Prediction of the structural integrity of buildings under hostile thermal environments is of considerable concern in safety assessments of structures. A mathematical model, simulating the coupled heat and mass transfer in cementitious structures exposed to extremely high temperatures, has been developed and solved numerically. With the prediction of the pore pressure, temperature, and moisture redistribution, the effect of fire on the reinforced concrete column is investigated. The rate of moisture clog penetration into the concrete column cylinder and the locations of the maximum pore pressure peaks developed in a disastrous fire are determined. The possibilities of concrete spallings occurring under fire are studied and predicted.