1. No category

Comparison of Steel Tube Concrete Column with Steel Tube
Concrete Composite Column
Name: 于海燕
ID Number: 1130598
Column occupies an important position for the structural engineers, as a kind of important
component in architectural structures. For high-rise buildings, although structure systems are
divers, columns are still essential vertical bearing components and lateral resistance components.
And, the form has being changed, from the normal reinforced concrete column, a steel reinforced
concrete column, steel tube concrete column, to the composite column, mega columns. This report
only introduces the related contents concerning concrete filled steel tube (CFST) column and
concrete filled steel tube composite column (hereinafter referred to as the composite column).
1. BASIC CONCEPT
1.1 Concrete filled steel tube column: filling the high strength concrete into the steel pipe, is an
economic efficient way to overcome the high strength concrete brittleness, by combining steel
tube concrete technology with high strength concrete technology. This is because: 1) steel tube’s
hoop constraint effect to core high strength concrete can effectively overcome the high strength
concrete brittleness; 2) steel tube can be used as a template, and has both longitudinal
reinforcement and the transverse stirrup function, and facilitates to place high strength concrete,
especially can use advanced pump concrete pouring process, because inside steel reinforced
skeleton is not needed; 3) without concrete cover outside, makes full use of the capacity of high
strength concrete.
1.2 Composite column: consists of the core CFST and the concrete outside, can be as square section,
rectangular section or circular cross section. Composite column inside and outside parts can be
constructed in different period, or in the same period. Construction in different period means first
casting inside concrete to form CFST, bearing part of the vertical load during the period of construction,
then the outside concrete. Construction in the same period means casting the inside and outside
concrete at the same time.
The comparison shows that both consist of high strength concrete and steel tube, and the
hoop sets effect gives full play to the role of high strength materials. The main difference is that,
no concrete cover outside the CFST but composite column RC outside the pipe, also the inside
and outside concrete can be casted in different periods. In short, CFST composite column is the
development of concrete filled steel tube column.
2. BUILDING MAXIMUM HEIGHT
The second and third class high-rise building maximum height using composite column
structure, for frame structure and 9 degree seismic fortification, is the same with A level height
high-rise building’s largest height according to the current industry standard concrete structures of
tall building technical regulation JGJ3-2010 ; in the non-seismic design and seismic fortification
intensity6,7,8 area, except the frame structure, the maximum height for other structure is the same
with B level height high-rise building’s largest height according to the current industry standard
concrete structures of tall building technical regulation JGJ3-2010 .
Table 1 comparison of building maximum height of CFST with composite column structures
Structure system
non-seismic
design (CFST/
composite
column)
seismic fortification intensity(CFST/ composite
column)
intensity 6
intensity 7
intensity 8
intensity 9
frame
70
60
55
45
25
Frame-shear wall
170
160
140
120
50
Partial
frame-supported
shear wall
150
140
120
100
No allowed
frame core-tube
240/220
260/210
210/180
160/140
80/70
Tube in tube
300/300
280/280
230/230
170/170
80/90
The table data shows that, both the maximum height in tube structure are equal, it is
important to note that the maximum height in the frame- core tube structure for composite column
is smaller.
3. CAPACITY CALCULATION
Confinement effect greatly improves CFST’s bearing capacity (30% ~ 50%), and the
materials stress under service conditions improved with the same amplitude corresponding. Test
and theoretical analysis shows that, when the confinement index is within 3 and procedures set by
safety level, CFST still in elastic stage under test load, which satisfy with the basic requirements
of the limit state design principle.
Take the CFST as the research object, and contrast the similarities and differences between
the two on axial bearing capacity calculation.
It can be seen from the form above：
1. The formulas about CFST axial compression capacity are basically agreed.
2. Processes are different when considers the different confinement effect. Generally the high strength
concrete in the composite column is within C55 ~ C80 range or even larger, thus the CFST
compression bearing capacity design value
N u  0.9 l  e Ac f c (1     )  0.9 l  e Ac f c (1  1.56  1.56)  0.9 l  e Ac f c (1  1.8 )
can be smaller than that of CFST composite column.
3. Composite column does not consider eccentricity axis pressure to the influence of bearing capacity,
only consider the effect of slenderness ratios. Although the CFST is set in the composite column
section center, mainly carrying axial compression, but when the steel pipe diameter to the column
section side length ration is large, the CFST should bear the a small amount of bending moment. To
make sure there are certain reserves, fully axial compression bearing capacity can’t be used, therefore,
limit the axial pressure. The reduction coefficient can be taken as 1.0 because of the RC outside
4. Equivalent calculation length. Composite column’s equivalent length is calculated in
accordance with the relevant provisions of the CECS28-90. Both of the two consider the
constraint condition and column bending moment distribution gradient effect.
Table 2 comparison of axial compression capacity of CFST with the CFST in composite column
types
CFST column
CFST in composite column
Axis pressure
design value
N  Nu
N cc  0.9 N u
Axial
pressure
bearing
capacity
N u  0.9 l  e Ac f c (1  f ( ))
N u  1 f cc Acc (1  1.8 )
 l  1  0.115 Le / D  4，
1  1  0.115(l e / d a  4)1 / 2 ，
( Le / D  4)
(l e / d a  4 )
reduction
coefficient(sl
enderness
ratio)
reduction
coefficient
（eccentricity
ratio）
 l  1，Le / D  4
e 
1  1.0，l e / d a  4
1
，e0 / rc  1.55
1  1.85e0 / rc
without consideration
e 
0 .3
，e0 / rc  1.55
e0 / rc  0.4
Equivalent
calculation
Le  kL
l e  H
length
Note: L-the actual length of the column; H- length of the cantilever column.
Table 3 comparison of axial compression capacity of CFST with composite column
types
axial
compressio
n capacity
effective
length
CFST column
composite column
N u  0.9 l  e Ac f c (1  f ( )) N u  0.9 ( f co Aco  f y Ass )  f cc A cc (1  1.8 )
Le  kL
Bottom columns：1.0H，others：1.25H
Note: H for the bottom column can be taken the height from foundation top face to the first layer, H for
the others each layer can be taken the height between the two top of the floor layer.
Both the concrete inside and outside contribute the composite column axial compression
capacity, and the interior CFST reduction coefficient is taken as 1.0. So the bearing capacity of
composite column of is higher than that of CFST column.
4. SHEAR CAPACITY
The steel tube in CFST column, is a kind of special form of reinforcement, and the three
dimensional continuous reinforcement field, acting as both longitudinal reinforcement and lateral
stirrup. Usually, CFST mainly bears compression-bending effect, and the shear reinforcement
field correspond is determined after the determination of the steel pipe specifications and hoop
index according to the compression-bending member, so shear reinforcement design is not needed
the other reinforced concrete member does. Previous test observation shows that failures are
bending type when shear span to column diameter ratio a/D is larger than 2, and in the general
construction project ,the value is greater than 3. In some cases, such as large-span overloaded
beam joints area, small shear span problem, which will influence the design of CFST, should be
considered. In order to solve the problem, China construction science research institute carried out
the special shearing test research, which is applicable to transverse shear act on the pipe outer wall
in pressure.
Table 4 comparison of shear capacity of CFST with composite column
types
CFST
composite column
shear
capacity
V  (V0  0.1N )(1  0.45 a / D )
V  0.25[  c f co Aco  f cc Acc (1  1.8 )]
V0  0.2 Ac f c (1  3 )
—
conditions
a/D<2 and transverse shear act on the
pipe outer wall in pressure
others
—
Consider the tube constraints’ enhancing
Applicable
effect on the compressive strength
5. LOCAL COMPRESSION
In addition, there are related regulations about local compression and tension and moment
capacity for the CFST, but nothing for composite columns.
6.COMPOSITE RATIO
In the composite column constructed in different period, the core CFST has been under part
vertical load, before the RC outside casted. CFST’s vertical load value to the composite column’s axial
compression value ratio called composite ratio.
The strength of empty steel pipe should be checked according to the construction stage load
for the laminated column constructed in different period, and the maximum compressive stress
value is unsuitable more than 0.6fa(fa is steel pipe steel the compressive strength of the design
value). Composite than can be through the test are determined, usually desirable 0.3-0.6.
composite ratio m  N i / N
M—composite ratio of composite column constructed in different period.
N—Composite column axis pressure design value.
Ni—axis compression design value act on the CFST before the outer RC casted
If Composite ratio is too large, the requirements of the composite bearing capacity cannot be
satisfied; If too small, the characteristics of composite column cannot be given full play.
7 BEAM COLUMN JOINTS
Table 5 beam-column joints types of CFST and composite column
types
Steel beam-column connection
CFST column
1 outer strengthen rings (smaller
column diameter)
2. inner strengthen rings (larger
column diameter)
Transfer shear: 1 ring bracket
2. Bearing pin
Transfer
RC beam-column connection
bending moment:
1. Well type double beam
2. ring beam 3. wear muscle
single-girder
4. various width beam
composite column
1. only one steel beam, see
figure 5
2. all the steel beams, see
figure 6
1. Steel pipe breakthrough type
2. Steel plate fin transformation
3. Steel pipe reinforced
transformation (Construction in the
same period)
Note: the shear transfer and moment transfer forms are introduced respectively in the CFST
structure, and Suitable forms combination is need in practice.
7.1 CFST structure
7.1.1 Steel beam-column connection：
Figure 1 outer strengthen rings
inner strengthen rings
7.1.2 Steel beam-column connection transfer shear：
Figure 2 ring bracket
Bearing pin
7.1.3 Steel beam-column connection transfer bending moment：
Figure 3 Well Type Double Beam
Ring Beam
Well type double beam：1—CFST column；2—longitudinal reinforcements of double beam；
3—Additional inclined bars
Ring beam：1—CFST column；2—the ring bars of ring beam；3—longitudinal reinforcements of
frame beam；4—stirrups of ring beam
Figure 4 wear muscle single-girder
various width beam
7.2 composite column
7.2.1 Steel beam-column connection：
Figure 5 only one steel beam
Figure 6 all the steel beams
7.2.2 RC beam-column connection：
Figure 7 Steel pipe breakthrough type
Figure 8 Steel plate fin transformation
Figure 9 Steel pipe reinforced transformation