Analysis and Design of Elliptical Concrete-Filled Thin-Walled Steel Stub Columns Under Axial Compression

To analyze the axial compressive performance of elliptical concrete-filled thin-walled steel tube (ECFTST) columns, finite element (FE) modeling was built up by ABAQUS software in this paper. The material nonlinearity and the complex interaction between steel tube wall and core concrete in an elliptical section were considered in this numerical analysis. Failure modes and interaction mechanism of ECFTST stub columns were also studied. Moreover, a modified equivalent circular diameter approach for ellipse feature was proposed to substitute for the constitutive relation of ECFTST columns. The prediction accuracy of this method was verified by the comparison of the FE and test results in terms of failure modes, axial compressive capacities and axial force-axial displacement relation curves. Further, the influence of diameter-to-thickness ratio, cross-section slenderness and scale effect etc. on the performance of ECFTST stub columns were estimated under axial compressive loading. The results of numerical analysis showed that the axial force-axial displacement curves of the ECFTST stub columns were obviously affected by the confinement factor. Lastly, based on the simple superposition approach and the unified theory approach, two simplified design methods were proposed to predict the axial compressive capacities of ECFTST columns.