Experimental and numerical investigations of eccentrically loaded rectangular concrete-filled double steel tubular columns

Rectangular concrete-filled double steel tubular (CFDST) columns have increasingly been utilized in high-rise buildings to support heavy loads. However, the responses of eccentrically loaded rectangular CFDST short columns have rarely been studied. This paper reports experimental and numerical investigations into the behavior of rectangular thin-walled short CFDST columns composed of a rectangular inner steel tube loaded eccentrically. Tests on rectangular and square CFDST short columns under eccentric loading and axial loading were carried out to examine their responses to various design parameters, including the cross-sectional dimensions, loading eccentricity, and width-to-thickness ratios of the external and internal tubes. The experimental program and results are described. A mathematical model underlying the theory of fiber elements is developed for simulating the moment-curvature responses as well as axial load-moment interaction envelopes of short CFDST columns. The computational model explicitly incorporates the experimentally observed failure mode of the progressive local buckling of the outer thin-walled rectangular steel tube. A computer simulation procedure is proposed for capturing the nonlinear behavior of short CFDST columns loaded eccentrically together with efficient solution algorithms that implement the inverse quadratic method for solving nonlinear equations. The experimental verification of the computer modeling technique is undertaken. The verified modeling technique is utilized to ascertain the significance of various design parameters on the structural behavior of CFDST columns made of rectangular thin-walled sections. It is confirmed that the computer model developed is capable of predicting well the experimentally observed responses of CFDST short columns.