Performance of concrete-filled double-skin circular tubes in compression

Tests were conducted on 32 concrete-filled double-skin circular tube (CFDSCT) columns. The CFDSCT columns were loaded in axial compression until failure. The parameters that were varied were the lengths, diameters and strength of the outer steel tubes. The lengths ranged from 1.0-2.5 m, in half a metre increments. The CFDSCTs of 1 m lengths, failed by yielding of the steel tubes. All the other CFDSCTs failed by overall buckling due to their large slenderness. Using the philosophy in the South African standard (SANS 10162-1) and Eurocode 4 (EN 1994-1-1), new formulas were developed to predict the results of the strengths of the CFDSCTs. The new formulae are in a similar format to SANS 10162-1 and EC4. A plot of the results from the proposed formulae over the test results, versus the slenderness ratio shows that the results were predicted well.