The analysis of thermal and fire performance of cementitious building components
This work is concerned with the thermal and structural behaviour of reinforced concrete members in fire conditions. The numerical analyses of temperature histories and mechanical behaviour of reinforced concrete structural members subjected to fire are the major components of this research. In this thesis a non-linear finite element procedure is proposed to predict the temperature distribution history in the cross section of structural members, such as beams composed of reinforced concrete, in fire conditions. A theoretical analysis of heat and moisture transfer in concrete was made which incorporated the simplifications that energy transfer by convection and diffusion in concrete could be neglected. However, the effect of water evaporation in concrete was considered. The thermal properties of concrete were considered as temperature and moisture dependent and the thermal properties of steel as temperature dependent only. The fire conditions were described by standard time-temperature fire curves and convection and radiation boundary conditions were used. In order to validate the model a series of verification tests have been carried out through a quantitative comparison of the model predictions against known test results. Fairly good accuracy has been found. A non-linear finite element procedure for predicting the structural behaviour of the planar reinforced concrete members is also developed. The proposed procedure is based on "plane stress" theory and an iterative, secant stiffness formulation is employed. The complex features of structural behaviour in fire conditions, such as thermal expansion, shrinkage, creep, transient strains, cracking or crushing and change of material properties with temperature are considered in this model. Predictions from the model proposed are compared against experimental results, as well as against the model proposedb y previous researchers, and a better correlation to experimental data is found. It is shown that the secant stiffness approach can provide good numerical stability for the analysis of planar reinforced concrete members in fire conditions. The model proposed in this study has the potential to predict the fire resistance of a planar reinforced concrete members with an accuracy that is adequate for practical purposes if realistic material properties are available.