experiences of hss structures in scandinavia -hilong...

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Experiences of HSS structures in Scandinavia

-HILONG Workshop-

London, 30th June, 2015

Milan Veljkovic

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Outline

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

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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

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

Thermo-mechanically rolled steel for cold forming

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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

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Requirements for ductility

EN1993-1-1 ( S460)

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

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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

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Ductility

Rat

io o

f yie

ld st

reng

th to

tens

ile st

reng

th

Yield strength 0.2% [MPa]

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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

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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)

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Comparison S275 vs. S700 beam

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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

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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

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- Design of hybrid girders- Bending resistance

Section 1 &2

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Design of hybrid girders- Bending resistance

Section 3 &4Classification acc. to fyf

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Design of hybrid girdersServiceability requirements

Reversiblebehaviour

JCSR paper 2004

±0.92 fyf

ratio 1.67

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- Design of hybrid girders

- Bending resistance

Lateral torsional buckling the same as for homogeniousgirders

Flange induced buckling The web does not have anyeffect

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Flange induced buckling (validation of Basler 1961)

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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

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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

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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

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- 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

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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

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Composite bridge in Sweden with hybrid I-girders.

Flanges S500

Web S355

Engineering examples

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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

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Web Flanges

S355 S355

S355 S690

S355 S690

Costs

1.0

-5%

-6%

Engineering examples-cost comparison-

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“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

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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

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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

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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.