Användning av höghållfasta stål i byggsektorn

Användning av höghållfasta stål i byggsektorn 2015.02.06. Milan Veljkovic 1

Höghållfasta stål Allmänt Dimensionering av konstruktioner av HSS Tillämpningar Användning av HHS i balkar med långa spännvidder Användning av HHS i bärande konstruktioner för förnybarenergi Hybrida balkar 2

Eurocode SS-EN1993-1-12 (for now) 3

EN structural steel grades Yield Strength MPa Non standard grade (900) 890 960 1100 235 275 Commo n grade in US and Sweden 355 420 Highest grade in Eurocode 3-1-1 460 500 550 620 (700) 690 420 460 500 As rolled Normalised Thermomechanicall yrolled Both exist Quenched tempered 4

Exempel: Mild steel - S275 Mild steel - S355 HS Steel - S700 Material properties Nominal stress (MPa) 800 700 600 500 400 300 200 100 S275 S355 S700 0 0 5 10 15 20 25 30 35 40 Nominal strain (%)

Requirements for ductility (based on behaviour of a structure) 6

Ductility requirements EN1993-1-1 ( S460) EN1993-1-12 ( above S460 to S690/S700) 7

Cross-section classification and type of analysis Cross-section class Global analysis Crosssection/member verifications Class 1 Class 2 Plastic Elastic Elastic Elastic Elastic Plastic Plastic Elastic Plastic Elastic S700 Class 3 Class 4 Elastic Elastic 8

Rotation capacity Eurocode limit for class1 9

EN1993-1-1 ( S460) Net cross-section in tension to fracture EN1993-1-12 ( above S460 to S690/S700) 10

Flexural buckling

Flexural buckling l/i =100 80 Bernt Johansson 60 N 2 π EI cr 2 l N N y cr 40 Yield strength MPa Relative cost of steel as function of yield strength normalized for 235 MPa Yield strength MPa Relative cost of column as function of yield strength normalized for 235 MPa for different slenderness ratios L/i. 12

Flexural buckling l/i =100 80 Bernt Johansson 60 N 2 π EI cr 2 l N N y cr 40 Yield strength MPa Yield strength MPa Relative cost of steel as function of yield strength normalized for 235 MPa Relative cost of column as function of yield strength normalized for 235 MPa for different slenderness ratios L/i. SHS 100.10 l=2,0m i=35,5mm l/i=56 (l=2,84m l/i=80) 0, 61 N =2134 kn N = 682 kn S235 N = 586 kn cr b,rd b,rd 0, 74 N =2134 kn N = 960 kn S355 N = 733 kn cr b,rd b,rd 0, 84 N =2134 kn N =1249 kn S460 N = 870 kn cr b,rd b,rd 13

Ilkka Sorsa, 2014

Economy Web S355 Flanges S355 Costs 1.0 S355 S690-5% S355 S690-6% 15

Economy L=23m b=7m -8% -15% Top flange governed by L-T buckling before casting, (no advantage of S690) 16

- Design of hybrid girders - Bending resistance Section 1 &2 17

- Design of hybrid girders - Bending resistance Sweden, Finland Section 3 &4 18

Hybrid girder -numerical example- Web: mild steel S355: f y = 351 MPa; f u = 521 MPa; A = 27.8 %: f u /f y = 1.48 Flanges: high Strength Steel - S700: f y = 698 MPa; f u = 784 MPa; A = 17.5 %: f u /f y = 1.12 800 700 Nominal stress (MPa) 600 500 400 300 200 S700 S355 100 0 0 5 10 15 20 25 30 Nominal strain (% )

Geometry of the cross-section Cross-sections slenderness is bellow the limit for class 1: S355 ( = 0.81): Web: 72 = 58.3 S700 ( = 0.58): Flanges: 9 = 5.2 Two cases are considered: With continous lateral restraint With lateral restraint only at the mid-span c/t = 4.4 c/t = 37.3

Compact cross seciton behavior 1400 1200 1000 With continous lateral restraint Force (kn) 800 600 400 200 0 Continual lateral restrained Restrained at the mid-span Initial stiffness 0 500 1000 1500 Deflection (mm) With lateral restraint only at the mid-span

Rotation capacity of hybrid girder 2.0 1.8 With continous lateral restraint 2.0 1.8 With lateral restraint only at the mid-span Non Dimensional Moment (M/Mp) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 S700 S355 S700+S355 Non Dimensional Moment (M/Mp) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 S700 S355 S700+S355 0.0 0 100 200 300 400 Non Dimensional Curvature ( / p ) 0.0 0 10 20 30 40 Non Dimensional Curvature ( / p ) R = 219 hybrid girder R = 20

Hybrid girders - 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 f yfl <2 f yw for serviceability reasons, as shown in experimental verification 23

Fatigue Fatigue rules in EN1993-1-9 - endurance independent of the steel grade Improved fatigue endurance by: - post-weld treatment - improved detailing - improved welding procedures

Post weld treatment -joints suitable/non suitable for improvements-

Remove or reduce size of flow in a weld toe - Burr grinding Post-welding measures - changing of geometry - - - TIG dressing

Post-welding measures - introduction of compressive residual stresses- - Hammer peening, compressive residual stresses are induced by repeatedly hammering the weld toe region with a blunt-nosed chisel. Need peening

Post-welding measures - introduction of compressive residual stresses - High Frequency Impact Treatmant Limits: - Plate thickness max 15 mm - R=0.1 (Max R=0,5) - Max stress 0,8 fy

Redesign of details Fatigue strength 1,5 times larger with casted nodes Hybrid Design Concept Using High-Strength Cast Steel Inserts For Tubular Joints of Offshore Structures, C. M. Sonsino and R. Umbach, 1998 Chord S420MC Diagonals S355MC Chord S700MC Diagonals S700MC Chord S700MC Diagonals S355MC Ruukki Construction

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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 function. ATS Paris 2002-12-11 31

Obstacles and solutions Too high deformations -» precamber, composite action Fatigue resistance too low -» improved detailing, post weld treatment Local buckling -» Stiffening by cold formed folds Availability -» Increased use will increase production ATS Paris 2002-12-11 32

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High Strength Long Span Structures (2012-2015) Projekt som är 60% finansierad av EU. Tre fackverk bör provas i labbet: - Ett traditionell fackverk gjord av rör svetsade i knutpunkter. - Två nya fackverk gjorda av innovativa lösningar (polygonal tvärsnitt i överflänsen) och U-tvärsnitt i underflänsen (motivation från Friends Arena). 34

High Strength Steel in Long Span Structures 3D truss design High Strength Steel Cold formed chords Polygonal semi-closed compression chords U-shape tension chord Seamless CHS diagonals Fabrication and testing 7 modules 13.3 meters total length 4 modules tested for the strength of the U-chord joints 3 modules tested under 4 point bending for the behavior of the compression chords Research subjects Stiffness of the joints, buckling effective length Buckling od the semi-closed profile HSS welding 35

CN connection Brief characteristics Aesthetical and structural improvements Friction connection HSS hollow sections and plates Tests 4 strength tests ultimate strength and failure pattern 4 long term tests pretension relaxation with instrumented bolts Parameters Necessity of stiffener Tapering inclination 36

Möjliga tillämpningar i konstruktioner av HSS Stor spänvidder av fackverk: arenor, shoppingmall, industrianledningar, Stora höjder: torn för vindkraftverk mer än 100m höjd, mest konkursenkraftig lösning, 37

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Economics of Wind Power UK experience Element On-shore Cost as % of total Offshore Cost as % of total Turbine 33% 21% Blades 22% 15% Tower 20% 13% Foundation 9% 21% Grid connection 6% 21% Design & Management 10% 9% Total cost per MW 1.5-2 million 300-400 k 2.5 3.5 million 325-455 k 40

Market opportunities for wind towers Cost assumptions Steel towers are 15 to 25 % of installation costs If 80% towers are made of steel for the cost of 250 k /MW) 12,7 GW of new turbines in Europe (2012) 15 billion (total value of new installed eq. 1,2 mil / 1MW Tower costs 250 k /MW 3,2 billion GEWC-Europe 1,0-1.3 mil / MW Sweden 1,6 mil / MW 41

Onshore challenges Height and Foundation Matthias Schubert, former CTO at the REpower Systems: By raising the hub height from 93m to 143m, the company expects an increase in yield of up to a whopping 50% in low-wind locations. 3.2-MW turbine http://www.windpowerengineering.com/ Vattenfall, 40-50 % 42

The main project idea of the HISTWIN project 2006-2009 REPOWER 5M assembled in 2004, Germany New proposal Repower 5MW assembled 2004, Germany New proposal 43

Evolution of Tubular Steel Assembly Joint 2006-2009 2010-2013 44

Common connections in towers for wind turbines High fabrication costs (app. 4-7k /flange), long delivery time Relatively low fatigue resistance, approx. 50MPa, max 70MPa Main limitations (design, transport) Impairs whole structure efficiency 45

Möjliga tillämpningar i konstruktioner av HSS Stora höjder: rörtorn för vindkraftverk mer än 100m höjd, en ny lösning som delvis har utvecklats inom CHS och HISTWIN2 projekt. Huvud innovationer: Polygonaltvärsnitt Friktionsförband (och slip resistent bultar) istället av svetsad flänsring och bultar i drag. 46

Tubular tower: Alternative Bolted polygonal shell tower 47

Two Methods of Door Opening Stiffening Stiffening by varying the plate thickness Stiffening by the stiffener

Stresses at the maximum load 412.6 MPa -398.7 MPa 382.4 MPa -457.0 MPa 373.2 MPa -495.8 MPa Model without door opening Model of the door opening with varying the plate thickness Model of the door opening with the stiffener

σ Laboratory tests preparation 2 4 2 E 2 t π t π t crit 12 2 1 υ 6 1 υ r b b Critical stress for simply supported curved plates C.W. YOUNG

Material Cost Reduction for Stiffening of Door Opening 120% 100% 80% 100% Plate of different thicknesses 95% 92% 120% 100% 80% 100% Stiffener 93% 84% 60% 60% 40% 40% 20% 20% 0% S355 S500 S650 Yield stress f y (MPa) 0% S355 S500 S650 Yield stress f y (MPa)

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Pablo Castillo Meseguer Luleå 16/01/15 OC4 JACKET SUPPORT SUSCOS_M

Pablo Castillo Meseguer Luleå 16/01/15 OC4 JACKET SUPPORT ρs = 7850 kg/m3 Es = 2.1e11 N/m νs = 0.3 SUSCOS_M

Pablo Castillo Meseguer Luleå 16/01/15 Fatigue Analysis SUSCOS_M 1 9

Pablo Castillo Meseguer Luleå 16/01/15 Cast/Welded nodes Cast Steel node (EPFL) Cast KK-node Welded joint (EPFL) EPFL: École Polytechnique Fédérale de Lausanne Crack at weld toe (EPFL) Girth butt weld crack (EPFL) SUSCOS_M

Pablo Castillo Meseguer Luleå 16/01/15 Fatigue Analysis Optimised Support Structure Material saving using a support with cast nodes compared to normal tubular welding : 1-570,14/626,99 = 9,07%

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Summering Största utmaningarna för högpresterande stål i stora konstruktioner är fogning och stabilitet. Begränsningar inom Eurokoder gällande högpresterande stål, det saknas experimentella underlag för att förbättra regler. Mer arbete krävs för att överbrygga glappet mellan kunskaperna kring högpresterande stål och de konstruktionsregler som används. Det krävs större informations spridning till verkstäder om hur materialet ska behandlas. Samarbete mellan verkstäder, konstruktörer och forskning är nödvändiga för att använda konstruktionslösningar som är lämpliga för verkstäder. 59

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Engineering examples Composite bridge in Sweden with hybrid I- girders. Flanges S500 Web S355 61

Engineering examples -cost comparison- 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% 62