Experimental study of the behaviour of the concrete-filled double-skin columns with stainless-steel outer tubes subjected to post-earthquake fire

Abstract

This paper presents an experimental investigation of the behaviour of concrete-filled double-skin columns with stainless-steel outer tubes (CFDSST) subjected to post-earthquake fire. A total of eighteen (CFDSST) specimens were tested in three phases: (1) cyclic loading test, (2) fire test, and (3) cyclic loading test after fire. The specimens consist of two cross-section combinations: circular-circular and circular-square, with different diameters of circular hollow section (CHS) inner tubes and dimensions of square hollow section (SHS) inner tubes. First, all of the specimens were tested under constant axial load and lateral cyclic loading; then the specimens were divided into three groups, and each group was exposed to fire at 750 °C for a specific duration time: 60 min for group 1, 120 min for group 2, and 180 min for group 3. Following the fire test, all specimens were subjected to constant axial load and cyclic lateral load until failure in order to investigate the influence of the inner tube’s geometry and dimensions, as well as the duration of fire exposure, on the behaviour of the (CFDSST) columns after post-earthquake fire conditions. The results of the study show that the (CFDSST) columns behaved in a ductile manner and maintained high strength even though they were subjected to post-earthquake fire. In general, the specimens with circular-circular cross-sections showed higher performance than the specimens with circular-square cross-sections. Also, the increasing diameter of the inner tube improved the behaviour of the circular-circular specimens. Fire exposure had a considerable effect on lateral load capacity, with greater reductions observed for longer exposure durations. For instance, the ultimate load of the specimen (C-C-125) decreased by 22.3 %, 27.8 %, and 31 % after 60, 120, and 180 min of fire exposure, respectively. Moreover, increasing the inner tube diameter improved the ultimate lateral load; for example, specimen (C-C-125–60) had a 6.8 % and 11.8 % higher ultimate lateral load compared to specimens (C-C-100–60) and (C-C-75–60), respectively.