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