Axial compressive performances of prefabricated T-section fireproof board and thin concrete encased steel columns after fire exposure

This paper aimed to study the axial compressive performances of T-section fireproof board and thin concrete encased steel (T-FBTCES) columns after fire exposure. Five composite column specimens and two pure steel column specimens were tested to analyze the failure mode, the temperature distribution, the load-displacement curve and the compressive resistance and stiffness of T-FBTCES columns. Finite element (FE) models were then established and validated against experimental results. According to the validated FE model, the effects of the thickness of fireproof board, skeleton steel ratio, stirrup spacing, heating time, and concrete strength on the axial resistance and stiffness of T-FBTCES columns after fire exposure were discussed. Based on the experimental and numerical study results, the proposed fireproof board and thin concrete encasement can significantly increase the post-fire resistance and stiffness of the composite columns than barely fireproof coating protected steel short columns. Increasing the fireproof board thickness or the skeleton steel ratio of the composite columns can improve the residual resistance and stiffness after fire exposure. When the heating time is less than 60 min and the thickness of the fireproof board is more than 15 mm, the resistance does not decrease after fire exposure. When the skeleton steel ratio of the composite column with 20 mm thick fireproof board increases from 5.83 % to 9.99 %, the post-fire resistance of the composite columns suffered 180 minutes fire time increases by 40.49 %. The resistance and stiffness of the columns using high-grade concrete have a more loss than that using low-grade concrete. Decreasing the stirrup spacing can improve the residual resistance of the composite column after fire exposure, but has little effect on the residual stiffness. The simplified calculation formulas were proposed to predict the residual resistance and stiffness of the T-FBTCES columns after fire exposure.