Axial compression behaviour and design of square tubed steel reinforced-concrete stub columns after fire exposure

Abstract

The tubed steel reinforced-concrete (TSRC) column is an innovative type of steel-concrete composite column, the steel tube of which mainly provides confinement to concrete core without sustaining axial load directly. This paper presents the axial compressive behaviour of square TSRC stub columns after ISO 834 standard fire exposure, experimentally and numerically. Eighteen square TSRC stub columns were heated and cooled and subsequently loaded to failure under axial compression. The influences of heating time, concrete compressive strength and steel tube area ratio on the load vs. displacement response, failure mode, residual capacity and stiffness of the tested columns were investigated. Finite element analysis (FEA) models were then developed and validated against test results. The working mechanism, e.g. confinement effect and axial force distribution within the composite section, was studied via parametric studies. Both the residual ultimate capacity and axial stiffness of square TSRC stub columns decrease significantly with the increase in heating time. The negative effect of fire exposure on residual stiffness is more significant than on the residual capacity. Finally, practical equations for determining the residual ultimate capacity and residual compressive stiffness of square TSRC stub column were proposed, which remain consistent with the ambient-temperature methods given in current design standard.