軸方向圧縮力と一端単調曲げモーメントを受ける角形鋼管柱の実験的研究

Abstract

When the building is subject to a seismic load, columns will subject bending moment and axial force 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. In Japan, widely used shape for columns are square steel tubular column. However, the requirements stipulated in LSD are based on the test results that were conducted by H-shaped steel columns in 1980s. 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 and 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) Square steel tubular column which satisfies width-to-thickness ratio classification P-I-1 and column classification C-1 of LSD had full plastic limit strength which is stipulated in LSD. 2) Three types of collapse mechanism are confirmed. i) Local buckling occurred at the end of the column determined the ultimate state. ii) Pδ moment determined the moment capacity at the loading point, and local buckling occurred around the most deflected portion determined the ultimate state. iii) Pδ moment determined the moment capacity at the loading point, increment of the deflection around the middle portion of the column determined the ultimate state. Local buckling was not observed during the testing. Collapse mechanism that will be categorized to iii) can be observed to the columns that are located further from the LSD limitation. 3) Plastic deformation capacity obtained from testing showed larger values than that stipulated in LSD, even if the column does not satisfy the LSD requirements. 4) When the plastic deformation capacity R of the column is determined by Pδ moment, the plastic deformation capacity R and the value of ny·λc02 are in a linear relationship. Some of the columns which had larger width-to-thickness ratio observed local buckling; therefore, plastic deformation capacity of the column will be determined either Pδ moment or local buckling. Therefore, it is also important to evaluate quantitatively the plastic deformation capacity which is determined by local buckling. 5) When the collapse mechanism of the column is determined by Pδ moment, the maximum deflection appeared around the middle of the column which is not expected in structural design. From the point of view of deflection, LSD provides a reasonable limitation to guarantee the expected mechanism where the plastic deformation will concentrate at the end of the column.