Strength of Concrete Filled Steel Tubular Columns

Composite columns of steel and concrete have been used and studied world wide, but filled tubu- lar columns need more attention. This paper presents an experimental study on the behavior of short con- crete filled steel tubular columns (CFT) axially loaded in compression to failure. A total of 28 specimens (16 were filled with concrete and 12 were kept hollow) with different cross-sections were tested to investigate the load capacity. The length-to-diameter ratios of these columns were between 4 and 9. Parameters for the tests were tube shape and diameter-to-thickness ratio. Some of the concrete filled columns had internal bracing of #3 deformed bars. The test results are compared with the theoretical results and previous studies. The results show that the confinement effect on concrete does play a role in increasing the compressive strengths to almost 60% in some cases. Based on the test results, an equation to estimate the ultimate axial compressive loading capacities is also proposed for square CFT columns.