STUDY ON THE METHOD OF EVALUATING CONFINEMENT EFFECTS IN CONCRETE FILLED CIRCULAR STEEL TUBULAR COLUMNS

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The following conclusions are reached on bases of the research which was supported by this Grant.1.Analytical method considering a confinement effect for concrete filled circular steel tubular columns (referred to as CFT columns) subjected to concentric axial compression(1) The elastic-plastic behavior of CFT columns can be predicted by the proposed plastic theory in which yield criterion proposed by Richart and constitutive law and non associated plastic flow rule proposed by Xiao for concrete are assumed.(2) The stress strain relationship for confined concrete proposed by Sakino and Sun can be used for more simple analytical method which is developed for practical use. In this practical method, the biaxial stress state of steel tube must be estimated by the proposed plastic theory described above.2.Analytical method considering the confinement effect for CFT columns subjected to combined stresses of axial load and bending moment(1) The stress strain relationship for confined concrete propose by Sakino and Sun, which have been verified to be applicable to analysis of CFT columns under concentric axial compression as described above, can also be used for moment curvature relationship analysis. This is verified by the comparisons between analytical results and experimental results of specimens tested in experimental phase of this research program.(2) A practical design formula for ultimata moment of CFT columns can be proposed based on the moment curvature relationship analysis described above.