Vol.26, No.2, 2026, pp. 223–232
https://doi.org/10.69644/ivk-2026-02-0223

The objective of this paper is to analyse the ultimate capacity of recycled aggregate concrete-filled steel tube (RACFST) columns exposed to elevated temperatures. As current design codes do not offer recommendations for their design, the study aims to evaluate the applicability of the simplified method of the second-generation Eurocode 4 for predicting the fire capacity of these columns. Additionally, the method for predicting their post-fire axial capacity is proposed and validated. This method is also based on the calculation of equivalent temperatures from the simplified method of Eurocode 4. The study analyses columns made of both carbon- and stainless steel tubes. To evaluate the methods, the results from previous experimental campaigns are compiled. The results show that the application of Eurocode 4’s method and the proposed method for post-fire capacity calculation can be extended to RACFST columns. Furthermore, to gain deeper insight into the benefits of the RACFST solution over traditional RC columns from a sustainability perspective, the analysis of fire and post-fire capacity of two selected sections is performed. Through a fair comparison, the weak points of the unprotected concrete-filled steel tube solution are identified; however, these can be resolved by appropriate fire insulation measures.

Keywords: • recycled aggregate • composite columns • fire analysis • Eurocode 4 • nonlinear analysis