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Klaus Hofwimmer, May 2005 1www.femfat.com
EUROCODE 3 & BS 7608EUROCODE 3 & BS 7608in FEMFAT WELDin FEMFAT WELD
Klaus Hofwimmer, May 2005 2www.femfat.com
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 3www.femfat.com
Eurocode 3 and BS 7608: used stresses in weld materialEurocode 3 BS 7608
• Chapter 3.3: The difference between the greatest and least vector sum of shear stresses in weld metal will be used;
2||
2||/)( τσσσ += ⊥⊥signw
=σ⊥
τ|| =
= σw
22⊥⊥ += τσσ w
||τ=w
• Direct stresses lateral to the weld seam σw and shear stresses τw will be used
σ1 =σ⊥σ2 =σ||τ1 =τ⊥τ2 =τ||
2||
2||
2 3)( τσσσσσσ ⋅+⋅−+= ⊥⊥⊥signw
⊥= σσ w
2||
2||/|| )( τστσ += ⊥signw
⊥= σσ w
1.)
2.)1.)
3.)τ3.)2.)
Klaus Hofwimmer, May 2005 4www.femfat.com
Eurocode 3 and BS 7608: shear stresses in weld materialEurocode 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.
τzy =0
τzx =0 τyz=0
τyx≠0
τxz=0
τxy ≠0
z
x
y
⊥= σσ w
||ττ =w
2||
2 τσσ += ⊥w
Thus using thin shell elements for FE-simulation (state of the art) τ⊥ can not be computed and τ|| =τxy=τ.
22⊥⊥ += τσσ w
ττ =w
22 τσσ += ⊥w
Klaus Hofwimmer, May 2005 5www.femfat.com
Eurocode 3 and BS 7608: used stresses in parent materialEurocode 3 BS 7608
1σσ =w
• Max. principal stress in the parent material without local stress concentration effects due to weld geometry => hot spot stress
• Case 1: Direction of principal stress nearly constant
),,( 321 σσσσ ∆∆∆=∆ MAXw
• 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 6www.femfat.com
Eurocode 3 and BS 7608: fatigue assessmentEurocode 3 BS 7608
1≤= ∑i
i
NnDσ
• Fatigue assessment for stresses lateral to the weld seam σw=σ⊥
1≤= ∑i
i
NnD
• Fatigue assessment for combined stress σw=σw(σ⊥,τ||)
1≤= ∑i
i
NnDτ
• Fatigue assessment for shear stresses parallel to the weld seam τw
• No particular Fatigue assessment for shear stresses parallel to the weld seam τw
1≤+ τσ DD
• Fatigue assessment for combined loading
=> will be done manually (postprocessor)
Klaus Hofwimmer, May 2005 7www.femfat.com
Eurocode 3 and BS 7608: S-N curves for normal stressesEurocode 3 BS 7608
• Fatigue strength S0=Sr(N=107)• Change of slope from m to (m+2) at N=107 cycles
Pü=97.7%Pü=97.7%
Adjustableby the user
Klaus Hofwimmer, May 2005 8www.femfat.com
Eurocode 3 and BS 7608: S-N curves for normal stresses
S-N Curves of Eurocode 3, BS 7608 and FEMFAT
10
100
1000
1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09
log N
Log
S
160 140 125112 100 9080 71 6356 50 4540 36 BC D EF F2 GW S TFF-NWU FF-NUE/End
Klaus Hofwimmer, May 2005 9www.femfat.com
Eurocode 3 and BS 7608: S-N curves for shear stressesEurocode 3 BS 7608
Pü=97.7% Only curve 80 will be used for welds; curve 100 is validonly for bolt joints
=> one curve in database for welds and parentmaterial
• No particular S-N curves for shear stresses are used
Klaus Hofwimmer, May 2005 10www.femfat.com
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 11www.femfat.com
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:
25.0
,25
⋅∆=∆tRtR σσ für t > 25mm
RtR σσ ∆=∆ , für t 25mm≤
• Sheet thickness influence:
25.0
,16
⋅∆=∆tRtR σσ für t > 16mm
RtR σσ ∆=∆ , für t 16mm≤
Klaus Hofwimmer, May 2005 12www.femfat.com
Eurocode 3 and BS 7608: thickness influence
Sheet Thickness Influence (0-100mm)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 10 20 30 40 50 60 70 80 90 100Sheet Thickness t [mm]
Influ
ence
Fac
tor σ
R/ σ
R,t [
-]
thickness influence FEMFAT
thickness influence Eurocode 3
thickness influence BS 7608
Klaus Hofwimmer, May 2005 13www.femfat.com
Eurocode 3 and BS 7608: mean stress influence
• 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.
⇒ 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
Haigh diagram acc. DS 952 for St52-3 curve F
Klaus Hofwimmer, May 2005 14www.femfat.com
Eurocode 3 and BS 7608: S-N curve display
N1 / N2
3.0 / 5.0
Klaus Hofwimmer, May 2005 15www.femfat.com
Eurocode 3 and BS 7608: GUI
Klaus Hofwimmer, May 2005 16www.femfat.com
Eurocode 3 and BS 7608: compressive stress reduction parent material
Klaus Hofwimmer, May 2005 17www.femfat.com
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 18www.femfat.com
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 19www.femfat.com
Eurocode 3 and BS 7608: material labels for detail categories
BS 7608
140 --
141 B
142 C
143 D
144 --145 T146 E
147 F
148 F2149 --150 G151 --152 W153 --154 90 --155 71 --156 56 --157 50 --158 45 --159 36 --160 50* --161 45* --162 36* --163 S
36
--
56504540
FEMFAT Material
No.
80
71
63
Detail Category
tubu
lar jo
ints
mod
ified
S/N
Eurocode 3
160
140
125
112
10090
EC3: 160
• 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
Klaus Hofwimmer, May 2005 20www.femfat.com
Eurocode 3 and BS 7608: verification using test results∆ ∆
(b) cover plate joint(a) non-load carrying cruciform joint
∆
pulsating loading
(R=0.1)
(c) longitudinal stiffener joint
Klaus Hofwimmer, May 2005 21www.femfat.com
Eurocode 3 and BS 7608: verification using test results
Fatigue life, Nf (cycles)
1e+4 1e+5 1e+6 1e+7
Nom
inal
stre
ss ra
nge,
∆S
(MP
a)
80
90
100
120
140
160
180
200220240260280300
350
400
Non-load carrying cruciform joint Cover plateLongitudinal stiffener
Test Results
k = 4.5
k = 4.5
k = 3.1
Klaus Hofwimmer, May 2005 22www.femfat.com
Eurocode 3 and BS 7608: verification using test results
Finite Element Models
(a) non-load carrying cruciform joint
Klaus Hofwimmer, May 2005 23www.femfat.com
Eurocode 3 and BS 7608: verification using test results
Finite Element Models
(b) cover plate joint
Klaus Hofwimmer, May 2005 24www.femfat.com
Eurocode 3 and BS 7608: verification using test results
Finite Element Models
(c) longitudinal stiffener joint
Klaus Hofwimmer, May 2005 25www.femfat.com
Eurocode 3 and BS 7608: verification using test resultsCruciform JointR=0.1; ∆S=0.9*Pmax/A
100
120
140
160
180
200
220
240
260
280
300
1,00E+04 1,00E+05 1,00E+06 1,00E+07
Load Cycles
Stre
ss R
ange
[M
Pa]
Test ResultsEUROCODE 3 (P=50%)BS 7608 (P=50%)FEMFAT 4.4.1 (P=50%)Potenziell (Test Results)Test Results (P=50%)
Klaus Hofwimmer, May 2005 26www.femfat.com
Eurocode 3 and BS 7608: verification using test results
Cover Plate JointR=0.1, DS=0.9*Pmax/A
100
120
140
160
180
200
220
1,00E+04 1,00E+05 1,00E+06 1,00E+07
Load Cycles
Stre
ss R
ange
[M
Pa]
Test ResultsEUROCODE 3 (P=50%)BS 7608 (P=50%)FEMFAT 4.4.1 (P=50%)Potenziell (Test Results)Test Results (P=50%)
Klaus Hofwimmer, May 2005 27www.femfat.com
Eurocode 3 and BS 7608: verification using test results
Longitudinal Stiffener JointR=0.1, DS=0.9*Pmax/A
80
100
120
140
160
180
200
1,00E+04 1,00E+05 1,00E+06 1,00E+07Load Cycles
Stre
ss R
ange
[MPa
]
Test ResultsEUROCODE 3 (P=50%)BS 7608 (P=50%)FEMFAT 4.4.1 (P=50%)Potenziell (Test Results)Test Results (P=50%)