Numerical investigation on the thermal behaviour of steel-reinforced CFST columns in fire

Abstract

[EN] In previous research, the authors highlighted the limited fire resistance of slender concrete-filled steel tubular (CFST) columns. A possible solution for enhancing the fire resistance of such columns consists of embedding an open steel profile within the concrete infill of the CFST section, generating the so-called steel-reinforced concrete-filled steel tubular (SR-CFST) section, where the inner steel profile results thermally protected by the surrounding concrete, thus delaying its degradation at elevated temperatures. This strategy may result beneficial in the fire situation as compared to other sectional configurations where the steel parts are directly exposed to the heat source. In this paper, a two-dimensional finite element model will be developed for studying the thermal behaviour of SR-CFST columns and validated by comparing the temperature distribution results with experimental tests available in the literature. The numerical model will be subsequently used to carry out parametric studies, in order to analyse the influence of the different parameters, such as the cross-section shape, outer tube thickness or the inner steel profile sectional dimensions over the thermal response of these composite sections when subjected to fire. Finally, a simplified temperature distribution proposal will be developed, which may help practitioners for a fast evaluation of the cross-sectional temperature field of SR-CFST columns at a given fire resistance period by assigning an equivalent temperature to each component of the composite section (hollow steel tube, concrete encasement and inner steel profile). This simplified temperature proposal may result helpful when evaluating the sectional capacity of SR-CFST columns in fire, by using a single strength and stiffness value for each component of the composite cross-section corresponding to its temperature.