1

Experiences of HSS structures in Scandinavia

-HILONG Workshop-

London, 30th June, 2015

Milan Veljkovic

2

Outline

Material properties, steel grades, costs Design of Hybrid Beams in Pure Bending Engineering examples Conclusions (obstacles and solutions)

3

EN structural steel grades and costs*)

YieldStrength[MPa]

420 500460

1100

960890

690620

550500460

420355

275235

As rolledNormalised

Thermo-mechanicallyrolled

Quenched tempered

(700)

(900)

Both

exist

Common grade in US and Sweden

Highest grade in Eurocode3-1-1

Non standard grade

Highest grade in Eurocode3-1-12

*) Prof. B. Johansson, LTU, 2005

4

Eurocode SS-EN1993-1-12 (for now) to be in EN1993-1-1Hot-rolled structural steel

Thermo-mechanically rolled steel for cold forming

5

SSAB steels (examples)

S460 rolling direction S690 90o to rolling dir.

http://www.ssab.com/en/Products--Services/Service--Support/Technical-Tools-and-films/Steelfacts/Steelfacts/- Forming data- Stress-strain curves- Welding tests, details on welding consumables

6

Requirements for ductility

EN1993-1-1 ( S460)

• EN1993-1-12 ( above S460 to S690/S700)

7

Material properties

Exempels:– Mild steel - S275– Mild steel - S355– HS Steel - S700

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35

Nom

inal

str

ess (

MPa

) Nominal strain (% )

S275

S355

S700

Acc. to EN 10025, parts 2, 3, 4 and 6

Min

yie

ld st

reng

th

Ultimate strain

8

Ductility

Rat

io o

f yie

ld st

reng

th to

tens

ile st

reng

th

Yield strength 0.2% [MPa]

9

Material properties (FEA-explicit)

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25 30 35 40

Stre

ss (M

Pa)

Strain (%)

S275

S355

S700

Engineering stress-strain True stress-strain

10

Beam bending

Simple span beam L = 7.0 m

Different cross-sections are assumed to achieve the same beam resistance:

S275 S700

Load application (displ. control)

11

Comparison S275 vs. S700 beam

12

Hybrid girder S275/S700 vs. S355/S700

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000

Forc

e (k

N)

Deflection (mm)

S275S700flanges: S700; web: S275Initial stiffness

Ppl,Rd,S700 = 1022 kN

Ppl,Rd,S275 = 401 kN

Ppl,Rd,S700+S275 = 867 kN

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000Fo

rce

(kN

) Deflection (mm)

S355S700flanges: S700; web: S355Initial stiffness

Ppl,Rd,S700 = 1022 kN

Ppl,Rd,S355 = 512 kN

Ppl,Rd,S700+S355 = 895 kN

13

Cross-section classification and type of analysis

Cross-section class Global analysis

Cross-section/member

verifications

Class 1Plastic PlasticElastic PlasticElastic Elastic

Class 2 Elastic PlasticElastic Elastic

Class 3 – Class 4 Elastic Elastic

S700

14

- Design of hybrid girders- Bending resistance

Section 1 &2

15

Design of hybrid girders- Bending resistance

Section 3 &4Classification acc. to fyf

16

Design of hybrid girdersServiceability requirements

Reversiblebehaviour

JCSR paper 2004

±0.92 fyf

ratio 1.67

17

- Design of hybrid girders

- Bending resistance

Lateral torsional buckling the same as for homogeniousgirders

Flange induced buckling The web does not have anyeffect

18

Flange induced buckling (validation of Basler 1961)

19

Flange induced buckling, homogeneous vs. hybrid girders

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

Forc

e (k

N)

Deflection (mm)

flanges & web: S255

flanges & web: S460

flange: S460; web: S255

Elastic bending stiffnes

20

Flange induced buckling – verification with Hand calculation

0

1000

2000

3000

4000

5000

6000

0.000 0.002 0.004 0.006 0.008 0.010

Mom

ent (

kNm

)

Curvature (mrad)

flange & web: S460

flnge & web: S255

flange: S460; web: S255

Mpl,Rd,S460 = 4201 kNm

Mpl,Rd,S460+S255 = 3935 kN

Mpl,Rd,S255 = 2365 kN

21

Flange induced buckling – ductility assessment

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Non

Dim

ensi

onal

Mom

ent (

M/M

p)

Non Dimensional Curvature (/p)

flange & web: S460flnge & web: S255flange: S460; web: S255

22

- Design of hybrid girders

- Shear resistance, patch loading

Class 3&4 as it is

EC3-1-5 formulae with different yield strength

- Interaction V-M

Class 1&2 neglect Practice in USA and Sweden

23

Hybrid girder – example

- Partial yielding in the web will occur but the girder will still show a repeatable behaviour.

- If the yield strength of the flanges is not more than twice that of the web the yielding can be neglected in serviceability limit state.

- “Easy fabrication of hybrid girders is no problem; matching electrodes can be met up to S690.

- Hybrid girders are more economical;

Limit fyfl<2 fyw for serviceability reasons, as shown in experimental verification

24

Composite bridge in Sweden with hybrid I-girders.

Flanges S500

Web S355

Engineering examples

25

Composite bridge with 23 m simple span, width 7 m,*) .

With S355 as reference the alternative S460+S690 gives:

Cost for site welding -15 %Cost for painting -20 %Total cost -12%

Engineering examples-cost comparison-

*) Mittådalen bridgeSteel designer: Scandiaconsult(Ramböll today), Luleå

26

Web Flanges

S355 S355

S355 S690

S355 S690

Costs

1.0

-5%

-6%

Engineering examples-cost comparison-

27

“Fast Bridge 48”, patented, developed in last 1980 and beginning of 90-ies for the Swedish army*). Truss girders in 5 mm thick S1100. Span 48 m, designed for 65 t tank, deflection 0,65 m.

S1100 has the same weight/strength ratio as advanced Al-alloys

Engineering examples

*)Steel Designer: Kockums AB, Karlskronavarvet and KTH, Stockholm

28

Launching beam for erecting the bridge in S1100. Carries one man as cantilever and the bridge sections as simply supported beam. The bridge is erected in 1 h 15 min.

Cross section of launching beam. Note: the folds used to stiffen the web.

Engineering examples

29

Conclusions:Why High Strength Steel?

Reduced costs due to:–Less material (but more expensive)–Less welding (thinner plates)–Less painting (smaller area)–Lower transport costs

Reduced weight allows higher payload.Reduced environmental impact due to

less material for a given performance

30

Conclusions: Obstacles and possible solutions

•Too high deformations -» precamber, composite action, trusses,…

•Local buckling -» Stiffening by cold formed folds, innovative cross-sections.

•Availability -» Increased use will increase production and availability.

•Fatigue -» Post-weld treatments, improved detailing.