An experimrntal study on development of local ductility of tapered box columns

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Structural ductility can be achieved by the successive plastic hinge formations in the vicinity of column-beam connections when the steel structures possess high degree of redundancy. On the contrary, civil engineering structures are often of low degree of redundancy and low structural ductility can be expected. In order to overcome the deficiency, higher ductility can be developed by the spread of plastic zones in the members.The elastic-plastic hysteretic behavior of unstiffened and stiffened square box columns with tapered plates is investigated experimentally. The cyclic horizontal loads at the column top are subjected under the specified axial compressive load. Five unstiffened 400x400mm and four stiffened 450x450mm box shaped test specimens are fabricated from SM 400 using the linearly tapered four plate elements. Taper plates are shaped by milling cutter.The taper ratios at the both ends of the unstiffened specimens are 12/12, 12/9, 12/7.5 and 12/6, respectively, between the length of 900mm. Also, the taper ratios of the stiffened specimens are 9/6, 9/5 and 12/6, respectively, between the length of 1350mm. Monotonic and cyclic loading tests for the unstiffened and stiffened specimens are conducted for the two 12/9 and 9/6specimens, respectively.It is concluded from this study that the wider spread of the plastic zones due to the cyclic horizontal loading can be developed upward from the bottom panel with the different action and resistant moment ratios along the specimens. The maximum horizontal load may be lowered linearly with the weight ratio to the uniform columns. In spite of the decrease of thickness due to tapered plates, the higher ductility can be kept by the spread of plastic zones in the members.