ANALYTICAL MODELLING OF THE DEGRADATION PHASES OF GLUED LAMINATED WOOD (GLULAM) STRUCTURES OF LOCAL TROPICAL SPECIES: APPROACHES BASED ON INTERNAL ENERGY DISSIPATION AND VARIATIONAL FORMULATION

Abstract

The use of local tropical species in plate and shell structures could be of considerable interest. This is all the more possible when the properties and technological characteristics of the assemblies are known. However, this is not enough when several species are combined. It is therefore necessary to be able to understand the behaviour of the material in different states of degradation, including exposure to flames. With this in mind, the work we are presenting deals with the analytical modelling of GLW structures in plates and shells in different degradation phases, in the face of rheological and fire resistance stresses. Rheological behaviour is mainly represented by elasto-plastic and elasto-viscoplastic models. The three phases of mechano-thermal degradation of the GLW plate and shell structure are mainly drying, pyrolysis and combustion. For each of these three phases, we have modelled the strain rates, the corresponding strain stresses and the membrane forces. These analytical models enabled us to develop two finite element approaches: the first using a global equation to be solved, based on the internal energy, and the second using the variational formulation taking account of the temperature tensor. For the specific behaviour of adhesive joints, we have not described a modelling model, but have integrated this into the overall approach to the structure.  However, to model the glue joints, it is necessary to start with the evolution of the material in the absence of temperature, with priority given to the elastic models, and end with the influence of the flames that degrade the GLW structure, where the viscoelastic models are taken into account. Overall, the analytical modelling in this study starts from the hypotheses put forward, and leads to analytical models of internal energy and of the various degradation phases of our GLW plate and shell structure. Numerical work will then be carried out using these analytical models to understand the displacement and strain rate fields.