Steel Connection Welding

8/10/2019 Steel Connection Welding

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Design of Steel StructuresDurgesh C. Rai

Department of Civil Engineering, IIT Kanpur

SteelSteel

ConnectionsConnections --IIIIWeldingWelding


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BasicsBasics

Field welded truss


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Welds seem simpler, but Large welding required at each connection

Need for following a predetermined weld sequence

BasicsBasics


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Types of welded jointsButt

Lap

CornerTee

Edge

BasicsBasics


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Types of welds

BasicsBasics


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Types of Groove Welds

BasicsBasics


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Types of Fillet welds

BasicsBasics


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Types of welding technology Submerged arc welding (SAW)

BasicsBasics


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Types of welding technology Gas Metal Arc Welding (GMAW)Metal Inert Gas (MIG) Welding

BasicsBasics


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Types of welding technology Gas Tungsten Arc Welding (GTAW) Tungsten Inert Gas (TIG) Welding

BasicsBasics


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Welding machines Manual to Fully Automatic Equipment

BasicsBasics


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Choosing an Electrode

BasicsBasics


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Positions of welding electrode

BasicsBasics


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Welding Symbols

BasicsBasics


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Welding Symbols

BasicsBasics

6

6

8

12

6

6

150

150

150

150

150

Process OF WeldingProcess OF Welding


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Edge preparations for groove welds

Quality ofQuality of WeldINGWeldING


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Quality ofQuality ofWeldINGWeldING

Possible weld defects


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Preferred weld profile For better flow of forces

Quality OF WeldingQuality OF Welding

PoorPoor

GoodGood


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Weld profile


Fillet WeldFillet Weld Groove WeldGroove Weld


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Weld profile


1.5-2mm


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Weld profile



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Checking size of fillet welds Weld inspection gauge

Tolerance


Problems of weldingProblems of welding


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Heat affected zoneMaterial properties are changed

Base metalFusion zone

Heat affected zone

ge s f e g


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Distortion and dimensional changes Unsymmetric welds


Angular distortion

cess F e gProcess OF Welding


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Curvature developed after weldingCurvature developed after welding

Distortion due to welding

Sequence of intermittent weldsto avoid weld-induced curvature


or or



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Distortion and dimensional changes Unsymmetric welds




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Internal stresses Weld restraints




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Internal stresses Weld restraints



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Closing welds in indeterminate structures Weld and base metals contract on cooling

Accompanied by yielding, cracking or elongation of

members




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Avoid problems of closing welds Use proper weld sequence

Adopt prescribed number of passes for a required

total weld size

Allow the prescribed cooling time after each weld



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How to reduce lamellar tearing




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Residual stresses in welded sections Comparable to that in hot-rolled sections




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Beam bottom flange welding - a challenge Weld access hole, cope and backup bar required Un-fused interface at bottom of back-up bar

Potential crack initiation of CJP weld

Detail A

Beam

Column

Detail A

Weld AccessHole

CJP

Weld

Cope

Un-Fused Interface

Backup Bar




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Performance of Welds Tri-axial state of stress at column face Avoid high stresses in welds

3

1

2

1= u1=y

y/2

u/2

2= 3=0

123

u

y/2

y

max

Uni-axial StressesUni-axial Stresses Tri-axial StressesTri-axial Stresses

Yield stress y/2 is not reachedin shear; brittle fracture

r le s wel nle s el



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Welding is difficult in tapered sections Only obtuse-angled small-thickness weld possibleat tapered tip

Use parallel flange sections

Cover plate

I-section

Only small thicknessweld possible Proper welds

possible

Cover plate

I-section

l s l

Structural weldsStructural welds


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Design of weldsButt WeldButt Weld

FilletWeld

FilletWeld

Structural Design of weldsStructural Design of welds


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Weld sizes Fillet Welds Max. size:

smax = t-1.5 mm for square edges of t > 6 mmsmax = t for square edges of t < 6 mm

smax = 0.75t for the rounded edges of rolled sections

Cl. 10.5.8



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Weld sizes Fillet Welds Max. size:

End fillet weld normal toforce direction

Throat thickness not lessthan 0.5t

[ Cl. 10.5.8.5 ]


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Weld sizes Butt Welds Min. groove depths for different situations applicable

End returns: min of 2 times weld size Min length Lmin = max (4 s, 40 mm)

Lap Joints: min. lap length Llap = 4t min or 40 mm



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Stresses in Fillet Welds

s

s

s

s

s lw


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Stresses in Butt Welds Due to combination of stresses [ Cl. 10.5.10 ]

Butt WeldButt Weld

Combined bearing, shear and bending

2 2 23br

e b b br f f f f f q= + + +

[ Cl. 10.5.10.1.1 ]

Structural design of weldsStructural design of welds


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Design offillet weld connection

Design strength

( )wdf w t wdf lwR l t f =

Effectivethroat area

Design stress

[ Cl. 10.5.7.1.1 ]

wd wn mwf f =

; min( , )3u

wn u uw up

f

f f f= =

Field welds

Shop welds1.25

1.50mf =



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Design offillet weld connection

Design strength


Reduction factor for long joints

[ Cl. 10.5.7.3 ]

0.21.2 1.0150

j

lw

t

lt

=



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Design of butt weld connection

Design strength

( )wdb w t wdb lwR l t f =

Effectivethroat areaWith throatthicknessequal totickness ofplate

Design stress

[ Cl. 10.5.7.1.1 ]

wdb wnb mwf f =

min( , )wn u uw upf f f= =

Field welds

Shop welds1.25

1.50mf =



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Design Example offillet weld connectionDesign weld on face AB and GF with no eccentricity, plate thickness is 16mm

Strength per unit length for 6 mm weld Ex50xx and E250(Fe410) plates, shop welds

4101 (0.7 6 ) 0.8 /

3 1.25wdf

MPaR mm kN mm= =

Eqm. requires

160 kN

160 kN

125mm

75 mm

200 mm


0.8kN/mm LAB

0.8kN/mm LGF

160AB GFF F kN + =

160 /0.8 / 200AB GFL L kN kN mm mm+ = =

Moment condition requires

(75 ) (125 )AB GFF mm F mm=

(5/3)AB GFL L=

A

B

Solving A and B

125 , 75AB GFL mm L mm= =

Eccentric connectionEccentric connection


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Definition Resultant of applied forces does not pass through the c.g. of

weld group

Two types

Cause only shear in fastenersCause shear + tension in fasteners

Shear-only Weld Group Shear + Tension Weld Group

M=Pe

PP


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Eccentric connectionEccentric connection


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Shear +Tension bolt group

Bending behaviour (elastic) Direct Shear

t wt t wct x dx t x dx=

Locate NA, i.e., c

Tensile stress at a point

c

Pe

= +NA

e PP

c

w t

Pf

l t=

( )m

na

Pe yf

I=

Resultant

at a point of interest

2 2( ) ( )R t t m t cf t t f t f= +


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Steel Connection Welding