Assignment Cover Sheet

haltingnosyUrban and Civil

Nov 29, 2013 (3 years and 10 months ago)

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University of Southern Queensland




Faculty of Engineering and Surveying


Assignment Cover Sheet


Research Proposal


2

A Student


Q
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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







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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.

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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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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.




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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.

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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.


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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.

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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.





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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.









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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






































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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

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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
.









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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.

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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


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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.