Simplified calculation methods for reinforced concrete columns in case of fire in the new EN 1992-1-2

Author: Juri Strickler
Language: English

Abstract

Four levels of approximation are generally available for dimensioning reinforced concrete columns in case of fire: tabulated design data, simplified design methods, advanced design methods (often implemented in FE analyses), and tests. EN 1992-1-2 contains a total number of three different simplified design methods to determine the ultimate normal force resistance of columns subjected to fire. With the amended Annex C (2019), a further method with potential for further use is proposed. In the new EN 1992-1-2 (under revision 2017-2021), the number of simplified design methods should be reduced in the common sense of ease-of-use.
The structural behaviour of a reinforced concrete column in fire conditions is characterised by a temperature induced loss of strength and stiffness of concrete and steel as well as thermal strains. The property reduction of steel is easily considered due to the discrete position of reinforcement while the strength and stiffness reduction attributed to concrete is more difficult to capture, especially in a simplified manner.
In this Master’s Thesis, an extensive parametric study respecting more than 300’000 possible column configurations was carried out in order to suggest the best simplified design method to be implemented in the future EN-1992-1-2. Within this parametric study, a Matlab implementation was developed considering all available simplified design methods and testing their sensitivity to potential amendments. The parametric study showed that simplified design methods currently available in EN 1992-1-2 yield largely unconservative results for columns made of reinforced concrete subjected to fire. The Refined Zone Method (basis of amended Annex C of EN 1992-1-2), however, delivers reliable and safe results when compared to more advanced design methods and to tests.