# Chung, Chung, and Choi 2007

This paper presents the development of a numerical model for the simulation of square CFT beam columns under axial compression and cyclic lateral load. Using the fiber method and uniaxial material models, pre- and post-peak behavior is predicted. The formulation is compared to previously published experimental results.

## Analytical Study and Discussion

The solution procedure consists of two iterative loops, the first loop to determine cross-section behavior, and the second loop to determine member behavior. A number of assumptions were made for this formulation, namely, plane sections remain plane, no slip between steel tube and concrete core, and the wavelength of plastic local buckling along the length of the member is four-fifths of the tube width.

Uniaxial material models for the steel tube and concrete core were developed for the analysis. For the steel tube subjected to low strains, the material model was simply the average of response of hollow tube stub columns tests. At higher strains, local buckling was modeled as two linear descending braches followed by a constant residual stress. Cyclic rules were added to account for strain-hardening, Baushinger’s effect, and deterioration of resistance due to local buckling. The concrete model followed a nonlinear equation, noting that the confinement provided by the steel tube was assumed to enhance ductility but not strength and that the tensile strength of concrete was neglected.

Analysis results were compared to experimental results from a prior investigation. Comparative load deformation plots were presented for each of the specimens. In addition, cumulative plastic strain energy was compared between analytical and experimental results.

## References

Chung, K., Chung, J., and Choi, S. (2007). “Prediction of Pre- and Post-Peak Behavior of Concrete-Filled Square Steel Tube Columns under Cyclic Loads using Fiber Element Method.” Thin-Walled Structures, Vol. 45, No. 9, pp. 747-758.