Post-fire bond between the steel tube and concrete in concrete-filled steel tubular columns

Abstract

Push-out tests were carried out on 64 concrete-filled steel tubular columns, which had been exposed to ISO 834 standard fire for 90 min or 180 min, respectively. At the same time, 12 unheated specimens were also prepared and tested for comparison. The variables investigated in the bond tests were selected as (a) fire exposure time; (b) cross-section type; (c) cross-sectional dimension; (d) interface length to diameter (or width) ratio; (e) concrete type; (f) fly ash type; and (g) concrete curing condition. The effects of the above different parameters on the bond behaviour are discussed. The test results indicate that fire exposure had a significant effect on the bond between a steel tube and its concrete core. A decrease in bond strength was generally observed for specimens after a fire exposure of 90 min; however, bond strength recovery was found when the fire exposure time was extended to 180 min. Other factors also had influence to some extent.