Search

This paper presents an experimental investigation on the compression behaviour of cold-formed octagonal, circular and square tubular steel stub columns. Three octagonal hollow steel tubes were examined under axial compression while three circular steel tubes and two square steel tubes were tested for comparison. Nine existing test data on octagonal hollow steel tubes were also collated for comparison. The hollow tubes were fabricated by welding two cold-formed half-section steel plates. To examine the material characteristics, flat, curved and corner coupons were extracted and tested. Residual stress distribution in longitudinal direction was also measured by sectioning method. Fifty longitudinal strips with a nominal width of 10 mm were machined by a wire cutting machine. The test results obtained from the tensile coupon tests and residual stress measurements were examined to evaluate the effect of the fabrication process on different cross-sectional shapes. The geometric imperfections of each specimen were carefully measured. Cross-sectional capacity, load-deformation relationships and failure modes of the stub columns were presented by the stub column tests. Finite element model was developed and validated against the experimental results. The experimental cross-sectional capacities were accurately predicted by the finite element models. The test data accompanied with the FE results were assessed with reference to current design provisions on cross-section classification and a suggested cross-section slenderness limit and an alternative design approach for octagonal cross-sections were proposed.

Existing studies have shown that fiber-reinforced polymer (FRP) jacketing/wrapping is highly effective in strengthening circular concrete columns but is much less effective for rectangular/...

This paper presents an investigation on axially loaded polygonal-shaped steel-tube columns filled with high-strength concrete. The tubes had triangular, hexagonal and octagonal cross-sections, the concrete had a nominal concrete compressive cylinder strength of 100 MPa and the steel had a nominal yield strength of 285 MPa. For each tube cross-section, two identical specimens of concrete-filled tubes and one specimen of a hollow tube were examined. Load shortening, strain histories and failure modes were recorded and compared. Finite-element analysis with three different existing constitutive models of concrete were also developed and validated against the experimental results. The load-carrying capacities of the concrete-filled tubes were compared with the derived values from BS EN 1994-1-1:2004, ACI 318-11/AISC 360-16 and GB 50936-2014. The feasibility of current design standards for concrete-filled steel-tube columns of different cross-sections is discussed.

This paper presents an experimental and numerical investigation into stub column behaviour of cold-formed steel octagonal hollow sections (OctHSs). A total of 16 OctHS stub columns were tested. Tensile coupons were extracted from both flat and corner portions of hollow sections to determine corresponding material properties. Finite element (FE) models were developed using commercially available software ABAQUS to replicate the test results generated in this study. The degree to which the enhanced material properties at corners should be extended was investigated. It was found that FE models with corner material properties extended to a width of material thickness beyond the corner portions offer the best agreement with test observations. The validated FE models were then adopted to conduct parametric studies to supplement test database. Cross-sectional slenderness limits specified in current design codes, including EN 1993-1-1, ANSI/AISC 360-16, ASCE/SEI 48-11 and AISI S100-16 (DSM) were evaluated against the test results in conjunction with the FE results. It was found that current limits are not suitable for the design of OctHSs. New cross-sectional slenderness limits in accordance with EN 1993-1-1, ANSI/AISC 360-16, ASCE/SEI 48-11 and DSM were then proposed based on the test and FE results. Cross-sectional capacity predictions obtained from EN 1993-1-1, ANSI/AISC 360-16, ASCE/SEI 48-11 and DSM were also compared with test and FE results. It is shown that the capacity predictions for slender sections from ASCE/SEI 48-11 are slightly unsafe, and ANSI/AISC 360-16 produces relatively satisfactory capacity predictions.

An experimental investigation on steel tube confined concrete (STCC) stub columns with circular, square and octagonal cross-section shapes under monotonic axial compression was conducted. Different concrete grades were examined with measured compressive cylinder strengths ranging from 38 MPa to 112 MPa. The nominal yield strength of the steel tube was 355 MPa. The load capacity, load-axial shortening curves and axial-hoop strain behaviour of the STCC stub columns are compared to that of the counterparts, concrete filled steel tubes (CFST), with different cross-section shapes based on the same material and geometric properties. Comparisons indicated that the load capacity of STCC stub columns are very close to that in the CFST with circular and octagonal cross-sections, while the performance of square STCC is not as good as the CFST counterparts due to low effectiveness of confinement. According to the experimental results of lateral behaviours of STCC, CFST and plain concrete columns, it was concluded that with very high strength concrete (cylinder strength over 100 MPa), the axial performance of STCC stub columns is better than that in CFST. A design assessment was also conducted on STCC stub columns and shows that the current design formulae for load capacity of CFST are also applicable to that of STCC stub columns.