CFST

DEVELOPMENT IN CONCRETE-FILLED STEEL
TUBULAR STRUCTURES
A SEMINAR REPORT SUBMITTED IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF
Master of Technology
in
Structural
Engineering
BY
ALOK B. RATHOD
Bhartiya Vidya Bhavan’s
SARDAR PATEL COLLEGE OF ENGINEERING, MUMBAI
DEPARTMENT OF STRUCTURAL ENGINEERING
2015

Bhartiya Vidya Bhavan’s
SARDAR PATEL COLLEGE OF ENGINEERING, MUMBAI
DEPARTMENT OF
STRUCTURAL ENGINEERING
CERTIFICATE
This is to certify that Mr. ALOK BHAKTIRAM RATHOD Roll no. MCSI016 has
successfully completed the seminar work entitled “DEVELOPMENT IN CONCRETE
FILLED STEEL TUBULAR STRUCTURES” in the partial fulfillment of M.Tech.
(Structural Engineering)
Date :
Place : Mumbai

ACKNOWLEDGEMENT
I wish to express my thanks to Prof. Dr. M.M. Murudi (Head of the Structural
Engineering Department), Prof. Dr. A. A. Bage, Prof. Dr. Tanuja Bandivadekar for their
support in the completion of this Report.
I also express my deep sense of gratitude to all my Professors, Department of
Structural Engineering, Sardar Patel College of Engineering, Mumbai for valuable
guidance, constant encouragement and creative suggestions offered during the course
of this seminar and also in preparing this report.
Date: Alok B. Rathod
Place: Mumbai Roll No. MCSI-016
SPCE, Mumbai

I
CONTENTS
CHAPTER NO. TITLE PAGE NO.
ABSTRACT
lll
LIST OF FIGURES
lV
LIST OF TABLES
VI
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 REVIEW OF LITERATURE 2
CHAPTER 3 COMPONENT BEHAVIOUR 4
CHAPTER 4 DEVELOPMENT OF CFST FAMILY 6
CHAPTER 5
MATERIALS FOR CONCRETE-FILLED STEEL
TUBES
10
5.1 Steel 10
5.2 Concrete 11
CHAPTER 6
RESEARCH ON CONCRETE-FILLED STEEL
TUBULAR MEMBERS
13
6.1 Research framework 13
6.2 Static performance 13
6.3 Dynamic performance 15
6.4 Fire performance 16
6.5 Construction and durability issues 17
CHAPTER 7 DESIGN CRITERIA 20

II
CHAPTER 8 CONSTRUCTION CONSIDERATIONS 23
8.1 Placement of concrete 23
8.2 Fabrication issues 24
CHAPTER 9 SOME CONSTRUCTION EXAMPLES 25
9.1 Buildings 25
9.2 Bridges 28
9.3 Other structures 29
CHAPTER 10 CONCLUSIONS 32
REFERENCES 33

III
ABSTRACT
CFST is the member with concrete filled into steel tubes. It is a new structure that evolved and
developed based on SRC Structures, spiral stirrup structures and steel tube structures.
Concrete-filled steel tubular (CFST) structure offers numerous structural benefits, and has been
widely used in civil engineering structures. This report reviews the development of the family
of concrete-filled steel tubular structures up to date and effectively presents a detail study on
CFST members. The research development on CFST structural members in most recent years,
particularly in China, is summarized and discussed. The current design approaches from various
countries are examined briefly. Some projects in China utilizing CFST members are also
introduced.

IV
LIST OF FIGURES
FIGURE NO. TITLE PAGE NO.
Fig no. 1 Typical concrete-ﬁlled steel tubular cross sections. 4
Fig no. 2 Schematic failure modes of hollow steel tube,
concrete and CFST stub columns.
5
Fig no. 3 Axial compressive behavior of CFST stub column. 5
Fig no. 4 General CFST cross sections. 6
Fig no. 5 Combinations of CFST sections. 8
Fig no. 6 Inclined, tapered and curved CFST columns. 9
Fig no. 7 Framework of research on CFST structures. 13
Fig no. 8 Schematic failure modes of steel tube, concrete and
CFST under tension, bending and torsion.
14
Fig no. 9 Time (t) - load (N) - temperature (T) path. 17
Fig no. 10 Full scale test of core concrete placement (Z2). 18
Fig no. 11 Compressive strength for CFST short column. 21
Fig no. 12 φ-λ relationship for CFST column 21
Fig no. 13 Flexural strength for CFST column. 22
Fig no. 14 Axial load versus moment interaction curve for CFST
column
22
Fig no. 15 Schematic view of concrete placement. 23
Fig no. 16 CFST hybrid structural systems for high-rise buildings 25
Fig no. 17 SEG plaza in Shenzhen 26
Fig no. 18 Ruifeng building in Hangzhou. 26
Fig no. 19 Canton Tower. 27
Fig no. 20 Cross section for mega CFST column (units: mm). 28
Fig no. 21 CFST used in bridges. 28

V
LIST OF FIGURE
FIGURE NO. TITLE PAGE NO.
Fig no. 22 Wangcang East River Bridge. 29
Fig no. 23 Zhaohua Jialing River Bridge. 29
Fig no. 24 Subway stations using CFST columns. 30
Fig no. 25 A power plant workshop using CFST columns. 30
Fig no. 26 Zhoushan electricity pylon 31
Fig no. 27 A CFDST pole. 31

VI
LIST OF TABLES
TABLE NO. TITLE PAGE NO.
Table No. 1
Structural steel mechanical properties according to
GB/T 700 and GB/T 1591.
11
Table No. 2 Design value of steel strength (N/mm2) in GB50017. 11
Table No. 3 Material properties of concrete in GB50010. 11
Table No. 4
Scope of application for various building codes
relevant to CFST columns.
20

1
CHAPTER 1
INTRODUCTION
1. INTRODUCTION
The concrete-filled steel tubular (CFST) structure offers numerous structural benefits, including
high strength and fire resistances, favorable ductility and large energy absorption capacities.
There is also no need for the use of shuttering during concrete construction; hence, the
construction cost and time are reduced. These advantages have been widely exploited and
have led to the extensive use of concrete-filled tubular structures in civil engineering
structures.
China has seen a great deal of research and use of concrete-filled steel tubular structures in
practice. There are numbers of books published in public domain in recent years. Some codes
of practice and local specifications were developed to provide design guidance as well. This
report reviews the state-of-the-art for concrete-filled steel tubular structures, especially some
the most recent developments in China. Current design approaches from various countries are
examined briefly. Some practical projects using CFST members are presented, and the
development trends are discussed.

2
CHAPTER 2
LITERATURE REVIEW
Shankar Jagadesh in May 2014, Concrete-filled steel tubes are gaining increasing
prominence in a variety of engineering structures, with the principal cross-section shapes being
square, rectangular and circular hollow sections. The study about the behavior and the
characteristics of CFST columns is the prime need of the hour. This review paper outlines the
important contributions on CFST columns contributed in the recent years. This paper presents
the innovative experimental investigations conducted on CFST columns and the load deflection
response characteristics of columns are also addressed. A comprehensive summary of various
analytical and numerical studies on modeling of CFST members is portrayed in this paper. The
design specifications and standards by AIJ, Eurocode-4, ANSI/AISC and AIK are addressed.
Lin-Hai Han, Wei Li, Reidar Bjorhovde in June 2013, Concrete-filled steel tubular (CFST)
structure offers numerous structural benefits, and has been widely used in civil engineering
structures. This paper reviews the development of the family of concrete-filled steel tubular
structures to date and draws a research framework on CFST members. The research
development on CFST structural members in most recent years, particularly in China, is
summarized and discussed. The current design approaches from various countries are
examined briefly. Some projects in China utilizing CFST members are also introduced. Finally,
some concluding remarks are made for CFST members.
Baochun CHEN in July 2008, The Concrete Filled Steel Tubular (CFST) structure has been
applied prevalently and rapidly to arch bridges since 1990 and this trend is continued with more
and more long span CFST arch bridges been built since 2000. This paper briefly introduces
the present situation of CFST arch bridges, their five main structure types and the construction
methods. Many selected CFST arch bridges built since 2000 and some still under construction
are presented.
BaoChun Chen in 2009, this paper briefly introduces the present situation of concrete filled
steel tube (CFST) arch bridges in China. More than 200 CFST arch bridges were investigated and
analyzed based on the factors of type, span, erection method, geometric parameters, and
material. Some key issues in design calculation were presented, such as check of strength,
calculation of section stiffness, and joint fatigue strength. It will provide a comprehensive
reference of CFST arch bridges for the bridge designers and builders.

3
LinHai Han, ShanHu He, LianQiong Zheng, Zhong Tao in March 2012, A series of tests on
curved concrete filled steel tubular (CCFST) built-up members subjected to axial compression is
described in this paper. Twenty specimens, including 18 CCFST built-up members and 2 curved
hollow tubular built-up columns, were tested to investigate the influence of variations in the
tube shape (circular and square), initial curvature ratio (β, from 0 to 7.4%), nominal slenderness
ratio (λ, from 9.9 to 18.9), section pattern (two main components, three main components and
four main components), as well as brace pattern (battened and laced) on the performance of
such composite built-up members. The experimental results showed that the ultimate strength
and stiffness of CCFST built-up specimens decreased with increasing βr or. Different load-
bearing capacities and failure modes were obtained for the battened and laced built-up
members. A simplified method using an equivalent slenderness ratio was suggested to calculate
the strength of CCFST built-up members under axial compression.

4
CHAPTER 3
COMPONENT BEHAVIOUR
3. COMPONENT BEHAVIOUR
Fig. 1(a) depicts three typical column cross-sections, where the concrete is filled in a circular
hollow section (CHS), a square hollow section (SHS) or a rectangular hollow section (RHS),
where D and B are the outer dimensions of the steel tube and t is the wall thickness of the
tube. It is noted that the circular cross section provides the strongest confinement to the core
concrete, and the local buckling is more likely to occur in square or rectangular cross-sections.
However, the concrete-filled steel tubes with SHS and RHS are still increasingly used in
construction, for the reasons of being easier in beam-to-column connection design, high cross-
sectional bending stiffness and for aesthetic reasons. Other cross-sectional shapes have also
been used for aesthetical purposes, such as polygon, round-ended rectangular and elliptical
shapes, as shown in Fig. 1(b).
Fig. 1. Typical concrete-filled steel tubular cross sections.
It is well known that the compressive strength of concrete is much higher than its tensile
strength. Furthermore, the compressive strength is enhanced under bi-axial or tri-axial
restraint. For the structural steel, the tensile strength is high while the shape may buckle
locally under compression. In concrete-filled steel tubular members, steel and concrete are
used such that their natural and most prominent characteristics are taken advantage of. The
confinement of concrete is provided by the steel tube, and the local buckling of the steel
tube is improved due to the support of the concrete core. Fig. 2 shows schematic failure
modes for the stub concrete-filled steel tubular column and the corresponding steel tube and
concrete. It can be seen that both inward and outward buckling is found in the steel tube, and
shear failure is exhibited for the plain concrete stub column. For the CFST, only outward
buckling is found in the tube, and the inner concrete fails in a more ductile fashion.

5
Fig. 2. Schematic failure modes of hollow steel tube, concrete and CFST stub columns
Fig. 3(a) shows a comparison of the measured results between a steel stub column, a
reinforced concrete stub column and a concrete-filled steel tubular stub column without steel
reinforcement, where D and t are the outer diameter and the wall thickness of the circular
steel tube, respectively; fY is the yield strength of the steel; fcu is the compressive strength of
the concrete cube. The geometric dimension of the circular hollow steel section is the same as
in both steel column and composite column, and also the same for the concrete parts in both
the reinforced concrete column and the composite column. The term "steel tube + RC" in Fig. 3
indicates the summation of the ultimate strength of the steel tube and the reinforced concrete
(RC) specimens. It clearly shows that the ultimate strength for a concrete-filled steel tube is
even larger than the summation of the strength of the steel tube and the RC column, which
is described as “1(steel tube) + 1 (concrete core) greater than 2 (simple summation of the two
materials)”. Fig. 3(b) shows a schematic view of the load versus deformation relationship of
the hollow steel tube, the concrete stub column by itself and the concrete-filled steel tube. It
can be seen that the ductility of the concrete-filled steel tube is significantly enhanced, when
compared to those of the steel tube and the concrete alone.
Fig. 3. Axial compressive behavior of CFST stub column.

6
CHAPTER 4
DEVELOPMENT OF CFST FAMILY
4. DEVELOPMENT OF CONCRETE-FILLED STEEL TUBE FAMILY
Apart from the common concrete-filled steel tubes shown in Fig. 1, there are other types of
“general” member designation in the CFST family. Some of them are shown in Fig. 4, i.e.
concrete-filled double skin steel tubes (CFDST), concrete-encased concrete-filled steel tubes as
well as reinforced and stiffened concrete-filled steel tubes. The characteristics of these
“general” CFST members are as follows: 1) they consist of the steel tube(s) and the filled
concrete; 2) the concrete and the steel tube(s) sustain the axial load together.
Fig. 4. General CFST cross sections.
The CFDST consists of inner and outer tubes, and the sandwiched concrete between two
tubes, as shown in Fig. 4(a). The concrete-steel- concrete sandwich cross-section has high
bending stiffness that avoids instability under external pressure. Research results have shown
that the inner tube provides effective support to the sandwich concrete, and the behavior of
the composite member is similar to that of the concrete-filled steel tube. The outward
buckling of the outer tube and the inward buckling of the inner tube was observed after beam

7
and column ultimate strength tests. The steel tubes and the concrete can work together well
and the integrity of the steel-concrete interface is maintained. This composite column could
also have higher fire resistance than the regular CFST columns, due to the inner tubes being
protected by the sandwiched concrete during fire. The CFDST could be a good option when
designing members with large cross-sections. The thickness of the steel tube wall can be
reduced significantly when compared to the steel tube member by itself, and the self-weight is
less when compared to the concrete-filled steel tube. Another advantage of the CFDST is that
both the outer and the inner steel tubes can act as primary reinforcement and permanent
formwork, which is convenient for construction. At the same time, different materials can be
utilized for the inner and outer tubes in order to have the additional advantages of esthetics as
well as corrosion resistance. Thus, an outer stainless steel tube and an inner carbon steel tube
has been described as one option.
Fig. 4(b) displays the concrete-encased CFSTs which consist of an inner CFST and an outer
encased reinforced concrete (RC). This steel-concrete composite member is somewhat similar
to the traditional steel reinforced concrete member. The basic concept of this member is to
use the concrete-filled steel tube to replace the I-section steel in the steel reinforced concrete.
The embedded inner tube can provide extra confinement to the in-filled core concrete, such
that the ultimate strength of the column is improved. The outer encased reinforced concrete
can also provide fire protection to the inner tube, therefore the fire resistance of the concrete-
encased CFST is enhanced when compared to a conventional CFST column. In addition, the
local buckling and the corrosion of the steel tube can be avoided. This kind of column is fairly
easily connected to either reinforced concrete or steel beams in a structural system, and has
been utilized in some high-rise buildings and bridges in China. The inner steel tube can be
erected first, followed by the binding of reinforced bars, and the inner and outer concrete is
then placed. When it is connected to a reinforced concrete beam, the beam-column joint can
be designed according to the criteria of traditional reinforced concrete structure.
Structural steel and steel reinforcements are usually used to enhance the resistances of the
concrete-filled steel tubes, as shown in Fig. 4(c). The structural steel sections contribute a lot
to column capacities without changes of column profiles. The contribution to the column
capacities can be considered as the combined capacities of the structural steel and the
concrete-filled steel tubular parts. For the reinforcing bars, since they are well anchored in the
concrete, they may be taken into account for the resistance of the column. However, if the
longitudinal reinforcements and the stirrups are considered as construction measures, the
capacities of these bars could be conservatively neglected in design.
In the usual concrete-filled steel tubular columns, the local buckling of the steel tube normally
occurs after the ultimate strength of the composite member is reached. This could be a critical
issue for the development and application of thin-walled tubes with high strength steel.
Longitudinal or transverse stiffeners can be welded on the steel tube to improve the strength
and the ductility of the composite column. For the column with large cross section, the
stiffeners can be welded on the inner surface of the tube. Binding bars can also be welded to
the stiffeners to strengthen the tying force, as shown in Fig. 4(d). The effectiveness of the
longitudinal stiffeners in delaying the local buckling of the steel tube were demonstrated by

8
experimental studies.
On top of being used as single elements in construction, various combinations of concrete-
filled steel tubular members are also used. A schematic view of some examples is shown in Fig.
5. These combinations aim at utilizing the advantage of various composite components to
meet the construction requirements. For example, single concrete-filled steel tubular
members can be connected using double steel plates, and the cavity between steel plates
could be filled with concrete as well (Fig. 5(a)). Hollow steel tubes can be used to form a
latticed member (Fig. 5(b)), and concrete-filled steel tubes can also be connected by welding
together to form a cluster section (Fig. 5(c)) and had been used in arch bridges in China.
The concrete-filled steel tubes may also be combined with reinforced concrete to form a
composite section, which can serve as piers or arches in a bridge, as shown in Fig. 5(d). Such
cross sections have also been used in some recent bridges in China.
Fig. 5. Combinations of CFST sections
Most concrete-filled steel tubular members used in constructions are prismatic. However, due
to architectural or structural requirements, inclined or non-prismatic members were used. The
inclined column could serve as a load transfer member in the structure with irregular
architectural style, as illustrated in Fig. 6(a). The tapered members could be used for aesthetic
or economic purposes, as shown in Fig. 6(b).
In some large-span structures or bridges, curved members could be used, as shown in Fig.
6(c). The research results from short column tests have shown that the steel tube and the
concrete can work together well despite the inclined or tapered angle. The failure mode of the
non- prismatic inclined and tapered members under compression is similar to that of the
prismatic member, which is the outward buckling of the steel tube and the crushing of the
concrete. The failure location is perpendicular to the longitudinal direction of members. For
the curved members, their failure modes are similar to that of the corresponding CFST under
bending. The axial compressive strength of the curved member could be reduced when the
curvature is increased, while ductility is enhanced.

9
Fig. 6. Inclined, tapered and curved CFST columns.
Although some types of steel-concrete composite structures consist of concrete and steel
tube, such as the steel tube confined concrete structures, however, the mechanism and the
composite effect of the structures is generally different from that of the “general” CFST
structures mentioned in the current paper, therefore they are not discussed herein.
Much research work has been done to understand the “composite action” between the steel
and the concrete for these composite sections under axial compression. It has been confirmed
that the circular steel tubes can provide much more effective confinement to their core
concrete than other types of tubular sections. It is believed that the confinement effect is
related to the cross-sectional properties as well as the material properties. A confinement
factor (ξ) thus had been introduced to describe this effect:
ξ =
𝐴𝑠 𝑓𝑦
𝐴𝑐 𝑓𝑐𝑘
where As and Ac are the cross-sectional areas of the steel tube and the concrete,
respectively; fy is the yield strength of the steel; fck is the characteristic compressive
strength of the concrete cube, and can be taken as 0.67 fcu for normal strength concrete.
It was found that the confinement provided by the steel tube to its core concrete can be
increased with the increase of the confinement factor (ξ). It is also noted that this factor can
describe the confinement effect qualitatively for different kinds of cross-sectional shapes, such
as circular, square and rectangular.

10
CHAPTER 5
MATERIALS FOR CONCRETE-FILLED STEEL TUBES
5.1. Steel
It should be noted that various national standards contain structural steel designations, where
the chemical composition and the mechanical properties may be different. However, these
steel specifications are comparable in general. Various kinds of steel can be used in
concrete- filled steel tubular members, such as normal carbon (“mild”) steel, high strength
steel, high-performance fire-resistant steel, weathering steel, etc. For the steel tubes, their
properties must adhere to the steel material standards. In China, the dimension and
dimensional tolerances for common sections such as circular, square and rectangular tubes are
specified in national standards. Some mechanical properties of structural steel from the
Chinese specifications for the carbon steel (GB/T 700) and the high-strength low-alloy steel
(GB/T 1591) are shown in Table 1. The design values of structural steel from the Chinese code
GB 50017, are given in Table 2. The data are comparable to those of other countries' steel
grades.
The outer profile of the steel tube should not be too small in order to allow proper concrete
placement. On the other hand, the wall thickness of the steel tube should exceed a certain
value to ensure the stability. For instance, according to the DBJ/T 13–51 specification, a
Chinese local specification for CFST structures, the outer profile of the steel tube should be
no less than 100 mm, and the wall thickness of the steel tube for hot-finished and cold-
formed sections should not be less than 4 mm and 3 mm, respectively. For the concrete-filled
steel section, it is recommended that the diameter to wall thickness ratio can be larger than
that of the hollow section, since the local buckling capacity is improved by the concrete. For
instance, in the Chinese steel design code GB 50017, for circular hollow steel sections,
D
t
≤
100(
235
𝑓𝑦
) ; for rectangular hollow steel sections,
D
t
≤ 40√
235
𝑓𝑦
, where D is the outer diameter
or the depth of the circular or rectangular sections, respectively; t is the wall thickness of the
tube, and fy is the yield strength of steel. In the DBJ/T 13–51 specification, for circular
concrete-filled steel tubular sections,
D
t
≤ 150(
235
𝑓𝑦
); for rectangular concrete-filled steel
tubular sections (including square ones),
D
t
≤ 60√
235
fy
. If the
D
t
ratio exceeds the limitations,
additional longitudinal stiffeners shall be designed and provided.
It is noted that the stainless steel and the ultra-high strength steel can also be used to make
the steel tubes and filled with concrete, several investigations were carried out on these
aspects. However, the applications of these two materials are still very limited and the
corresponding design methods are not included in most specifications yet. Therefore the
contents regarding the CFST members using the stainless steel and the ultra-high strength

11
steel are not discussed in the current paper.
Table 1: Structural steel mechanical properties according to GB/T 700 and GB/T 1591.
Table 2: Design value of steel strength (N/mm2) in GB50017.
5.2. Concrete
The normal weight concrete and the high-strength concrete can be used as the filled concrete
in CFST structures. The material properties from the Chinese code GB 50010 are listed in Table
3. Since the excess water cannot be expelled from the sealed tube, the water to cement ratio
of the concrete should be strictly controlled. A water to cement ratio exceeding 0.4 is
inappropriate for normal weight concrete. One of the methods to ensure the construction
quality of the core concrete is to use self-consolidation concrete (SCC). SCC can be used in
filling the tube without additional vibration, which could be beneficial if some diaphragms are
arranged near the connection zone. Experimental results showed that concrete-filled steel
tubular columns using SCC exhibited high levels of energy dissipation and ductility, and the
load carrying capacities are not different from those of columns with normal concrete.
Table 3: Material properties of concrete in GB50010.

12
It is recommended that the strength of the steel and the concrete should be suitably matched
to improve the structural performance. It is appropriate to use the combinations of higher
strength steel with higher strength concrete, and lower strength steel with lower strength
concrete. For instance, if the yield strength of the steel tube is 235 N/mm2 to 345 N/mm2, the
appropriate compressive strength of concrete is around 40–60 N/mm2. If the yield strength of
the steel tube is higher than 345 N/mm2, the appropriate compressive strength of concrete is
around 60 N/mm2 or higher.

13
CHAPTER 6
RESEARCH ON CONCRETE-FILLED STEEL TUBULAR MEMBERS
6.1. Research framework
The research work on concrete-filled steel tubular structures can generally be classified as the
research dealing with members, connections/joints and structural systems. The general
framework of this work is illustrated in Fig. 7. Various aspects are covered, including the static
performance, the dynamic performance, the fire performance, and the construction and
durability issues. The results should aim to provide design formulas and recommendations, to
improve drafting of design codes or standards, and to promote the applications of this
composite structures in real civil engineering projects.
Fig. 7. Framework of research on CFST structures.
6.2. Static performance
Extensive studies regarding the static performance of concrete-filled steel tubes were carried
out over the last several decades. The databases for CFST columns and beam-columns were
also established, and various analytical models were proposed to predict the column behavior.
It was found that the concrete-filled steel tubes used the merits of concrete and steel, and the
performance of CFST members in axial compression/tension, bending, shear and torsion was
generally favorable.
For CFST members in tension, limited research results showed that the member behaved in a
ductile manner. Cracks of the inner concrete are evenly distributed along the member, as
shown in Fig. 8(a). For a concrete-filled steel tube in bending, the existing of the inner concrete
can change the failure modes of the outer tubes, with the wave like buckling exhibited in the
compressive area of the member. There are cracks of the core concrete in the area under
tension, while the crack width and the distance between two cracks are small when com-
pared to reinforced concrete members, as shown in Fig. 8(b). For a concrete-filled steel tube in

14
torsion, the compressive force is developed in the inner concrete while the tensile force in the
diagonal direction is developed in the steel tube. A space “truss action” is formed and the core
concrete improves the buckling of the steel tube. For the hollow steel tube, obvious torsional
buckling is exhibited when the torsion is applied, as shown in Fig. 8(c). For the slender CFST
members, experiments were conducted on long CFST columns subjected to complex load
protocols. The results showed that the CFST columns exhibited superior performance and the
current American specification under-predicted the column strength.
Fig. 8. Schematic failure modes of steel tube, concrete and CFST under tension, bending and torsion.
Built-up concrete-filled steel tubular members have been used in structures such as bridges
and large-span buildings. Han et al. conducted the research on curved concrete-filled steel
tubular latticed members to investigate the influence of variations in the tube shape, initial
curvature, nominal slenderness ratio, and cross-sectional pattern and brace pattern. The
experimental results showed that the load-bearing capacity, the initial stiffness and the
ductility of curved latticed members are significantly increased when chord tubes are filled
with concrete. The axial compressive strength of the hollow tube specimen is only 30%–40%
of those of the corresponding concrete-filled specimen.

15
The experimental results also demonstrated that the ultimate strength and stiffness of the
curved concrete latticed specimen decreases with the increase of the initial curvature and the
nominal slenderness ratio.
The CFST members are also influenced by creep and shrinkage of the concrete during its
service life. The time-dependent behavior was investigated in tests, and the theoretical model
to account for shrinkage and creep effects on concrete-filled steel tubular columns under
sustained loading has been proposed. As the cross sectional profile of the concrete-filled steel
tube becomes larger, the hydration heat and shrinkage of the core concrete becomes critical.
An experimental investigation was conducted towards the hydration heat and shrinkage of
concrete-filled steel tubes. Self-consolidating concrete was used in the test. It was found that
at an early stage, the shrinkage of the concrete increased rapidly until it reached a fairly
stable value after about 100 days. The characteristics of the temperature field in concrete-
filled tubes are similar to that of plain concrete members during cement hydration. The test
measuring the shrinkage of the concrete lasted for 3 years. The results showed that due to the
constraint of the outer tube, the shrinkage value of the concrete core in the filled tubes is only
about 25–40% of that of the exposed concrete. No obvious gap was observed between the
steel tube and concrete after the test.
6.3. Dynamic performance
The strength, the ductility and the hysteretic behavior are very important structural aspects in
seismic design. Large amounts of experimental and theoretical studies have been conducted
on the dynamic performance of CFST columns. For the moment - curvature response and the
lateral load versus lateral displacement relationship, hysteretic models were proposed for the
cyclic response based on parametric studies, including key parameters such as axial load level,
steel ratio, slenderness ratio and material strength. The predictions of the theoretical model
showed good agreement with the test results (with a difference less than 12%). On the other
hand, as the columns in bridges and complex buildings may be subjected to torsion load, CFST
column tests incorporating combined compression, bending and torsional cyclic loading were
conducted. It was found that hysteretic curves of CFST columns under combined loadings
exhibited very limited pinching effect. The torsion capacity of CFST columns was reduced by
the bending moment. The research on the low-cycle fatigue behavior of CFST column was also
conducted.
As the concrete-encased concrete-filled steel tubes are used in bridges and buildings in seismic
regions, the research on the cyclic behavior of such composite columns was conducted. In
general this kind of columns exhibited a favorable energy dissipation capacity. The ductility
and the energy dissipation ability of the concrete-encased CFST columns decreased with the
increase of the axial load level.
For the analytical models of CFST columns under cyclic loading, Haj jar and Tort [35], Denavit
and Hajjar conducted numerical studies on rectangular and circular CFST structures,
respectively, where the 3-D fiber-based beam finite-element models were developed. The
results showed that this mixed finite element formulation could predict both detailed local

16
response and overall structural response, and could be utilized in the analysis of a complete
structural system.
Concrete-filled steel tubular members may also be subjected to impact loading when they are
used as piers in a bridge or as exterior columns in a building. Some research was conducted on
this aspect. These studies showed that CFST members in general have an excellent impact
resistance. It was found that the CFST specimen with a large confinement factor exhibited
ductile behavior, while the specimen with a small confinement factor exhibited brittle
response. The study also found that for the specimen with a brittle failure mode, the critical
failure energy increased with the increase of the axial load level.
6.4. Fire performance
The fire resistance of unprotected hollow steel tubular columns in high-rise buildings is
normally found to be less than half an hour. For concrete-filled steel tubular columns, the
filled concrete can significantly increase the fire resistance. Because the heat is absorbed by
the core concrete, the temperature in the steel tube increases much slower than that of the
bare hollow steel tubes. Moreover, the outer tube provides a confinement to the core
concrete during the fire exposure, the spalling of the core concrete thus can be prevented.
Numerous studies have been conducted on the fire performance of CFST columns. Fire
resistance tests were also conducted for concrete-filled double skin steel tubular columns. For
the concrete- filled steel tube, several parameters could affect the fire resistance of the
composite column, such as the cross-sectional profile, the load eccentricity and the thickness
of fire protection. It was found that the cross- sectional profile and the fire protection
thickness had the most significant influence for the temperature distribution in the column.
For the concrete-filled double skin steel tube, test results showed that the temperature in the
inner tube was less than 500 ˚C even when the temperature in the outer tube was about 900
˚C, the CFDST column has better fire endurance than the corresponding CFST column.
It is noted that among these studies, most experiments were carried out under an ISO 834
standard fire, and the cooling phase was usually not considered. A time-force-temperature (T-
N-T) path was proposed to illustrate the fire and the load action during an entire fire exposure.
The full-range loading path included four stages as shown in Fig. 9, i.e. the initial loading stage
(AB) at ambient temperature (To); the heating stage (BC) with constant load (No); the cooling
stage (CD) with constant load (No) and the post-fire loading phase (DE). When the
temperature drops to ambient temperature (To) at time td, the load is applied till the structure
fails at ultimate strength (NC). In Fig. 9, the temperature starts to decrease after peak
temperature (Th) at heating time (th). The specimen was loaded at the ambient temperature,
and then it was heated while the load was kept constant. After the heating, the specimen was
cooled to the ambient temperature again, and then it was loaded until failure. Since the
mechanical properties of steel and concrete depend on the temperature and loading histories,
and even when the specimen has survived the heating stage, it would still be possible to fail in
the cooling stage. The proposed full- range analysis provides a reasonable approach to the
evaluation of the structural fire performance.

17
Fig. 9. Time (t) - load (N) - temperature (T) path (Adapted from Ref. [66]).
In practice, the fire exposed CFST column could be strengthened by placing concrete and thin-
walled steel tubes around the original damaged sections. Experimental results showed that all
specimens behaved in a ductile manner. The additional outer tube and concrete significantly
increased the stiffness and strength of the original specimen, and the failure mode of the
repaired specimens was outward buckling of the steel tube. To evaluate and repair the fire-
exposed building, an evaluation procedure should be applied, including a damage
investigation, numerical or experimental analyses and repair suggestion. The full range T-N-T
path can be adopted in this procedure. The full-range analysis has been applied in the post-fire
evaluation for some real projects. It was found that this procedure can reflect the effect of a
natural fire, and a more reasonable result was obtained.
6.5. Construction and durability issues
Many practicing engineers concerned about whether the concrete and steel tube could work
together sufficiently to achieve the “composite action” in a real column. Previously a large
amount of reduced scale experiments were carried out, and very few can reflect the real effect
of concrete placement. A field experiment for the concrete placement of the concrete-filled
steel tube with circular cross section was conducted. Two full-size columns were tested with
SCC as the infilling, as shown in Fig. 10(a) and (b). The SCC is placed by the pump filling
method. The columns were cut after the test, and it was shown that the compactness of the
core concrete was very good, even for the concrete adjacent to the internal diaphragm (shown
as in Fig. 10(c) and (d)). There were very few gaps between the concrete and the steel
tube, and the maximum width of the gap was 0.1 mm. The test results also showed that the
shrinkage strain of the core concrete in the longitudinal direction is larger than that in
transverse direction (the measured strain versus time relations of Column 2 were shown in Fig.
10(e)), which may be due to different constraints of these two directions. In general, the
consolidation of the core concrete can be ensured by the quality control of material, the
proper methods for both the construction and the inspection, and the core concrete and the
steel tube can work together well.

18
Fig. 10. Full scale test of core concrete placement (Z2)
The steel tube of the CFST member is usually erected first and then it serves as the permanent
and integral formwork for the concrete. Bare steel columns can resist a considerable amount
of construction loads, as well as the self-weight and the weight of wet concrete. These
preloads could bring the extra deformation and the initial stress to the steel tube, which
causes the decrease of the load carrying capacities of composite columns. Investigations have
been carried out to study the preload effect on composite columns. Experiments were
conducted on composite columns with preloads on steel tubes. The main parameter was the
preload ratio, which was defined by the applied pre-load divided by the ultimate strength of
the hollow steel tube. As expected, the preload on the steel tubes increases the deflections
and thus results in a decrease of the column strength. The maximum strength reduction of the

19
composite columns was about 20% when the preload ratio was about 0.7, and the strength
reduction of the composite columns was less than 5% when the preload ratio was less than
0.3. The research on concrete-filled double skin steel tubular columns subjected to preload
was carried out as well. A numerical investigation was performed using a verified finite
element model. The influences of the preload ratio, the slenderness ratio, the hollow ratio and
the material strength on the compressive strength showed that the strength reduction is less
than 5% when the preload ratio is less than 0.2 for both circular and square CFDST sections.
The geometric imperfections and the residual stresses from the steel tube affect the sensitivity
in local buckling. The possible imperfections from the concrete placement, such as gaps as well
as cavities in the concrete, could also affect the column performance. For CFST, the concrete
imperfection is a significant problem although the influence of the steel imperfection can be
reduced by concrete. The investigation was conducted on members with initial concrete
imperfection. It was found that for the CFST stub column with circumferential gap between
tube and concrete, the strength loss of the column is less than 3.5% if the gap ratio (2dc/D,
dc is the gap width and D is the tube diameter) is smaller than 0.05%.
The concrete-filled steel tube may also suffer from chloride corrosion in some cases, such as in
offshore structures. It is of great importance to understand the mechanism and the
consequences of structures subjected to corrosion in order to obtain more sustainable
structures. Studies were conducted on concrete-filled steel tubular stub columns and beams
under long-term load and chloride corrosion. It was found that the decrease of the ultimate
strength and stiffness is significant when concrete-filled steel tubular members are subjected
to both long-term sustained loading and chloride corrosion, since the wall thickness of the
steel tube is reduced. The load sustained by the steel tube was partially transferred to the
concrete core after the loss of the tube wall, and the strength and the stiffness decrease of
CFST column was smaller than its hollow steel tube counterpart. Li et al. investigated the
behavior of concrete-filled double skin steel tubes under the combination of preload on steel
tubes, long-term load and chloride corrosion using numerical models. Several stages were
identified by characteristic points on the load-deformation relationship. It was found that for
stub columns, the decrease of ultimate strength and the increase of overall deformation was
presented when the combinations of loads and environmental factors were considered.

20
CHAPTER 7
DESIGN CRITERIA
7. DESIGN CRITERIA
There are a number of design codes and specifications that address the design of concrete-
filled steel tubular members, such as the AIJ guide, the ANSI/AISC 360 and the Eurocode 4. The
ANSI/AISC 360 is the specification for steel structures in the United States; the Eurocode 4 is
the European code for composite structure design; and the AIJ guide is the Japanese guide
for concrete-filled steel tubular structures, respectively. In China, there are several industrial
and local specifications regarding the concrete-filled steel tubular structures, such as DBJ/T13-
51. All of them are applicable for the concrete-filled steel tubular members with circular and
rectangular (including square) cross sections. The scopes of application for various codes are
listed in Table 4 briefly. More details can be found in each code. For the ANSI/AISC 360 and
the AIJ guide, formulas for both load and resistance factor (limit state) design and allowable
stress design are provided, the Eurocode 4 and the DBJ/T13-51 provide formulas for limit
state design.
Table 4: Scope of application for various building codes relevant to CFST columns.
For the design of member under axial compression, most codes and specifications
acknowledge the effect of the “composite action,” especially for members with a circular cross
section, therefore the strength of the composite member is enhanced. The calculation results
for the column strength using various codes or specifications are plotted in Fig. 11, where a
strength index (SI) is defined as follows:
SI =
𝑁𝑢
𝐴𝑠 𝑓𝑦 +𝐴𝑐 f’c
in which Nu is the cross-sectional strength of the CFST columns predicted by codes or
specifications, As and Ac are the cross-sectional area of steel and concrete, respectively; fy

21
and fC' are the yield strength for steel and the cylinder strength for concrete,
respectively. In this example, FY = 345 N/mm2, fc = 50 N/mm, the diameter of the cross
section is 400 mm.
Because of the different assumptions, the results from each code are somewhat different. It
can be seen from Fig. 11 that, the calculated SI values are larger than 1. For the CFST short
column with circular section, the SI thus defined increases with the cross-sectional steel ratio
for most codes and specifications. In this example, the Eurocode 4 gives the highest prediction,
while the ANSI/AISC 360 gives the most conservative one.
Fig. 11. Compressive strength for CFST short column Fig. 12. Φ-λ relationship for CFST column
Fig. 12 depicts the calculated strength for the CFST column with various column length, where
λ is the slenderness ratio of the column, for the circular CFST column, λ = 4 L/D. It can be seen
that the column strength deceases with the increase of the slenderness ratio. In this particular
case, the Eurocode 4 give the highest prediction when the slenderness ratio λ is less than 80,
and the ANSI/AISC360 gives the lowest one when λ is less than 30.
For the design of flexural members, all codes and specifications take the composite effect into
account. Fig. 13 show the flexural strength estimated by various codes, where a flexural
strength index (FSI) is defined as follows:
FSI =
Mu
𝑓𝑦 𝑍𝑝
In which Mu is the flexural strength of the CFST cross section predicted by codes or
specifications; fy is the yield strength of steel; Zp is the plastic section modulus of hollow steel
tube, Zp = (D3
− (D − 2t) 3
)/6. In this example, the diameter of the circular cross-section is 400
mm, and the yield strength of the steel tube and the compressive strength for concrete

22
cylinder are 345 N/mm2 and 50 N/mm2, respectively. It can be seen from Fig. 13 that the
flexural strength index of the CFST cross section is higher than 1, and in general it decreases
with the increase of the cross-sectional steel ratio. That is due to the fact that the contribution
of core concrete decreases when the thickness of steel tube increases. In this particular case,
the Eurocode 4 gives the highest prediction of flexural strength index when the steel ratio is
less than 0.16.
Fig. 13. Flexural strength for CFST column. Fig. 14. Axial load versus moment interaction
curve for CFST column.
Fig. 14 shows the axial load versus moment interaction curves of the CFST column. In the
example, the cross section of the hollow steel tube is Φ 400 × 13 mm, the yield strength of
steel and the cylinder strength of concrete are 345 N/mm2 and 50 N/mm2, respectively, and
the length of the column is 3000 mm. It can be seen that the shape of the load- moment
interaction curve is similar to that of the reinforced concrete one. The flexural strength of the
column increases when the axial load increases before it reaches the maximum value, and
then it decreases with the increase of the axial load. It can also be seen that, in this particular
case, the Eurocode 4 gives the highest prediction.

23
CHAPTER 8
CONSTRUCTION CONSIDERATIONS
8.1. Placement of concrete
The frame of hollow steel tubes and beams are formed prior to the placement of the core
concrete. It is of great importance to ensure that the qualities of the materials as well as the
construction process are the highest possible, however, it is difficult to inspect the filled
concrete inside the hollow section tube. Generally, the strength and the compactness of the
inside concrete should be ensured despite the construction method.
Fig. 15. Schematic view of concrete placement.
In China, various ways are used to place the concrete mix into the steel tube. Fig. 15 shows
the schematic views of two typical concrete filling operation methods. One is the pump filling,
i.e., by pumping concrete from the bottom of the column, as shown in Fig. 15(a). The other

24
one is the gravity filling, i.e., by placing concrete from the top of the column, as shown in Fig.
15(b). Before the concrete placement, the inner surface of the steel tube must be free from
water, dirt and oil, and no other special surface treatment is necessary. The volume of the
placed concrete must be recorded to make sure that the actual concrete volume inside the
tube is sufficient.
For the pump filling method, a pumping hole is usually opened at the bottom of the column
when the concrete mix is pumped from the base. The strength of the tube wall near the
pumping hole should be rechecked, and the concrete can be pumped up to several floors in a
building according to the construction progress and the capacity of the pumping device. The
self-consolidating concrete (SCC) and the thoroughly mixed concrete are favored for
construction convenience. After the hardening of the concrete, the pumping openings should
be closed.
The concrete could also be placed from the top of the column. The funnel and the bottom
emptying hopper could be used to fill the hollow section column. The depth of the fresh
concrete is usually made in steps of 300 mm to 500 mm, and should be vibrated after being
placed. If a concrete pipe is used, the end of the pipe is recommended to be placed below the
concrete surface to ensure the compactness of concrete.
The concrete filling should be done right up to the plane of the connection, and then it should
be leveled off before the hardening of concrete. The concrete at the column corner must be
placed with particular care, especially when an internal diaphragm is used in the connection.
Air holes should be used in these regions.
8.2. Fabrication issues
In China, the fabrication of tubular structural members is the same with other steel structures,
and the dimension tolerances of the hollow steel sections should follow the specification of
steel fabrication. Small vent holes should be drilled in the tube walls of the concrete-filled
tubes, in order to prevent the column from bursting under the steam pressure from concrete
material under fire. The diameter of the vent holes should not be less than 20 mm. Measures
for the protection against corrosion should be applied for exposed columns, such as painting
and spraying. In general, the erection of hollow steel structures for concrete- filled steel tubes
are the same as that of common steel structures. Due to the in-fill concrete, the opening of the
tube should be covered before the concrete placement. If the concrete-filled steel tubular
members are prepared in the workshop, the erection operation should take place after the
strength of the concrete reaches 50% of its designed strength.

25
CHAPTER 9
SOME CONSTRUCTION EXAMPLES
Concrete-filled steel tubes have been used in China for almost 50 years. It was used as the
main columns in subway stations in Beijing since 1966, and also in workshops and power plant
buildings since the 1970s. In recent decades, the pace of the concrete-filled steel tube
construction has increased rapidly. The concrete-filled steel tubes are used as major
compressive components or key members under various loading conditions in buildings,
bridges and other structures. Several examples are presented below.
9.1. Buildings
In the 1980s, the concrete-filled steel tube was used in buildings to avoid having a very large
size column. Several buildings with CFST columns were built in Beijing and Fujian province.
Since the 1990s, more buildings were built in various cities in China.
The concrete-filled steel tube usually served as the member resisting compressive load, and is
usually connected to steel or reinforced concrete beams to form a composite frame system. In
high-rise buildings or super high-rise buildings, the CFST composite frame structures are often
combined with other lateral load resisting systems such as RC core tubes or steel shear walls.
The frame using concrete-filled steel tubular columns integrates the high stiffness and the high
ductility, and works well with the core tubes or shear walls in hybrid structural systems.
Shaking table tests showed that the first order damping ratios of the building system shown in
Fig. 16(a) range from 0.03 to 0.035 before earthquake excitations. Fig. 16(b) shows another
composite structural system with the CFST frame and RC shear walls. Tests results also showed
that the frame and the RC shear walls performed well, and favorable seismic behavior was
exhibited.
Fig. 16. CFST hybrid structural systems for high-rise buildings

26
Fig. 17 shows the SEG Plaza in Shenzhen, which was one of the earliest applications of
concrete-ﬁlled steel tubular columns in super high-rise buildings. The main structure is 291.6
m, and CFST columns with circular cross section were used. The proﬁle of the steel section is
Φ 1600 mm × 28 mm, and Q345 steel and C60 concrete were used. When compared to the
column using hollow steel section, the steel usage for the CFST column was only a half, and
the use of very thick steel plate was prevented.
Fig. 17. SEG plaza in Shenzhen.
Fig. 18. Ruifeng building in Hangzhou.

27
The concrete-filled steel tube with rectangular (including square) cross section also gained a
popular usage in buildings, for the convenience when dealing with the connections. Fig. 18
shows Ruifeng International Commercial Building built in Hanzhou in 2001, where concrete-
filled steel tubular columns with square cross sections were used. The west and the east
towers are 84.3 m (24 storeys) and 55.5 m (15 storeys) in height, respectively. The hybrid
structural system consists of a CFST composite frame and RC shear walls. The maximum CFST
column profile is 600 mm, and the maximum and minimum tube thicknesses are 28 mm and
16 mm, respectively.
Fig. 19 shows the Canton Tower in Guangzhou, where the structure consists of a space lattice
composite frame and a RC core. The height of the main body is 454 meters, and the pinnacle
height is 600 meters. Twenty-four inclined concrete-filled steel circular tubular members are
utilized, with a maximum tube diameter of 2000 mm and a maximum wall thickness of 50 mm.
Fig. 19. Canton Tower
The cross sections of the concrete-filled steel tubes used in high-rise or super high-rise
structures are usually very large. Fig. 20 shows a typical cross section of mega composite
column used in one super high-rise buildings. The mega column cross section is divided into
several chambers. The longitudinal stiffeners, reinforcing tie bars and internal diaphragms are
used to enhance the stability of the steel plates. Several vent holes and man holes are set for
the concrete placement and the installation. Usually shear connectors should be used for
members with large cross sections to ensure a proper load transfer between steel and
concrete.

28
Fig. 20. Cross section for mega CFST column (units: mm).
9.2. Bridges
Concrete-filled steel tubular members have been applied in many types of bridges, such as
arch bridges, cable stayed bridges, suspension bridges, and truss bridges. CFST members can
serve as piers, bridge towers and arches, and they can also be used in the bridge deck system.
Fig. 21 depicts the usage of CFST members in various bridge structures.
Fig. 21. CFST used in bridges
Fig. 22 shows one of the earliest CFST arch bridges in China, the Wincing East River Bridge,
which was built in 1992. The cross section of the main arch is in dumbbell shape, and the total
depth is 2 meters. Steel tubes with a diameter of 800 mm and a thickness of 10 mm are used
for upper and lower chords, and the hollow sections are filled with C30 concrete. The main
span of this bridge is 115 meters. The use of concrete-filled steel tube in arch bridges
effectively exploits the advantages of this kind of construction. An important advantage of
using CFST in an arch bridge is that, during the stage of erection, the hollow steel tubes can

29
serve as the formwork for casting the concrete, which significantly reduces the construction
cost. Furthermore, the composite arch can be erected without the aid of a temporary bridging
due to the inherent stability of tubular structure. The hollow steel tubes can be filled with
concrete to convert the system into a composite structure. Since the weight of the hollow
steel tubes is comparatively small, relatively simple construction technology can be used for
the erection. The most common methods include cantilever launching methods, and either
horizontal or vertical “swing” methods, whereby each half-arch can be rotated horizontally
into position.
Fig. 22. Wangcang East River Bridge Fig. 23. Zhaohua Jialing River Bridge
The general CFST members such as concrete encased concrete-filled steel tube are being used
in bridges in China. Fig. 23 shows the Zhao Hua Jialing River Bridge in Sichuan province, China,
which has a span length of 364 meters. The arch ring consists of two parallel arch ribs, and
each arch rib is 8 meters in width and 5.2 meters in height. The cross section of the arch rib is a
double-cell concrete encased concrete-filled steel tubular box one. The diameter of tubes is
451 mm and filled with C80 concrete inside. A truss skeleton consisted of 6 hollow steel tubes
and steel angles are established first to resist the construction load for each rib. The reinforced
concrete is then attached outside the truss skeleton to form the complex composite cross
section.
9.3. Other structures
Concrete-filled steel tubular columns have also been used in various structures such as subway
stations, workshops, electricity pylons and poles.
It is well known that the columns in subway stations are usually subjected to large axial
compressive loads. The concrete-filled steel tubular member is suitable being used as the
supporting column. Fig. 24(a) shows the Qianmen subway station in Beijing, which is one of
the earliest applications of CFST columns. Fig. 24(b) shows the transportation center
connecting subway line 2 and 9 in Tianjin, China, where CFST columns are connected with
single or double reinforced concrete beams in the structure.

30
Fig. 24. Subway stations using CFST columns
The concrete-filled steel tube has been used in industrial buildings in the north of China since
1970s. Single or build-up CFST members can be applied depending on the load resistance
requirement. Fig. 25 shows the concrete-filled steel tubular columns used in a power plant
workshop. The steel used in the CFST column is only 55% of that used in the hollow steel
column for similar workshops.
Fig. 25. A power plant workshop using CFST columns
The concrete-filled steel tubes can be used in the construction and the upgrade of poles and
transmission towers as well. Fig. 26 shows a long-span transmission tower built in Zhoushan,
China. The tower is the largest electricity pylons in the world with a height of 370 meters. This
tower is a tubular lattice one with four concrete-filled steel tubular columns. The diameter of
the CFST column is 2000 mm, and the concrete is filled up to 210 meters height. Concrete-
filled double skin steel tubes are being used in electrical grid infrastructures in recent years.
This composite section has high bending stiffness, and the self- weight is lighter when
compared with the fully filled CFST section. A photo of CFDST pole is shown in Fig. 27. The

31
bearing capacity of the pole is enhanced when compared to the traditional steel lattice tower,
while the occupied land area is reduced and the total cost is not raised.
Fig. 26. Zhoushan electricity pylon
Fig. 27. A CFDST pole

32
CHAPTER 10
CONCLUSIONS
10. CONCLUDING REMARKS
 With the rapid development of research and application of concrete- filled steel tubular
structures in China and all over the world in the past decades, the scope of “concrete-
filled steel tube” has been extended greatly by researchers and engineers.
 The characteristic of these concrete-filled steel tubular members is that the structural
properties can be improved due to the “composite action” between steel tube and filled
concrete.
 Some typical applications of concrete-filled steel tubular members are in buildings, bridges,
high towers and other few structures.
 The concrete-filled steel tubular structure can be treated as an alternative system to
the steel or the reinforced concrete system.
 Some questions on the feasibility of the CFST system should also be fully evaluated for its
widely expanded application.
 The thorough comparison of advantages and disadvantages of the CFST system with the
steel and RC system, the space truss structural system, the connection system, the hybrid
system using high performance and sustainable materials as well as the life-cycle
performance evaluation should be conducted in the future.

33
REFERENCES
 Li W, Han LH, Zhao XL. Axial strength of concrete-filled double skin steel tubular (CFDST)
columns with preload on steel tubes. Thin-Walled Struct 2012; 56(7):9–20.
 Liao FY, Han LH, Tao Z. Behavior of CFST stub columns with initial concrete imperfection:
analysis and calculations. Thin-Walled Struct 2013; 70(1):57–69.
 Han LH, Hou C, Wang QL. Square concrete filled steel tubular (CFST) members under
loading and chloride corrosion: Experiments. J Constr Steel Res 2012; 71(4):11–25.
 Li W, Han LH, Zhao XL. Numerical investigation towards life-cycle performance of concrete
filled double skin tubular (CFDST) columns. First Conference on Performance-based and
Life-cycle Structural Engineering, Honking, December 5–7; 2012.
 ASCCS: Concrete Filled Steel Tubes — a Comparison of International Codes and Practices.
ASCCS Seminar Report, Innsbruck; 1997.
 AIJ. Recommendations for Design and Construction of Concrete Filled Steel Tubular
Structures. Tokyo, Japan: Architectural Institute of Japan (AIJ); 2008.
 ANSI/AISC 360–10. Specification for Structural Steel Buildings. Chicago, USA: American
Institute of Steel Construction (AISC); 2010.
 Eurocode 4. Design of Composite Steel and Concrete Structures. Brussels: European
Committee for Standardization; 2005.
 Han LH, Li W, Yang YF. Seismic behavior of concrete-filled steel tubular frame to RC
shear wall high-rise mixed structures. J Constr Steel Res 2009; 65(5):1249–60.
 Liao FY, Han LH, Tao Z. Seismic behaviour of circular CFST columns and RC shear wall mixed
structures: experiments. J Constr Steel Res 2009; 65(8–9):1582–96.
 GB/T 700–2006. Carbon Structural Steels. Beijing: Standard Press of China; 2006. [18]
GB/T 1591–2008. High Strength Low Alloy Structural Steels. Beijing: Standard Press of
China; 2008.
 GB 50017–2003. Code for Design of Steel Structures. Beijing: Standard Press of China;
2003.
 DBJ/T13-51-2010. Technical Specifications for Concrete-Filled Steel Tubular Structures
(Revised Version. Fuzhou, China: The Housing and Urban–Rural Development Department
of Fujian Province; 2010 [in Chinese].
 GB 50010–2010. Code for Design of Concrete Structures. Beijing: Standard Press of China;
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