FIRE PERFORMANCE OF SELF-COMPACTED CONCRETE FILLED DOUBLE SKIN STEEL SQUARE TUBES UNDER CONCENTRIC AND ECCENTRIC LOADING

Abstract

While concrete filled double skin steel tubes offer superior structural performance, their behavior after fire exposure, particularly under eccentric loading conditions has not been adequately investigated, limiting the development of comprehensive fire safety design guidelines. They exhibited excellent load carrying capacity when compared to conventional columns. In this research, the performance of concrete filled double skin steel square tubular columns consisting of outer and inner square tubes with self-compacting concrete (SCC) infill between them after exposed to fire was studies experimentally. Twelve specimens were fabricated and tested under concentric and eccentric loading. For each loading conditions, two columns were exposed to 60 min fire, two were exposed to 90 min fire, and two columns were considered as control specimens which are not exposed to fire. These two columns, one with solid section and one with hollow section. The filling by SCC increased the capacity by 18-26% for concentric condition through enhanced confinement. Fire exposure reduced capacity by 8-25% due to steel softening and concrete thermal degradation with stiffness degrading more severely (44-59%), indicating interface deterioration. Eccentric loading caused 65-68 capacity reduction across all conditions. Failure modes included concrete crushing and local buckling with fire exposed specimens showing more sever buckling and concrete spalling from thermal damage. The dominant mode of failure was crushing of concrete at loaded end followed by tube local buckling. These findings contribute to understanding the fire resistance behavior of SCC-filled double skin steel tubes and provide essential data for developing fire safety design guidelines for such structural systems in building construction.