単調載荷に於けるコンクリート充填角形鋼管柱の曲げモーメント－曲率関係

抄録

 The advantages of concrete-filled steel tube (CFT) columns include high strength and remarkable ductility, since the steel tube provides confinement to the concrete while the concrete inhibits local buckling of the steel tube. CFT column composite frame systems with steel beams have been widely used in moment-resisting frame systems for mainly office buildings. The CFT columns of the building involve short columns with small ratios of buckling length to depth of cross section at typical floors and slender columns with a large ratio of buckling length-depth at the entrances of lower floors. CFT columns from short to slender have been used in buildings. The stress states of CFT columns applied to buildings are in a state of flexural-shear stress, and the structure designs are made for the predominant flexural yielding type. It is thought that accurate evaluation of flexural behavior in the evaluation of flexural-shear behavior leads to design of columns that have the features of CFT columns. In addition, there is a tendency to increase the strength of CFT columns due to higher rises and larger spans of buildings. For the moment curvature relationship, which is the basis of the restoring force characteristic model of CFT columns from short to slender, it is important to devise a simple model with a range up to high strength material.
 This paper proposes a new simplified model of the moment-curvature relationship for square CFT beam-columns under monotonic bending moment loading to estimate the elastic-plastic flexural behavior of beam-columns from short to slender. The model of square CFT beam-columns involves a range from ordinary-strength to high-strength materials. The proposed simplified model is a multi-linear model having a crack strength point, a yield strength point, an ultimate strength point, an ultimate strength holding point and strength reduction points. For the main points of the proposed model, each flexural strength is calculated by the general superposed strength method, and new multiple regression formulas for each curvature are proposed based on results of monotonic bending moment loading tests from previous researches. Predictions from the proposed model of the moment-curvature relationship are found to agree approximately with experimental results up to large flexural deformations.