Fire behaviour of concrete filled elliptical steel columns

In this work, a non-linear three-dimensional finite element model is presented in order to study the behaviour of axially loaded concrete filled elliptical hollow section (CFEHS) columns exposed to fire. This study builds on previous work carried out by the authors on concrete filled circular hollow section (CFCHS) columns both at room temperature and in fire. The numerical model is first validated at room temperature against a series of experiments on CFEHS stub columns available in the literature and subsequently extended to study the performance of slender columns at elevated temperatures. The aim of this work is to understand and represent the behaviour of axially loaded CFEHS columns in fire situations and to compare their effectiveness with that of the circular concrete filled tubular (CFT) columns. Parametric studies to explore the influence of variation in global member slenderness, load level, cross-section slenderness and section size are presented. Finally, guidance on the fire design of CFEHS columns is proposed: it is recommended to follow the guidelines of Clause 4.3.5.1 in EN 1994-1-2, but employing the flexural stiffness reduction coefficients established in the French National Annex with an equivalent EHS diameter equal to P/¿, where P is the perimeter of the ellipse.The authors would also like to acknowledge Universidad Politecnica de Valencia for providing fellowship funding for the first author's stay as a visiting academic at Imperial College London.Espinós Capilla, A.; Gardner, L.; Romero, ML.; Hospitaler Pérez, A. (2011). Fire behaviour of concrete filled elliptical steel columns. Thin-Walled Structures. 49(2):239-255. https://doi.org/10.1016/j.tws.2010.10.008S23925549

Fire design method for concrete filled tubular columns based on equivalent concrete core cross-section

In this work, a method for a realistic cross-sectional temperature prediction and a simplified fire design method for circular concrete filled tubular columns under axial load are presented. The generalized lack of simple proposals for computing the cross-sectional temperature field of CFT columns when their fire resistance is evaluated is evident. Even Eurocode 4 Part 1-2, which provides one of the most used fire design methods for composite columns, does not give any indications to the designers for computing the cross-sectional temperatures. Given the clear necessity of having an available method for that purpose, in this paper a set of equations for computing the temperature distribution of circular CFT columns filled with normal strength concrete is provided. First, a finite differences thermal model is presented and satisfactorily validated against experimental results for any type of concrete infill. This model consideres the gap at steel-concrete interface, the moisture content in concrete and the temperature dependent properties of both materials. Using this model, a thermal parametric analysis is executed and from the corresponding statistical analysis of the data generated, the practical expressions are derived. The second part of the paper deals with the development of a fire design method for axially loaded CFT columns based on the general rules stablished in EN 1994-1-1 and employing the concept of room temperature equivalent concrete core cross-section. In order to propose simple equations, a multiple nonlinear regression analysis is made with the numerical results generated through a thermo-mechanical parametric analysis. Once more, predicted results are compared to experimental values giving a reasonable accuracy and slightly safe results.The authors would like to express their sincere gratitude to the Spanish Ministry of Economy and Competitivity for the help provided through the project BIA2012-33144, and to the European Community for the FEDER funds.Ibáñez Usach, C.; Aguado, JV.; Romero, ML.; Espinós Capilla, A.; Hospitaler Pérez, A. (2015). Fire design method for concrete filled tubular columns based on equivalent concrete core cross-section. Fire Safety Journal. 78:10-23. https://doi.org/10.1016/j.firesaf.2015.07.009S10237