frc01_eurocode3

Klaus Hofwimmer, May 2005 1www.femfat.com

EUROCODE 3 & BS 7608EUROCODE 3 & BS 7608in FEMFAT WELDin FEMFAT WELD


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)


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.)


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


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)


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)


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


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


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


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


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≤


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


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


Eurocode 3 and BS 7608: S-N curve display

N1 / N2

3.0 / 5.0


Eurocode 3 and BS 7608: GUI


Eurocode 3 and BS 7608: compressive stress reduction parent material


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


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


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


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


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



Finite Element Models

(a) non-load carrying cruciform joint




(b) cover plate joint




(c) longitudinal stiffener joint


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%)



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]




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

]


frc01_eurocode3

Documents

shear stresses w

combined stress w

shear stress sncurves

nominal stress

stress classification

direction of principal

maxmin principal stress

w direct stresses