Yuner HUANG and Ben YOUNG
Department of Civil Engineering
The University of Hong Kong, Pokfulam Road, Hong Kong
Fourth International Structural Stainless Steel Experts Seminar
Introduction
Finite Element Model & Parametric Study
Comparison with Existing Design Rules
Modified Design Rules & Comparison with
Column Strengths
Conclusions
2
Introduction
Finite Element Model & Parametric Study
Comparison with Existing Design Rules
Modified Design Rules & Comparison with
Column Strengths
Conclusions
3
• Cold-formed stainless steel sections have been
increasingly used in architectural and structural
applications, due to their appearance, superior
corrosion resistance, ease of maintenance and
ease of construction.
Twin Tower Types 304 & 316
(2300 ton for one tower)
Stonecutters Bridge (Stainless Steel) Hong Kong
(Upper part of the tower: Duplex stainless steel)
6
In this study, lean duplex stainless steel columns of
grade EN 1.4162 (LDX 2101) was considered (low
Nickel of around 1.5%, compared to 5% >).
The lean duplex material is relatively new in civil
engineering construction, and it is not covered in
current design specifications.
Up-to-date, little research is being carried out on
structural behaviour of lean duplex stainless steel.
7
Price at July, 2011
Objective
Study the structural performance of cold-formed lean
duplex stainless steel column from a wide-ranging
parametric study and the available test data.
Data pool
259 experimental and numerical column strengths
from parametric study and previous researches
Design rules
6 existing design rules are assessed in this study, and
recommendations is proposed accordingly.
8
Introduction
Finite Element Model & Parametric Study
Comparison with Existing Design Rules
Modified Design Rules & Comparison with
Column Strengths
Conclusions
9
32 cold-formed lean duplex stainless steel pin-
ended column tests were conducted by Huang and
Young (2012).
Finite element program ABAQUS was used to
simulate the column tests.
The measured geometry, initial overall and local
geometric imperfections, and material properties of
the test specimens were used in the FEM.
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Specimen
Tests FEA Comparison
PExp
(kN)
Failure
mode
PFEA
(kN)
Failure
mode
PExp
PFEA
50×30×2.5L200 259.2 Y 251.8 Y 1.03
50×30×2.5L550 154.5 F 155.0 F 1.00
50×30×2.5L900 85.4 F 89.5 F 0.95
50×30×2.5L1200 55.3 F 57.2 F 0.97
50×30×2.5L1550 36.2 F 35.8 F 1.01
50×50×1.5L200 153.4 L 141.7 L 1.08
50×50×1.5L550 139.3 L 132.1 L 1.05
50×50×1.5L900 120.8 F 121.7 F 0.99
50×50×1.5L1200 92.3 F 98.1 F 0.94
50×50×1.5L1550 65.4 F 69.0 F 0.95
50×50×2.5L200 355.3 Y 328.1 Y 1.08
50×50×2.5L550 302.1 L 322.4 L 0.94
50×50×2.5L900 242.8 F 220.3 F 1.10
50×50×2.5L1200 146.1 F 159.0 F 0.92
50×50×2.5L1550 103.9 F 114.6 F 0.91
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Tests FEA Comparison
Specimen PExp
(kN)
Failure
mode
PFEA
(kN)
Failure
mode
PExp
PFEA
70×50×2.5L200 373.1 Y 354.1 Y 1.05
70×50×2.5L550 352.8 L 342.6 L 1.03
70×50×2.5L900 270.7 F 270.1 F 1.00
70×50×2.5L1200 211.2 F 217.3 F 0.97
70×50×2.5L1550 148.3 F 159.2 F 0.93
100×50×2.5L200 370.1 L 367.1 L 1.01
100×50×2.5L550 372.3 L 346.3 L 1.08
100×50×2.5L900 335.2 L+F 306.3 L+F 1.09
100×50×2.5L900R 336.0 L+F 306.3 L+F 1.09
100×50×2.5L1200 249.0 F 257.7 F 0.97
100×50×2.5L1200R 252.2 F 257.7 F 0.98
100×50×2.5L1550 193.7 F 205.2 F 0.94
150×50×2.5L200 404.1 L 413.2 L 0.98
150×50×2.5L550 353.2 L 340.1 L 1.04
150×50×2.5L900 333.5 L+F 308.7 L+F 1.08
150×50×2.5L1200 284.5 L+F 257.0 L+F 1.10
150×50×2.5L1550 230.0 L+F 212.0 L+F 1.08
Mean 1.01
COV 0.059
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Local Buckling
Interaction of Local
& Flexural Buckling
Flexural Buckling
14
0
10
20
30
40
50
60
0 1 2 3 4
Ax
ial lo
ad (k
N)
Axial shortening (mm)
Test
FEA
Comparison of load-displacement curves of test and FEA for specimen
50×30×2.5L1200
Finite element analysis on 125 pin-ended
columns and 25 stub columns were carried
out using the verified FEM.
5 SHS and 20 RHS with 6 different effective
lengths for each section. (d/t = 5 ~ 90)
Column slenderness ratio l = 20 ~ 100 for
each section.
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Introduction
Finite Element Model & Parametric Study
Comparison with Existing Design Rules
Modified Design Rules & Comparison with
Column Strengths
Conclusions
16
17
American Specification (ASCE)
Austrainlian/New Zealand Standard (AS/NZS)
European Code (EC3)
Suggested Design Rule for EC3 (Theofanous &
Gardner 2009)
Direct Strength Method (DSM)
Stub Column & Full Area Approach (Huang & Young
2012)
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*Stub Column Properties & Full Area Approach
Comparison of test and FEA strengths with design strengths for all specimens
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*Stub Column Properties & Full Area Approach
Comparison of test and FEA strengths with design strengths for slender sections (r < 1)
20
*Stub Column Properties & Full Area Approach
Comparison of test and FEA strengths with design strengths for non-slender sections
21
Existing Design Rule Comparison result
for specimens in this study
ASCE Specification Accurate & reliable prediction, but involves
inconvenient iterative process
AS/NZS Standard Generally conservative, especially to non-
slender sections; relatively simple calculating procedure
EC3 Code Conservative and reliable
Suggested design rule to EC3
Improve accuracy for slender sections than existing EC3; conservative to non-slender
sections
Direct Strength Method
Conservative and scattered
Stub Column and Full Area Approach
Accurate predictions
22
Existing Design Rule Comparison result
for specimens in this study
ASCE Specification Accurate & reliable prediction, but involves
inconvenient iterative process
AS/NZS Standard Generally conservative, especially to non-
slender sections; relatively simple calculating procedure
EC3 Code Conservative and reliable
Suggested design rule to EC3
Improve accuracy for slender sections than existing EC3; conservative to non-slender
sections
Direct Strength Method
Conservative and scattered
Stub Column and Full Area Approach
Accurate predictions
Introduction
Finite Element Model & Parametric Study
Comparison with Existing Design Rules
Modified Design Rules & Comparison with
Column Strengths
Conclusions
23
24
Clause 3.4.2 Alternatively Method
c e nN A f
2 2
y
n y
ff f
l
211
2 l
1 o
l l l
2
y
o
fkl
r El
26
Class 3 limit (c/te) relax from 30.7 to 40
Imperfection values and
Effective width equation:
Existing EC3 0.49 0.40
Modified EC3 0.27 0.43
27
ol
1125.0772.0
2
pp llr
0.1
28
0.87 1
1
0.769
0.769 0.16
29
Introduction
Finite Element Model & Parametric Study
Comparison with Existing Design Rules
Modified Design Rules & Comparison with
Column Strengths
Conclusions
30
31
The pin-ended cold-formed lean duplex stainless steel columns have been investigated.
A finite element model was developed and compared well with experimental results.
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A wide range of parametric study of 150 columns was carried out.
The results of parametric study together with 109 available data of lean duplex stainless steel columns were compared with various design strengths
Modifications for AS/NZS, EC3, and DSM are proposed in this study.
The modified design rules are shown to provide more accurate and reliable predictions for cold-formed lean duplex stainless steel columns.
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Considering the accuracy, reliability and the simplification of calculation, it is recommended that the modified AS/NZS and the modified DSM to be used in designing cold-formed lean duplex stainless steel columns.
The two recommended methods are capable of producing reliable limit state designs when calibrated with the resistance factor of 0.85.
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The research work described in this paper
was supported by a grant from The
University of Hong Kong under the seed
funding program for basic research.
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The University of Hong Kong
Thank you!
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The unfactored design strengths (nominal strength) were
calculated using various design rules.
The design strengths are compared with the 259 column
strengths, including both slender and non-slender specimens.
In this study, slender section is defined when the value of r
for calculating the effective area in the ASCE is less than unity
(r < 1), meaning that the section is not fully effective.
It should be noted that the lean duplex stainless steel is not
covered in the existing ASCE, AS/NZS, and EC3.
38
39
40
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0
Pu
/ P
ne
ll
DSM
FEA
Huang and Young (2012)
Theofanous and Gardner (2009)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0.0 0.4 0.8 1.2 1.6 2.0
Pu
/ P
ne
ll
Modified DSM
FEA
Huang and Young (2012)
Theofanous and Gardner (2009)