlayer polymer. The connection’s response in terms of load versus relative displacement is here presented. Then, numerical investigations on this type of metal-to-glass connection are performed, with the goal to compute the non-linear distribution of both strain and stress’s fields within the interlayer. In that regard, the experimental tests are simulated by a non-linear FE model. The effects of geometrical non-linearity are taken into account. Comparisons between experimental and numerical results are here presented focusing on the interface level between interlayer and glass material. From the study it is concluded that (i) the use of the adhesion properties of the interlayer material of laminated glass is a promising technique for joining structural glass member (ii) the numerical model developed in this work represents an efficient tool to predict the behaviour of such type of connection.

Taylor & Francis Group2013

Parametric numerical investigation of adhesive laminated point connections

Jean-Paul Lebet, Pieter Christian Louter, Manuel Santarsiero

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 regard, research activities on a novel type of metal-to-glass adhesive connections (called laminated connections) are currently on-going at EPFL. These joints make use of transparent thin polymer foils - i.e. an ionomer polymer (SentryGlas® from Dupont) and a structural silicon (TSSA from Dow Corning) – that are cured by an autoclave lamination process. The research activities involve both experimental and numerical studies with the aim to develop a design model and failure criterion for laminated connections. In this paper, the nonlinear numerical investigations on the behaviour of this type of adhesive joints are presented. In particular, the effects of mechanical and geometrical parameters on the response of the laminated connections are studied by non-linear modeling. The results are obtained performing several numerical simulations varying the parameters’ values and monitoring the related effects. Strong non-linearity in both strain and stress field distributions are observed, even in case of simple load conditions. The results suggest that, with the purpose of performing numericalexperimental comparisons, precise measurements have to be performed since very small displacements are to be expected. Additionally, an appropriate modeling of both boundary conditions (realized by the test setup) and adherents’ deformations (of both steel and glass adherent) is necessary.

Taylor & Francis Group2013

Material and structural performance of fiber-reinforced polymer composites at elevated and high temperatures

As the range of applications for fiber-reinforced polymer (FRP) composite materials in civil engineering constantly increases, there is more and more concern with regard to their performance in critical environments. The fire behavior of composite materials is especially important since complex physical and chemical processes such as the glass transition and decomposition occur when these materials are subjected to elevated and high temperatures, possibly leading to considerable loss of stiffness and strength. This stiffness and strength degradation in composite materials under elevated and high temperatures is the result of changes in polymer molecular structures. When polyester thermosets are subjected to elevated and high temperatures, they undergo three transitions (glass transition, leathery-to-rubbery transition, and rubbery-to-decomposed transition), corresponding to four different states (glassy, leathery, rubbery and decomposed). At a certain temperature, a composite material can therefore be considered as a mixture of materials that are in different states. As the content of each state varies with temperature, the composite material exhibits temperature-dependent properties. Since these changes in state can be described using kinetic theory, the quantity of material in each state can be estimated and the thermophysical and thermomechanical properties of the mixture can thus be determined. These concepts formed a basis for the development of thermophysical and thermomechanical property sub-models for composites at elevated and high temperatures and even for the description of post-fire status. Incorporating these thermophysical property sub-models into a heat transfer governing equation, thermal responses were calculated using a finite difference method. Integrating the thermomechanical property sub-models within structural theory, the mechanical responses were described using a finite element method and the time-to-failure was also predicted by defining a failure criterion. The modeling results for temperature responses, mechanical responses and post-fire behavior were compared with those obtained from structural endurance experiments on full-scale cellular GFRP (glass fiber-reinforced polymer, in this case polyester resin) panels subjected to a four-point bending configuration and fire from one side. The modeling results for time-to-failure were compared with those from the experiments carried out on GFRP tubes under combined compressive and thermal loadings. In each experimental setup, two different thermal boundary conditions were investigated – with and without water cooling through specimen cells – and good agreement was found. The understanding gained and modeling of the behavior of GFRP composites under elevated and high temperatures carried out in this thesis could be applicable for different composite materials, and also benefit investigations regarding both active and passive fire protection techniques in order to improve the fire resistance of structures made of such materials.

EPFL2009

Material and structural performance of fiber-reinforced polymer composites at elevated and high temperatures

EPFL2009

Experimental and numerical investigations of metal-to-glass embedded connections with thin stainless steel plate

Pieter Christian Louter, Manuel Santarsiero

Taylor & Francis Group2013