Under high temperatures concrete is exposed to several degradation processes. Multi-physical mechanisms in the porous concrete lead to thermal softening as well as thermal expansion, drying shrinkage and internal pore pressure build-up. When exposed to high temperature, heat is conducted and convected through material, resulting in changes in the chemical composition, physical structure and fluid (water, gas and vapor) contents in the porous material which in turn affect the overall mechanical (strength, stiffness, fracture, etc) and other physical properties (thermal conductivity, permeability, porosity, etc). Such degradation processes have come to the forefront in the safety assessment of structures, e.g. tunnel and high rise buildings and the need for a comprehensive understanding of concrete materials exposed to high temperature under fire environment has been reinforced. The basic principles and details of the physical, mathematical and numerical models forming the main system equation of the numerical simulation of the thermal, hygral and mechanical behavior of concrete structures subjected to heating are presented.