Behavior and design of CFST columns in fire conditions: The role of shear connectors

Abstract

Experimental studies on Concrete Filled Steel Tube (CFST) columns at elevated temperatures have shown that there is signific ant slip between the steel tube and the concrete core during the heating phase. As a result, the steel and the concrete components cannot work in tandem to resist the applied axial load. These experiments are conducted on columns with no shear connectors. Most of the design codes for CFST columns require that shear connectors must be provided in the load transfer zone . This work studies the effects of the shear connectors provided in the load transfer zone on the fire resistance of CFST columns. Numerical s imulation using finite element technique is employed for modeling the column behavior. Sequentially coupled heat transfer and stress analyses of three - dimensional CFT column models were conducted in ABAQUS. The steel tube was modelled using four - node shell elements and the concrete infill was modelled using eight - node solid elements. Shear studs were modelled using truss element for heat transfer analysis and beam element for stress analysis. Relevant thermal properties of steel and concrete were taken from the Eurocode and ASCE code. The interface between steel and concrete is modeled to have zero thermal resistance for the heat transfer analysis and as a hard contact with zero bond strength for the stress analysis. The modeling approach presented in this paper was validated against the experimental data available in literature. Numerical simulation of fire behavior of square CFST columns with shear studs provided in the load transfer zone indicated that shear studs restrain the slip between steel and concr ete significantly and increase the fire resistance of the column