Post-fire behaviour of reinforced concrete stub columns confined by circular steel tubes

Abstract

Abstract:Experimental and numerical studies into the structural behaviour of reinforced concrete columns confined by circular steel tubes after exposure to standard fire conditions are presented. These elements differ from conventional concrete-filled steel tubular (CFST) columns in that breaks in continuity are present at the member ends, which limit the longitudinal stresses in the steel and maximise the level of confinement afforded to the concrete through the generation of hoop stresses in the tube. The temperature distributions in the specimens were measured during the heating and cooling phases, while the load-displacement relationships and longitudinal and transverse strains in the steel tube were recorded during the subsequent compressive tests. 3D finite element (FE) models were also developed using the program ABAQUS to investigate the post-fire performance of circular steel tube confined reinforced concrete (CSTCRC) columns, including both heat transfer and stress analyses. The FE models were used to identify the influences of key parameters on the residual capacity of CSTCRC columns, following exposure to the ISO-834 standard fire. The considered parameters included heating time, cross-sectional dimensions, strength of the materials, steel tube to concrete area ratio and ratio of reinforcement. Finally, a design method was proposed for predicting the residual load bearing capacity and compressive stiffness of CSTCRC columns after standard fire exposure.

Post-fire behaviour of slender reinforced concrete columns confined by circular steel tubes

“…The results are shown in Table 2, in which ts is the thickness of the coupon, th is the heating time, Es is the elastic modulus, fy is the yield strength, fsu is the ultimate tensile strength and νs is the Poisson's ratio. The measured stress-strain curves of the steel matches closely with the elastic-perfectly plastic stress-strain relationship up to 3.5% and 4.0% for the unexposed and exposed conditions [15], respectively, neither of which were achieved during the specimen testing. Therefore the elastic-perfectly plastic stress-strain relationship will be employed in later analysis.…”

“…The steel tubes and reinforcing bars used for the STCRC slender columns were the same as those used for the STCRC stub columns tested in [15]. The mechanical properties of the steel after heating to 0 min, 30 min and 60 min were determined by tensile coupon testing, reported in [15] and conducted according to the Chinese Standard GB/T228-2010 [17].…”

“…The steel tubes and reinforcing bars used for the STCRC slender columns were the same as those used for the STCRC stub columns tested in [15]. The mechanical properties of the steel after heating to 0 min, 30 min and 60 min were determined by tensile coupon testing, reported in [15] and conducted according to the Chinese Standard GB/T228-2010 [17]. The results are shown in Table 2, in which ts is the thickness of the coupon, th is the heating time, Es is the elastic modulus, fy is the yield strength, fsu is the ultimate tensile strength and νs is the Poisson's ratio.…”

“…Therefore the elastic-perfectly plastic stress-strain relationship will be employed in later analysis. The results of tensile coupon tests conducted on the reinforcing bars and stirrups [15] are presented in Table 3, in which ds is the diameter of the bars, Eb is the elastic modulus, fb is the yield strength and fbu is the ultimate tensile strength.…”

“…Hence, the focus of the present investigation is the fire and post-fire behaviour of STCRC columns. Building upon the recently reported work by the authors on the post-fire behaviour of STCRC stub columns [15], this second paper examines the post-fire behaviour of STCRC slender columns.…”