REPRESENTATION OF CONCRETE-FILLED STEEL TUBE CROSS-SECTION STRENGTH

This paper presents the development of a polynomial equation to repres ent the three-dimensional (3D) cross-section strength of square or rec tangular concrete-filled steel tube (CFT) beam-columns. The equation p rovides an accurate representation of the cross-section strength of a CFT subjected to a combination of axial force, strong axis flexure, an d weak axis flexure. This expression is verified against the results o f a detailed fiber analysis formulation, and against experimental test s of shea, square CFTs available in the literature. This CFT cross-sec tion strength equation forms a compact expression of the failure surfa ce of square or rectangular CFTs having a wide range of cross-section dimensions and material strengths. The cross-section strength surface also provides the basis for a bounding-surface concentrated plasticity model in 3D force space for CFT beam-columns, presented in related wo rk by the writers. This beam-column model, in turn, is suitable for co nducting monotonic static, cyclic static, or transient dynamic seismic analysis of complete composite unbraced frame structures composed of steel I-girders framing biaxially into CFT beam-columns.