Cyclic behaviors of SHS columns subjected to small amplitude loading

Abstract

Structural components can be subjected to a limited number of cyclic large drifts during strong earthquakes (e.g., Northridge earthquake, 1994; Kobe earthquake, 1995), as well as many cyclic small amplitude loading during long-duration earthquake excitations (e.g., Tohoku earthquake, 2011). Traditional studies on cyclic behaviors of structural components mainly focused on large drifts and neglected small amplitude loading, rendering them inadequate to represent different seismic loading cases. Square hollow section (SHS) columns are widely used in low- and middle-rise steel building structures in Japan. The bottoms of the first story columns yield under severe earthquakes, even though the strong-column-weak-beam concept is adopted during building design. To better understand the deformation capacities and hysteretic behaviors of steel columns under cyclic small amplitude loading, tests on 26 SHS columns were carried out in this study. The width-to-thickness, axial force, shear span ratios, and loading history of the columns were the main test parameters. The loading histories consisted of monotonic loading, variable amplitude loading, and several constant small amplitude loadings. All specimens exhibited local buckling at the bottom of the columns. Under small amplitude loading, it was observed that the strength of the specimens deteriorated slightly within a certain number of cycles, while the restoring force decreased rapidly afterwards. The stability limit concept was proposed to represent the point when the column’s strength starts to deteriorate rapidly; it is based on the axial deformation in the flange in the local buckling region. Accurate prediction methods for the stability limit values and the numbers of cycles until the stability limits were reached were also proposed.