Modeling of the structural response to fire of a high-rise steel building

Observations from the tests and the real fire investigations have consistently shown that the performance of a whole steel-framed building in fire is very different from the performance of its individual members (Usmani et al, 2000). In this context, it is of interest to investigate the failures mechanism of a structure under fire and to highlight a possible disproportionate influence of a local failure triggered by the fire on the response of the whole structure (Bontempi et al., 2010).

The propagation of the collapse has to be traced up to the global collapse of the structure and numerical problems due to the triggering of local mechanism should be overcome to this purpose. In this paper, a steel structure has been considered as case study and the response of the structural system to fire and fire effects has been investigated with the avail of a finite element commercial code.

These kinds of investigations require the consideration of a full nonlinear response of the structure, due to material degradation under fire, possibility of buckling, large displacements and deformations suffered by elements and exploitation of plastic reserve of the structure. The assessment of structural performances and the computation of the structural system behavior have been conducted by considering some remarkable fire scenarios.

Basic preliminary investigations are carried on a substructure, which represents a single floor of the building (Fig.2 bottom) for understanding the effect of beam failures on the adjacent elements and for highlighting a possible propagation of the failures to zones of the structure not directly involved in the fire.

In order to show the influence of ratio of stiffness between beams and columns, the behavior of two different floors has been studied.