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N.W.F.P. University of Engineering and
Technology Peshawar
1
By: Prof Dr. Akhtar Naeem Khan
Lecture 05: Welded connections
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Welding
Types of welds
Welded Joints Welding processes
Nomenclature of welds
Welding symbols
Topics to be Addressed
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Stresses in Welds
Specifications for Welds
Code Requirements
Design Examples
Topics to be Addressed
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Welding
It is a process of joining parts by means ofheat & pressure, causes fusion of parts.
OR Heating metal to fusion temperature with or
without addition of weld metals.
Code & specification:American Welding Society(AWS)
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Types of Welds
Welds are classified according to their shape
and method of deposition into:
1. Groove Weld
2. Fillet Weld
3. Plug Weld
4. Slot Weld
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Types of Welds
1. Groove Weld is made in openingbetween two parts being joined.
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Types of Welds
2. Fillet Weld triangular in shape, joinssurfaces which are at an angle with one
another.
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Groove welds are more efficient than filletwelds.
Have greater resistance to repeated stress andImpact loaded. Hence preferable for dynamicallyloaded members.
Groove welds require less weld metal than filletweld of equal strength.
But fillet welds are often used in structuralwork. WHY ?
Types of Welds
Groove Weld and Fillet Weld
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But fillet welds are often used in structuralwork WHY ?
Partly because many connections are moreeasily made with fillet welds and
Partly because groove welds require themember of structure to be cut to rather closetolerances.
Types of Welds
Groove Weld and Fillet Weld
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Types of Welds
3. Plug Weld is made by depositing weld
metal in a circular hole in one of two
lapped places.
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Types of Welds
4. Slot Weld similar to plug but the hole is
elongated.
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Types of Welds
Groove weld
Fillet weld
Plug weldSlot weld
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Welds are classified according to theposition of weld during welding as
1. Flat
2. Horizontal
3. Vertical
4. Overhead
Types of Welds
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1. Flat: Executed from above, the weld
face approximately horizontal.
Types of Welds
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2. Horizontal: Similar to Flat weld but weld is
harder to make.
Types of Welds
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3. Vertical: Longitudinal axis of weld is
vertical.
Types of Welds
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4. Overhead: Welding is done from underside
of the joint.
Types of Welds
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Types of Welds
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Welded Joints
They are classified as:
1. Butt Joint is groove-welded
2. Lap Joint is fillet-welded
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1. Tee Joint can be fillet-welded or groove-welded
2. Corner Joint
Welded Joints
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Welding processes
There are three methods of Welding:
1. Forge welding
2. Resistance welding
3. Fusion welding
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Welding processes
1. Forge welding: It consists of simply heating the pieces
above certain temperature and
hammering them together
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Welding processes
2. Resistance welding Metal parts are joined by means of heat and
pressure which causes fusion of parts.
Heat is generated by electrical resistance toa current of high amperage & low voltagepassing through small area of contactbetween parts to be connected.
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Welding processes
3. Fusion welding: Metal is heated to fusion temperature
with or without addition of weld metal
Method of connecting pieces by moltenmetal
i. Oxyacetylene welding
ii. Electric arc welding
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Arc is a sustained spark between a metallicelectrode and work to be welded.
At the instant arc is formed the temperature of
work and tip of electrode are brought to meltingpoint.
As the tip of electrode melts, tiny globules of
molten metal form.
Welding processesMetal Arc Welding
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The molten metal, when exposed to aircombines chemically with oxygen & nitrogenforming oxides & nitrides, which tend to embrittle
it & less corrosive resistant.
Tough, ductile weld are produced if molten poolis shielded by an inert gas, which envelops
molten metal & tip of electrode.
Welding processesMetal Arc Welding
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Welding processesMetal Arc Welding
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When an arc is struck between the metal rod(electrode) and the work piece, both the rod andwork piece surface melt to form a weld pool.
Simultaneous melting of the flux coating on therod will form gas and slag which protects the weldpool from the surrounding atmosphere.
Shielded Metal Arc Welding (SMAW)
Welding processes
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Shielded Metal Arc Welding (SMAW)
Welding processes
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A bare wire is fed through welding head at a rateto maintain constant arc length.
Welding is shielded by blanket of granular fusible
material fed onto the work area by gravity, in anamount sufficient to submerge the arc completely.
In addition to protecting weld from atmosphere,the covering aids in controlling rate of cooling of
weld.
Submerged Arc Welding (SAW)
Welding processes
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Submerged Arc Welding (SAW)
Welding processes
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It utilizes the heat of an arc between acontinuously fed consumable flux cored electrodeand the work.
The heat of the arc melts the surface of the base
metal and the end of the electrode.
The metal melted off the electrode is transferredacross the arc to the work piece, where it
becomes the deposited weld metal. Shielding is obtained from the disintegration of
ingredients contained within the flux coredelectrode.
Flux Cored Arc Welding (FCAW)
Welding processes
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Flux Cored Arc Welding (FCAW)
Welding processes
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MIG Welding refers to the wire that is used to
start the arc.
It is shielded by inert gas and the feeding wire alsoacts as the filler rod.
Metal-Arc Inert Gas (MIG) Welding
Welding processes
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Metal-Arc Inert Gas (MIG) Welding
Welding processes
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The arc is started with a tungsten electrodeshielded by inert gas and filler rod is fed into theweld puddle separately.
The gas shielding that is required to protect themolten metal from contamination is suppliedthrough the torch.
Tungsten-Arc Inert Gas (TIG) Welding
Welding processes
W ldi
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Tungsten-Arc Inert Gas (TIG) Welding
Welding processes
W ldi
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Large fillet welds made manually require two ormore passes.
Each pass must cool, and slag must be removed beforenext pass.
Most efficient fillet welds are those which can bemade in one pass.
Welding processesImportant considerations
W ldi
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Largest size can be made in one pass dependsupon welding position & should not exceed thefollowing.
5/16 Horizontal or overhead 3/8 Flat position
1/2 Vertical position
Thickness of weld = Thickness of material1/16
Welding processesImportant considerations
W ldi
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A fillet weld that is too small compared with thethickness of the material being welded is affectedadversely during cooling.
The amount of heat required to deposit a smallweld is not sufficient to produce appreciableexpansion of the thick material, and as hotter
weld contracts during cooling it is restrained bybeing attached to the cooler material and tensilestresses produce, may cause crack of the weld.
Welding processesImportant considerations
N l t f W ld
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Nomenclature of Welds The part of weld assumed to be effective in
transferring stress is Throat.
The faces of weld in contact with the parts joined
is called its Legs..
For equal-legged fillet weld throat is 0.707s, wheres is leg size.
St d d W ldi b l
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Fillet Weld
Standard Welding symbols
St d d W ldi b l
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Fillet Weld
Standard Welding symbols
St d d W ldi b l
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Fillet Weld
Standard Welding symbols
St d d W ldi b l
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Fillet Weld
Standard Welding symbols
St d d W ldi b l
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Unequal legs
Fillet Weld
Standard Welding smbols
Standard Welding s mbols
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Standard Welding symbols
Groove Weld
Standard Welding symbols
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Standard Welding symbols
Groove Weld
Standard Welding symbols
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Standard Welding symbols
Groove Weld
Standard Welding symbols
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Standard Welding symbols
Plug & Slot Weld
Stresses In Welds
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Stresses In Welds
Groove weld may be stressed in tension,compression, shear, or a combination oftension, compression and shear, depending
upon the direction and position of loadrelative to weld.
Stresses In Welds
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Stresses In Welds
f= P / (LTe)
Stresses In Welds
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The load P in Fig is resisted by shearing force
P/2, on the throat of each fillet weld.f= (P /2) / (LTe)
Stresses In Welds
Stresses In Welds
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It is customary to take the force on a fillet weld
as a shear on the throat irrespective of thedirection of load relative to throat.
P 2 / 4
Stresses In Welds
Stresses In Welds
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Tests have shown that a fillet weld
transverse to the load is much strongerthan a fillet weld of same size parallel to
the load.
Stresses In Welds
Stresses In Welds
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Load sharing of P, between two
longitudinal fillet & one transverse filletweld depends either on:
Proportional to their
length if welds are of
same size.
Proportional to the areafor different size weld.
Stresses In Welds
Stresses In Welds
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Any abrupt discontinuity or change in section of
member such as notch or a sharp reentrantcorner, interrupts the transmission of stressalong smooth lines.
Joint is elongated in direction of load to produce a more uniformtransfer of stress
These concentrations are of no consequence for static loads, butthey are significant where fatigue is involved.
Stresses In Welds
Specifications for Welded
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Welding electrodes are classified on the basis ofmechanical properties of weld metal, Weldingposition, type of coating, and type of Currentrequired.
Each electrode is identified by code numberEXXXXX.
Estands for Electrode and each Xrepresentsnumber.
Specifications for Welded
Connections
Specifications for Welded
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First two or three numbers denote the tensilestrength in Ksi.
Next No. position in which electrode can be used.
e.g. 1: all positions, 2: flat & horizontal fillet welds, 3: flat welding only
Last No. denotes type of covering, type of current
& polarity.
Specifications for Welded
Connections
Specifications for Welded
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Example: E7018 means
Tensile strength 70 Ksi
1 means can be used in all positions
8 means it is iron-powder, low-hydrogen electrodeused with A.C or D.C but only in reverse polarity.
Specifications for Welded
Connections
Code Requirements
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AISC/ASD
Allowable stress in welded connection is given in Table2-21
AISC/LRFD
Design strengths of welds are given in Table 2-22 withresistance factor .
Code Requirements
Code Requirements
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AASHTO Allowable stress are more conservative than AISC. e.g.
0.27Fu for fillet weld, Fu is tensile strength of electrodebut not less than tensile strength of connected part.
AREA
Allowable shear stress on fillet welds are given asfunction of base material and strength of weld metal.e.g.
A36. Electrode or electrode-flux combinations with:
60,000 psi tensile strength 16,500 psi
70,000 psi tensile strength 19,500 psi
Code Requirements
Code Requirements
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Code Requirements
Code Requirements
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Code Requirements
Code Requirements
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Code Requirements
Code Requirements
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Code Requirements
Code Requirements
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Code Requirements
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Design Problem
Example Problem 1 - ASD
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Example Problem 1 - ASD
Example Problem 1 - ASD
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Example Problem 1 ASD
Example Problem 1 - ASD
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Final Design
Example Problem 1 ASD
Example Problem 1 - ASD
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Example Problem 1 ASD
Example Problem 2 LRFD
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p
Example Problem 2 LRFD
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p
Example Problem 2 LRFD
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p
Example Problem 2 LRFD
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Example Problem 3 LRFD
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Example Problem 3
LRFD
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Example Problem 3
LRFD
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Example Problem 3
LRFD
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Example Problem 3
LRFD
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Example Problem 3
LRFD
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Final Design
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Thanks