Behaviour of High Strength Concrete Filled Steel Tube Intermediate Length Columns in Offshore Applications

The concrete filled steel tubes (CFST) column systems consist of steel tubes
filled in concrete. The CFST columns systems have many advantages compared to
the reinforced concrete or steel structures. The CSFT have been widely used in
construction of tall buildings and bridges in countries located in high seismic activity
zones. The application of the CFST has been limited, due to lack of extensive
understanding of on the behaviour of the transform section. The main objective of
this research is to study the behaviour of intermediate length, CFST columns, filled
in with high strength concrete.
In this study, CFST specimens with 30,60 and 80N/mm2 concrete
compressive strength and external diameter-to-plate thickness (D / t) ratios of 11 and
14 are subjected to concentric axial compression loading. All the columns were
1200mm long. The results obtained are compared with the EC4, BS5400, ACI, AS
and AIJ design code predictions. The effect of thickness, grade of concrete and
confinement of concrete are examined. Moreover, application of CFST in offshore
structures is discussed.
The results indicate that the ultimate compressive strength of the CFST
increases as the concrete grade is increased. It also increases when the thickness of
the steel section is increased. Although, confinement of concrete increases with
thickness of the steel section, it has less effect on the overall failure mode. The
intermediate length CFST columns failed largely due to overall elastic buckling. The
application of CFST in offshore structures w ould decreaseth e costsm aintenancea nd
repairs.