Parametric Study on the Axial Behaviour of Concrete Filled Steel Tube (CFST) Columns

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American Journal of Applied Scientific Research
2017; 3(4): 37-41
http://www.sciencepublishinggroup.com/j/ajasr
doi: 10.11648/j.ajasr.20170304.11
ISSN: 2471-9722 (Print); ISSN: 2471-9730 (Online)
Parametric Study on the Axial Behaviour of Concrete Filled
Steel Tube (CFST) Columns
Raghabendra Yadav, Baochun Chen
College of Civil Engineering, Fuzhou University, Fuzhou, China
Email address:
raghabendrayadav@gmail.com (R. Yadav)
To cite this article:
Raghabendra Yadav, Baochun Chen. Parametric Study on the Axial Behaviour of Concrete Filled Steel Tube (CFST) Columns. American
Journal of Applied Scientific Research. Vol. 3, No. 4, 2017, pp. 37-41. doi: 10.11648/j.ajasr.20170304.11
Received: October 27, 2016; Accepted: December 17, 2016; Published: November 15, 2017
Abstract: Concrete filled steel tube (CFST) columns are widely used in civil engineering structures due to its abundant
structural benefits like excellent seismic behaviour, ultimate load bearing capacity, fire resistivity, excellent ductility and
energy absorption capacity, particularly in zones of high seismic risk. Due to their excellent engineering properties, CFST
columns are used in buildings, bridges, electric transmission line and offshore structures. The ultimate load carrying capacity
of CFST columns depends upon various parameters such as D/t ratio, steel grade, concrete grade, etc. Abaqus software is used
for the finite element modelling of CFST Columns. In this study the ultimate axial load carrying capacity of CFST column is
investigated by changing diameter-to-thickness (D/t) ratio, steel grade and concrete grade. Results shows that the ultimate load
capacity decreases by increase in D/t ratio but increases by increase in steel grade and concrete grade.
Keywords: CFST, Axial Behaviour, Parametric Study, Finite Element
1. Introduction
The CFST column has in the recent years evolved as
alternative to the conventional methods in vogue [1-2]. A
concrete-filled steel tubular (CFST) column is formed by
filling a steel tube with concrete, as shown Figure 1. CFST
columns are used in buildings, bridges, electric transmission
lines and offshore structures [3-6] due to their abundant
properties. Steel sections with concrete infill are being
widely used as structural members, since filling the steel
section with concrete increases both its strength and ductility
without increasing the section size. Many researchers found
that the CFST column system has numerous advantages
compared with the ordinary steel or the reinforced concrete
system due to its high-strength, stiffness, ductility, and better
seismic performance [7-9]. Since the outside steel confines
the concrete and the inside concrete prevents the steel from
local buckling. The concrete is directly filled in the steel tube
so the use of formwork can be discarded. The potential
economical advantages of CFST columns in tall buildings
could lead to significant savings of steel usage in comparison
with pure steel columns. However, cement concrete has
certain drawbacks like high shrinkage, creep and low tensile
strength of cement concrete have lately been determined to
significantly weaken the steel-concrete interface bond, thus
hampering beneficial composite interaction, and resulting in
the concrete transformation of some of its stress to the steel.
The structural behavior of CFST elements are considerably
affected by the difference between the Poisson’s ratios of the
steel tube and concrete core. In the initial stage of loading,
the Poisson’s ratio for the concrete is lower than that of steel.
Thus, the steel tube has no confining effect on the concrete
core. As longitudinal strain increases, the lateral expansion of
concrete gradually becomes greater than expansion of steel
tube.
The ultimate axial load carrying capacity of CFST
columns are being affected by many parameters such as the
diameter to the thickness ratio, steel grade and concrete grade
[6]. This paper presents the effect of different parameters like
diameter to thickness ratio, steel grade and concrete grade, on
the axial load carrying of CFST columns.
2. Modelling
In order to simulate the actual behaviour of CFST
columns, the main components of these columns have to be
modelled properly. A simplified nonlinear finite element
method was developed in this paper for circular CFST

38 Raghabendra Yadav and Baochun Chen: Parametric Study on the Axial Behaviour of
Concrete Filled Steel Tube (CFST) Columns
columns under the axial load loading. Abaqus is used for
finite element model to efficiently predict the axial behaviour
of the CFST column.
Figure 1. Cross Section of CFST Column.
The element library of finite element software ABAQUS
6.12-1 is used to select the type of element. Solid elements
were found to be more efficient in modeling the steel tube
and the concrete as well as it clearly defined boundaries of
their elements. Three-dimensional eight-node solid element
(C3D8) was used in this study.
To define the concrete behavior in the FE model, a stress
strain diagram for the confined concrete should be
established first. The equivalent stress–strain diagram for
confined concrete under compressive loading, as shown in
Figure 2 is used in the proposed FE model.
Figure 2. Equivalent stress–strain curves of unconfined and confined
concrete.
Young’s modulus (Ecc), compressive strength (fck),
Poisson’s ratio (µ) and tensile strength (ft k) of confined
concrete are taken from GB50010 [10]. An elastic-plastic
model with the von Mises yield criterion is used to describe
the constitutive behavior of steel tube. The complete stress-
strain relation obtained from uniaxial tension tests has been
used in steel material model. Different properties of steel as,
Young’s modulus (Es), yield stress (fy), Poisson’s ratio (µ)
and ultimate stress (fu) are taken from GB50017 [11].
Displacement δx = δy = δz = 0 is applied as boundary
condition on the bottom end. The top end of the column is
free, allowing displacement to take place in all directions.
The uniform compressive loading in axial direction is applied
on the top of column. The behavior of column when only
Steel tube is loaded has been depicted with loading only
Concrete section and loading on both concrete and steel tube
section simultaneously and the combination gave higher
ultimate loads. The base reactions and the top displacements
are monitored.
The calculation involves one step of a static buckling
analysis. Due to high nonlinearities at local and global levels,
accompanying the traced inelastic, unstable and collapse
behavior, Riks analysis was chosen as the solution. The Riks
method is based on the concept of arc length as a measure of
the solution progress in load-displacement configuration
space. The increments are established automatically by the
program. The user specifies only initial, minimum and
maximum increments. The magnitude of an increment
depends on the number of iterations and attempts, needed in
the previous increment.
3. Parametric Study
Numerous experimental and analytical studies have been
conducted to realize the behaviour of CFST columns with
various sectional shapes, such as circular section [12-14],
rectangular section [16-17], T shaped section [16] and double
skin section [18]. Authors concluded that, the behaviour of
CFST column is affected by the diameter to thickness ratio
(d/t), steel yield strength (fy), concrete compressive strength
(fck), axial compression ratio (n) and slenderness ratio, for
circular section and also depth to breadth ratio for rectangular
section. Four different parameters are considered as stated
above, having 13 numbers of specimens with the constant
height of 400 mm. Details of specimens and parameters are
summarized in Table 1.
Table 1. Details of the Specimens considered for Analysis.
Specimen no. Diameter
(mm)
Thickness
(mm)
Steel
Grade
Concrete
Grade
S1 150 1.2 Q345 C50
S2 150 2 Q345 C50
S3 150 4 Q345 C50
S4 150 6 Q345 C50
S5 150 8 Q345 C50
S6 150 10 Q345 C50
S7 150 2 Q235 C50
S8 150 2 Q390 C50
S9 150 2 Q420 C50
S10 150 2 Q345 C30
S11 150 2 Q345 C40
S12 150 2 Q345 C60
S13 150 2 Q345 C70
4. Results and Discussions
Numerical analysis of CFST columns was done using

American Journal of Applied Scientific Research 2017; 3(4): 37-41 39
Abaqus. The effect of different parameters on the ultimate
axial load carrying capacity of CFST columns are
illustrated below:
4.1. Diameter to Thickness Ratio
This study is conducted on six circular CFST columns to
investigate the effect of thickness variation on the
performance of column. D/t ratio in this study ranges from 15
to 125. Increase in D/t ratio may be either due to the increase
in diameter or due to the decrease in thickness of the section.
Hence it is analysed by keeping the diameter constant and
varying the thickness. The increase in D/t ratio with
increased thickness for a constant diameter represents the
improvement in cross section of the steel tube and hence
produces greater section capacity. Figure 3 shows the load
displacement curve and the Figure 4 shows the effect of
variation of diameter to thickness ratio on the ultimate load
carrying capacity of CFST columns. The results shows that
the ultimate axial load carrying capacity of CFST columns
increases with the decrease in the diameter to the thickness
ratio of the columns. The axial capacity of a CFST columns
can be increases by increasing the thickness of the steel tube
without increasing the total diameter of the column. When
the D/t ratio is increased from 15 to 125, the ultimate load
carrying capacity of the column is found to decrease by
67.9%.
Figure 3. Load–displacement curves for different D/t ratio.
Figure 4. Effect of Thickness variation of steel tube on loading carrying
capacity.
4.2. Grade of Steel
Four circular CFST columns are modelled to investigate
the effect of variation of steel grade on the axial
performances. The capacity of CFST column is decided by
the yield strength of steel. The ultimate load of columns is
found to increase significantly with an increase in the steel
yield strength. Figure 5 shows the load displacement curve
and the Figure 6 shows the effect of variation of grade of
steel on the ultimate load carrying capacity of CFST
columns. The results shows that the ultimate axial load
carrying capacity of CFST columns increases with the
increase in the yield strength of steel. The load carrying
capacity increases linearly. The load carrying capacity
decreases exponentially. The ultimate load carrying capacity
of the column is found to increase by 25.4% with the
increment of steel yield strength from 235 MPa to 420 MPa.
Figure 5. Load–displacement curves for different Grade of Steel.
Figure 6. Effect of Grade variation of Steel on loading carrying capacity.
4.3. Grade of Concrete
For this modelling five circular CFST piers are modelled
to investigate the effect of variation of concrete on the axial
performances. The strength of concrete core decides
stiffness of CFST columns. Stiffness increases with
increase in concrete strength but columns fail due to
crushing of concrete exhibiting brittle behaviour when
filled with high strength concrete. But it is a fact that
increase in concrete core strength increases the strength of
filled columns to a larger extent, no matter of either D/t
ratio or L/D ratio. The ultimate axial loads of CFST
columns increases with an increment in the concrete
compressive strength. Figure 7 shows the load displacement
curve and the Figure 8 shows the effect of variation of
grade of concrete on the ultimate load carrying capacity of
CFST columns. The ultimate load carrying capacity of

40 Raghabendra Yadav and Baochun Chen: Parametric Study on the Axial Behaviour of
Concrete Filled Steel Tube (CFST) Columns
CFST columns increases with an increment in the concrete
compressive strength. The load carrying capacity increases
linearly. Increasing the concrete compressive strength from
30 MPa to 70 MPa increases the ultimate load carrying
capacity by 54.3%.
Figure 7. Load–displacement curves for different Grade of Concrete.
Figure 8. Effect of Grade variation of concrete on loading carrying
capacity.
5. Conclusions
This paper presents a numerical model for the nonlinear
inelastic analysis of thin-walled circular CFST columns
under uniform axial load. Based on the parametric study, the
following important conclusions are drawn:
a) The ultimate load capacity of a CFST columns can be
significantly increased by a smaller D/t ratio for the cross-
section in the design.
b) The steel yield strength is independent on the initial
flexural stiffness of the columns. However, the ultimate load
carrying of column is directly proportional with steel yield
strength.
c) The initial stiffness of the columns increases slightly due to
the use of high strength concrete. Further, use of high strength
concrete leads to increase in the load carrying capacity.
Acknowledgements
This research described here was sponsored in part by the
National Science Foundation under Grant No.51178118 and
Fuzhou University as well as the SIBERC (Sustainable and
Innovative Bridge Engineering Research Center), China.
Their support is gratefully acknowledged. The opinions
expressed in this paper are those of the authors and do not
necessarily reflect the views of the sponsors. The Authors
also like to thanks Bhawana Rauniyar, Santosh Bhattarai and
Subhash Pantha for their valuable suggestions and supports.
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