Axial Residual Capacity of Circular Concrete-Filled Steel Tube Stub Columns Considering Local Buckling

Abstract

This paper proposes a superposition method considering local buckling to estimate the residual capacity of circular concrete-filled steel tube stub columns (CFSTs) under axial compression based on substantial experimental data, consisting of 3 recently conducted tests as well as 150 test results from available literature. The proposed approach accounts for the influence of local buckling of the steel tube on confining effect, by introducing a coefficient to reduce the compressive strength of concrete in the post-buckling stage. Three specimens, including a bare steel stub column with circular hollow section (CHS), a CHS with concrete restraint and a CFSTs, were tested to investigate the contribution of concrete on the local buckling. Further, the mechanical model of steel tube was established and the design equations for residual bearing capacity of the tube were derived. The nominal load-shortening curves of the concrete core are extracted from 150 collected experimental curves of the CFSTs, with different parameters such as diameter-to-thickness (D/t) ratio, yield strength fsy and concrete strength fcp. The variation of the stiffness degradation in the curves indicates that the effect of local buckling on both ductility and residual compressive strength of the concrete core are correlated with the section type of the steel tube. The residual compressive strength decreases exponentially with the increase of the generalized outer diameter-to-thickness ratio.

Aluminium members in composite structures – a review

“…-the cross-section type (the confining effect is stronger in a circular cross-section than in a rectangular cross-section) [40,43], -concrete strength (the confining effect becoming worse with the increasing of concrete strength) [44,45], -generalized outer diameter-to-thickness ratio 𝛼 (the confining effect becoming worse with the increasing of the ratio) [45]:…”

“…In this paper, the authors compared generalized outer diameter-tothickness ratio 𝛼 of steel and aluminium tubes (Table 1). According to [45], the tube cross-section were divided into six categories based on the ratio 𝛼. Depending on the ratio 𝛼 and concrete strength, the ductility and failure modes of concrete cores (splitting failure of the concrete core or shear and sliding failure) in the post-buckling stage may be evaluated (Table 2).…”

“…Depending on the ratio 𝛼 and concrete strength, the ductility and failure modes of concrete cores (splitting failure of the concrete core or shear and sliding failure) in the post-buckling stage may be evaluated (Table 2). the failure mode of the concrete core (A -splitting failure of the concrete core, B -shear and sliding failure), # I -an unlimited growth trend of the strength of the concrete core [45], the highest ductility and confining effect [39], ∧ II -a considerable compressive strength for the concrete core but with obvious damages [45], significant ductility and confining effect [39], & III -the serious damages of concrete core, the residual capacity of circular concrete-filled tube columns is not available [45], the lowest ductility and confining effect [39] One can observe from Table 1 that the use of aluminium alloy instead of steel provide to higher value of ratio 𝛼 and may change the cross-section category (compare S235 grade steel and AW-6082 T6 aluminium alloy). The intensity of the confinement effect decreasing with concrete strength and cross-section category rising.…”