Lecture -05 Welded Connections

8/21/2019 Lecture -05 Welded Connections

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N.W.F.P. University of Engineering and

Technology Peshawar

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By: Prof Dr. Akhtar Naeem Khan

[email protected]

Lecture 05: Welded connections


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CE-409: Lecture 05 Prof. Dr Akhtar Naeem Khan 2

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.



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



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



Types of Welds

3. Plug Weld is made by depositing weld

metal in a circular hole in one of two

lapped places.



Types of Welds

4. Slot Weld similar to plug but the hole is

elongated.



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.



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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


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.


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


St d d W ldi b l


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Fillet Weld


St d d W ldi b l


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Fillet Weld


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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Groove Weld



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Groove Weld



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Groove Weld



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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.


Connections



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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.


Connections



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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.


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



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Final Design




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Example Problem 2 LRFD


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p



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p



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p



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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

Lecture -05 Welded Connections

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