軸方向圧縮力と単調逆対称曲げモーメントを受ける角形鋼管柱の実験的研究

抄録

 In Japan, square steel tubular columns are widely used. When the building is subject to a seismic load, columns will subject axial force with antisymmetric bending moment simultaneously. Therefore, it is important to design the column under these combined loading in the ultimate limit state to guarantee the safety. Recommendation for Limit State Design of Steel Structure (LSD) specifies the requirements for columns to guarantee sufficient strength and ductility. The plastic deformation capacity of the columns that are subjected to compressive axial force with one end monotonic bending moment are ensured more than 3 by LSD. However, specific deformation capacity of the column that are subjected to compressive axial force with monotonic antisymmetric bending moment is not shown. Test results that can confirm the appropriateness of LSD requirements for square steel tubular column are limited. It is necessary to gather more data of maximum strength, deformation capacity, and elasto-plastic behavior of square steel tubular columns by testing. Moreover, column that is subjected to compressive axial force is important to take into account second-order effects.
 In this study, testing where axial force with monotonic antisymmetric bending moment are applied to the columns simultaneously are conducted. Maximum bending moment, deformation capacity, and second-order effect that will be caused by Pδ moment were evaluated from the test results. Comparison between LSD requirements and test results were also shown.
 From the test results, followings are found.
 1) Three types of collapse mechanism are confirmed.
  i) Local buckling occurred at one end of the column determined the ultimate state and deformation capacity.
  ii) Pδ moment determined the moment capacity at the loading point. After the maximum bending moment, local buckling occured at the maximum deflection point and it determined the ultimate state and deformation capacity.
  iii) Pδ moment determined the moment capacity at the loading point; increment of the bending deflection determined the ultimate state. Local buckling was not observed during the testing.
 2) When the value of n_y·λ_c0² is larger than 0.25, second-order effects determined the plastic deformation capacity. Plastic deformation capacity R of the columns that were determined by Pδ moment had a linear relation between n_y·λ_c0². When the value of n_y·λ_c0² is smaller than 0.25, plastic hinge was formed at the end of the column and determined the collapse mechanism. Width-to-Thickness ratio equals to 21.7 that was used in the testing and collapsed by local buckling had a plastic deformation capacity around 3.5.
 3) Plastic deformation capacity of the square steel tubular column will be determined by either local buckling or Pδ moment. It was found that deformation capacity of the columns that were determined by Pδ effects have a linear relationship between n_y·λ_c0²; therefore, it is also important to evaluate quantitatively the plastic deformation capacity which is determined by local buckling.
 4) Plastic deformation capacity greater than 3 were observed even if the current LSD limitation was not satisfied. However, from the point of view of collapse mechanism, LSD limitation can form a plastic hinge at the end of the column which is expected in design.