Abstract: Axially compressive behavior of 12 circular concrete-filled steel tubular columns with built-in high-strength steel tube was experimentally studied． The influences of yield strength of the inner tube，clearance between the outer and inner tubes，steel ratio of inner tube，and replacement ratio of demolished concrete lumps (DCLs) on the columns’behavior were investigated． The test results show that，firstly，when the total steel usage keeps un-changed，the column’s axial load bearing capacity as well as initial stiffness can be greatly improved by thinning the outer steel tube and placing a high-strength steel tube inside; secondly，the axial load bearing capacity of such co-lumn can be further improved by appropriate increasing the clearance between the inner and outer steel tubes;thirdly，steel ratio change of inner tube and the reusing of DCLs have limited influence on the axial behavior of such column; finally，the proposed calculation method proves a high precision in measuring axial load bearing capacities of such columns．

Key words: built-in high-strength steel tube, concrete-filled steel tubular column, demolished concrete lump, axially compressive behavior, experimental investigation