Concrete exposed to fire: From fire scenario to structural response

In this paper a model for the analysis of concrete structures exposed to fire, based on Porous Media Mechanics, is coupled with a computational fluid dynamics model. To show the capability of this strategy the numerical simulation of a simple concrete slab exposed to fire is presented. The thermal loads as well as the moisture exchange between the structure surface and the environment are calculated by means of computational fluid dynamics program. Thanks to this strategy the structural verification is no longer based on the standard fire curves commonly used in the engineering practice, but it is directly related to a realistic fire scenario. With the simple example proposed, it is possible to highlight how the localized thermal load generates a nonuniform pressure rise in the material, which results in an increase of the structure stress state and of the spalling risk. Spalling is likely the most dangerous collapse mechanism for a concrete structure. Numerical results of various sections of the slab exposed to fire are presented, showing the effects of a more realistic distribution of the thermal loads with respect to the ones obtained by using the standard fire curves. This coupling approach still represents a "one way" strategy, i.e. realized without considering explicitly the exchange of boundary conditions from the structure to the fluid. This results in an approximation, but from physical point of view the current form of the solid-fluid coupling is considered sufficiently accurate in this first phase of the research.