Square concrete-filled double steel tubular (CFDST) beam-columns consisting of an internal circular steel tube
have increasingly been utilized in composite building structures because of their high structural performance.
This paper describes experimental and numerical studies on the structural responses of square thin-walled
CFDST columns loaded eccentrically. Tests on twenty short square CFDST columns were undertaken that included
sixteen columns under eccentric loading and four columns under concentric loading. The parameters
examined in the experiments included the cross-sectional dimensions, the width-to-thickness ratios of outer and
internal tubes and loading eccentricity. The measured ultimate strengths, load-shortening responses, load-lateral
displacement curves, stress-strain curves and observed failure modes are presented. A numerical model incorporating
the fiber analysis is developed that predicts the moment-curvature responses and axial load-moment
strength envelops of CFDST columns. The model explicitly accounts for the influences of the confinement exerted
by the internal circular steel tube on the core concrete and the progressive post-local buckling of the external
steel tube. Efficient computer algorithms implementing the inverse quadratic method is developed to produce
converged solutions to the nonlinear dynamic equilibrium equations generated in the analysis. Measurements
from the tests are employed to validate the proposed numerical model. It is shown that there is a good agreement
between theory and experiment. The computer model is utilized to demonstrate the significance of various
parameters on the behavior of thin-walled short CFDST beam-columns.