Development of sandwich panels for multi-functional strengthening of RC buildings: characterization of constituent materials and shear interaction of panel assemblies

Abstract

This paper presents an experimental and numerical study aiming at the development of a sustainable and multifunctional composite sandwich panel for the rehabilitation of reinforced concrete (RC) buildings from the 1960s to the mid-1980s. The sandwich panel, which was designed for the structural, thermal and acoustic refurbishment of building facades, comprises three main components: (i) thin outer layers of Recycled Steel Fibre Reinforced micro–Concrete (RSFRC) that fulfil the strength, ductility and durability requirements of the panel; (ii) a lightweight core made of polystyrene that provides thermal insulation; and (iii) internally distributed glass fibre reinforced polymer (GFRP) connectors that join the different layers of the panel, providing an adequate structural behaviour to the composite system. The mechanical characterization tests highlighted the viability of using RSFRC for the production of structural sandwich facade panels, as relatively high post-cracking tensile capacity was obtained for thin RSFRC layers. Pushout and pullout tests were carried out on intermediate-scale specimens representative of the sandwich panel solution for assessing the overall composite behaviour of the sandwich panels and analysing the influence of the type of core insulation layer (expanded/extruded polystyrene cores, with different surface finishing), of the anchoring conditions (25 and 35 mm of embedment depth) and diameter of the GFRP connectors (8 and 12 mm). These tests showed that the structural GFRP connectors with diameters of 8 and 12 mm are able to ensure shear load transfer between RSFRC layers, exhibiting better composite behaviour when combined with anchorage depths of 25 and 35 mm, respectively. The numerical part of this study aimed at modelling the failure mechanisms observed at the interface between RSFRC and polystyrene, showing good agreement between experimental and numerical results, with important conclusions being drawn regarding cohesion and friction angle between these materials.