A model is proposed for the simulation of the thermo-mechanical behaviour pultruded Glass Fibre Reinforced Polymer (GFRP) profiles subjected to the action of a standard fire curve. It consists of two sequential steps: (i) determination of the temperature distribution over time in a representative cross section using a thermal model that includes conduction, convection, radiation and (ii) determination of generalised strains and displacements through a mechanical model that represents the section walls through a geometrically exact shell theory using large deformations 3D constitutive relations. The problem is solved numerically using the Finite Element Method (FEM). The independently approximated fields are: temperature, pressure, velocity, decomposition, displacements, rotations and thickness variation parameters.