Thermal performance of lightweight composite slabs: FEM and DOE analyses

Abstract

The aim of this work is to investigate the thermal performance of a new lightweight composite slab using advanced numerical methods based on nonlinear finite element models (FEM). Furthermore, the thermal optimization of the composite slab is done by means of the design of experiments (DOE) methodology. At present, this type of floor is very efficient in terms of energy saving and sustainability, due to its downward thermal transmittance and weight (or dead load) values. Six different lightweight composite slabs are modelled using a steel plate, lightweight concrete, inner layers made of expanded polystyrene and lightweight mortar insulation. In order to obtain the thermal properties of the different materials, a non-destructive test (NDT) system based on the modified transient plane source technique, following the ISO/DIS 22007-2.2, has been used. The convection and radiation in the cavities are modelled using an equivalent film coefficient from the UNE-EN-ISO 6946 Standard. Then, the nonlinear analysis for upward and downward fluxes in each different composite slab is solved. Based on the best slab configuration, an optimization using the DOE methodology is developed. The thermal transmittance value, for both upward and downward fluxes, is adopted as the objective function. The input variables considered are the composition and thickness of the lightweight concrete, the thickness and insulation properties of the lightweight mortar and the thickness and size of the inner expanded polystyrene. The DOE methodology provides the sensitivity analysis and response surface for each variable with respect to the objective function. In this way, the best configuration of the composite slab to obtain the best thermal behavior is reached. In summary, the methodology described in this research work can be applied to other composite slabs in order to optimize their thermal behavior