Structural Design of Stainless Steel Members

Journal of Constructional Steel Research 54 (2000) 51–73www.elsevier.com/locate/jcsr

Structural design of stainless steel members —comparison between Eurocode 3, Part 1.4 and

test results

B.A. Burgan*, N.R. Baddoo, K.A. GilsenanThe Steel Construction Institute, Silwood Park, Ascot, Berkshire SL5 7QN, UK

Abstract

The paper describes the test results of an ongoing major European research project whichis concerned with the further development and refinement of structural design guidance forstainless steel. The paper concentrates on the work carried out to date on the design of beams,columns and beam–columns and compares the test results with resistances predicted by thedesign pre-standard for structural stainless steel, ENV 1993-1-4. In general, the design guid-ance is conservative. The tests on CHS beams indicate that the limiting diameter-to-thicknessratios for section classification can be considerably increased. For welded I-section beams, theENV 1993-1-4 lateral torsional buckling curve appears very conservative and the less con-servative curve adopted in ENV 1993-1-1 for carbon steel appears to give a better fit to thedata. 2000 Elsevier Science Ltd. All rights reserved.

Keywords:Stainless steel; Eurocode 3 Part 1.4; Structural design

1. Introduction

The attractive appearance, corrosion resistance, ease of maintenance and low lifecycle cost of stainless steels have led to their use within the construction industry forover 60 years. Typical applications include fixings, fasteners and cladding. However,structural materials with exceptionally high durability and corrosion resistance arerequired for certain applications within many industries such as the offshore, nuclearand paper-making industries. In many cases, stainless steel can provide a cost-effec-tive and low maintenance structural solution to meet these demands. Austenitic

* Corresponding author. Tel.:+44-1344-623345; fax:+44-1344-622944.E-mail address:[email protected] (B.A. Burgan).

0143-974X/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved.PII: S0143 -974X(99)00055-3

52 B.A. Burgan et al. / Journal of Constructional Steel Research 54 (2000) 51–73

grades of stainless steel also exhibit exceptional ductility, good fire resistance andnon-magnetic properties, all of which may lead to structural applications in parti-cular circumstances.

Despite the fact that around 10% of stainless steel produced is used structurallyor architecturally, comparatively little research has been carried out on structuralbehaviour. This has led to a lack of suitable design guidance for structural engineers,the one notable exception being the American code for cold-formed sections [1]. In1988, a joint industry project was undertaken by the Steel Construction Institute todevelop design guidance for European offshore and onshore stainless steel structuralapplications. The design recommendations arising from this project were publishedby EURO INOX in 1994 as the ‘Design manual for structural stainless steel’ [2].

2. European design standard for structural stainless steel

Eurocode 3 deals with the design of steel structures. Part 1.1, containing generalrules and rules for buildings, was issued by CEN as ENV 1993-1-1 in 1992 [3].Around this time, work started on preparing a Eurocode covering the design of struc-tural stainless steel and this was later designated ENV 1993-1-4 (Part 1.4 of Eurocode3) [4]. The ‘Design manual for structural stainless steel’ was used as a starting pointfor ENV 1993-1-4, with modifications and additions made to reflect the results ofongoing research and the new European material standard for stainless steel, EN10088 [5]. It was published by CEN in 1996 and gives supplementary provisionsfor the design of buildings and civil engineering works which extend the applicationof ENV 1993-1-1 to austenitic and duplex stainless steels.

Fig. 1. Reduction factor,c, versus generalised slendernessl̄ for CHS columns — test results and ENV1993-1-4 design. curve

53B.A. Burgan et al. / Journal of Constructional Steel Research 54 (2000) 51–73

Tab

le1

Geo

met

rican

dm

ater

ial

prop

ertie

sof

the

CH

Sco

lum

nsp

ecim

ens

Spe

cim

enre

fere

nce

nam

e14

0×4

-SC

140×

4-C

114

×4-C

214

0×4-

C3

140×

3-S

C14

0×2-

SC

140×

2-C

114

0×2-

C2

140×

2-C

3

Ste

elgr

ade

toE

N10

088

1.45

411.

4541

1.45

411.

4541

1.44

351.

4435

1.44

351.

4435

1.44

35C

olum

nle

ngth

,L(m

m)

499

2251

3350

4450

498

499

2250

3350

4449

End

cond

ition

s(p

inne

d/fix

ed)

FP

PP

FF

PP

PD

iam

eter

,d(m

m)

138.

614

013

9.1

140.

113

9.3

139.

413

9.8

139.

813

9.9

Thi

ckne

ss,t

(mm

)3.

983.

993.

993.

982.

871.

971.

951.

951.

97Y

ield

stre

ngth

,f y(N

/mm

2)

294

293

293

294

352

318

319

319

318

Ulti

mat

ete

nsile

stre

ngth

,f u57

657

657

657

657

759

859

859

859

8(N

/mm

2)

Mod

ulus

ofel

astic

ity,E

193

195

195

193

190

201

197

197.

520

1(k

N/m

m2)

Mea

sure

dfa

ilure

load

,Nte

st

665

437

330

236

468

278

202

156

122

(kN

)


Tab

le2

Sec

tion

clas

sific

atio

nan

dpr

edic

ted

buck

ling

resi

stan

ceof

the

CH

Sco

lum

nsp

ecim

ens

Spe

cim

enre

fere

nce

nam

e14

0×4

-SC

140×

4-C

114

×4-C

214

0×4-

C3

140×

3-S

C14

0×2-

SC

140×

2-C

114

0×2-

C2

140×

2-C

3

(d/t)

/e2

47.4

47.1

146

.81

47.9

280

.35

100.

0410

3.74

103.

4810

0.4

Sec

tion

clas

s1

11

13

44

44

l̄0.

065

0.57

70.

865

1.14

80.

071

0.06

50.

591

0.87

91.

155

f0.

420

0.71

00.

988

1.34

30.

422

0.42

00.

722

1.00

41.

352

c1.

000

0.89

00.

682

0.49

11.

000

1.00

00.

881

0.67

20.

487

Des

ign

buck

ling

resi

stan

ce,

494.

8744

4.6

338.

6324

5.49

433.

0027

0.47

237.

2618

0.98

132.

12N

b.R

d(k

N)

Nte

st/N

b.R

d1.

344

0.98

30.

975

0.96

11.

081

1.02

80.

851

0.86

20.

923


Table 3Geometric and material properties of the I-section column specimens — minor axis tests, grade 1.4301

Specimen reference I-160×80 I-160×80 I-160×80 I-160×160 I-160×160 I-160×160name(minor axis tests) C1 C2 C3 C1 C2 C3

Specimen length,L 650 1248 2046 1248 2049 3347(mm)Web yield strength, 300 300 300 300 300 300fyw (N/mm2)Web ultimate 624 624 624 624 624 624tensile strength,fuw

(N/mm2)Flange yield 299 299 299 304 302 304strength,fyf

(N/mm2)Flange ultimate 609 609 609 614 612 614tensile strength,fuf

(N/mm2)Modulus of 200 200 200 200 199 200elasticity,E(kN/mm2)Section depth,H 158 161.7 161.4 158.3 157.7 158(mm)Section width,B 79.5 80.8 79.8 159.2 159.9 160.1(mm)Web thickness,tw 6 6 6 6 6 6(mm)Flange thickness,tf 9.8 9.8 9.8 9.8 9.9 9.8(mm)Weld throat 3 3 3 3 3 3thickness,a (mm)Measured failure 627 420 270 1120 745 582load, Ntest (kN)

The basic approach followed during the preparation of the ‘Design manual forstructural stainless steel’ was to adopt the rules for carbon steel, making modifi-cations as necessary where stainless steel test data indicated different behaviour. Inthe cases where no data were available, the rules for carbon steel were generallysuggested. Although this approach almost certainly led to ‘safe’ designs, the complexmaterial behaviour of stainless steel was not being taken into account and its desir-able properties not fully exploited. Since the material cost of stainless steel is high bynormal construction material standards, economic design is of paramount importance.

3. Ongoing development of design guidance

In January 1997, a major European project started which is concerned with thefurther development and refinement of structural design guidance. The project is


Table 4Geometric and material properties of the I-section column specimens — major axis tests, grade 1.4301

Specimen reference I-160×80 I-160×80 I-160×80 I-160×160 I-160×160 I-160×160name(major axis tests) C1 C2 C3 C1 C2 C3

Specimen length,L 2048 3343 5031 2025 3348 5145(mm)Web yield strength, 300 300 300 300 300 300fyw (N/mm2)Web ultimate 624 624 624 624 624 624tensile strength,fuw

(N/mm2)Flange yield 299 299 299 300 300 299strength,fyf

(N/mm2)Flange ultimate 609 609 609 610 610 610tensile strength,fuf

(N/mm2)Modulus of 200 200 200 198 198 199elasticity,E(kN/mm2)Section depth,H 157 157.6 158.5 158.3 158.4 158(mm)Section width,B 79.4 78.9 80.1 160 159.8 159.2(mm)Web thickness,tw 6 6 6 6 6 6(mm)Flange thickness,tf 9.8 9.8 9.8 9.9 9.9 9.9(mm)Weld throat 3 3 3 3 3 3thickness,a (mm)Measured failure 668 535 402 1130 860 725load, Ntest (kN)

being supported by the European Coal and Steel Community, the Nickel Develop-ment Institute and stainless steel producers in the UK, Sweden, Finland, France,Germany and Italy.

Both experimental and modern numerical methods (including non-linear finiteelement analyses) are being utilized to produce the data which is required to developa structurally efficient design method for stainless steel structures. The tests measureactual resistances which include strain hardening and residual stresses. Numericalmethods are used for describing the effects of different material stress–strain curves,for simulating the experimental tests and for analysing the effects of a wider rangeof parameters than those tested. Design rules are under development which will besuitable for updating ENV 1993-1-4 before it is converted to an EN (EuropeanStandard).

The scope of work covers static loading on members and connections, cyclic load-ing on welded connections and the behaviour of stainless steel members in fire.


Table 5Geometric and material properties of the I-section column specimens — major axis tests, grade 1.4462

Specimen reference name I-160×160 I-160×160 I-160×160(major axis tests) C1 C2 C3

Specimen length,L (mm) 2050 3348 5046Web yield strength,fyw (N/mm2) 523 523 523Web ultimate tensile strength,fuw 777 777 777(N/mm2)Flange yield strength,fyf (N/mm2) 522 522 522Flange ultimate tensile strength,fuf 755 755 755(N/mm2)Modulus of elasticity,E (kN/mm2) 201 201 201Section depth,H (mm) 162.7 161.4 160.4Section width,B (mm) 159.8 159.5 161Web thickness,tw (mm) 6.8 6.8 6.8Flange thickness,tf (mm) 10.6 10.6 10.6Weld throat thickness,a (mm) 3 3 3Measured failure load,Ntest (kN) 1930 1490 990

Table 6Section classification and predicted buckling resistance of the I-section column specimens — minor axistests, grade 1.4301

Specimen reference I-160×80 I-160×80 I-160×80 I-160×160 I-160×160 I-160×160name(minor axis tests) C1 C2 C3 C1 C2 C3

d/(twe) 25.1 25.8 25.7 25.1 25.0 25.1c/(tfe) 3.8 3.9 3.9 8.6 8.6 8.7Section class 1 2 2 1 1 1l̄ 0.4309 0.8156 1.3562 1.0170 0.6181 1.0105f 0.6806 1.0665 1.8590 0.64 0.8499 1.3185c 0.8282 0.5702 0.3195 0.8654 0.6977 0.4618Design buckling 592.2 415.9 230.9 549.4 840.3 555.6resistance,Nb.Rd

(kN)Ntest/Nb.Rd 1.06 1.01 1.17 1.08 0.89 1.05

The main objectives of the structural member tests are to provide test data on theeffects of:

O a non-linear stress–strain curve on the cross-section resistance and buckling resist-ance of different members,

O higher residual stresses arising from fabricating stainless steel,O a non-linear stress–strain curve on member deflection.

As part of this project, VTT Building Technology in Finland tested over 80 stainless


Table 7Section classification and predicted buckling resistance of the I-section column specimens — major axistests, grade 1.4301

Specimen reference I-160×80 I-160×80 I-160×80 I-160×160 I-160×160 I-160×160name(major axis tests) C1 C2 C3 C1 C2 C3

d/(twe) 24.9 25 25.2 25.2 25.2 25.1c/(tfe) 3.8 3.8 3.9 8.6 8.5 8.5Section class 1 1 1 1 1 1l̄ 0.3941 0.6414 0.9584 0.366 0.6047 0.928f 0.6514 0.8734 1.2475 0.63 0.8367 1.2072c 0.8547 0.682 0.4888 0.875 0.7068 0.5052Design buckling 609.1 484.8 351.6 1049.7 847.2 601.8resistance,Nb.Rd

(kN)Ntest/Nb.Rd 1.1 1.1 1.14 1.08 1.02 1.2

Table 8Section classification and predicted compression resistance of the I-section column specimens — majoraxis tests, grade 1.4462

Specimen reference name I-160×160 I-160×160 I-160×160(major axis tests) C1 C2 C3

d/(twe) 29.8 29.5 29.3c/(tfe) 10.4 10.4 10.5Section class 3 3 3l̄ 0.476 0.7837 1.188f 0.7182 1.0289 1.5806c 0.7962 0.5898 0.3812Design buckling resistance,Nb.Rd (kN) 1808.7 1335.1 867.8Ntest/Nb.Rd 1.07 1.12 1.14

steel members under compression, bending and combined compression and bending.A summary of the results of tests carried out on circular hollow sections (CHS) andwelded I-section members is given below. The test results are compared with thedesign curves proposed in ENV 1993-1-4.

Stub-column tests were carried out on all the cross-sections to determine theeffects of local buckling, strain-hardening (due to cold-forming) and residual stresses(due to welding). A stub-column test gives an average stress–strain curve for agiven member.

3.1. Compression members — circular hollow sections

Nine CHS specimens, three stub columns with fixed-end boundary conditions andsix columns of varying wall thickness with pin-ended boundary conditions were


Fig. 2. Reduction factor,c, versus generalised slendernessl̄ for I-section columns — test results andENV 1993-1-4 design curve (grade 1.4301).

tested. A summary of the geometric and material properties of the specimens is givenin Table 1. The specimens were manufactured by roll-forming stainless steel stripinto tubes and seam welding along the length of the tubes. Four of the specimenswere grade 1.4541 (321) and the remaining five were grade 1.4435 (316L).

Table 2 shows the section classification of all the tested specimens calculated inaccordance with ENV 1993-1-4 using the measured properties. The 2-mm thick sec-tions are Class 4 and therefore are not covered by the standard (slender CHS beingbeyond the scope of ENV 1993-1-4). Also in this table, the test results (characterisedby the maximum applied load in the test) are compared with the resistances predictedfrom ENV 1993-1-4. The bold type in the table highlights the specimens for which

Fig. 3. Reduction factor,c, versus generalised slendernessl̄ for I-section columns — test results andENV 1993-1-4 design curve (grade 1.4462).


Tab

le9

Geo

met

rican

dm

ater

ial

prop

ertie

sof

the

CH

Sbe

amsp

ecim

ens

103

153

203

219

114.

316

8.3

219.

121

9.1

140

140

140

Spe

cim

enre

fere

nce

nam

e×1

.5×1

.5×1

.5×2

.0×3

.05

×3.4

×3.0

×3.7

6×4

×3×2

Ste

elgr

ade

toE

N10

088

1.43

011.

4301

1.43

011.

4301

1.44

621.

4462

1.44

621.

4462

1.45

411.

4435

1.44

35D

iam

eter

,d(m

m)

103

153

203

219

114.

316

8.3

219.

121

9.1

139.

613

914

0.2

Thi

ckne

ss,t

(mm

)1.

31.

31.

31.

82.

73.

73

3.76

42.

872.

04Y

ield

stre

ngth

,f y(N

/mm

2)

461

456

370

332

643

602

598

560

292

352

313

Ulti

mat

ete

nsile

stre

ngth

,f u(N

/mm

2)

778

801

739

621

836

811

824

782

573

577

602

Mod

ulus

ofel

astic

ity,E

(kN

/mm

2)

200

200

200

200

200

200

200

200

198

190

195

L1=7

50m

m,L

2=5

00m

mL

1=7

65m

m,

L2=5

00m

m

Mea

sure

dfa

ilure

load

,F(k

N)

17.4

35.7

47.1

73.7

58.6

162

167

272

6851

.430

.3


Tab

le10

Sec

tion

clas

sific

atio

nan

dpr

edic

ted

mom

ent

resi

stan

ceof

the

CH

Sbe

amsp

ecim

ens

103

153

203

219

114.

316

8.3

219.

121

9.1

140

140

140

Spe

cim

enre

fere

nce

nam

e×1

.5×1

.5×1

.5×2

.0×3

.05

×3.4

×3.0

×3.7

6×4

×3×2

(d/t)

/e2

163.

223

9.8

258.

218

0.5

121.

612

2.4

196.

114

5.8

45.9

980

.18

98.5

8S

ectio

ncl

ass

44

44

44

44

13

4E

last

icm

omen

tre

sist

ance

ofgr

oss

4.81

10.6

215

.27

21.9

616

.59

46.3

865

.24

75.3

916

.40

14.4

19.

44se

ctio

n,M

el.R

d(W

elf y

)(k

Nm

)P

last

icm

omen

tre

sist

ance

ofgr

oss

6.18

13.6

119

.52

28.1

221

.57

60.2

183

.99

97.4

121

.43

18.6

812

.16

sect

ion,

Mp

l.R

d(W

plf y

)(k

Nm

)T

est

mom

ent

capa

city

,Mte

st(k

Nm

)6.

5313

.39

17.6

627

.64

21.9

860

.75

62.6

310

226

.01

19.6

611

.59

Mte

st/M

el.R

d1.

357

1.26

01.

157

1.25

81.

325

1.31

00.

965

1.35

31.

586

1.36

51.

228

Mte

st/M

pl.R

d1.

055

0.98

40.

905

0.98

31.

019

1.00

90.

746

1.04

71.

214

1.05

30.

953

Sec

tion

clas

sific

atio

nba

sed

onte

st#

23

33

#2

#2

4#

2#

2#

23


the standard is not applicable. It can be seen that overall the standard predicts theflexural buckling resistance very accurately. However, the following observationscan be made:

O The design standard underestimates the resistance of the Class 1 stub columnsection by some 34% as no benefit was taken of the strain hardening of thematerial.

O The design standard consistently over-estimates the column resistance by a verysmall margin (,4%).

The results are summarised in Fig. 1 which plots the critical buckling reductionfactor, c, as a function of the generalised slendernessl̄. The figure also displaysresults from earlier tests by Rasmussen and Hancock [6] on seam welded CHS mem-bers in grade 1.4306 (304L). The figure shows that the recommended buckling curve(a=0.49, l̄0=0.40) represents good agreement with the test results.

Table 11Geometric and material properties of the I-section beam specimens — 160×80 and 160×160, grade 1.4301

Specimen reference I-160×80- I-160×80- I-160×80- I-160×160- I-160×160- I-160×160-name B0 B1 B2 B0 B1 B2

Specimen length,L 1025 1024 2522 1025 2520 5018(mm)

L1 266 266 266 266 266 266

L2 493 492 1990 493 1988 4486Web yield strength,fyw 300 300 300 300 300 300(N/mm2)Web ultimate tensile 624 624 624 624 624 624strength,fuw (N/mm2)Flange yield strength, 299 299 299 302 302 300fyf (N/mm2)Flange ultimate tensile 609 609 609 612 612 610strength,fuf (N/mm2)Modulus of elasticity, 200 200 200 199 199 198E (kN/mm2)Section depth,H (mm) 161 158.7 158.2 158.8 158 158.5Section width,B (mm) 80.3 80.6 80.6 159 159.4 160Web thickness,tw 6 6 6 6 6 6(mm)Flange thickness,tf 9.8 9.8 9.8 9.9 9.9 9.9(mm)Weld throat thickness, 3 3 3 3 3 3a (mm)Specimen failure load, 409 366 248 687 578 396F (kN)


Table 12Geometric and material properties of the I-section beam specimens — 160×160, grade 1.4462 and320×160, grade 1.4301


Steel grade to EN 1.4462 1.4462 1.4462 1.4301 1.4301 1.430110088Specimen length,L 1027 2528 5025 2025 2526 5028(mm)

L1 266 266 266 517 517 517

L2 495 1996 4493 991 1492 3994Web yield strength,fyw 523 523 523 300 300 300(N/mm2)Web ultimate tensile 777 777 777 624 624 624strength,fuw (N/mm2)Flange yield strength, 522 522 522 304 304 304fyf (N/mm2)Flange ultimate tensile 755 755 755 614 614 614strength,fuf (N/mm2)Modulus of elasticity, 201 201 201 200 200 200E (kN/mm2)Section depth,H (mm) 159.2 158.7 160.2 319.6 318.9 319.9Section width,B (mm) 161.6 161.2 160.2 160.6 160.5 159.6Web thickness,tw 6.8 6.8 6.8 6 6 6(mm)Flange thickness,tf 10.6 10.6 10.6 9.8 9.8 9.8(mm)Weld throat thickness, 3 3 3 3 3 3a (mm)Specimen failure load, 1225 955 715 835 705 444F (kN)

3.2. Compression members — welded I sections

Twelve grade 1.4301 (304) column tests with three different heights were perfor-med for two I sections. The flexural buckling tests were carried out about both themajor and minor axes. A further three tests using one cross-section and three columnheights were carried out on specimens fabricated from grade 1.4462 (duplex 2205)stainless steel. The tests were designed with some specimens failing about their majoraxis and others about their minor axis. A summary of the geometric and materialproperties of the specimens is given in Tables 3–5. The specimens were fabricatedby continuous submerged arc welding.

Tables 6–8 show the section classification of all the tested specimens calculatedin accordance with ENV 1993-1-4, using the measured properties. This shows thatten of the grade 1.4301 specimens were Class 1 and the remaining two were Class


Table 13Section classification and predicted moment resistance of the I-section beam specimens — 160×80 and160×160, grade 1.4301


d/(twe) 25.6 25.2 25.1 25.2 25.1 25.3c/(tfe) 3.9 3.9 3.9 8.5 8.5 8.6Section class 1 1 1 1 1 1Moment resistance of 44.6 43.9 43.7 79.5 79.2 79.3the cross-section,Mc.Rd

(kNm)Elastic critical moment, 1056.9 1057.0 77.6 8012.6 520.6 123.5Mcr (kNm)l̄LT 0.205 0.204 0.750 0.100 0.390 0.801fLT 0.52 0.52 0.99 0.47 0.65 1.05cLT 1.00 1.00 0.61 1.00 1.00 0.58Buckling resistance 44.6 43.9 26.7 79.5 79.2 45.9moment,Mb.Rd (kNm)Test moment resistance, 54.4 48.7 33.0 91.4 76.9 52.7Mtest (kNm)Mtest/Mb.Rd 1.22 1.11 1.24 1.15 0.97 1.15

2. The grade 1.4462 specimens were all Class 3. The test results (characterised bythe maximum applied load in the test) are also compared with the resistances pre-dicted from ENV 1993-1-4 in these tables. It can be seen that the standard predictsthe flexural buckling resistance very accurately.

The results for grade 1.4301 (304) are summarised in Fig. 2 which plots the criticalbuckling reduction factor,c, as a function of the generalised slendernessl̄. Thefigure also displays results from earlier tests on 3CR12 steel carried out by van denBerg et al. [7] and results from tests on grade 1.4404 (316L) carried out by the SteelConstruction Institute [8]. The figure shows that the selected buckling curve (a=0.76,l̄0=0.20) represents good agreement with the test results.

The results for grade 1.4462 (duplex 2205) are summarised in Fig. 3, which alsoplots the critical buckling reduction factor,c, as a function of the generalised slender-nessl̄. The figure shows that the selected buckling curve (a=0.76,l̄0=0.20) is about10% conservative. This may be attributed to the lower residual stresses in duplexstainless steel compared to those in austenitic stainless steel.

3.3. Flexural members — circular hollow sections

A total of 11 four-point bending tests were carried out on stainless steel CHS ofvarying cross-sectional slenderness and material grade in order to determine theircross-sectional behaviour and moment resistance. The specimens were manufacturedby roll-forming stainless steel strip into tubes and seam welding along the length of


Table 14Section classification and predicted moment resistance of the I-section beam specimens — 160×160, grade1.4462 and 320×160, grade 1.4301


Steel grade to EN 1.4462 1.4462 1.4462 1.4301 1.4301 1.430110088d/(twe) 29.0 28.9 29.3 56.3 56.1 56.3c/(tfe) 10.5 10.5 10.4 8.7 8.7 8.6Section class 3 3 3 2 2 2Moment resistance 134.0 133.2 134.0 188.7 188.1 188.0of the cross-section,Mc.Rd

(kNm)Elastic critical 9011.1 581.8 138.6 4231.4 1867.6 269.7moment,Mcr

(kNm)l̄LT 0.122 0.478 0.983 0.211 0.317 0.835fLT 0.48 0.72 1.28 0.53 0.59 1.09cLT 1.00 0.79 0.48 1.00 1.00 0.56Buckling resistance 134.0 105.8 63.7 188.7 188.1 105.0moment,Mb.Rd

(kNm)Test moment 162.9 127.0 95.1 215.8 182.2 114.8resistance,Mtest

(kNm)Mtest/Mb.Rd 1.22 1.20 1.49 1.14 0.97 1.09

the tubes. A summary of the geometric and material properties of the specimens isgiven in Table 9. Three tests were carried out by VTT and the remaining eight werecommissioned by SCI at Imperial College.

Table 10 shows the section classification of all the tested specimens calculated inaccordance with ENV 1993-1-4, using the measured properties. This shows that allbut two of the specimens are Class 4 and are therefore predicted to fail by localbuckling before reaching the elastic moment of the gross section. The test results(characterised by the maximum moment reached in the tests) are compared with theresistances predicted from ENV 1993-1-4 in the table, assuming that the section wasfully effective in all cases. It can be seen that all but one of the specimens with(d/t)/e2,163 did in fact achieve a resistance in excess of the theoretical plasticmoment. The one exception ((d/t)/e2=98.6) warrants further investigation.

Only one specimen with (d/t)/e2=196.1 failed to reach the elastic moment resist-ance of the gross section by a margin of 3.5%, although two samples with higher(d/t)/e2 values (239.8 and 258.2) had resistances which exceeded the elastic moment


resistance by 26% and 16%. The results therefore suggest that the limit on (d/t)/e2

between Class 3 and 4 can be increased substantially for circular hollow sectionsacting in bending, compared to the present limit in the standard of 90.

3.4. Flexural members — welded I sections

The cross-sectional behaviour of the I sections in bending was studied by bendingtests on short beams. In addition, lateral–torsional buckling tests with two differentspans were performed. Nine of the beams were grade 1.4301 (304) and three were1.4462 (duplex 2205). A summary of the geometric and material properties of thespecimens is given in Table 11 and Table 12. The specimens were fabricated bycontinuous submerged arc welding.

Tables 13 and 14 show the section classification of all the tested specimens calcu-lated in accordance with ENV 1993-1-4, using the measured properties. The deepestgrade 1.4301 (304) sections were found to be just outside the standard limit for Class1 based on the web classification and the 1.4462 (duplex 2205) sections were allClass 3 based on the flange classification. The test results (characterised by the buck-ling reduction factor) are compared with the design curve from ENV 1993-1-4 inthe tables and show that the design standard is conservative. The elastic criticalbuckling moment,Mcr was calculated in accordance with Annex F of ENV 1993-1-1.

The results for grade 1.4301 (304) are summarised in Fig. 4 which plots the lateraltorsional buckling factorcLT as a function of the generalised slenderness for lateraltorsional bucklingl̄LT. The figure also displays results from earlier tests by van Wyket al. [9] and the Japanese Institution of Architecture [10]. The figure shows that thedesign curve in the standard (aLT=0.76) is conservative. The carbon steel bucklingcurve in ENV 1993-1-1 (aLT=0.49) is also shown in the figure and it can be seen

Fig. 4. Reduction factor,cLT, versus generalised slendernessl̄LT for I-section beams — test results andENV 1993-1-1 and ENV 1993-1-4 design curves (grade 1.4301).


to be a closer fit to the data than the more conservative curve currently adopted inENV 1993-1-4.

In a similar way, the results for grade 1.4462 are summarised in Fig. 5. Againthere appears to be a closer fit to the carbon steel buckling curve.

3.5. Members subject to combined loading — circular hollow sections

A total of eight pin-ended specimens of varying wall thickness were tested withan axial load applied eccentrically through the centre of wall thickness. The speci-mens were manufactured by roll-forming stainless steel strip into tube and seamwelding along the length of the tube. Four specimens were grade 1.4541 (321) andfour were grade 1.4435 (316L). The specimen dimensions were selected so thatfailure would not occur by local buckling and the measured properties are presentedin Table 15.

Local buckling occurred at failure in the two shorter specimens of these Class 4members. The test results (characterised by the maximum applied load in the test)are compared with the resistances predicted from ENV 1993-1-4 in Table 16. Thebold type in the table highlights the specimens for which the standard is not appli-cable. It can be seen that the standard is conservative in all cases, including the twospecimens which buckled locally. (For the Class 4 sections, the elastic section modu-lus was used to calculate the moment resistance.) It can also be seen that the extentto which the standard predictions are conservative decreases as overall bucklingbecomes more dominant (i.e. as the specimen length increases).

Fig. 6 shows the interaction curve between flexural buckling and moment resist-ance predicted in ENV 1993-1-4. The test points plotted on the curve are calculated

Fig. 5. Reduction factor,cLT, versus generalised slendernessl̄LT for I-section beams — test results andENV 1993-1-4 and ENV 1993-1-1 design curves (grade 1.4462).


Tab

le15

Geo

met

rican

dm

ater

ial

prop

ertie

sof

the

CH

Sbe

am–c

olum

nsp

ecim

ens

Sec

tion

140×4

-EC

014

0×4-

EC

114

0×4-

EC

214

0×4-

EC

314

0×2-

EC

014

0×2-

EC

114

0×2-

EC

214

0×2-

EC

3

Ste

elgr

ade

toE

N10

088

1.45

411.

4541

1.45

411.

4541

1.44

351.

4435

1.44

351.

4435

Dia

met

er,d

(mm

)13

913

9.2

140.

114

0.1

139.

913

9.6

139.

813

9.8

Thi

ckne

ss,t

(mm

)3.

983.

983.

983.

991.

971.

951.

951.

95N

omin

alyi

eld

stre

ngth

,f y29

4.5

297.

529

7.5

293.

531

8.5

320

320

316

(N/m

m2)

Ulti

mat

ete

nsile

stre

ngth

,f u57

657

357

357

259

8.5

599

599

597.

5(N

/mm

2)

Mod

ulus

ofel

astic

ityE

193

194

194

196

201

195

195

199

(kN

/mm

2)

Col

umn

leng

th,L

(mm

)55

022

5033

5144

5155

022

5133

5144

51T

est

failu

relo

ad,N

test(k

N)

297

202

155

121

122

8973

58


Tab

le16

Sec

tion

clas

sific

atio

nan

dpr

edic

ted

buck

ling

resi

stan

ceof

the

CH

Sbe

am–c

olum

nsp

ecim

ens

Spe

cim

enre

fere

nce

nam

e14

0×4

-EC

014

0×4-

EC

114

0×4-

EC

214

0×4-

EC

314

0×2-

EC

014

0×2-

EC

114

0×2-

EC

214

0×2-

EC

3

Ste

elgr

ade

toE

N10

088

1.45

411.

4541

1.45

411.

4541

1.44

351.

4435

1.44

351.

4435

(d/t)

/e2

47.6

247

.93

48.2

446

.99

100.

5610

4.98

105.

1310

1.73

Sec

tion

clas

s1

11

14

44

4M

c.R

da21

.321

.621

.921

.69.

29.

29.

29.

1l̄

0.14

30.

586

0.86

81.

139

0.14

30.

596

0.88

61.

158

f0.

447

0.71

80.

991

1.32

90.

447

0.72

61.

012

1.35

7c

1.00

00.

884

0.68

00.

496

1.00

00.

877

0.66

60.

485

Nb

.Rd

(kN

)49

7.18

444.

6434

4.53

248.

4627

1.88

236.

7318

0.09

129.

37B

uckl

ing

resi

stan

cein

the

195

161

133

114

8571

6052

pres

ence

ofa

mom

ent,

Nb

.M.R

d(k

N)

Axi

allo

adra

tio,N

test/N

b.M

.Rd

1.52

1.26

1.16

1.06

1.43

1.26

1.23

1.11

aF

orC

lass

4se

ctio

ns,

the

elas

ticm

odul

usw

asad

opte

din

the

calc

ulat

ions

;th

isis

not

inac

cord

ance

with

the

stan

dard

.


Fig. 6. CHS beam–column specimens — test results and ENV 1993-1-4 interaction curve.

on the basis of the measured axial resistance and predicted plastic moment resistance.In all cases the test points show that the standard is conservative.

3.6. Members subject to combined loading — welded I sections

A total of eight eccentric compression tests were carried out on two different I-section members of varying lengths. Bending about the major axis only was studied.The load was applied to the centreline of the flange. The specimens were fabricatedby continuous submerged arc welding and were all from grade 1.4301 (304) material.The specimen dimensions were selected so that failure would not occur by localbuckling and the measured properties are presented in Table 17.

Table 18 shows the section classification of all the tested specimens calculatedin accordance with ENV 1993-1-4, using the measured properties. The test results(characterised by the maximum applied load in the test) are compared with the resist-ances predicted from ENV 1993-1-4 in the table. It can be seen that the standard isconservative in all cases. As with the CHS beam–column tests, the extent to whichthe standard predictions are conservative tends to decrease as overall bucklingbecomes more dominant (i.e. as the specimen length increases).

4. Conclusions

The results of a series of member tests forming part of an ongoing ECSC researchproject concerned with further development and refinement of structural design guid-ance are presented. Comparisons of this experimental data with the design provisionsin ENV 1993-1-4 are made. In general, the guidance in ENV 1993-1-4 is conserva-


Tab

le17

Geo

met

rican

dm

ater

ial

prop

ertie

sof

the

I-se

ctio

nbe

am–c

olum

nsp

ecim

ens,

grad

e1.

4301

Spe

cim

enre

fere

nce

nam

e(f

ailu

reI-

160

×80-

I-16

0×80

-I-

160×

80-

I-16

0×80

-I-

160×

160-

I-16

0×16

0-I-

160×

160-

I-16

0×16

0-ab

out

maj

orax

is)

EC

0E

C1

EC

2E

C3

EC

0E

C1

EC

2E

C3

Spe

cim

enle

ngth

,L(m

m)

500

2045

3339

5041

502

2048

3345

5043

Web

yiel

dst

reng

th,f y

w(N

/mm

2)

300

300

300

300

300

300

300

300

Web

ultim

ate

tens

ilest

reng

th,f uw

624

624

624

624

624

624

624

624

(N/m

m2)

Fla

nge

yiel

dst

reng

th,f y

f(N

/mm

2)

299

299

299

299

300

299

299

300

Fla

nge

ultim

ate

tens

ilest

reng

th,

f uf

609

609

609

609

610

609

609

610

(N/m

m2)

Mod

ulus

ofel

astic

ityE

(kN

/mm

2)

200

200

200

200

198

200

200

198

Sec

tion

dept

h,H(m

m)

158.

316

0.3

158.

915

8.7

162.

315

915

8.5

159.

5S

ectio

nw

idth

,B(m

m)

82.7

79.4

79.1

80.9

159.

816

0.8

160.

116

0.4

Web

thic

knes

s,tw

(mm

)6

66

66

66

6F

lang

eth

ickn

ess,t

f(m

m)

9.8

9.8

9.8

9.8

9.9

9.8

9.8

9.9

Wel

dth

roat

thic

knes

s,a(m

m)

33

33

33

33

Mea

sure

dfa

ilure

load

,Nte

st(k

N)

505

338

270

222

705

540

454

356


Tab

le18

Sec

tion

clas

sific

atio

nan

dpr

edic

ted

mom

ent

resi

stan

ceof

the

I-se

ctio

nbe

am–c

olum

nsp

ecim

ens,

grad

e1.

4301

Spe

cim

enre

fere

nce

num

ber

I-16

0×8

0-I-

160×

80-

I-16

0×80

-I-

160×

80-

I-16

0×16

0-I-

160×

160-

I-16

0×16

0-I-

160×

160-

EC

0E

C1

EC

2E

C3

EC

0E

C1

EC

2E

C3

(d/t

w)(

13a

21)

/e30

1.5

306.

130

2.9

302.

431

1.9

303.

130

2.0

305.

4c/

(tfe

)4

3.8

3.8

3.9

8.5

8.6

8.6

8.6

Sec

tion

clas

s1

11

12

11

1M

c.R

d44

.643

.943

.344

.081

.579

78.4

80l̄

0.09

50.

386

0.63

50.

958

0.08

90.

366

0.60

00.

904

f0.

465

0.64

50.

867

1.24

70.

462

0.63

00.

832

1.17

7c

10.

861

0.68

60.

489

1.00

00.

875

0.71

00.

518

Nb

.Rd

(kN

)73

4.3

618.

449

0.0

354.

212

05.7

1044

.184

3.9

624.

1B

uckl

ing

resi

stan

cein

the

pres

ence

329.

126

8.1

220.

818

6.7

560.

446

9.1

391.

233

3.2

ofa

mom

ent,N

b.M

.Rd

(kN

)A

xial

load

ratio

,Nte

st/N

b.M

.Rd

1.53

1.26

1.22

1.19

1.26

1.15

1.16

1.07


tive. The tests on CHS beams indicate that the limiting diameter-to-thickness ratiosfor section classification can be considerably increased. For welded I-section beams,the ENV 1993-1-4 lateral torsional buckling curve appears very conservative andthe less conservative curve adopted in ENV 1993-1-1 for carbon steel appears togive a better fit to the data.

Acknowledgements

The following organisations sponsored the projects described in this paper: AcciaiSpeciali Terni SpA, Avesta Sheffield AB Research Foundation, Avesta Sheffield Ltd,Department of the Environment, Transport and the Regions, European Coal and SteelCommunity, Outokumpu Polarit Oy, Studiengesellschaft Stahlanwendung eV, TheNickel Development Institute and Ugine S.A. Their support is gratefully acknowl-edged.

References

[1] ANSI/ASCE-8-90. Specification for the design of cold-formed stainless steel structural members.American Society of Engineers, USA, 1991.

[2] EURO INOX. Design manual for structural stainless steel, 1994.[3] ENV 1993-1-1. Eurocode 3 Design of steel structures: Part 1.1, General rules and rules for buildings.

CEN, 1992.[4] ENV 1993-1-4. Eurocode 3 Design of steel structures: Part 1.4, General rules and supplementary

rules for stainless steels. CEN, 1996.[5] EN 10088. Stainless steels. CEN, 1995.[6] Rasmussen KJR, Hancock GJ. Stainless steel tubular columns — test and design. Tenth International

Speciality Conference on Cold Formed Steel Structures, St Louis, MO, USA, 23–24 October 1990.[7] van den Berg GJ, van der Merwe P, Bredenkamp PJ. The strength of Type 3CR12 corrosion resisting

steel built-up I section column and beams. Report MD-51, Faculty of Engineering, Rand AfrikaansUniversity, March 1990.

[8] The Steel Construction Institute. Technical report 29: Tests on stainless steel beams and columns.SCI report no. RT/231, July 1991.

[9] van Wyk ML, van den Berg GJ, van der Merwe P. The lateral torsional buckling strength of doublysymmetric stainless steel beams. Report MD-58, Faculty of Engineering, Rand Afrikaans University,May 1990.

[10] Japanese Institution of Architecture. Strength and deformation of H-shaped stainless steel beams.Journal of the Kanto Branch, 1988 (in Japanese).

Structural Design of Stainless Steel Members

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