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

Abstract

Ibañez C, Aguado JV, Romero ML, Espinos A, Hospitaler A. Fire design method for concrete filled tubular columns based on equivalent concrete core cross-section. Fire Safety Journal. 2015; 78:10-23. doi: 10.1016/j.firesaf.2015 ABSTRACTIn 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 crosssectional 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 considers the gap at steel-concrete interface, the moisture content in concrete and the Ibañez C, Aguado JV, Romero ML, Espinos A, Hospitaler A. Fire design method for concrete filled tubular columns based on equivalent concrete core cross-section. Fire Safety Journal. 2015; 78:10-23. doi: 10.1016/j.firesaf.2015 2 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 Eurocode 4 Part 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.

Effects of axial and rotational restraints on concrete-filled tubular columns under fire

“…A method was proposed in a previous paper [2] which permits evaluating the fire resistance of unreinforced CFT columns of circular cross-section. Again, a brief review of this method is given next for a better understanding of the reader.…”

“…The subsequent study of the results is presented jointly with the evaluation of the provisions given by Eurocode 4 Part 1.2 [13]. Finally, the assessment of a simple calculation method proposed by the authors in a previous publication [2] is included and the corresponding proposal for the effective length in fire is given.…”

“…In a second step, current provisions given by Eurocode 4 Part 1.2 (EC4) are analyzed together with those given in the UK National Annex to Eurocode 4. Finally, these values are also used in the assessment of the simple calculation model presented by the authors in a previous paper Ibañez et al (2015) and subsequently a proposal is made obtaining reasonably accurate but slightly safe results since the guidelines of CEN-Horizontal Group Fire were followed. As a result, the fire effective length value of 0.5 L given by EC4 is found to lead to unsafe results, being more appropriate to adopt the value of 0.7 L suggested in the UK National Annex.…”

Performance of recycled aggregate concrete–filled square steel tubular columns exposed to fire

“…During the last three decades, a considerable amount of experimental and theoretical work has been performed to investigate the fire behaviour of CFST columns (Kodur, 2007;Rush et al, 2012), and the simplified formulae for the fire resistance and thickness of fire protective coating of CFST columns have also been proposed (Comite´Europe´en de Normalisation (CEN), 2005; Han et al, 2003;Kodur, 2007;Twilt et al, 1995;Zhao et al, 2010). Recently, Iban˜ez et al (2015) presented a method for the realistic cross-sectional temperature prediction and the simplified fire resistance design of circular CFST columns under axial compression. Moliner et al (2013) reported the fire test results of 24 slender circular CFST columns under eccentric compression, and both normal and high-strength concrete were considered in the tests.…”

Proposal of a new method in EN1994-1-2 for the fire design of concrete-filled steel tubular columns

“…2016; 128:237-55. doi: 10.1016/j.engstruct.2016.09.037 7 temperature field as a preliminary step, for the subsequent calculation of the design axial buckling load, while the code does not provide any simplified method for that purpose. This makes designers feel unwilling to use these methods, and therefore a simplified way for obtaining the cross-sectional temperature field, like that proposed by Ibañez et al [17] for CHS columns, would be of interest for practitioners and ultimately for promoting the use of this type of composite sections. Other way to deal with this drawback, different from the one exposed in this work, was developed by the authors through the concept of an equivalent concrete core cross-section at room temperature [17].…”