Effects of structural size and confinement on CFST column plastic hinge length

The objectives of this work are to study the influence of structural size on the plastic hinge length of square concrete-filled steel tubular (CFST) columns and to discover the influence of confinement generated by steel tubes on the plastic hinge length. A total of 24 square CFST columns were designed and tested with different column widths (i.e., 200 mm ∼ 800 mm) and different confinement effects (described by width-to-thickness ratio, i.e., 50, 80 and 100). The failure behavior and the curvature distributions of the tested columns subjected to axial compression loads and horizontal cycling loads were reported, and the corresponding plastic hinge lengths of the columns were obtained. The test results indicate that, as the column width increases, the plastic hinge length increases linearly, about 0.6– 0.9 times the column cross-sectional widths. Also, as the confinement effect increases, namely, the magnitude of the width-to-thickness ratio decreases, the plastic hinge length decreases slightly. Moreover, the non-dimensional plastic hinge length, defined as the ratio of plastic hinge length and column width, was proposed. The non-dimensional plastic hinge length decreases with increasing the column width, showing a significant size effect. An empirical formula for predicting the magnitude of the plastic hinge length of CFST columns was established.