Interaction diagram based method for fire resistance design of eccentrically loaded concrete-filled steel tubular columns

Previous investigations have highlighted that the current design method in Annex H of EN 1994-1-2 for the calculation of fire resistance of slender concrete-filled steel tubular (CFST) columns was unsafe, which led to the appointment of a Project Team (SC4.T4) by the European Committee for Standardization (CEN) to develop a new Annex H in EN1994-1-2 to replace the existing one. This paper presents the outcome of the Project Team, a new simplified fire design method for CFST columns, focusing in particular on eccentrically loaded columns for which there had been no systematic research. An extensive parametric study consisting of 5046 analysis cases has been carried out, covering all the practical ranges of application of CFST columns. The method accounts for minor and major axis eccentricities with large eccentricities up to e/D =1. Different bending moment diagrams, ranging from single curvature to double curve bending, were considered. The proposed new design method is in line with the cold design method in EN1994-1-1 and achieves the criteria of acceptance for safe and accurate design of structures in fire which were set by the CEN/TC250 Horizontal Group Fire.