Zhang and Zhou 2000

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An experimental and an analytical study on square CFT columns were presented. The steel tube response was isolated from the overall behavior of the specimens and the response of the concrete and steel were examined separately. Formulations were proposed for the confined concrete strength, the confined concrete strain, and the longitudinal stress in the steel tube.

Experimental Study, Results, and Discussions

Thirty-six CFT columns were tested under monotonically applied axial loading. The D/t ratio of the specimens ranged between 20 and 50. The measured compressive strength of concrete was 5.87 ksi and the yield strength of the steel ranged from 41.28 ksi to 58.51 ksi. The L/D ratio varied between 4 and 5. From the experimental results, it was found that the confinement effect increased the concrete strength and ductility. They also determined that the longitudinal stress in the steel tube was always less than the yield stress due to the biaxial stress condition. Confinement was found to be larger when the D/t ratio was smaller.

Analytical Study

By fitting a curve to the test data, an equation for confined concrete strength, fcc, was derived as (all stress values are in MPa):


The ultimate concrete strain and the longitudinal stress in the steel tube were also determined as follows through fitting to the test data:


The proposed equations were compared with the experimental results from the current study and from the available literature. Good correlation was achieved.


Zhang, S. and Zhou, M. (2000). “Stress-Strain Behavior of Concrete-Filled Square Steel Tubes,” Composite and Hybrid Structures, Proceedings of the Sixth ASCCS International Conference on Steel-Concrete Composite Structures, Xiao, Y. and Mahin, S. A. (eds.), Los Angeles, California, March 22-24, 2000, Association for International Cooperation and Research in Steel-Concrete Composite Structures, Los Angeles, California, pp. 403-409.