FRc01_Eurocode3

EUROCODE 3 & BS 7608 in FEMFAT WELD

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: overview • Assessment of weldings and parent material of steel structures • Assessment using nominal stress or hot-spot-stress • Classification of the load-time history using rainflow or reservoir counting method • Fatigue assessment using linear damage accumulation according Palmgren-Miner in conjunction with one or two slope SN-curves • Assessment of direct stress and shear stress • SN-Curves for particular classified details are given • Modifications of the basic SN-curves (sheet thickness influence; weld improvement; annealing) Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: used stresses in weld material Eurocode 3 BS 7608 •

Direct stresses lateral to the weld seam σw and shear stresses τw will be used

•

Chapter 3.3: The difference between the greatest and least vector sum of shear stresses in weld metal will be used; =σ⊥

σ1 =σ⊥ σ2 =σ|| τ1 =τ⊥ τ2 =τ||

= σw

τ|| =

2 2 1.) σ w = sign(σ ⊥ ) σ ⊥ /|| + τ ||

σ w = σ ⊥2 + τ ⊥2 1.) σ w = sign(σ ⊥ ) σ ⊥2 + σ ||2 − σ ⊥ ⋅ σ || + 3 ⋅τ 2 2.) σ w = σ ⊥

3.) τ w = τ ||

Klaus Hofwimmer, May 2005

2 2 2.) σ w = sign(τ || ) σ ⊥ /|| + τ ||

3.) σ w = σ ⊥ www.femfat.com

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Eurocode 3 and BS 7608: shear stresses in weld material Eurocode 3 BS 7608 •

Thin shell finite elements delivers only one pair of shear stress components (τxy =τyx=τ) that is not zero and cause distortion within the element plane. All other shear stresses are zero. z

τzy =0 y

τzx =0 τyz=0 x

τyx≠0

τxz=0 τxy ≠0

Thus using thin shell elements for FE-simulation (state of the art) τ⊥ can not be computed and τ|| =τxy=τ.

σ w = σ ⊥2 + τ ⊥2

σw =σ⊥

τ w = τ ||

τw =τ

Klaus Hofwimmer, May 2005

σ w = σ ⊥2 + τ ||2

σ w = σ ⊥2 + τ 2

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Eurocode 3 and BS 7608: used stresses in parent material Eurocode 3 • Max. principal stress in the parent material without local stress concentration effects due to weld geometry => hot spot stress

σ w = σ1

BS 7608 • Case 1: Direction of principal stress nearly constant

∆σ w = MAX (∆σ 1 , ∆σ 2 , ∆σ 3 ) • Case 2: Direction of principal stress rotates during a load cycle

The algebraic difference between the numerically greater peak principal stress and the numerically greater trough principal stress should be used

=> Standard equivalent stresses already implemented in FEMFAT can be used (max/min principal stress in FEMFAT BASIC, and max. principal stress and material characteristic shear stress respectively in FEMFAT MAX) Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: fatigue assessment Eurocode 3 • Fatigue assessment for stresses lateral to the weld seam σw=σ⊥

Dσ = ∑

ni ≤1 Ni

BS 7608 • Fatigue assessment for combined stress σw=σw(σ⊥,τ||)

D =∑

ni ≤1 Ni

• Fatigue assessment for shear • No particular Fatigue assessment for shear stresses parallel to the weld stresses parallel to the weld seam τw seam τw ni Dτ = ∑ ≤1 Ni • Fatigue assessment for combined loading

Dσ + Dτ ≤ 1 => will be done manually (postprocessor) Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: S-N curves for normal stresses Eurocode 3

BS 7608

Pü=97.7%

Pü=97.7%

Adjustable by the user

• Fatigue strength S0=Sr(N=107) • Change of slope from m to (m+2) at N=107 cycles Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: S-N curves for normal stresses S-N Curves of Eurocode 3, BS 7608 and FEMFAT

Log S

1000

160 112 80 56 40 C F W FF-NWU

140 100 71 50 36 D F2 S FF-NUE/End

125 90 63 45 B E G T

100

10 1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

log N Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: S-N curves for shear stresses Eurocode 3 Pü=97.7%

Only curve 80 will be used for welds; curve 100 is valid only for bolt joints

BS 7608

• No particular S-N curves for shear stresses are used

=> one curve in database for welds and parent material

Klaus Hofwimmer, May 2005

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Eurocode 3: tubular joints and modified S-N curves

Pü=97.7% Pü=97.7%

• Entrys in the weld database for tubular joints and modified S-N curves are necessary Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: modifications of the fatigue strength Eurocode 3

BS 7608

• 40% Reduction of the compressive part of the stress amplitude at parent material or annealed weldings

• 40% Reduction of the compressive part of the stress amplitude at parent material or annealed weldings

• Sheet thickness influence:

• Sheet thickness influence:

∆σ R , t

 25  = ∆σ R ⋅    t 

∆σ R ,t = ∆σ R Klaus Hofwimmer, May 2005

0.25

 16  = ∆σ R ⋅    t 

für t > 25mm

∆σ R ,t

für t ≤ 25mm

∆σ R ,t = ∆σ R

0.25

für t > 16mm

für t ≤ 16mm

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Eurocode 3 and BS 7608: thickness influence Sheet Thickness Influence (0-100mm) 2 1.8

Influence Factor σR/σR,t [-]

1.6 1.4 1.2 1 0.8 thickness influence FEMFAT

0.6

thickness influence Eurocode 3

0.4

thickness influence BS 7608

0.2 0 0

10

Klaus Hofwimmer, May 2005

20

30

40 50 60 Sheet Thickness t [mm]

70

80

90

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100

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Eurocode 3 and BS 7608: mean stress influence •

Haigh diagram acc. DS 952 for St52-3 curve F

⇒ haigh diagram according DS 952 for material St52-3 ⇒ => Care should be taken both considering of mean stress influence and reduction of compressive stresses at the same time Klaus Hofwimmer, May 2005

It has been experimentally shown that at weldings, when high tensile residual stresses are present, fatigue strength is a function of stress range alone; mean stress and stress ration have no significant effect. Eurocode 3 and BS 7608 make the assumption that high tensile residual stresses are present and mean stress influence is neglected . A possible way to consider mean stress influence is according DS 952.

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Eurocode 3 and BS 7608: S-N curve display

N1 / N2 3.0 / 5.0

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: GUI

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: compressive stress reduction parent material

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: modelling guidelines for welds

! σw σw

• Element material label to assign the detail category • Node color or displacement coordsys. label to define weld seam line • Weld ends and the middle of the seam will be treated the same way • Dominant stress direction will be determined by FEMFAT automatically Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: modelling guidelines for parent material

•

Developing material data files for each detail category

• •

Nodes assigned with special material according detail category No stress gradient effect should be considered; this could be done by either: - using node color C200; no gradient influence only for nodes with color 200 or: - switch off stress gradient influence manually on the GUI; this effects all nodes

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: material labels for detail categories FEMFAT Material No.

Detail Category Eurocode 3

BS 7608

160 EC3: 160

--

141

140

B

142

125

C

143

112

D

144 145 146

100 90 80

-T E

147

71

F

148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163

63 56 50 45 40 36 90 71 56 50 45 36 50* 45* 36* --

Klaus Hofwimmer, May 2005

modified S/N

tubular joints

140

F2 -G -W ----------S

• Fatigue assessment of parent material using detail class A is not included in the BS 7608 => Detail category 160 of EC3 was used instead (only slope 3 and fatigue strength) • Class S in BS 7608 is for shear connectors in concrete. => not implemented

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Eurocode 3 and BS 7608: verification using test results ∆

(a) non-load carrying cruciform joint

∆

∆

(b) cover plate joint

pulsating loading (R=0.1)

(c) longitudinal stiffener joint Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: verification using test results Test Results 400

Nominal stress range, ∆S (MPa)

350 300 280 260 240 220 200

k = 4.5

k = 4.5

180 160 140

k = 3.1

120 100 90 80 1e+4

Non-load carrying cruciform joint Cover plate Longitudinal stiffener 1e+5

1e+6

1e+7

Fatigue life, Nf (cycles) Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: verification using test results Finite Element Models

(a) non-load carrying cruciform joint

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: verification using test results Finite Element Models

(b) cover plate joint

Klaus Hofwimmer, May 2005

www.femfat.com

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Eurocode 3 and BS 7608: verification using test results Finite Element Models

(c) longitudinal stiffener joint

Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: verification using test results Cruciform Joint R=0.1; ∆ S=0.9*Pmax/A

300 Test Results

280

EUROCODE 3 (P=50%) BS 7608 (P=50%)

260 Stress Range [MPa]

FEMFAT 4.4.1 (P=50%) 240

Test Results(Test (P=50%) Potenziell Results)

220 200 180 160 140 120 100 1,00E+04

1,00E+05

1,00E+06

1,00E+07

Load Cycles Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: verification using test results Cover Plate Joint R=0.1, DS=0.9*Pmax/A

220 Test Results EUROCODE 3 (P=50%) BS 7608 (P=50%) FEMFAT 4.4.1 (P=50%) Potenziell (Test Results) Test Results (P=50%)

Stress Range [MPa]

200

180

160

140

120

100 1,00E+04

1,00E+05

1,00E+06

1,00E+07

Load Cycles Klaus Hofwimmer, May 2005

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Eurocode 3 and BS 7608: verification using test results Longitudinal Stiffener Joint R=0.1, DS=0.9*Pmax/A 200

Stress Range [MPa]

180

160

140

120

Test Results EUROCODE 3 (P=50%) BS 7608 (P=50%)

100

FEMFAT 4.4.1 (P=50%) Test Results(Test (P=50%) Potenziell Results)

80 1,00E+04

1,00E+05

1,00E+06

1,00E+07

Load Cycles

Klaus Hofwimmer, May 2005

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