Análise da confiabilidade estrutural de uma coluna de aço em situação de incêndio

Abstract

Although it is widely used as a structural material, steel presents as a disadvantage the vulnerability to fire, with steel columns being most affected by the accident. In Brazil, ABNT NBR 14323 (2013) is the standard that presents the procedures for the sizing of steel structures in a fire situation, including compressed elements. However, the use of prescriptive (deterministic) norms, which do not directly consider the uncertainties associated with the problem, can lead to uneconomical projects or inadequate levels of safety, especially for exceptional fire situations. On the other hand, the application of the theory of reliability to the structures subject to fire arises as an option in relation to the deterministic methods found in the norms, allowing the uncertainties to be considered and providing a quantitative measure of structural safety, the probability of failure. In this context, the present work analyzes the reliability of a steel column in a fire situation, sized according to Brazilian standards. For this, it was developed in Microsoft® Excel software a mechanical computational module, whose main function was to perform thermal and structural analysis of the column. The developed tool was coupled to a reliability module, which consisted of a set of MATLAB® programmed subroutines through which the reliability methods FORM and Monte Carlo were applied. The results obtained showed that the random variables with greater influence in the problem change with the time of the variables associated with the structural analysis were more important in the initial instants and those related to the fire modeling and the thermal analysis a greater participation in more advanced instants. In addition, curves of the probability of failure variation were constructed as a function of fire time, temperature and other variables involved in the problem. The results illustrate that the structure does not present an adequate level of safety, reaching high probabilities of failure during the Required Fire Resistance Time (TRRF) indicated by the standard. Finally, it was possible to conclude that although the rules lead to safe projects under normal conditions of use, the same does not occur for the exceptional case of fire.