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The non-linear structural analysis of reinforced concrete beams in fire consists of threseparate steps: (i) The estimation of the rise of surrounding air temperature due to fire; (ii) thedetermination of the distribution of the temperature within the beam during fire; (i) the evaluation of themechanical response due to simultaneous time-dependent thermal and mechanical loads. Steps (i) and (iii)are dealt with in the present paper. We present a two-step computational procedure where a 2D transientthermal analysis over the cros-sections of beams are made first, followed by mechanical analysis of thestructure. Fundamental to the acuracy of the mechanical analysis is a new planar beam finite element.The efects of plasticity in concrete, and plasticity and viscous crep in stel are taken into consideration.The properties of concrete and stel along with the values of their thermal and mechanical parameters aretaken acording to the European standard ENV 1992-1-2 (1995). The comparison of our numerical andful-scale experimental results shows that the proposed mechanical and 2D thermal computationalprocedure is capable to describe the actual response of reinforced concrete beam structures to fire.