MOISTURE AND HEAT-FLOW IN CONCRETE WALLS EXPOSED TO FIRE

Time-dependent distributions for temperature and moisture content in a concrete wall subjected to fire are determined by a model of heat and mass transfer in porous media. Free-water flow, bound-water diffusion , gas-phase flow, water-vapor diffusion, and thermal energy are accoun ted for in the model. The governing transient differential equations a re discretized by a control-volume formulation reported by Patankar in 1980, and solved in time using a fully implicit scheme. Two different fire exposure curves (namely, standard curve according to ASTM E-119 and a more realistic curve reported by Ellingwood in 1991) are employe d in the analysis. The assessment of two simplified models, in which a ll pore water is assumed to evaporate at 100 degrees C, is performed b y comparing their predictions to the full analysis. For temperature an d saturation, the time developments predicted by the two simplified mo dels and by the full analysis present similar trends; however, the sim plified models seem to be appropriate only for very preliminary fire s afety analyses, since they tend to underestimate temperatures.