The fire analysis of a steel–concrete side-plated beam

A new finite element model for steel–concrete side-plated beams exposed to mechanical and thermal loading is presented. The moisture and heat transfer through concrete is considered independent on mechanical deformations. The hygro-thermo-mechanical analysis is performed in two separate steps starting with the moisture and heat transfer analysis and continuing with the mechanical stress–strain analysis. The finite-element model of Davie, Pearce, and Bićanić was implemented for the moisture and heat transfer analysis in the concrete part of the beam. The Fourier equation of heat transfer for non-porous solids was applied in the steel part. A novel, strain-based finite-element formulation of the planar beam is proposed to perform the mechanical part of the fire analysis. Each of the two steps of the model is first verified by comparing the present numerical results with the experimental and numerical data available in the literature. The finite-element formulations of both the hygro-thermal and the mechanical steps of the analysis are found to be reliable and accurate. Finally, effects of the side reinforcing of a RC beam as one of the methods of structural retrofitting are explored in the case of a typical fire scenario and an important contribution of the side-plates to the ultimate fire resistance of the beam is discovered, particularly when higher levels of the service load are applied to the beam.