Post-fire resistance of internally ring stiffened high performance concrete filled steel tube columns

Use of composite construction is increasing exponentially across the world, since such structures offer the combined benefits of constituent materials and provide cost effective solutions. Concrete filled steel tube (CFST) columns have been proven to be a very efficient way of composite construction. Although the behaviour of CFST columns under many different loading scenarios has been well detailed, a search of the literature revealed few studies on the post-fire resistance of these members. This paper gives an account of internally ring stiffening of CFST columns with the aim of advancing their post-fire resistance. To this end, CFST columns with and without internal rings were subjected to a standard fire exposure. To address their post-fire performance, fire exposed specimens and counterparts without fire exposure (in total 30 specimens) were tested under concentric compression to failure. CFST column specimens were manufactured using self-compacted high performance concrete to acquire key knowledge which could be exploited in highly stressed engineering structures. Experimental results indicate that with a proper design, internal rings are very efficient in providing high post-fire resistances. Some specific configurations achieved post-fire resistances greater than that of the capacities of classical CFST counterparts without fire exposure. Accordingly, it is shown that internal rings have the potential to eliminate the need for external coating or any other expensive fire protection measure to circumvent post-fire design concerns. The findings of this research provide novel insights and offer cost effective solutions to improve the performance of CFST columns under ambient temperature and after fire exposure.