EXPERIMENT AND FINITE-ELEMENT CALCULATION STUDY ON CONCRETE-FILLED DOUBLE SKIN STEEL TUBULAR MEMBERS UNDER COMPRESSION AND TORSION

A total of seven concrete-filled double skin steel tubular( CFDST) members and one concrete-filled steel tubular( CFST) member were tested under compression and torsion． The outer steel tube of CFDST and CFST members was square hollow section ( SHS) ，and the inner steel tube of CFDST members was circular hollow section ( CHS) ． The test results showed that all the specimens exhibited good ductility． The sandwiched concrete was not broken，and approximate 45 diagonal cracks appeared． When the axial compression ratio was small( such as n 0. 3) ，torsional capacity of the test specimen increased as the axial compression ratio increased． When the axial compression ratio was large ( such as n ＞ 0. 3 ) ，torsional capacity of the test specimens decreased as the axial compression ratio increased． Torque versus angle curves of the test specimens calculated by the finite element method agreed well with experimental ones．