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.

10

11

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

12

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

13

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.

15

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)

18

*Stub Column Properties & Full Area Approach

Comparison of test and FEA strengths with design strengths for all specimens

19

*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.

32

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.

33

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.

34

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.

35

36

The University of Hong Kong

Thank you!

37

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)