On the simulation of real fire for post fire resistance evaluation of steel structures

Post fire resistance assessment of industrial steel structures is of prime importance to companies having to deal with such accidental situations. Most of the time, the structure or at least a major part of it still stands. Being able to quickly assess the temperature it was once submitted to is very important to re-evaluate its load-bearing capacity. The latter is to help take wise decisions regarding its dismantling or replacement and to avoid unnecessary delays during which the industry can no longer carry out its business. After being heated during a certain time, any kind of structure and material can be affected by locked in forces for continuous structures and possible material deterioration. Developing or simulating a real fire that is at least in agreement with visual observations or tests done on the structure after the fire, is the only way to assess the remaining resistance and thus reliability of the structure. The use of a standard heating curve is inappropriate to deal with post-fire situations and there is a clear need to establish the fire exposure characteristics in order to estimate the residual properties of a structure that survived the event. This paper aims to evaluate existing methodologies for post-fire assessment of structures having been submitted to a real fire. Results from models built with very sophisticate tools (computational fluid dynamics) are compared to very simple and quick two-zone models (in Ozone). One well instrumented academic test is firstly used to compare these techniques. Then, two additional case-studies are used to illustrate that it is possible to simulate a fire with all its intrinsic features with relatively simple tools and to illustrate the influence of the chosen model on the structural response