Experimental and Numerical Studies on Circular Steel Tube-Encased Concrete Columns Confined by Circular Thin Steel Tube

This paper presents experimental and numerical investigations on the structural performance of six steel tube-encased concrete (SC) columns confined by bolted thin-walled circular steel tubes. All specimens were circular columns with a 300 mm diameter, incorporating an encased circular steel tube of 200 mm in outer diameter. Reversed cyclic lateral force and constant axial compression were applied to these specimens. Key experimental parameters included axial load ratio, presence of infilled concrete and the rank of the encased steel tube. Test results demonstrated that confinement by thin-walled circular steel tubes ensured sufficient deformation capacity up to 0.06 rad drift for SC columns with FB-rank and higher encased steel tube, even without concrete infilled and under high axial compression. Test results also indicated that infilling concrete into the FC-rank encased steel tube enhanced the deformability up to 0.06 rad drift. Parallel to the experimental work, a simple evaluation method for the ultimate flexural strength of the SC column was proposed, and a numerical analysis was conducted to predict the overall structural behavior of the SC columns. Both calculated strength and numerical prediction showed close agreement with experimental results.