Behaviour of concrete-filled double skin (CHS inner and CHS outer) steel tubular stub columns and beam-columns

A series of tests on concrete filled double skin steel tubular (CFDST) stub columns (14) and beam-columns (12) were carried out. Both outer and inner tubes were circular hollow sections (CHS). The main experimental parameters for stub columns were the diameter-to-thickness ratio and hollow section ratio, while those for beam-columns were slenderness ratio and load eccentricity. A theoretical model is developed in this paper for CFDST stub columns and beam-columns. A unified theory is described where a confinement factor (xi) is introduced to describe the composite action between the outer steel tube and the sandwiched concrete. The predicted load versus deformation relationships are in good agreement with stub column and beam-column test results. Simplified models are derived to predict the load-carrying capacities of the composite members. (C) 2003 Elsevier Ltd. All rights reserved.