Structural behavior and strength prediction of elliptical concrete-filled steel tubular stub columns

This paper presents structural behavior and a unified equation for elliptical concrete-filled steel tubular (CFST) stub columns. An experimental database containing 94 tests for elliptical CFST stub columns was first compiled. A Finite element (FE) model was then developed and validated against the test results. Following the successful validation, parametric studies involving 330 FE models were conducted, with variations in the cross-sectional dimensions and strengths of the steel tube and infilled concrete. The test and FE results were used to investigate the structural behavior, including the effect of effective diameter-to-thickness ratio, relative strength factor (ξ) and aspect ratio on the strength enhancement index. The strength enhancement indexes of the steel tube and concrete were calculated and analyzed against the variation of ξ. The test and FE strengths were compared with the predictions from design codes (AISC 360, EC 4 and ACI 318). It is shown that these codified predictions are overall conservative. A unified equation incorporating the effect of ξ was proposed, which generally provides more accurate and less scattered strength predictions than current codified equations. The proposed equation is applicable for elliptical CFST stub columns with yield strengths of steel tube up to 1000 MPa and compressive strengths of infilled concrete up to 100 MPa.