521 SDSS’Rio 2010 STABILITY AND DUCTILITY OF STEEL STRUCTURES E. Batista, P. Vellasco, L. de Lima (Eds.) Rio de Janeiro, Brazil, September 8 - 10, 2010 NUMERICAL ANALYSIS OF STEEL COLUMNS CONSIDERING THE WALLS ON FIRE CONDITION Jonas B. Dorr*, Jorge M. Neto* and Maximiliano Malite* * Engineering School of Sao Carlos of the University of Sao Paulo, Brazil emails: jonasbdorr@gmail.com, jmunaiar@sc.usp.br, mamalite@sc.usp.br Keywords: Steel column, thermal gradient, masonry, thermal analysis, thermo-structural analysis, numerical analysis. Abstract. Steel columns are structural elements widely used in multi-storey buildings, industrial, commercial warehouse, among others. However, the reduction of stiffness and strength of steel in response to a temperature raise imposes the need to predict the critical time of exposure of the structure in fire, looking for safety and economic design structures. The presence of walls introduces change in gradient temperature at the steel cross section. In those circumstances, this paper aims to present a numerical study of steel columns with open section of type I, whereas the compartment of the environment in fire. The buckling of the compressed element will be marked by a reduction factor obtained using the relationship between the buckling load in a fire situation, characterized by asymptotic displacement, and buckling load identified at room temperature. 1 INTRODUCTION Fire is one of the natural phenomenon which, if it is not properly considered in the design of structures, can cause devastating consequences. Among the main materials used in the structures of the buildings it can be mentioned the steel structural, which has severe behavior changes on fire condition. The behavior of steel structures on fire condition, including the composite structure, for a long time it has been seen as dominated by the effects of the resistance loss from the material caused by the temperature rise, and large deformation through the load imposed to a weakened structure. To overcome this disadvantage it can be considered the application of fire protection to ensure that the steel can be exposed to fire for more time so it can reach similar temperatures to those that would be reached without the use of this protection. However, this procedure involves costs that, generally, make the steel structures less competitive related to the use of other structural material. Regarding to the requirements of fire resistance from steel and composite structures elements on a fire condition, most of the standards and main normative codes of the world are still based on isolated elements in furnace experiments. This is because of the difficulty, both economic and technical, to perform experiments with complex structures, which would represent better the real structures behavior. The current international standards show simplified procedures to determine the critical time of fire resistance of steel structure. However, these simplifications are restricted to few cases and show approximated results; usually those results are not what really happen. In this way the numerical models in finite elements help to explain, in a more coherent way, the structural behavior of these elements on fire condition. In this research [1] performed at the University of Sao Paulo was made structural numerical analysis at room temperature and thermo-structural analysis using the finite element method with the computational package Ansys [2], whose intent was to show the structural materials behave under high temperatures considering many situations and configurations, checking if the standards requirements provide with safe this behavior. However, on that study, due to uncertainties relative to the analysis