Residual strength capacity of fire-exposed 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, post-fire resistance of these members is not well specified in literature yet. This thesis gives an account of internally ‎reinforcing bars and ring stiffening of CFST columns with the aim of advancing their post-fire ‎resistance. To this end, CFST columns with and without internal bars and rings were ‎subjected to a standard fire exposure. To address their post-fire performance, fire exposed ‎specimens and counterparts without fire exposure all specimens were tested under concentric ‎compression to failure.‎ ‎Experimental results indicate that with a proper design, internal bars ‎and 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 bars and 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 thesis provide novel insights and offer cost effective ‎solutions to improve the performance of CFST columns under ambient temperature and after ‎fire exposure.‎