単調載荷に於けるコンクリート充填角形鋼管長柱の変形性能

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 buildings. These frame systems for the first floors of high-rise office building involve slender CFT beam-columns. The deflection capacity of the plastic region needs to be evaluated for slender CFT beam-columns subjected to large forces under lateral seismic loading. A design formula for the deflection capacity of slender CFT beam-columns was specified in the AIJ Recommendations for Design and Construction of Concrete Filled Steel Tubular Structures in 2008. The deflection capacity is defined as a limit rotation angle at which the shear force is reduced to 95% of maximum strength. For future performance-based design corresponding to various structural design criteria, it is necessary to develop a formulation of deflection capacity that includes limit rotation angle corresponding to various strength reduction points after maximum strength for predicting plastic behavior.
 This paper proposes a new formulation of deflection capacity for slender square CFT beam-columns under monotonic lateral loading. The deflection capacity is defined by the limit rotation angle at which the shear force is reduced to 95%, 90%, 85% or 80% of maximum shear strength. New multiple regression formulas for limit rotation angles are provided based on a database including parameters such as axial compression ratio, width-thickness ratio of steel tube, ratio of buckling length to depth of cross section, strength ratio of steel tube to CFT section and concrete strength from test results of this and previous researches. Predictions from the formulas for deflection capacity, which involve fore parameters, agree with test results for rotation angles of these strength reduction points.