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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.