STABILIZED COMPRESSIVE STRENGTH UNDER PLASTIC DEFORMATION OF　CONCRETE FILLED SQUARE STEEL TUBE SHORT COLUMNS

The authors estimated the deteriorated compressive strength of concrete filled square steel tube (square CFT)short col-umns after the maximum strengh attained， which is defined as the stabilizedcompressive strength (Nstab).，Next the stabilized bending moment (M.stab)of square CFT columns were calculated by use of Nstab'. Compression tests of high strength square CFT short columns usingsteel-fibered concrete (FR-CFT) were also carried out，in order to improve the compressive ductiliy. As rests，the following has been found: i)Nstab decreases as the yield stress increases. ii) calcu-lated Mstab shows good agreement with the experimental results. iii) axial compressive ductility of square FR -CFT short column is higher than square CFT with concrete without steel fibere