Seismic behavior of reinforced-concrete and steel reinforced concrete ultra short columns

In this paper, 4 RC (reinforced-concrete) ultra short columns, 4 SRC (steel reinforced-concrete) ultra short columns and 6 separated RC columns were tested under combined constant axial load and cyclic lateral load. The shear span to depth ratio of 8 ultra short columns was 1, and the shear span to depth ratio of 6 separated RC columns was 2.4. The test results indicate that the deformation capacity of RC ultra short columns does not satisfy the requirement in Chinese code for seismic design of buildings. The failure mode of SRC ultra short columns without shear stud is bond failure, and the shear strength and deformationability of SRC ultra short columns without shear stud are not evidently higher than that of RC ultra short columns. The failure mode of SRC ultra short columns with shear stud is diagonal compression failure, and the shear strength and deformation ability of SRC ultra short columns with shear stud are higher than that of RC ultra short columns. Whereas the deformation ability of SRC ultra short columns with shear stud does not satisfy the requirement in Chinese code for seismic design of buildings. The test results also indicate that separating RC ultra short column into separated columns (shear span to depth ratio higher than 2) by gapping longitudinally at the middle of ultra short column can improve the ductility and deformation capacity of the columns effectively. The moment strength of RC separated columns increase with an increase in axial load ratio, while the ductility and deformation capacity of RC separated columns decrease with an increase in axial load ratio. The deformation capacity of RC separated columns does not satisfy the requirement in Chinese code for seismic design of buildings when the design axial load ratio is greater than 0.7. The design method of shear studs of SRC ultra short columns and the design advices of RC separated columns are suggested based on the experimental results.