Abstract
The square steel tube component has a beautiful appearance, simple joint connection, and it is widely available. However, the uneven distribution of effective constraints in the cross-section of a square steel tube hinders its application. A novel concrete-filled square steel tubular column was tested under axial compression. There were 11 specimens [10 concrete-filled square steel tube columns reinforced with rhombic stirrups with 90-degree internal angle (SSSC specimens) and 1 concrete-filled square steel tube column (SC specimen)]. The load-displacement curves, the law of failure process, failure mode, mechanism analysis, energy consumption, ductility, and stiffness degradation were described, we then investigated the influence of stirrup diameter, stirrup side length, stirrup spacing, steel tube thickness, aspect ratio, and steel ratio on the mechanical properties of the specimens. The results show that the failure process of the SSSC specimens was basically the same. The ultimate failure mode of the specimens with an aspect ratio of 4 was local buckling failure. The specimens with an aspect ratio of 5 and 6 failed due to bending failure in the plastic stage. The steel tube bulged out in different degrees in most of the debonding areas. The longitudinal bars also produced outward bending deformation in the larger bulging area of the steel tube. Some of the stirrups were broken in the later stage of loading. The characteristics of load-displacement curve changed with the changing of stirrup spacing. The strength of longitudinal constraint had an obvious influence on the bearing capacity. In a certain range of steel ratio (ρs = 8.97% ∼ 9.05%), the weakening of the lateral restraint of the stirrup cage had a greater adverse effect on the bearing capacity than the weakening of the effective restraint of the corner. In a certain range of steel ratio (ρs = 8.97% ∼ 9.49%), strengthening the effective corner constraint of stirrups improved the stiffness of the specimen, however, the ductility performance was reduced. The opposite was true for strengthening the lateral constraint of the stirrup cage.
Highlights
A concrete-filled steel tubular column is a vertical load-bearing member made of concrete fully injected into a thin-walled steel tube
The results showed that the spiral reinforcement effectively improved the axial compression bearing capacity and deformation ductility of concrete-filled square steel tubular columns
The bearing capacity and ductility of the SSSC specimens were improved to some extent, the steel ratio was less than the SC1 specimen. This proves that the effective constraint at the corner of the stirrup cage improved the weak constraint in the middle of the side length of the steel tube section, and made the axial compression performance better than that of the ordinary concrete-filled square steel tube column
Summary
A concrete-filled steel tubular column is a vertical load-bearing member made of concrete fully injected into a thin-walled steel tube. The results showed that the spiral reinforcement effectively improved the axial compression bearing capacity and deformation ductility of concrete-filled square steel tubular columns.
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