Size effect on the seismic behavior of square CFST short columns

Abstract

The objective of this work is to study the effect of structural size on the seismic behavior of the square concrete-filled steel tubular (CFST) short columns experimentally. A total of eight CFST short columns with different structural sizes (maximum column width of 800 mm) were designed and tested. All columns have a constant width-to-thickness ratio B/t of 50, an axial load ratio n of 0.4, and a slender ratio L/B of 2.0. The seismic performances of the columns were tested and analyzed, involving the failure pattern, the hysteretic characteristic, the ductility capacity, the stiffness degradation and the energy dissipation. The typical compressive-flexural failure pattern was observed for all tested columns, and the local buckling of the steel tube and the crushing of the core concretes were also found at the bottom of the column. With the increase of the cross-sectional width, the energy dissipation capacity and the ductility capacity of the square CFST short columns decrease. In addition, it is found that as the cross-sectional width of the square CFST short column increases, the nominal flexural strength decreases significantly, exhibiting a remarkable size effect. As the cross-sectional width varies from 200 mm to 800 mm, the peak flexural stress, i.e. the nominal flexural strength, decreases by 46.9%. Finally, the comparisons of the experimental results were made against some design codes including GB50936, AISC-360 and EC4. It is found that most design codes without consideration of size effect would be unsafe for the larger-sized columns.