The strength of annealed, heat-strengthened and fully tempered float glass

In the last two decades architectural glass has made an enormous leap from a secondary material to a material that combines structural and cladding roles. The structural role is a new and problematic one. In contrast to most other engineering materials the strength of glass is not a material parameter but a parameter dependent on processing quality and damage to the glass surface. There is also no real agreement on how strong glass is. There is a concept Euronorm for structural glass that has values for the characteristic strength for annealed, heat-strengthened, fully tempered and chemically toughened glass. There is however no real agreement on the validity of these values for design of glass beams or columns. To provide an independent set of values a statistically significant series of four-point bending tests on glass were conducted using both lying and standing positions resulting in a set of values for the characteristic strength.

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

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

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 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.

2014

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