Abstract
Concrete-filled double skin steel tubular (CFDST) columns with outer steel tubes varying in diameter and thickness were exposed to ASTM E-119 fire curve for 60 and 90 minutes. All specimens (control and heated) failed by outward local buckling of outer steel tube, crushing of concrete and outward and inward buckling of inner steel tube. Residual Strength Index (RSI), secant stiffness and Ductility Index (DI) were calculated in order to compare the performance of control and fire-damaged CFDST columns. It was found that specimens with 90 minutes of fire exposure time possessed highest RSI. Meanwhile, secant stiffness seems to decrease with increased exposure time. And finally, CFDST columns became more ductile after being heated.
Highlights
In the event of fire, fire safety is first addressed by sprinklers or smoke detectors which are part of the active fire protection system
The usage of Concrete-filled double skin steel tubular (CFDST) columns is limited to outdoor construction such as transmission towers [7], and bridge piers [8,9,10] even though the performance of CFDST column is superior to RC and CFST columns
The following conclusions can be drawn: 1) All specimens failed by outward local buckling of outer steel tube, crushing of concrete and outward and inward local buckling of inner steel tube
Summary
In the event of fire, fire safety is first addressed by sprinklers or smoke detectors which are part of the active fire protection system. The passive fire protection system exists in order to ensure the integrity of the structures for a period of time so that the occupant can safely evacuate the building or until the arrival of fire fighters. Among them are; 1) higher fire resistance to fire even without fire protection layer on outer steel tube, 2) higher load bearing capacity, 3) prevent the spalling of concrete, 4) eliminate the need for formwork, 5) increase the strength, ductility and energy absorption and 6) reduced column footing [3,4,5,6,7,8,9]. As for the residual strength of CFDST columns after fire, none can be found in the literature. The Residual Strength Index, Secant Stiffness and Ductility Index of fire-damaged CFDST columns are calculated and compared with unheated CFDST columns
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