Experimental Investigation Of Post-fire Bond-slip Performances Of Interface For Concrete-filled Steel Tubular Columns

With the increasingly wide application of concrete filled steel tubular(CFST)structure in the practical engineering,the probability of CFST structures under fire exposure is also increasing.Therefore,the deep research on post-fire mechanical performance and damage of load-bearing capacity for CFST is of great significance to take proper measures for repairing and strengthening of the fire-exposed structures.Especially for the fire-exposed buildings,it will make a big economic difference whether the fire-exposed building is to be rebuilt or strengthened.The interfacial bond behaviours of CFST is the basis for coordinating deformation and load-bearing between both steel tube and concrete.Recently,Most of the research results were focused on the bond performance between steel tube and concrete of CFST columns at ambient temperatures;However,scarce research was aiming at the bond behavior of CFST after fire exposure.Existing research results show that the material properties(such as strength and elastic modulus)of steel and concrete deteriorate in fire,which makes the degradation of interfacial bond strength.As a result,the deformation and load-bearing capacity of CFST members after fire are strongly influenced.Set against the above background,the bond performance of interfacial for CFST after the designed fire exposure was investigated experimentally.The main research work and outcomes are summarized as follows:(1)52 CFST specimens with fire exposure including heating and cooling and the subsequent repeated push-out tests were performed.And then,the influences of parameters on bond strength and load-slip curves were analyzed,such as sectional types and ratio of radius and thickness of steel tube,slenderness ratio,heating time,cooling rate and fire types.Besides,the distribution of bond strength of interfacial was calculated.(2)According to the analysis of tested results,the key parameters that affected bond strength between steel tube and concrete were identified,and formulas for the post-fire bond strength and the corresponding slip based on the key parameters were regressed and the bond-slip constitutive relations of CFST interfacial were also modified.