University of Southern Queensland
Faculty of Engineering and Surveying
Assignment Cover Sheet
Research Proposal
2
A Student
Q
123456789
A study of l
ocal and post

local
buckling of concrete filled thin

walled steel
tubu
lar
columns
Abstract
The l
ocal
and post

local buckling of steel tubes r
educes the ultimate loads of
thin

walled concrete

filled steel tubular (CFST) columns under axial compression.
Experimental research on
CFST columns has been conducted. H
owever
,
the
effect of
local and post

local buckling
on the
behavior
on
CFST columns
ha
s not been
adequately researched.
This project aims to investigate the local and post

local
buckling behavior of thin

walled CFST columns using the finite element method.
A 3D
finite element model will be developed using the Strand7 finite element software
package to obtain t
he
c
ritical local and post

local
buckling strength
of
the steel tubes
i
n CFST columns. From the results obtained, effective
strength formulas for the
design
of steel tubes in CFST columns and design
formulas incorporating local
buckling
effects for the design of CFST columns
will be developed.
The proposed
design formulas will be verified by comparisons with existing experimental results
and those developed by other researchers
Table of Contents
Abstract
................................
................................
................................
...............................
2
1
Introduction
................................
................................
................................
.................
4
2
Project Background
................................
................................
................................
.....
5
3
Literature Review
................................
................................
................................
........
7
3.1
Overview
................................
................................
................................
.............
7
3.2
Design Codes
................................
................................
................................
......
7
3
.3
Local and Post

Local Buckling
................................
................................
...........
7
3.4
CFST Columns
................................
................................
................................
....
9
4
Project Methodology
................................
................................
................................
.
11
5
Project Timeline
................................
................................
................................
........
12
6
Conclusion
................................
................................
................................
................
14
7
Assessment of Consequential Effects
................................
................................
.......
15
7.1
Consequential Effects
................................
................................
.......................
15
7.2
Ethical Responsibility
................................
................................
.......................
15
7.3
Risk Assessment
................................
................................
...............................
15
7.4
Resource Requirements
................................
................................
....................
15
8
References
................................
................................
................................
.................
16
Research Proposal
4
A Student
Q
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1
Introduction
This project aims to investigate the local and
post

local buckling behavior
of
thin

wall
e
d
CFST
columns using the finite element method.
Buckling can be defined as
structural failure by gross lateral deflection of a slender element under bending
or
compressive
stress, such as the sideward buckling of a
long, slender column.
Thin

walled CFST columns are those which are designed to take account of the beneficial
effect of the concrete restraint against local bu
ckling of the steel tube
.
The objectives
of this
project are
as follows:
1.
Research existing info
rmation relating to local and post

lo
cal buckling of thin

walled CFST
columns.
2.
Study the nonlinear finite element analysis method and develop three

dimensional finite element model
s for the nonlinear analysis of
thin

w
alled
CFST columns
.
3.
Conduct geometr
ic and material nonlinear finite element analyses on steel
tubes under uniform/non

uniform edge compression to determine critical load
and post

local buckling strengths. Initial geometric imperfections, residual
stresses, material yielding and strain harde
ning will be considered in the
analysis.
4.
Furthermore, investigate the effects of stress gradients and tube width

to

thickness ratios on the load

deflection curves and the post

local buckling
strengths.
5.
Based on the results obtained propose a set of des
ign formulas for determining
the ultimate strengths of concrete

filled thin

walled steel tubular beam

columns.
6.
Verify the proposed design formulas by comparisons with existing
experimental results and those developed by other researchers.
Research Proposal
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2
Project Backgro
und
CFST
columns are
finding widespread use in contemporary construction
as primary
axial load

carrying members in high

rise buildings, bridges and offshore structure
s.
The structural properties of CFST columns include high strength, high ductility and
hig
h energy absorption capacity. Thin

walled CFST columns have been used in many
Australian high

rise buildings including; Casselden Place and Commonwealth Centre
in Melbourne, Riverside and Myer Centre in Adelaide and Market Plaza in Sydney
[14]. These colum
ns are constructed using circular hollow steel sections filled with
either normal or high strength concrete. A typical cross section is illustrated in Figure
1.
Figure
1
: Cross section of CFST column.
For the purpose of this project, i
t is assumed that the steel has not bonded to the
concrete infill and therefore the concrete only provides restraint to inward local
buckling. Furthermore, two possible failure modes for the steel tube can be identifi
ed;
Research Proposal
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A Student
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outward
local buckling and yield failure.
The
local
buckling
restraint
provided by the
concrete
leads to an increase in the local buckling strength of
the steel tube
and the
ultimate strength of the composite column.
The concrete is fully encased by
the steel tube
so that the ductility of the enca
sed
concrete can be improved. The steel tube
also serves as longitudinal reinforcement
and permanent formwork for the concrete core, which results in significant savings in
materials and labor costs.
A study
by Uy [10] has shown that concrete

filled box
column construction can produce savings of up to 50% on material costs when
compared with reinforced concrete box columns. The CFST column construction
process
also
provides several economic
adva
ntages
over rei
nforced concrete:
Ability of steel column to support construction loads prior to placement of
concrete;
Steel tube provides necessary formwork allowing for rapid construction;
Less steel is required as concrete resists majority of axial forces.
Increased
lettable floor area due to a reduction in the required column cross

section size.
It was documented by Shanmugam and Lakshmi [21] that intensive research is
required on the effect of concrete restraining local buckling of thin

walled CFST
columns. The lo
cal and post

local buckling characteristics of steel tubes with
geometrical imperfections and residual stresses have also not been adequately studied
theoretical.
This project aims to investigate the local and post

local buckling behavior
of
thin

wall
ed CF
ST
columns
using the finite element method.
Research Proposal
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3
Literature Review
3.1
Overview
Over the last 20 years, a significant amount of experimental research on CFST
columns has been conducted throughout the world, particular in Australia, Asia and
Europe. The vast m
ajority of experiments have been on moderately scaled specimens
with a diameter of less than 200mm and filled with normal and high

strength concrete
[21]
.
3.2
Design
Code
s
Currently, there is no design standard that can be used for the design of thin

wal
led
CFST columns. For the design of thick

walled CFST columns, some design guidance
is given in codes such as Eurocode 4 [1], ACI318 [2] and DL/T5085 [3].
All three
codes are different in concept.
O’Shea
and Bridge [4] documented that
Euroco
de 4
uses a col
umn curve to determine the influence of column
slenderness, while the
ACI
318 method uses the traditional reinforced concrete approach, with a minimum load
eccentricity used to determine the column strength under nominal axial load.
Zhong
and Goode [5] doc
umented that
DL/T5085
differs from Eurocode 4 in that it is based
on a ‘unified theory’ which considers the CFST as a composite material and not as the
separate components concrete and steel.
DL/T5085
also includes for shear and
torsion, in addition to ben
ding and axial load.
3.3
Local and Post

Local
Buckling
The design of thin

walled circular steel
hollow
sections (CHS) under axial
compression is often governed by their local buckling capacity. The local buckling
strength of circular and rectangular hollow se
ctions can be determined by adjustment
of the theoretical elastic buckling stress [6]. The post

buckling strength can be
determined based on an appropriate simplified buckling model [6].
In CFST columns
the concrete prevents inward local buckling and the s
teel tube can only buckle
outward locally [8]. This buckling mode leads to an increase in the local buckling
strength of steel tubes and the ultimate
strength of the composite column.
Research Proposal
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By using a Rayleigh

Ritz based method, Bradford et al. [7] derived a cl
osed form
solution for the local buckling stress of a thin

walled CFST column and
demonstrated
that the elastic
local
buckling stress is
3
times that of its unfilled counterpart.
Additionally, the theoretical use of the von Karman mod
el when interpreted in an
effective diameter framework showed that there is no post

buckling reserve of
strength. Therefore, the critical buckling stress governs the strength of thin

walled
sections.
Experimental tests were conducted by O’Shea and Bridge
[18] on the behaviour of
thin

walled steel tubes, with D/t ratios from 55 to 200. Tests included; unfilled steel
tubes, concrete

filled steel tubes with only steel loaded, tubes with steel and concrete
loaded and tubes with only concrete loaded. The exper
imental results suggested that
the concrete infill for thin

walled CFST columns has a negligible effect on the local
buckling strength of the steel tube. However, O’Shea and Bridge [19] documented
that concrete infill can improve the local buckling strengt
h for rectangular and square
sections. Additionally, O’Shea and Bridge [4] reported that for axially loaded thin

walled CFST columns,
with D/t ratios from 60 to 220, local buckling of the steel tube
does not occur if there is sufficient bond between the st
eel and concrete.
Uy [6] conducted an extensive set of tests for the study of local and post

local
buckling of steel plates in concrete

filled steel box (CFSB) columns. The paper
presented a semi

analytical finite strip method d
eveloped elsewhere for determining
the required slenderness limits for inelastic local buckling in a thin

walled CFSB
column and compared favorably with international standards. The model incorporated
the presence of residual stresses and strains. However,
the effect of geometrical
imperfections was not included in the analysis. A post

local buckling model based on
the effective width method was developed to determine the strength of a CFSB
column. Uy [6] suggests the AS4100 method,
based on the effective w
idth principle,
for
determining the post

local buckling behavior of a column under pure compression
for use in an ultimate strength analysis.
Research Proposal
9
A Student
Q
123456789
The critical local buckling and ultimate strength of steel plates in double skinned
composite (DSC) planes under
combined biaxial compression and shear was
investigated using the finite element method by Liang
et al. [20]. The finite element
models incorporated initial imperfections, material stress

strain behaviour and the
shear

slip characteristics of stud shear co
nnectors. Steel plates in DSC panels are
restrained by concrete infill and welded shear connectors at discrete positions [20].
Local buckling may occur in a unilateral mode between stud shear connectors when
subjected to combined states of stress [20].
3.4
C
FST C
olumns
Giakoumelis and Lam [16] conducted experiments on 15 short CFST columns, with
D/t ratios from 2.9 to 30.5 and a h/D
ratio of 2.6, under axial compression. The results
suggested that as the concrete strength increases the effects of the bond of
the
concrete and the steel tube became more critical. For normal strength concrete (30
N/mm
2
), the
reduction
on the axial capacity of the column due to bonding was
negligible. For high

strength concrete (100 N/mm
2
), the variation between
Non

greased
and
gr
eased
was 17%. When the experimental results of Giakoumelis and
Lam were compared to Eurocode 4 [1], 17% was the largest variation between the
experimental and calculated values for the axial capacity. For high

strength CFST
columns the
variation between t
he experimental and calculated values was negligible.
The predicted axial strengths using
AS4100 [17] and
ACI318 [2]
were 35%
lower
than the experimental results.
Experimental studies on the ultimate strengths of short CFST columns have been
conducted by
Furlong [11]. The tests indicated that the axial load was resisted by the
steel and concrete components independently and there was no increase in the
ultimate strengths of composite columns due to concrete confinement.
However, results from tests cond
ucted by Knowles and Park [12] showed that the
circular steel tube offered confinement to the concrete core and the confinement
increased the ultimate loads of the columns. The increase in ultimate loads due to
confinement effects was observed only in shor
t circular columns. No confinement
effect on the ultimate loads, however, was observed in concrete

filled square and
rectangular steel box columns.
Research Proposal
10
A Student
Q
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O’Shea and Bridge [19] suggest that increased strength due to confinement of high

strength concrete can be
obtained if only the concrete is loaded and there is no bond
between the steel and concrete. For high

strength CFST columns, with D/t ratio
greater than 55, the steel tubes provide limited confinement to the concrete when the
steel tube and concrete are l
oaded simultaneously. Additionally, O’Shea and Bridge
[4] concluded that the degree of confinement offered by a thin

walled circular steel
tube, with D/t ratio from 60 to 220, to the concrete infill is dependent upon the
loading condition. Furthermore, Eur
ocode 4 [1] was shown to provide the best
strength estimate for thin

walled CFST columns when the steel tube and concrete
infill are loaded simultaneously.
Nonlinear analysis of CFST columns was conducted by Hu
et al. [22] using the
software program
ABAQU
S
. It was shown that CFST columns provide effective
confining effect when the D/t ratio is greater than 40 and that local buckling of the
steel tube is not likely to occur.
Research Proposal
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4
Project Methodology
The methodology adopted in this research
project
is as fo
llows
:
The critical local and post

local buckling strengths of steel tubes in CFST columns
:
The finite element analysis method will be used to study the critical local and post

local buckling strengths of steel tubes in CFST columns.
A 3D finite element
model
will be developed
using the Strand7
finite element
software package
for the geometric
and material nonlinear analysis of steel tubes in CFST columns.
The
steel tubes will
be loaded under uniform/non

uniform edge compression to determine critical loa
d and
post

local buckling strengths.
The progressive local and post

local buckling will be
stimulated by gradually redistributing the normal stresses within the steel tube
s
.
Initial
geometric imperfections, residual stresses, material yielding and strain h
ardening will
be considered in the analysis.
Effective strength formulas for the design of steel tubes in CFST columns
Analytical methods will be used to develop the effective strength formulas for the
design of steel tubs in CFST columns based on the no
nlinear finite element analyses.
Similar approaches by Liang et al.
[23]
will be employed to develop design formulas
for steel tubes in CFST columns.
Design formulas incorporating local buckling effects for the design of CFST columns
Analytical methods
will be used to develop design formulas for the design of CFST
columns. These design formulas will take into account of local buckling effects of the
steel tubes. Existing experimental data of CFST columns will be used to verify the
design formulas propose
d.
Research Proposal
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5
Project Timeline
Figure
5
.1: Research Project Timeline,
identifies milestones and particular tasks which can assess the progress of this project.
WEEK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
WEEK STARTING
5/3/07
12/3/07
19/3/07
26/3/0
7
2/4/07
9/4/07
16/4/07
23/4/07
30/4/07
7/5/07
14/5/07
21/5/07
28/5/07
4/6/07
11/6/07
18/6/07
25/6/07
2/7/07
Organise resources (Strand7 software)
Literature Review
Study nonlinear finite element analysis (Strand7)
Study topic related theory
Chapter 1

Introduction (finalise)
Chapter 2

Literature Review (finalise)
Develop 3

dimential model
Research Proposal
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WEEK
19
20
21
22
23
24
25
26
27
28
29
30
3
1
32
33
34
35
36
WEEK STARTING
9/7/07
16/7/07
23/7/07
30/7/07
6/8/07
13/8/07
20/8/07
27/8/07
3/9/07
10/9/07
17/9/07
24/9/07
1/10/07
8/10/07
15/10/07
22/10/07
29/10/07
5/11/07
Chapter 1

Introduction (finalise)
Chapte
r 2

Literature Review (finalise)
Develop 3

dimential model
Conduct nonlinear finite element
analysis (Strand7)
Investigate effects of stress gradients etc
Calculate proposed set of design formula
Verify design formulas
Chapter 3

Experimental Methodology
Chapter 4
–
Results and Discussions
Chapter 5

Conclusions and
Recommendations
Submit partial draft (to supervisor)
17/9/07
Make corrections to draft and finalise
Submit Research Project
9/11/07
Figure
5
.1: Research Project Timeline
Research Proposal
14
A Student
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6
Conclusion
This project aims to investigate the local and post

local buckling behavior
of
thin

wall
ed CFST
columns using the finite element method.
The
project will investigate
the following important aspects:
1.
The critical
local and post

local buckling strengths of steel tubes in CFST
columns.
2.
The d
evelop
ment of
effective strength formulas for the design of steel tubes in
CFST columns.
3.
The d
evelop
ment of
design formulas incorporating local buckling effects for
the design
of CFST columns.
The structural properties of CFST
columns
includ
e
high strength, high ductility and
high energy absorption capacity,
making
them excellent for use
as
primary axial load

carrying members in high

rise buildings, bridges and offshore structu
re
s.
Currently, there is no design standard that can be used for the design of thin

walled
CFST columns.
T
heir increased use in contemporary construction
intensifies the need
for
effective strength formulas
and
design formulas
for
the design of thin

walle
d
CFST columns
.
Research Proposal
15
A Student
Q
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7
Assessment of Consequential Effects
7.1
Consequential Effects
When considering the consequences of this technical project the following document
was consulted:
Towards Sustainable Engineering Practice: Engineering Frameworks for
Susta
inability,
Institute of Engineers, Australia, Canberra, 1997
.
B
oth steel and concrete are widely regarded as
inexpensive everyday
building
materials
. Consequently,
there are no sustaina
bility, safety or ethical issues
associated
with this project work
and or the
results of this project work.
However, the debate
over whether
or not both materials are in infinite supply still continues.
7.2
Ethical Responsibility
When considering the ethical responsibility of this technical project the following
document was
consulted:
The Engineers Australia Code of Ethics,
Institute of Engineers, Australia,
Canberra, 2000
There are
no
ethical issues associated with this project work and or the results of this
project work.
7.3
Risk Assessment
There is no risk of physical h
arm to any individuals during the execution and beyond
the completion of this project.
7.4
Resource Requirements
The execution of this project will require the following resources:
1.
The finite element analysis software system Strand7.
2.
Capable computer hardware
.
3.
Access to published literature and other contextual information appropriate to
the topic.
Research Proposal
16
A Student
Q
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8
Reference
s
[1]
European Committee for Standardization (CEN). (1992). ‘‘Design of
composite steel and concrete structures, part 1.1
—
General rules and rules for
buil
dings.’’
Eurocode 4
, Brussels.
[2]
American Concrete Institute (ACI). (1989). ‘‘Building code requirements for
reinforced concrete.’’
ACI 318
, Detroit.
[3]
Design Code for Concrete Filled Steel Tubes (DL/T5085

1999). Electric
Power Publishing House, Peopl
e’s Republic of China, 1999.
[4]
O’Shea MD, Bridge RQ. Design of circular thin

walled concrete filled steel
tubes. Journal of Structural Engineering ASCE 2000; 126(11):1295
–
303.
[5]
Zhong ST, Goode CD. Composite construction for columns in high

rise
buildi
ngs in China. Structures and Buildings 2001; 146(4): 333

40.
[6]
Uy B. Local and post

local buckling of concrete filled steel welded box
columns. Journal of Constructional Steel Research 1998; 47: 47

52.
[7]
Bradford MA, Loh HY, Uy B. Slenderness limits fo
r circular steel tubes.
Journal of Constructional Steel Research 2002; 58: 243

52.
[8]
Liang QQ, Uy B, Liew JYR. Nonlinear analysis of concrete

filled thin

walled
steel box columns with local buckling effects. Journal of Constructional Steel
Research 2006;
62: 581

91.
[9]
Bridge RQ, O’Shea MD, Gardner P, Grigson R, Tyrell J. Local buckling of
square thin

walled steel tubes with concrete infill. In: Proceedings of the
international conference on structural stability and design. 1995, p.307

14.
[10]
Uy B. Be
haviour and design of thin

walled concrete filled box columns.
Australian Civil and Structural Engineering Transactions 1995; 38(1): 31

8.
[11]
Furlong RW. Strength of steel

encased concrete beam

columns. Journal of
Structural Division, ASCE 1967; 93(5):11
3

24.
[12]
Knowles RB, Park R. Strength of concrete

filled steel tubular columns.
Journal of Structural Division, ASCE 1969; 95(12):2565

87.
[13]
Liang QQ, Uy B. Theoretical study on the post

local buckling of steel plates in
concrete

filled box columns. C
omputers and Structures 2000; 75:479

90.
Research Proposal
17
A Student
Q
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[14]
Watson KB, O’Brien LJ. Tubular composite columns and their development in
Australia. Proceedings of the Structural Engineering Conference, The Institute
of Engineers, Adelaide, Australia, 1990: 186

90.
[15]
St
rand7. Reference manual and user guide. Sydney, Australia: G + D
Computing Pty Ltd., 2004
[16]
Giakoumelis G, Lam Dennis. Axial capacity of circular concrete

filled tube
columns. Journal of Constructional Steel Research 2004; 60: 1049

68.
[17]
AS4100 ref
erence
[18]
O’Shea M, Bridge R. Circular thin

walled tubes with high strength concrete
infill. Composite construction in steel and concrete ІІ. Irsee (Germany):
ASCE; 1996, 780

93.
[19]
O’Shea M, Bridge R. The Design for local buckling of concrete filled steel
t
ubes. In: Composite Construction
–
Conventional and Innovate, Innsbruck,
Austria; 1997, p.319

24.
[20]
Liang QQ, Uy B, Wright HD, Bradford MA. Local Buckling of Steel Plates in
Double Skinned Composite Panels under Biaxial Compression and Shear.
Journal of
Structural Engineering ASCE 2004; March: 443

51.
[21]
Shanmugam NE, Lakshmi. State of the art report on steel

concrete composite
columns. Journal of Constructional Steel Research 2001; 57: 1041

80.
[22]
Hu HT, Huang CS, Wu MH, Wu YM. Nonlinear Analysis of Axially Loaded
Concrete

Filled Tube Columns with Confinement Effect. Journal of Structural
Engineering ASCE 2003; October: 1322

9.
[23]
Liang QQ, Uy B, Wright HD, Bradford MA. Local and post

local b
uckling of
double skin composite panels. Proceedings of the Institute of Civil Engineers:
Structures and Buildings 2003; 156(2): 111

119.
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