Study On Performance Of Concrete-Filled Steel Tubular Stub Columns After Being Exposed To Freezing And Thawing

Concrete-filled steel tube (CFST) columns are widely used in the field of civil engineering due to their excellent structural performance. At present, most attention has been devoted to the short-term mechanical properties of such composite members. However, similar to reinforced concrete members, their long-term durability is crucial as they may also suffer from chloride corrosion and concrete frost heaving. In recent years, several low-temperature failure accidents of CFST columns have happened in the north of China. It is concluded that the failure of CFST in freeze-thaw environment is caused by the combination of the icing and migration of free water in the concrete and the low-temperature fracture of the steel. As a result, the investigation on the performance in freeze-thaw environment is a very important issue to ensure the safety of CFST structures in cold region.This paper experimentally and theoretically studies the performance of CFST stub columns after being exposed to freezing and thawing, and the main works are as following:(1) The studies on the axial compressive performance of CFST, frost resistance of FRP strengthened concrete and frost resistance of CFST were reviewed. Moreover, the contents and methods of this paper are elaborated.(2) Fifteen circular specimens and fifteen square specimens after being exposed to freezing and thawing were tested under axial compression. The number of freeze-thaw cycles and the steel ratio (cross-section area ratio of steel to concrete) were considered as main parameters.(3) Based on the analysis of the tested results, the stress versus strain relationship of concrete after being exposed to freezing and thawing was suggested. The performance of CFST stub columns after being exposed to freezing and thawing was simulated by the finite element analysis model developed using the software ABAQUS.(4) The effect of the number of freeze-thaw cycles, material strength and steel ratio on the mechanical index of axially loaded CFST stub columns after being exposed to freezing and thawing was analyzed by the finite element analysis model. Finally, The simplified formulae for the bearing capacity and composite elastic modulus of CFST stub columns after being exposed to freezing and thawing were suggested.