EXPERIMENTAL STUDY ON AXIAL COMPRESSIVE PROPERTIES OF CONCRETE-FILLED STEEL SQUARE TUBULAR COLUMNS WITH INNER TIE-BAR FRAMES

A partially fabricated concrete-filled steel square tubular column with a inner tie bar frame was designed. In order to reduce the cost and determine the optimal proportion of steel mass consumed in the structure, according to the orthogonal experimental design method, 9 groups of specimens and 3 groups of control specimens were designed for axial compression tests of short columns. The results indicated that the bearing capacity of the new kind of column subjected to axial compression could be improved effectively in the same consumption of steel. The axial compressive bearing capacity of the member was higher when the steel consumption of steel pipes, vertical rebars and horizontal tie bars was about 45∶35∶20. If the ratio of horizontal tie bars was too small, a significant reduction in axial bearing capacity would take place due to insufficient tie forces, and the recommended value was not less than 20%. Besides, the influence with or without tie-bar frames on the ductility of the structure was not obvious in the same total consumption of steel. For pre fabricated structures, the influence of the fabrication errors of members and the quality of cast concrete on the bearing capacity of members could be ignored.