Effects of Core Concrete Initial Imperfection on Performance of Eccentrically Loaded CFST Columns

Gap between the outer steel tube and core concrete is a type of initial imperfection that may exist in concrete-filled steel tubular (CFST) columns. This paper is devoted to investigate the influence of the gap on the performance of eccentrically loaded CFST columns. Twelve CFST column specimens and two reference hollow steel tubes were tested under eccentric compression. The main test parameters included the gap type (circumferential and circular-segment) and gap ratio. A finite element model was established to simulate the behavior of the CFST columns with gaps, and the model was validated against the experimental results in terms of failure mode, load versus deformation response, and ultimate strength. Based on the experimental and numerical investigations, the performance of eccentrically loaded CFST columns with gaps was analyzed. Parametric studies were then conducted to reveal the influence of different parameters on the ultimate strength of the CFST columns with gaps. Finally, the maximum allowable gap ratio in practice was proposed for the eccentrically loaded CFST columns with circumferential gaps, and a simplified model was proposed to predict the ultimate strength of the composite columns.