局部座屈変形に基づく鋼柱の残存耐力評価

Abstract

From lessons of the 2011 Tohoku earthquake and other earthquakes, it becomes clear that the quick procurement of an emergency public shelter is very important to restore a function of a city. In the event of a disaster, structural engineers are required to estimate the seismic damage of structural components in buildings, and to judge whether these buildings are able to be immediately occupied or not as soon as possible. However, the visible damage can hardly be related to the damage of steel structural components directly, while crack width has been used as a clear damage index for RC structures. It is very important to establish a visible damage index for quick damage estimation of steel structures. In the previous papers, visible damage indices for exposed column base and an single brace with angle section have been established from the experimental studies. This paper focuses on the residual out-of-plane deformations in local buckling region of steel column to estimate its residual strength. In order to find the relation between the residual deformation and the out-of-plane deformation in local buckling region, cyclic loading tests of a steel column under axial compression force were carried out. The main parameter in these tests is the cross section of the column, which are cold-formed RHS-200x6 (depth x thickness), 200x9, 300x9, welded H-200x180x6x6 and H-200x200x6x9. In addition, the constant axial force which is 0.15 and 0.30 defined as the ratio to its yield axial strength is also selected as one of the parameters of the test. The major findings obtained from the test are summarized as follows: (1) the out-of-plane deformation in local buckling region was strongly related with the residual strength deteriorated due to the local buckling; (2) the out-of-plane deformation almost remained constant regardless of various residual story drift; (3) the rotation angle of column after deterioration is able to be converted to the out-of-plane deformation by a 3-hinge deformation model of the local buckling. Finally, from these results, the diagrams of the residual strength of steel columns based on the out-of-plane deformation in its local buckling region have been expressed as an example by using the Kato-Akiyama hysteresis model18),19).