Gap defect and freeze-thaw cycles effects on mechanical characteristics of concrete-filled steel tube stub columns with experimental and theoretical investigation

As concrete-filled steel tube (CFST) structures become more prevalent in engineering, their durability garners significant attention. Mechanical characteristics of concrete-filled steel tube stub columns under the combined influence of gap defect and freeze-thaw cycles is presented with experimental and theoretical investigation in the paper. Twenty-six concrete-filled steel tube stub columns were designed to study the combined effects on failure mechanisms, axial compression-strain response, strength, and ductility. The experimental results indicate that as the number of freeze-thaw cycles and gap ratio increase, the deformation of the specimen increases and the deformation time advances. The specimen's strength and ductility are decreased by the combined effect of these factors. In the most severe cases, the specimen's overall strength and ductility are reduced by 29.4 % and 44.0 %, respectively. Subsequently, a finite element numerical model is established to parametrically analyze the concrete-filled steel tube stub column. Results show that the degree of restraint in the concrete-filled steel tube significantly influences the reduction in strength and ductility of the specimens. The stronger the restraining effect, the less the degradation of strength and ductility caused by the combined impact of the two factors. Therefore, it is crucial to effectively restrain the concrete within the concrete-filled steel tube to ensure structural safety and durability.