Abstract:
In recent times, concrete filled steel tubes have gained worldwide acceptance in the
construction of high rise and large span structures due to their structural efficiency. Steel
tube serves as both reinforcement and formwork, eliminating the need for both, and
provides large tensile and compressive capacities. The concrete fill restrains buckling of
the steel tube, which increases the strength and stiffness of the section. However, their
designs involve tiresome calculations and interaction charts development procedures.
This study involves numerical investigations on the performance of concrete-filled-steeltube (CFST) finite element models subjected to axial loading. Nonlinear material models
for confined concrete and steel tubes were used. The results obtained from the finite
element analysis were verified against prior experimental results by comparing its results
and axial load-displacement curves. Finally, outputs from the finite element analysis were
used to develop uniaxial interaction charts for circular CFST columns. Axial load
eccentricity due to lateral mid height deflection of column, P-Δ or second order effect was
considered to determine moment capacity.
The study shows confinement of concrete core provided by the steel tube increases strength
and ductility of concrete, which considerably maximizes axial load and bending moment
capacity of the CFST column by about 25% and 17% respectively. It has been noted that
increase in diameter of circular CFSTs enhanced load and moment capacity. It was also
observed that eccentric axial loading conditions have notable effects on load resistance of
a column. This numerical analysis perceived that column length also have a remarkable
effect in which mid height deflections were pronounced by 82% for longer columns. The
proposed interaction diagram was compared with that predicted by Eurocode4. The
comparison confirmsthat strength of CFST column computed by EC4 is more conservative.
