Axial Load Behavior of Self-Consolidating Concrete-Filled Steel Tube Columns in Construction and Service Stages

Abstract

This paper compares the performance of axially loaded concrete-filled steel tube (CFST) columns cast using a conventionally vibrated normal concrete (NC) and a self-consolidating concrete (SCC) made with a new viscosity-modifying admixture (VMA). A total of 16 columns with a standard compressive strength of approximately 50 MPa for both SCC and NC were tested by applying concentric axial load through the concrete core. The effect of various parameters such as slenderness ratios, types of concrete, and the addition of longitudinal and hoop reinforcements at different degrees of confinement was studied. Columns were fabricated without and with longitudinal and hoop reinforcement (Series CI and Cll, respectively) in addition to the tube confinement. The slenderness ratio of the columns, expressed as height-to-diameter ratio (H/D), ranged between 4.8 and 9.5 for Series CI and between 3.1 and 6.5 for Series CII. In the construction stage, the performance was evaluated based on the consolidation characteristics with different degrees of congestion and the required casting time. In the service stage, the performance was judged based on strength, ductility, stress-strain characteristics, degrees of confinement, load sharing between steel tube and confined concrete, and failure modes. Test results showed that the ease of placement and time of casting were considerably improved for columns with SCC compared to those with NC. The strength of SCC columns was found comparable to that of their NC counterparts as the maximum strength enhancement in NC columns ranged between 1.1 and 7.5% only. The ductility of comparatively shorter columns (H/D ranging between 3.1 and 4.8) with both SCC and NC was similar. However slender NC columns (H/D ranging between 6.3 and 9.5) showed higher ductility compared to their SCC counterparts. Ductility also decreased with the increase of slenderness ratio (H/D) of columns. No significant differences in strain development was found due to the presence of SCC or NC or due to the presence of longitudinal and hoop reinforcement. The confined strength f' c c of SCC was found to he lower than that of NC, and f' c c also decreased with the increase of slenderness of the columns.