High strength steel square and rectangular tubular stub columns infilled with concrete

This paper presents the experimental and numerical investigations of high strength steel square and rectangular tubular stub columns infilled with concrete. Firstly, a series of tests was conducted on cold-formed high strength steel (CFHSS) square and rectangular tubular sections infilled with three different concrete compressive strengths, i.e., 40, 80 and 120 MPa. The CFHSS tubular sections had the nominal 0.2% proof stress (yield stress) up to 900 MPa. Secondly, an extensive numerical study accounting for the confinement effect, as well as the non-linearities of materials, geometry and contacts was performed. Upon validation against the test results, a parametric investigation was conducted. The structural behaviour of concrete-filled CFHSS stub columns was investigated, including the ultimate load, end shortening, strength enhancement index and ductility index. Finally, the experimental and numerical results were used to assess the suitability of the design rules specified in the current American Specification (AISC) and European Code (EC4) for the compressive strength of the concrete-filled CFHSS square and rectangular stub columns. It was found that the predictions from EC4 were generally unconservative while those from the AISC were conservative. However, the predictions by EC4 became conservative if the effective strength of infilled concrete or the effective area of outer steel tubes were considered in the design. In addition, the predictions by EC4 became less scattered for different infilled concrete strengths when the effective concrete strengths were used. However, using the effective concrete strengths or the effective areas did not lead to the improvements of for the AISC specifications.