EXPERIMENTAL STUDY ON FIRE BEHAVIOR OF HIGH STRENGTH DOUBLE-SKIN CONCRETE-FILLED STEEL TUBULAR COLUMNS

Standard fire tests on double-skin concrete-filled steel tubular (CFST) columns using high strength steel (HSS) and ultra-high strength concrete (UHSC) were conducted. The effects of section shape, boundary condition, thickness of fire protection, load ratio on the fire performance were investigated, ductility index was proposed and the differences between normal- and high strength double-skin CFST columns were discussed. Test results show that the time-displacement response of such high strength columns is very similar to their counterparts with normal strength materials. The parametric analysis indicates that, with the other conditions remaining the same, the fire resistance time of columns using HSS is shorter than their counterparts with normal strength steel (NSS), whereas the fire resistance time of such columns with UHSC is longer than those with normal- or high strength concrete (NSC or HSC). Besides, the high temperature-dependent buckling resistance and fire resistance time were calculated based on the ambient temperature calculation modes of axially and eccentrically loaded columns in Eurocode 4 and using the temperature-dependent material properties of UHSC and HSS, and the predicted results agree reasonably with the test values.