FIRE RESISTANCE OF CONCRETE-FILLED STEEL TUBE COLUMNS : Under deformation to simulate the elongation of steel beams

Abstract

The thermal elongation of steel beams should be taken into account for fire-resistant design of concrete-filled steel tube (C.F.T.) columns in case of fire. Five C.F.T. column specimens using rectangular steel tubes and four C.F.T. column specimens using circular steel tubes were heated under constant axial load and deformation to simulate the elongation. The tests results are summarized as follows: 1) The fire resistance was 2 hours for rectangular specimens and 1 hour for circular specimens, when the axial load ratio was equal to 0.45 and the displacement angle was equal to 1/100. 2) All C.F.T. columns were axially elongated most at early stage, and then shrinked gradually to failure. 3) After 30 minute heating, the C.F.T. columns could not resist the bending moment due to the elongation of beams, however the columns could sustain the axial load.