Compressive strength of circular concrete filled steel tube columns

An experimental study was undertaken to investigate the behaviour of 24 concrete-filled steel tube (CFST) columns, loaded concentrically in compression to failure. Variables in the tests include the length, diameter, strength of the steel tubes and the strength of the concrete. The large slenderness ratio caused all composite columns in Series 1 to fail by overall flexural buckling. Although overall flexural buckling was also experienced in the composite columns of Series 2 tests, the stockier columns failed by crushing of the concrete and yielding of the steel tube. A comparison of the experimental results with the loads predicted by the South African code (SANS 10162-1) and Eurocode 4 (EC4) shows that the codes are conservative by 8.4% and 13.6%, respectively, for Series 1 tests, and 10.5 and 20.2%, respectively, for Series 2 tests. A plot of the compressive load versus the vertical deflection shows the composite columns to be fairly ductile.

► Slender columns failed by flexural buckling with no sign of local buckling.
► Stockier columns failed by concrete crushing and yielding of the steel tube.
► A higher hoop stress results in increased load capacity of the CFST columns.
► EC4 was found to be much more conservative than SANS 10162-1.
► All columns behaved in a fairly ductile manner.