Fire resistance behaviour of GFRP-polyurethane composite sandwich panels for building floors

Abstract

This paper presents an experimental study about the fire resistance behaviour of composite sandwich floor panels made of glass-fibre reinforced polymer (GFRP) faces and polyurethane foam core subjected to a standard fire scenario and a mechanical load. Three full-scale sandwich specimens were tested: an unprotected specimen and two specimens protected with calcium silicate (CS) boards, applied either adherent to the underside of the panel or suspended from it and forming an air cavity. The study addressed the thermal and mechanical responses of the panels, including the evolution of (i) temperature distributions, (ii) deflections and deformations, (iii) failure modes, and (iv) time to failure, as well as the effects of the fire protection systems in those responses. The results obtained confirm the susceptibility of composite sandwich panels to fire: the unprotected panel failed after only ~25 min, due to a failure mode that involved different damage mechanisms, such as rupture of the glass fibres of the lower face, total degradation of the core, and flexural failure of the top face. On the other hand, with CS board protections, due to the thermal insulation conferred to the sandwich panels, the fire resistance was considerably increased to ~80 min (adherent) and ~100 min (air cavity). These tests also provide new insights about the thermo-mechanical behaviour in fire of composite sandwich panels, indicating a progressive change of their structural system, from a beam system to an arch system and finally to a simple laminate (the top face sheet) in bending.