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

当钢结构具有较高的冗余度时，结构的延性可以通过在梁柱节点附近连续形成塑性铰来实现。相反，土木工程结构往往是低冗余度和低结构延性可以预期。为了克服这一缺陷，通过扩大塑性区来提高构件的延性，本文对带楔形板的方箱形截面柱进行了弹塑性滞回性能试验研究。在规定的轴压荷载作用下，柱顶部承受循环水平荷载。使用线性锥形四个板元件由SM 400制造五个未加筋的400 × 400 mm和四个加筋的450 × 450 mm箱形试样。在900 mm长度范围内，未加筋试件两端锥度比分别为12/12、12/9、12/7.5和12/6。在1350 mm的长度范围内，加筋试件的锥度比分别为9/6、9/5和12/6。对12/9和9/6两种不同截面的无筋和加筋试件分别进行了单调和循环加载试验，结果表明，在水平循环荷载作用下，不同截面的作用弯矩比和抗力弯矩比沿着分布，塑性区的扩展范围可从底板向上扩展。最大水平荷载随均布柱重量比的增加而线性降低。尽管由于楔形板厚度减少，但通过塑性区在构件中的扩展，可以保持较高的延性。

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.