CONCRETE-FILLED STEEL TUBULAR COLUMNS WITH INTERNAL CONFINEMENT BY HIGH STRENGTH STEEL SPIRALS

Concrete filled steel tubular columns of non-circular section is much less ductile than their circular counterparts, particularly when high-strength concrete and thin/high strength steel tubes are used, which is a major concern fir structures designed to resist seismic loading. This paper presents the details of a new form of concrete-filled steel tubular columns recently proposed to address this problem and the rationale behind the new form; it also presents the first series of axial compression tests on such columns of square cross-section to demonstrate their advantages. These columns consist of a steel tube filled with concrete that is confined with high strength steel spirals typically with a yield stress exceeding 1000 MPa. The test results showed that the new form of columns, referred to as confined concrete-filled steel tubular (CCFST) columns, possesses much greater ductility than those without internal confinement as a result of the use of only a small amount of high strength steel as confining spirals.