Behavior of Concrete-Filled Double Skin Short Columns Under Axial Loads

Abstract

Concrete filled double skin columns (CFDS) consist of double concentric thin steel tubes filled with concrete between them. The purpose of this study is to investigate numerically the behavior of these columns; i.e. strength and ductility, under axial loads. The finite element method is used to study the behavior of such columns by using the finite-element software package ANSYS. In this way, a finite element model is proposed to account for the nonlinearity of both the two steel tubes and the concrete core and the contact element and its conditions between the inner and outer steel tubes and the concrete to model the confinement effect. To calibrate the finite-element model, experimental data, available in the literature are compared with the finite element results and good agreement is obtained. The hollowness ratio, the diameter-to-thickness ratio of the outer steel tube, and the length-to-diameter ratio are chosen as main parameters affect the behavior of CFDS columns. The parametric study shows that the CFDS columns can effectively provide strength and ductility under axial loads especially for small hollowness ratio. Also, from the results obtained, the applicability of the current design codes such as ACI, Australian Standards (AS), AISC, AIJ, Eurocode 4 and Chinese Standards (DL/T) used for calculating the axial capacity of circular concrete filled steel tubes (CFT) stub columns is used to calculate the axial capacity of CFDS stub columns. From the results obtained, limitations to use design codes is introduced depending on the hollowness ratio of the column.
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