Parametric study for the fire safety design of steel structures

Despite the increasing knowledge on the behaviour of structures in fire and the development of new design tools for fire safety, current prescriptive regulations and design procedures present several shortcomings. These are mostly due to an oversimplification of the problem, in order to allow for a simple integration of the fire design procedures in the common practice. In this view, the structural fire safety of a building can be accomplished by verifying that single elements can resist a standard fire exposure for a required time, without taking into consideration the effect of restrained or hindered thermal expansion induced on the element by the rest of the structure. Nevertheless, restrained thermal expansion is known to significantly affect the behaviour of steel structures in fire, and the compliance with a prescribed resistance class doesn’t ensure the integrity of the building after the considered time of fire exposure. A deeper knowledge on the failure mode of steel structure is however important in order to ensure the safety of the people and properties outside the building.
Aim of this paper is to analyze the behaviour of single elements, sub-assemblies and frames exposed to fire and find out the basic collapse mechanisms of structural elements in fire conditions, considering the rest of the construction with appropriate constraints. The analysis is carried out taking into account material and geometrical nonlinearities as well as the degradation of steel properties at high temperatures. Different parameters, as the grade of restrain, the loading resistance ratio and the slenderness of the elements are varied, thus a parametric study of the phenomenon is realized.