A reappraisal of the nominal curvature method in the fire design of reinforced concrete columns

This paper deals with the reappraisal of the method based on nominal curvature (also called model column method) for checking the safety of reinforced concrete columns in fire. More in detail, the focus is on an alternative way of applying the method, which differs from the current provisions of EN 1992-1-2. To this end, a systematic comparison between experimental and numerical results is carried out on 39 columns tested at the Technical University of Braunschweig in Germany. The numerical results obtained are also compared to other calculation methods, namely finite element simulations and the simplified methods provided in EN 1992-1-2 (500°C isotherm and zone method). The comparisons show that the model column method yields safe results when compared to experimental results. In addition, the numerical results obtained are also reasonably close to those obtained by means of finite element calculations. By contrast, if the method is applied in combination with the simplified methods devised in EN 1992-1-2, the numerical results are not conservative, with significant overestimations of the bearing capacity of the columns, and thus of the time to failure, mainly because of an overestimation of section stiffness and of the role played by the thermal dilations at high temperature.