Abstract
CFDSCT columns are structural members that are filled with concrete and supported by circular steel tubes on the interior and exterior. These steel tubes serve as formwork and hence these members are economical and quicker to construct when compared to conventional concrete reinforced columns. They are also efficient because they take advantage of the high compressive strength of the concrete and high tensile strength of steel. Despite the fact that much research is ongoing internationally in the field of CFDSCTs, no experimental tests have been conducted on intermediate and slender CFDSCTs. Current research has been focused on short CFDSCT columns and varying amounts of confinement have been found in these tests. Design codes also do not cover CFDSCTs. In order to gain a more comprehensive understanding of the behaviour of CFSDSCTs, experimental tests were conducted on 32 concrete-filled double-skin circular tube (CFDSCT) columns. The CFDSCT columns were loaded in axial compression till failure. The parameters that were varied were the lengths and diameters of the outer steel tubes, and the strength of the outer steel tubes. The lengths ranged from 1 and 2.5 m, in half a metre increments. The CFDSCTs of one metre lengths, failed by yielding of the steel tubes. All the other CFDSCTs failed by overall buckling due to their large slenderness. Using the same philosophy as SANS 10162-1 and EC4, new formulas were developed to predict the results of the strengths of the CFDSCTs. The new formulas are in a similar format to SANS 10162-1 and EC4, and are 5% and 6% more conservative than the tests results, respectively. The ratio of the predicted results over the test results versus the slenderness was plotted and shows that the results were predicted fairly well.
M.Ing. (Civil Engineering)